Analysis and Modeling of Shear Waves Generated by Explosions at the San Andreas Fault Observatory at Depth

DTIC Science & Technology

2011-09-01

No. BAA09-69 ABSTRACT Using multiple deployments of an 80-element, three-component borehole seismic array stretching from the surface to 2.3 km...NNSA). 14. ABSTRACT Using multiple deployments of an 80-element, three-component borehole seismic array stretching from the surface to 2.3 km depth...generated using the direct Green’s function (DGF) method of Friederich and Dalkolmo (1995). This method synthesizes the seismic wavefield for a spherically

Monitoring El Hierro submarine volcanic eruption events with a submarine seismic array

NASA Astrophysics Data System (ADS)

Jurado, Maria Jose; Molino, Erik; Lopez, Carmen

2013-04-01

A submarine volcanic eruption took place near the southernmost emerged land of the El Hierro Island (Canary Islands, Spain), from October 2011 to February 2012. The Instituto Geografico Nacional (IGN) seismic stations network evidenced seismic unrest since July 2012 and was a reference also to follow the evolution of the seismic activity associated with the volcanic eruption. From the beginning of the eruption a geophone string was installed less than 2 km away from the new volcano, next to La Restinga village shore, to record seismic activity related to the volcanic activity, continuously and with special interest on high frequency events. The seismic array was endowed with 8, high frequency, 3 component, 250 Hz, geophone cable string with a separation of 6 m between them. The analysis of the dataset using spectral techniques allows the characterization of the different phases of the eruption and the study of its dynamics. The correlation of the data analysis results with the observed sea surface activity (ash and lava emission and degassing) and also with the seismic activity recorded by the IGN field seismic monitoring system, allows the identification of different stages suggesting the existence of different signal sources during the volcanic eruption and also the posteruptive record of the degassing activity. The study shows that the high frequency capability of the geophone array allow the study of important features that cannot be registered by the standard seismic stations. The accumulative spectral amplitude show features related to eruptive changes.

Analysis of the Noise in Data from the Mt. Meron Array

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chambers, D. H.; Breitfeller, E.

2010-07-15

This memo describes an analysis of the noise in data obtained from the Mt. Meron seismic array in northern Israel. The overall objective is to development a method for removing noise from extraneous sources in the environment, increasing the sensitivity to seismic signals from far events. For this initial work, we concentrated on understanding the propagation characteristics of the noise in the frequency band from 0.1 – 8 Hz, and testing a model-based method for removing narrow band (single frequency) noise.

Seismo-acoustic Signals Recorded at KSIAR, the Infrasound Array Installed at PS31

NASA Astrophysics Data System (ADS)

Kim, T. S.; Che, I. Y.; Jeon, J. S.; Chi, H. C.; Kang, I. B.

2014-12-01

One of International Monitoring System (IMS)'s primary seismic stations, PS31, called Korea Seismic Research Station (KSRS), was installed around Wonju, Korea in 1970s. It has been operated by US Air Force Technical Applications Center (AFTAC) for more than 40 years. KSRS is composed of 26 seismic sensors including 19 short period, 6 long period and 1 broad band seismometers. The 19 short period sensors were used to build an array with a 10-km aperture while the 6 long period sensors were used for a relatively long period array with a 40-km aperture. After KSRS was certified as an IMS station in 2006 by Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), Korea Institute of Geoscience and Mineral Resources (KIGAM) which is the Korea National Data Center started to take over responsibilities on the operation and maintenance of KSRS from AFTAC. In April of 2014, KIGAM installed an infrasound array, KSIAR, on the existing four short period seismic stations of KSRS, the sites KS05, KS06, KS07 and KS16. The collocated KSIAR changed KSRS from a seismic array into a seismo-acoustic array. The aperture of KSIAR is 3.3 km. KSIAR also has a 100-m small aperture infrasound array at KS07. The infrasound data from KSIAR except that from the site KS06 is being transmitted in real time to KIGAM with VPN and internet line. An initial analysis on seismo-acoustic signals originated from local and regional distance ranges has been performed since May 2014. The analysis with the utilization of an array process called Progressive Multi-Channel Correlation (PMCC) detected seismo-acoustic signals caused by various sources including small explosions in relation to constructing local tunnels and roads. Some of them were not found in the list of automatic bulletin of KIGAM. The seismo-acoustic signals recorded by KSIAR are supplying a useful information for discriminating local and regional man-made events from natural events.

Using Network Theory to Understand Seismic Noise in Dense Arrays

NASA Astrophysics Data System (ADS)

Riahi, N.; Gerstoft, P.

2015-12-01

Dense seismic arrays offer an opportunity to study anthropogenic seismic noise sources with unprecedented detail. Man-made sources typically have high frequency, low intensity, and propagate as surface waves. As a result attenuation restricts their measurable footprint to a small subset of sensors. Medium heterogeneities can further introduce wave front perturbations that limit processing based on travel time. We demonstrate a non-parametric technique that can reliably identify very local events within the array as a function of frequency and time without using travel-times. The approach estimates the non-zero support of the array covariance matrix and then uses network analysis tools to identify clusters of sensors that are sensing a common source. We verify the method on simulated data and then apply it to the Long Beach (CA) geophone array. The method exposes a helicopter traversing the array, oil production facilities with different characteristics, and the fact that noise sources near roads tend to be around 10-20 Hz.

Development of a time synchronization methodology for a wireless seismic array

NASA Astrophysics Data System (ADS)

Moure-García, David; Torres-González, Pedro; del Río, Joaquín; Mihai, Daniel; Domínguez Cerdeña, Itahiza

2017-04-01

Seismic arrays have multiple applications. In the past, the main use was nuclear tests monitoring that began in mid-twentieth century. The major difference with a seismic network is the hypocenter location procedure. With a seismic network the hypocenter's 3D coordinates are calculated while using an array, the source direction of the seismic signal is determined. Seismic arrays are used in volcanology to obtain the source azimuth of volcanic signals related to fluids movement, magma and/or gases, that do not show a clear seismic phases' onset. A key condition in the seismic array operativity is the temporal synchronization of all the sensors, better than 1 microsecond. Because of that, usually all sensors are connected to the acquisition system by cable to ensure an identical sampling time. In this work we present the design of a wireless low-cost and low-power consumption volcanic monitoring seismic array where all nodes (sensors) acquire data synchronously and transmit them to the center node where a coherent signal is pursued in near real time.

Detecting Seismic Activity with a Covariance Matrix Analysis of Data Recorded on Seismic Arrays

NASA Astrophysics Data System (ADS)

Seydoux, L.; Shapiro, N.; de Rosny, J.; Brenguier, F.

2014-12-01

Modern seismic networks are recording the ground motion continuously all around the word, with very broadband and high-sensitivity sensors. The aim of our study is to apply statistical array-based approaches to processing of these records. We use the methods mainly brought from the random matrix theory in order to give a statistical description of seismic wavefields recorded at the Earth's surface. We estimate the array covariance matrix and explore the distribution of its eigenvalues that contains information about the coherency of the sources that generated the studied wavefields. With this approach, we can make distinctions between the signals generated by isolated deterministic sources and the "random" ambient noise. We design an algorithm that uses the distribution of the array covariance matrix eigenvalues to detect signals corresponding to coherent seismic events. We investigate the detection capacity of our methods at different scales and in different frequency ranges by applying it to the records of two networks: (1) the seismic monitoring network operating on the Piton de la Fournaise volcano at La Réunion island composed of 21 receivers and with an aperture of ~15 km, and (2) the transportable component of the USArray composed of ~400 receivers with ~70 km inter-station spacing.

3-component beamforming analysis of ambient seismic noise field for Love and Rayleigh wave source directions

NASA Astrophysics Data System (ADS)

Juretzek, Carina; Hadziioannou, Céline

2014-05-01

Our knowledge about common and different origins of Love and Rayleigh waves observed in the microseism band of the ambient seismic noise field is still limited, including the understanding of source locations and source mechanisms. Multi-component array methods are suitable to address this issue. In this work we use a 3-component beamforming algorithm to obtain source directions and polarization states of the ambient seismic noise field within the primary and secondary microseism bands recorded at the Gräfenberg array in southern Germany. The method allows to distinguish between different polarized waves present in the seismic noise field and estimates Love and Rayleigh wave source directions and their seasonal variations using one year of array data. We find mainly coinciding directions for the strongest acting sources of both wave types at the primary microseism and different source directions at the secondary microseism.

Analysis and Modeling of the Shear Waves Generated by Explosions at the San Andreas Fault Observatory at Depth

DTIC Science & Technology

2012-09-01

09NA29328 Proposal No. BAA09-69 ABSTRACT Using a deep deployment of an 80-element, 3-component borehole seismic array stretching from 1.5 to 2.3...Administration (NNSA). 14. ABSTRACT Using a deep deployment of an 80-element, 3-component borehole seismic array stretching from 1.5 to 2.3 kilometer (km) depth...in the lower half of the borehole array . The strong velocity discontinuity at 2.0 km depth gives rise to another converted S wave, best seen in

Subspace Dimensionality: A Tool for Automated QC in Seismic Array Processing

NASA Astrophysics Data System (ADS)

Rowe, C. A.; Stead, R. J.; Begnaud, M. L.

2013-12-01

Because of the great resolving power of seismic arrays, the application of automated processing to array data is critically important in treaty verification work. A significant problem in array analysis is the inclusion of bad sensor channels in the beamforming process. We are testing an approach to automated, on-the-fly quality control (QC) to aid in the identification of poorly performing sensor channels prior to beam-forming in routine event detection or location processing. The idea stems from methods used for large computer servers, when monitoring traffic at enormous numbers of nodes is impractical on a node-by node basis, so the dimensionality of the node traffic is instead monitoried for anomalies that could represent malware, cyber-attacks or other problems. The technique relies upon the use of subspace dimensionality or principal components of the overall system traffic. The subspace technique is not new to seismology, but its most common application has been limited to comparing waveforms to an a priori collection of templates for detecting highly similar events in a swarm or seismic cluster. In the established template application, a detector functions in a manner analogous to waveform cross-correlation, applying a statistical test to assess the similarity of the incoming data stream to known templates for events of interest. In our approach, we seek not to detect matching signals, but instead, we examine the signal subspace dimensionality in much the same way that the method addresses node traffic anomalies in large computer systems. Signal anomalies recorded on seismic arrays affect the dimensional structure of the array-wide time-series. We have shown previously that this observation is useful in identifying real seismic events, either by looking at the raw signal or derivatives thereof (entropy, kurtosis), but here we explore the effects of malfunctioning channels on the dimension of the data and its derivatives, and how to leverage this effect for identifying bad array elements through a jackknifing process to isolate the anomalous channels, so that an automated analysis system might discard them prior to FK analysis and beamforming on events of interest.

Performance of 3-Component Nodes in the IRIS Community Wavefield Demonstration Experiment

NASA Astrophysics Data System (ADS)

Sweet, J. R.; Anderson, K. R.; Woodward, R.

2017-12-01

In June 2016, a field crew of 50 students, faculty, industry personnel, and IRIS staff deployed a total of 390 stations as part of a community seismic experiment above an active seismic lineament in north-central Oklahoma. The goals of the experiment were to test new instrumentation and deployment strategies that record the full seismic wavefield, and to advance understanding of earthquake source processes and regional lithospheric structure. The crew deployed 363 3-component, 5Hz Generation 2 Fairfield Z-Land nodes along three seismic lines and in a seven-layer nested gradiometer array. The seismic lines spanned a region 13 km long by 5 km wide. A broadband, 18 station "Golay 3x6" array with an aperture of approximately 5 km was deployed around the gradiometer and seismic lines to collect waveform data from local and regional events. In addition, 9 infrasound stations were deployed in order to capture and identify acoustic events that might be recorded by the seismic array. The variety and geometry of instrumentation deployed was intended to capture the full seismic wavefield generated by the local and regional seismicity beneath the array and the surrounding region. Additional details on the instrumentation and how it was deployed can be found by visiting our website www.iris.edu/wavefields. We present a detailed analysis of noise across the array—including station performance, as well as noise from nearby sources (wind turbines, automobiles, etc.). We report a clear reduction in noise for buried 3-component nodes compared to co-located surface nodes (see Figure). Using the IRIS DMC's ISPAQ client, we present a variety of metrics to evaluate the network's performance. We also present highlights from student projects at the recently-held IRIS advanced data processing short course, which focused on analyzing the wavefield dataset using array processing techniques.

Estimating Local and Near-Regional Velocity and Attenuation Structure from Seismic Noise

DTIC Science & Technology

2008-09-30

seismic array in Costa Rica and Nicaragua from ambient seismic noise using two independent methods, noise cross correlation and beamforming. The noise...Mean-phase velocity-dispersion curves are calculated for the TUCAN seismic array in Costa Rica and Nicaragua from ambient seismic noise using two...stations of the TUCAN seismic array (Figure 4c) using a method similar to Harmon et al. (2007). Variations from Harmon et al. (2007) include removing the

Investigation of cortical structures at Etna Volcano through the analysis of array and borehole data.

NASA Astrophysics Data System (ADS)

Zuccarello, Luciano; Paratore, Mario; La Rocca, Mario; Ferrari, Ferruccio; Messina, Alfio Alex; Galluzzo, Danilo; Contrafatto, Danilo; Rapisarda, Salvatore

2015-04-01

A continuous monitoring of seismic activity is a fundamental task to detect the most common signals possibly related with volcanic activity, such as volcano-tectonic earthquakes, long-period events, and volcanic tremor. A reliable prediction of the ray-path propagated back from the recording site to the source is strongly limited by the poor knowledge of the local shallow velocity structure. Usually in volcanic environments the shallowest few hundreds meters of rock are characterized by strongly variable mechanical properties. Therefore the propagation of seismic signals through these shallow layers is strongly affected by lateral heterogeneity, attenuation, scattering, and interaction with the free surface. Driven by these motivations, between May and October 2014 we deployed a seismic array in the area called "Pozzo Pitarrone", where two seismic stations of the local monitoring network are installed, one at surface and one borehole at a depth of about 130 meters. The Pitarrone borehole is located in the middle northeastern flank along one of the main intrusion zones of Etna volcano, the so called NE-rift. With the 3D array we recorded seismic signals coming from the summit craters, and also from the seismogenetic fault called Pernicana Fault, which is located nearby. We used array data to analyse the dispersion characteristics of ambient noise vibrations and we derived one-dimensional (1D) shallow shear-velocity profiles through the inversion of dispersion curves measured by autocorrelation methods (SPAC). We observed a one-dimensional variation of shear-velocity between 430 m/s and 700 m/s to a depth of investigation of about 130 m. An abrupt velocity variation was recorded at a depth of about 60 m, probably corresponding to the transition between two different layers. Our preliminary results suggest a good correlation between the velocity model deducted with the stratigraphic section on Etna. The analysis of the entire data set will improve our knowledge about the (i) structure of the top layer and its relationship with geology, (ii) analysis of the signal to noise ratio (SNR) of volcanic signals as a function of frequency, (iii) study of seismic ray-path deformation caused by the interaction of the seismic waves with the free surface, (iv) evaluation of the attenuation of the seismic signals correlated with the volcanic activity. Moreover the knowledge of a shallow velocity model could improve the study of the source mechanism of low frequency events (VLP, LP and volcanic tremor), and give a new contribution to the seismic monitoring of Etna volcano through the detection and location of seismic sources by using 3D array techniques.

Broadband Array Analysis of the 2005 Episodic Tremor and Slip Event in Northern Cascadia

NASA Astrophysics Data System (ADS)

Wech, A.; Creager, K.; McCausland, W.; Frassetto, A.; Qamar, A.; Derosier, S.; Carmichael, J.; Malone, S.; Johnson, D.

2005-12-01

The region of Cascadia from the Olympic Mountains through southern Vancouver Island and down-dip of the subduction megathrust has repeatedly experienced episodes of slow slip. This episodic slip, which has been observed to take place over a period of two to several weeks, is accompanied by a seismic tremor signal. Based on the average recurrence interval of 14 months, the next episodic tremor and slip (ETS) event should occur within six weeks of mid-September, 2005. Indeed, it appears to have begun on September 3, as this abstract was being written. In order to record this anticipated event, we deployed an array of 11 three-component seismometers on the northern side of the Olympic Peninsula augmenting Pacific Northwest Seismographic Network stations as well as the first few EarthScope BigFoot stations and Plate Boundary Observatory borehole seismometers. This seismic array was comprised of six short-period and five broadband instruments with spacings of 500 m and 2200 m respectively. In conjunction with this Earthscope seismic deployment, we also installed a dense network of 29 temporary, continuous GPS stations across the entire Olympic Peninsula to integrate seismic and geodetic observations. One of the primary goals of this research is to utilize the broadband instrumentation in the array to investigate the possible correlation of low frequency energy with the rest of the tremor activity. ETS has been carefully investigated at high-frequency (seismic tremor at 2-6 Hz) and very low-frequency (slip occurring over weeks, observed by GPS). An important goal of this experiment is to investigate the possibility that the tremor generates intermediate, low-frequency signals. Preliminary analysis of short-period array recordings of the July, 2004 ETS event suggests that the tremor displays signs of lower-frequency energy (~0.5 Hz) correlated with its higher frequency activity. Our array should enable us to distinguish low- frequency signals originating in the direction of high-frequency tremor from noise in other directions. We will present an analysis of the low-frequency energy associated with this slip event.

Aleutian Array of Arrays (A-cubed) to probe a broad spectrum of fault slip under the Aleutian Islands

NASA Astrophysics Data System (ADS)

Ghosh, A.; LI, B.

2016-12-01

Alaska-Aleutian subduction zone is one of the most seismically active subduction zones in this planet. It is characterized by remarkable along-strike variations in seismic behavior, more than 50 active volcanoes, and presents a unique opportunity to serve as a natural laboratory to study subduction zone processes including fault dynamics. Yet details of the seismicity pattern, spatiotemporal distribution of slow earthquakes, nature of interaction between slow and fast earthquakes and their implication on the tectonic behavior remain unknown. We use a hybrid seismic network approach and install 3 mini seismic arrays and 5 stand-alone stations to simultaneously image subduction fault and nearby volcanic system (Makushin). The arrays and stations are strategically located in the Unalaska Island, where prolific tremor activity is detected and located by a solo pilot array in summer 2012. The hybrid network is operational between summer 2015 and 2016 in continuous mode. One of the three arrays starts in summer 2014 and provides additional data covering a longer time span. The pilot array in the Akutan Island recorded continuous seismic data for 2 months. An automatic beam-backprojection analysis detects almost daily tremor activity, with an average of more than an hour per day. We imaged two active sources separated by a tremor gap. The western source, right under the Unalaska Island shows the most prolific activity with a hint of steady migration. In addition, we are able to identify more than 10 families of low frequency earthquakes (LFEs) in this area. They are located within the tremor source area as imaged by the bean-backprojection technique. Application of a match filter technique reveals that intervals between LFE activities are shorter during tremor activity and longer during quiet time period. We expect to present new results from freshly obtained data. The experiment A-cubed is illuminating subduction zone processes under Unalaska Island in unprecedented detail.

Instrument Correction and Dynamic Site Profile Validation at the Central United States Seismic Observatory, New Madrid Seismic Zone

NASA Astrophysics Data System (ADS)

Brengman, C.; Woolery, E. W.; Wang, Z.; Carpenter, S.

2016-12-01

The Central United States Seismic Observatory (CUSSO) is a vertical seismic array located in southwestern Kentucky within the New Madrid seismic zone. It is intended to describe the effects of local geology, including thick sediment overburden, on seismic-wave propagation, particularly strong-motion. The three-borehole array at CUSSO is composed of seismic sensors placed on the surface, and in the bedrock at various depths within the 585 m thick sediment overburden. The array's deep borehole provided a unique opportunity in the northern Mississippi embayment for the direct geological description and geophysical measurement of the complete late Cretaceous-Quaternary sediment column. A seven layer, intra-sediment velocity model is interpreted from the complex, inhomogeneous stratigraphy. The S- and P-wave sediment velocities range between 160 and 875 m/s and between 1000 and 2300 m/s, respectively, with bedrock velocities of 1452 and 3775 m/s, respectively. Cross-correlation and direct comparisons were used to filter out the instrument response and determine the instrument orientation, making CUSSO data ready for analysis, and making CUSSO a viable calibration site for other free-field sensors in the area. The corrected bedrock motions were numerically propagated through the CUSSO soil profile (transfer function) and compared, in terms of both peak acceleration and amplitude spectra, to the recorded surface observations. Initial observations reveal a complex spectral mix of amplification and de-amplification across the array, indicating the site effect in this deep sediment setting is not simply generated by the shallowest layers.

Ambient Vehicular Noise recorded on a 2D Distributed Fiber Optic Sensing Array :Applications to Permafrost Thaw Detection and Imaging

NASA Astrophysics Data System (ADS)

Ajo Franklin, J. B.; Lindsey, N.; Wagner, A. M.; Dou, S.; Martin, E. R.; Ekblaw, I.; Ulrich, C.; James, S. R.; Freifeld, B. M.; Daley, T. M.

2016-12-01

Distributed Acoustic Sensing (DAS) is a recently developed technique that allows the spatially dense ( 1m) continuous recording of seismic signals on long strands of commercial fiber optic cables. The availability of continuous recording on dense arrays offers unique possibilities for long-term timelapse monitoring of environmental processes in arctic environments. In the absence of a repeatable semi-permanent seismic source, the use of ambient surface wave noise from infrastructure use (e.g. moving vehicles) for seismic imaging allows tomographic monitoring of evolving subsurface systems. Challenges in such scenarios include (1) the processing requirements for dense (1000+ channel) arrays recording weeks to months of seismic data, (2) appropriate methods to retrieve empirical noise correlation functions (NCFs) in environments with non-optimal array geometries and both coherent as well as incoherent noise, and (3) semi-automated approaches to invert timelapse NCFs for near-surface soil properties.We present an exploratory study of data from a sparse 2D DAS array acquisition on 4000 linear meters of trenched fiber deployed in 10 crossing profiles. The dataset, collected during July and August of 2016, covers a zone of permafrost undergoing a controlled thaw induced by an array of resistive heaters. The site, located near a heavily used road, has a high level of infrastructure noise but exhibits distance-dependent variation in both noise amplitude and spectrum. We apply seismic interferometry to retrieve the empirical NCF across array subsections, and use collocated geophone and broadband sensors to measure the NCF against the true impulse response function of the medium. We demonstrate that the combination of vehicle tracking and data windowing allows improved reconstruction of stable NCFs appropriate for dispersion analysis and inversion. We also show both spatial and temporal patterns of background noise at the site using 2D beamforming and spectral analysis. Our results suggest that valuable information can be extracted from ambient noise recorded with DAS, particularly in the context of monitoring transformations in cold region environments.

Triggered MEQ Events on LBNL Permanent Seismic Array, Brady's EGS, March 2016

DOE Data Explorer

Michelle Robertson

2016-06-01

List of triggered events recorded on LBNL's permanent EGS seismic array at Brady's geothermal field. This submission also includes links to the NCEDC EGS Earthquake Catalog Search page and to the metadata for the seismic array installed at Brady's Geothermal Field.

Deployment of a seismic array for volcano monitoring during the ongoing submarine eruption at El Hierro, Canary Islands

NASA Astrophysics Data System (ADS)

Abella, R.; Almendros, J.; Carmona, E.; Martin, R.

2012-04-01

On 17 July 2011 there was an important increase of the seismic activity at El Hierro (Canary Islands, Spain). This increase was detected by the Volcano Monitoring Network (Spanish national seismic network) run by the Instituto Geográfico Nacional (IGN). As a consequence, the IGN immediately deployed a dense, complete monitoring network that included seismometers, GPS stations, geochemical equipment, magnetometers, and gravity meters. During the first three months of activity, the seismic network recorded over ten thousand volcano-tectonic earthquakes, with a maximum magnitude of 4.6. On 10 October 2011 an intense volcanic tremor started. It was a monochromatic signal, with variable amplitude and frequency content centered at about 1-2 Hz. The tremor onset was correlated with the initial stages of the submarine eruption that occurred from a vent located south of El Hierro island, near the village of La Restinga. At that point the IGN, in collaboration with the Instituto Andaluz de Geofísica, deployed a seismic array intended for volcanic tremor monitoring and analysis. The seismic array is located about 7 km NW of the submarine vent. It has a 12-channel, 24-bit data acquisition system sampling each channel at 100 sps. The array is composed by 1 three-component and 9 vertical-component seismometers, distributed in a flat area with an aperture of 360 m. The data provided by the seismic array are going to be processed using two different approaches: (1) near-real-time, to produce information that can be useful in the management of the volcanic crisis; and (2) detailed investigations, to study the volcanic tremor characteristics and relate them to the eruption dynamics. At this stage we are mostly dedicated to produce fast, near-real-time estimates. Preliminary results have been obtained using the maximum average cross-correlation method. They indicate that the tremor wavefronts are highly coherent among array stations and propagate across the seismic array with an apparent slowness of ~0.8 s/km and a back-azimuth of 135°N. These estimates have remained approximately constant since the onset of volcanic tremor, indicating a unique source and thus a single, continuing eruptive center.

SKS splitting results in central Italy and Dinaric region inside the AlpArray-CASE project

NASA Astrophysics Data System (ADS)

Salimbeni, S.; Prevolnik, S.; Pondrelli, S.; Molinari, I.; Stipcevic, J.; Kissling, E.; Šipka, V.; Herak, M.

2017-12-01

In the framework of the AlpArray project (AlpArray Seismic Network, 2015), the complementary "Central Adriatic Seismic Experiment" (CASE; AlpArray Seismic Network, 2016) was established as collaboration between ETH Zürich, University of Zagreb, INGV and Republic Hydrometeorological Service of Republic of Srpska. The CASE project consists of 9 temporary stations, installed in October 2016, located in Bosnia and Herzegovina, Croatia and Italy. Temporary broadband seismic stations, with the permanent stations present in the region shared by the Croatian Seismological Service and INGV, make an almost continuous transect cutting the Central-Southern Appenines, the central Adriatic region, central External Dinarides and finishing at the eastern margin of the Internal Dinarides. The presence of the the Apenninic and Dinarides slabs, verging in opposite directions and plunging along the opposite sides of the Adriatic plate, make this area a peculiar spot to understand the complex dynamic of the region. Various tomographic images (e.g. Bijwaard and Spakman, 2000; Piromallo and Morelli, 2003) shows not continuous slabs under the Appenines and the Dinarides, suggesting the presence of slab-gaps right beneath the region covered by the CASE experiment. Here we present the preliminary results of the SKS splitting analysis performed on the data recorded by the temporary and permanent seismic stations included in the CASE project. The new results, in combination with previous interpretation, will provide clues about how Northern and Southern Apennines are connected at depth, how the slab rollback of the Apennines thrust belt acted and if and how the Apennines are in relation with the Dinaric region. Together with the measurements from previous studies and from the AlpArray project, our new data will support the mapping of the seismic anisotropy deformation pattern from Western Alps to Pannonian region.

Seismic array observations for monitoring phreatic eruptions in Iwojima Island, Japan

NASA Astrophysics Data System (ADS)

Ueda, H.; Kawaguchi, R.; Chiba, K.; Fujita, E.; Tanada, T.

2015-12-01

Iwojima is an active volcanic island located within a 10 km wide submarine caldera about 1250 km to the south of Tokyo, Japan. The volcanic activity is characterized by intensive earthquake activity associated with an island-wide uplift with high uplift rate (30~40 cm/year) and hydrothermal activity. In the last 10 years, phreatic eruptions took place in and near the island in 2012, 2013, and 2015. In such restless volcano, predictions and detections of occurrence points of phreatic eruptions are important for ensuring safety of residents. In the previous studies, we found that the earthquake activity of Iwojima highly correlates with the island wide large uplift, but the precursory activity of the phreatic eruption in 2012 was deviated from the correlation (Ueda et al. 2013 AGU Fall Meeting). For prediction of occurrence points of phreatic eruptions and investigation of the eruption mechanism, we began observation by seismic arrays at two areas in December 2014. The seismic arrays enable to locate epicenters of volcanic tremors, which are not well located by existing seismic stations. In May and June 2015, Japan Maritime Self-Defense Force stayed in Iwojima and a live camera of Japan Meteorological Agency found very small phreatic eruptions occurred at the northern beach. Existing seismic stations could not detect seismic signals related with the eruptions. The seismic array could detect weak seismic signals related with the eruptions. Although the seismic arrays could not detect precursory signals because of too small eruption, we expect the seismic arrays can detect precursory seismic signals suggesting occurrence points of small or medium-sized phreatic eruptions. The seismic arrays also detected epicenters of harmonic and monotonic tremors took place at an active fumarolic field in the north earthen part of Iwojima. The apparent velocity of seismic waves (~1km/s) strongly suggests that the tremors relate with hydrothermal activity near ground surface.

Seismicity of Central Asia as Observed on Three IMS Stations

DTIC Science & Technology

2008-09-01

and BVAR are all high-quality seismic arrays . Noise levels at the stations are generally acceptable for the period reviewed, except during the...following conditions: (1) a 4.5-Hz intermittent noise source at MKAR, (2) periodic high-frequency bursts on portions of the SONM array , and (3) a...seismic events (including single station events) observable on three central Asian IMS seismic array stations: Makanchi, Kazakhstan (MKAR); Songino

Localization of short-range acoustic and seismic wideband sources: Algorithms and experiments

NASA Astrophysics Data System (ADS)

Stafsudd, J. Z.; Asgari, S.; Hudson, R.; Yao, K.; Taciroglu, E.

2008-04-01

We consider the determination of the location (source localization) of a disturbance source which emits acoustic and/or seismic signals. We devise an enhanced approximate maximum-likelihood (AML) algorithm to process data collected at acoustic sensors (microphones) belonging to an array of, non-collocated but otherwise identical, sensors. The approximate maximum-likelihood algorithm exploits the time-delay-of-arrival of acoustic signals at different sensors, and yields the source location. For processing the seismic signals, we investigate two distinct algorithms, both of which process data collected at a single measurement station comprising a triaxial accelerometer, to determine direction-of-arrival. The direction-of-arrivals determined at each sensor station are then combined using a weighted least-squares approach for source localization. The first of the direction-of-arrival estimation algorithms is based on the spectral decomposition of the covariance matrix, while the second is based on surface wave analysis. Both of the seismic source localization algorithms have their roots in seismology; and covariance matrix analysis had been successfully employed in applications where the source and the sensors (array) are typically separated by planetary distances (i.e., hundreds to thousands of kilometers). Here, we focus on very-short distances (e.g., less than one hundred meters) instead, with an outlook to applications in multi-modal surveillance, including target detection, tracking, and zone intrusion. We demonstrate the utility of the aforementioned algorithms through a series of open-field tests wherein we successfully localize wideband acoustic and/or seismic sources. We also investigate a basic strategy for fusion of results yielded by acoustic and seismic arrays.

Earthquake recording at the Stanford DAS Array with fibers in existing telecomm conduits

NASA Astrophysics Data System (ADS)

Biondi, B. C.; Martin, E. R.; Yuan, S.; Cole, S.; Karrenbach, M. H.

2017-12-01

The Stanford Distributed Acoustic Sensing Array (SDASA-1) has been continuously recording seismic data since September 2016 on 2.5 km of single mode fiber optics in existing telecommunications conduits under Stanford's campus. The array is figure-eight shaped and roughly 600 m along its widest side with a channel spacing of roughly 8 m. This array is easy to maintain and is nonintrusive, making it well suited to urban environments, but it sacrifices some cable-to-ground coupling compared to more traditional seismometers. We have been testing its utility for earthquake recording, active seismic, and ambient noise interferometry. This talk will focus on earthquake observations. We will show comparisons between the strain rates measured throughout the DAS array and the particle velocities measured at the nearby Jasper Ridge Seismic Station (JRSC). In some of these events, we will point out directionality features specific to DAS that can require slight modifications in data processing. We also compare repeatability of DAS and JRSC recordings of blasts from a nearby quarry. Using existing earthquake databases, we have created a small catalog of DAS earthquake observations by pulling records of over 700 Northern California events spanning Sep. 2016 to Jul. 2017 from both the DAS data and JRSC. On these events we have tested common array methods for earthquake detection and location including beamforming and STA/LTA analysis in time and frequency. We have analyzed these events to approximate thresholds on what distances and magnitudes are clearly detectible by the DAS array. Further analysis should be done on detectability with methods tailored to small events (for example, template matching). In creating this catalog, we have developed open source software available for free download that can manage large sets of continuous seismic data files (both existing files, and files as they stream in). This software can both interface with existing earthquake networks, and efficiently extract earthquake recordings from many continuous recordings saved on the users machines.

Complex Seismic Anisotropy at the Edges of a Very-low Velocity Province in the Lowermost Mantle

NASA Astrophysics Data System (ADS)

Wang, Y.; Wen, L.

2005-12-01

A prominent very-low velocity province (VLVP) in the lowermost mantle is revealed, and has been extensively mapped out in recent seismic studies (e.g., Wang and Wen, 2004). Seismic evidence unambiguously indicates that the VLVP is compositionally distinct, and its seismic structure can be best explained by partial melting driven by a compositional change produced in the early Earth's history (Wen, 2001; Wen et. al, 2001; Wang and Wen, 2004). In this presentation, we study the seismic anisotropic behavior inside the VLVP and its surrounding area using SKS and SKKS waveform data. We collect 272 deep earthquakes recorded by more than 80 stations in the Kaapvaal seismic array in southern Africa from 1997 to 1999. Based on the data quality, we choose SKS and SKKS waveform data for 16 earthquakes to measure the anisotropic parameters: the fast polarization direction and the splitting time, using the method of Silver and Chan (1991). A total of 162 high-quality measurements are obtained based on the statistics analysis of shear wave splitting results. The obtained anisotropy exhibits different patterns for the SKS and SKKS phases sampling inside the VLVP and at the edges of the VLVP. When the SKS and SKKS phases sample inside the VLVP, their fast polarization directions exhibit a pattern that strongly correlates with stations, gradually changing from 11°N~to 80°N~across the seismic array from south to north and rotating back to the North direction over short distances for several northernmost stations. The anisotropy pattern obtained from the analysis of the SKKS phases is the same as that from the SKS phases. However, when the SKS and SKKS phases sample at the edges of the VLVP, the measured anisotropy exhibits a very complex pattern. The obtained fast polarization directions change rapidly over a small distance, and they no longer correlate with stations; the measurements obtained from the SKS analysis also differ with those from the SKKS analysis. As the SKS and SKKS phases have similar propagation paths in the lithosphere beneath the array, but different sampling points near the core mantle boundary. The anisotropy in the lithosphere should have a similar influence on SKS and SKKS phases. Therefore, the similar anisotropy obtained from the SKS and SKKS phases sampling inside the VLVP and its correlation with seismic stations suggest that the observed anisotropy variation across the seismic array is mainly due to the anisotropy in the lithosphere beneath the Kaapvaal seismic array, and the interior of the VLVP is isotropic or weakly anisotropic. On the other hand, for the SKS and SKKS phases sampling at the edges of the VLVP, the observed complex anisotropy pattern and the lack of correlation between the results from the SKS and SKKS analyses indicate that part of that anisotropy has to originate from the lowermost mantle near the exit points of these phases at the core mantle boundary, revealing a complex flow pattern at the edges of the VLVP.

4-D crustal structure of the conterminous U.S.: Continental assembly, crustal growth, and deformation history from receiver functions, xenoliths, and structural mapping

NASA Astrophysics Data System (ADS)

Schulte-Pelkum, V.; Mahan, K. H.

2015-12-01

We investigate seismic and geological features related to the tectonic evolution of the crust on a continent-wide scale. We present continent-wide features using Transportable Array data receiver function analysis, followed by regional comparisons to tie to ground truth from xenolith studies and structural mapping. We stress that the Transportable Array, at ~75 km station spacing, only offers a collection of point measurements of the crust due to the lack of crossing raypaths. 7.x layers (lower crust with high seismic velocities) can be created during crustal growth processes such as magmatic or mechanical underplating and during crustal modification such as large-scale melting. We present receiver function results and a compilation of previous regional studies using refraction data or receiver functions from regional dense networks. 7.x layers appear predominantly in parts of the northern U.S. Cordillera and across the southeastern U.S. We compare the seismic results with a xenolith study in Montana that details incremental growth of the 7.x layer from the Archean on. Hydration of a granulitic lower crust can destroy the 7.x layer and has the potential to cause epirogenic uplift. We interpret the pattern seen across the Transportable Array in the light of this hypothesis. Ductile deformation of the deep crust generates shear fabrics that can be detected seismically. Receiver functions detect shear zones via contrasts in foliation to the surrounding material. We map foliation strikes and depths in the crust across the Transportable Array using azimuthal analysis of receiver functions. Strikes from receiver functions typically align with surface fault traces in tectonically active regions, with depths of the converters exceeding the brittle zone. We discuss continent-wide strikes mapped with receiver functions. Contrasting orientations of Proterozoic shear zones and pervasive surrounding foliations in basement exposures in Colorado are reflected in seismic results from the Transportable Array and CREST experiment.

Analysis of the low-level seismicity along the Southern Indian Ocean spreading ridges recorded by the OHASISBIO array of hydrophones in 2012

NASA Astrophysics Data System (ADS)

Tsang-Hin-Sun, Eve; Royer, Jean-Yves; Sukhovich, Alexey; Perrot, Julie

2014-05-01

Arrays of autonomous hydrophones (AUHs) proved to be a very valuable tool for monitoring the seismic activity of mid-ocean ridges. AUHs take advantage of the ocean acoustic properties to detect many low-magnitude underwater earthquakes undetected by land-based stations. This allows for a significant improvement in the magnitude completeness level of seismic catalogs in remote oceanic areas. This study presents some results from the deployment of the OHASISBIO array comprising 7 AUHs deployed in the southern Indian Ocean. The source of acoustic events, i.e. site where - conversion from seismic to acoustic waves occur and proxy to epicenters for shallow earthquakes - can be precisely located within few km, inside the AUH array. The distribution of the uncertainties in the locations and time-origins shows that the OHASISBIO array reliably covers a wide region encompassing the Indian Ocean triple junction and large extent of the three mid-oceanic Indian spreading ridges, from 52°E to 80°E and from 25°S to 40°S. During its one year long deployment in 2012 and in this area the AUH array recorded 1670 events, while, for the same period, land-based networks only detected 470 events. A comparison of the background seismicity along the South-east (SEIR) and South-west (SWIR) Indian ridges suggests that the microseismicity, even over a year period, could be representative of the steady-state of stress along the SEIR and SWIR; this conclusion is based on very high Spearman's correlations between our one-year long AUH catalog and teleseismic catalogs over nearly 40 years. Seismicity along the ultra-slow spreading SWIR is regularly distributed in space and time, along spreading segments and transform faults, whereas the intermediate spreading SEIR diplays clusters of events in the vicinity of some transform faults or near specific geological structures such as the St-Paul and Amsterdam hotspot. A majority of these clusters seem to be related to magmatic processes, such as dyke intrusion or propagation. The analysis of mainshock-aftershock sequences reveals that flew clusters fit a modified Omori law, non-withstanding of their location (on transform faults or not), reflecting complex rupture mechanisms along both spreading ridges.

Dispersion analysis of passive surface-wave noise generated during hydraulic-fracturing operations

USGS Publications Warehouse

Forghani-Arani, Farnoush; Willis, Mark; Snieder, Roel; Haines, Seth S.; Behura, Jyoti; Batzle, Mike; Davidson, Michael

2014-01-01

Surface-wave dispersion analysis is useful for estimating near-surface shear-wave velocity models, designing receiver arrays, and suppressing surface waves. Here, we analyze whether passive seismic noise generated during hydraulic-fracturing operations can be used to extract surface-wave dispersion characteristics. Applying seismic interferometry to noise measurements, we extract surface waves by cross-correlating several minutes of passive records; this approach is distinct from previous studies that used hours or days of passive records for cross-correlation. For comparison, we also perform dispersion analysis for an active-source array that has some receivers in common with the passive array. The active and passive data show good agreement in the dispersive character of the fundamental-mode surface-waves. For the higher mode surface waves, however, active and passive data resolve the dispersive properties at different frequency ranges. To demonstrate an application of dispersion analysis, we invert the observed surface-wave dispersion characteristics to determine the near-surface, one-dimensional shear-wave velocity.

One to Large N Gradiometry

NASA Astrophysics Data System (ADS)

Langston, C. A.

2017-12-01

The seismic wave gradient tensor can be derived from a variety of field observations including measurements of the wavefield by a dense seismic array, strain meters, and rotation meters. Coupled with models of wave propagation, wave gradients along with the original wavefield can give estimates of wave attributes that can be used to infer wave propagation directions, apparent velocities, spatial amplitude behavior, and wave type. Compact geodetic arrays with apertures of 0.1 wavelength or less can be deployed to provide wavefield information at a localized spot similar to larger phased arrays with apertures of many wavelengths. Large N, spatially distributed arrays can provide detailed information over an area to detect structure changes. Key to accurate computation of spatial gradients from arrays of seismic instruments is knowledge of relative instrument responses, particularly component sensitivities and gains, along with relative sensor orientations. Array calibration has been successfully performed for the 14-element Pinyon Flat, California, broadband array using long-period teleseisms to achieve relative precisions as small as 0.2% in amplitude and 0.35o in orientation. Calibration has allowed successful comparison of horizontal seismic strains from local and regional seismic events with the Plate Boundary Observatory (PBO) borehole strainmeter located at the facility. Strains from the borehole strainmeter in conjunction with ground velocity from a co-located seismometer are used as a "point" array in estimating wave attributes for the P-SV components of the wavefield. An effort is underway to verify the calibration of PBO strainmeters in southern California and their co-located borehole seismic sensors to create an array of point arrays for use in studies of regional wave propagation and seismic sources.

Multi-sensor investigation of the Sumatran Tsunami: observations and analysis of hydroacoustic, seismic, infrasonic, and tide gauge data

NASA Astrophysics Data System (ADS)

Bhattacharyya, J.; Pulli, J.; Gibson, R.; Upton, Z.

2005-05-01

We present an analysis of the acoustic signals from the December 26, 2004 Sumatra earthquakes, in conjunction with the seismic and tide gauge information from the event. The M9.0 mainshock and its aftershocks were recorded by a suite of seismic sensors around the globe, giving us information on its location and the source process. Recently installed sensor assets in the Indian Ocean have enabled us to study additional features of this significant event. Hydroacoustic signals were recorded by three hydrophone arrays, and the direction finding capability of these arrays allows us to examine the location, time and extent of the T-wave generation process. We detect a clear variation of the back-azimuth that is consistent with the spatial extent of the source rupture. Recordings from nearly co-located seismometers provide insights into the acoustic-to-seismic conversion process for T-waves at islands, along with the variation in signal characteristics with source size. Two separate infrasound arrays detect the atmospheric signals generated by the event, along with additional observations of the seismic surface wave and the T-phase. We will present a comparison of the signals from the mainshock, as a function of location and size, with those from aftershocks and similar events in the nearby region. Our acoustic observations compare favorably with model predictions of wave propagation in the region. For the hydroacoustic data, the azimuth, arrival time, and signal blockage characteristics, from three separate arrays, associate the onset of the signal with the mainshock and with a time extent consistent with the rupture propagation. Our analysis of the T-phase travel times suggests that the seismic-to-acoustic conversion occurs more than 100 km from the epicenter. The infrasound signal's arrival time and signal duration are consistent with both stratospheric and thermospheric propagation from a source region near the mainshock. We use the tide gauge data from stations around the Indian Ocean to identify the arrival time of the Tsunami. The acoustic and seismic signals associated with the earthquakes arrive at the remote stations significantly ahead of the Tsunami. We combine the information from the various sensors to investigate the ability of the acoustic stations to detect the Tsunami.

Ambient seismic noise monitoring of the Super-Sauze landslide from a very dense temporary seismic array

NASA Astrophysics Data System (ADS)

Chtouki, Toufik; Vergne, Jerome; Provost, Floriane; Malet, Jean-Philippe; Burtin, Arnaud; Hibert, Clément

2017-04-01

The Super-Sauze landslide is located on the southern part of the Barcelonnette Basin (French Alps) and has developed in a soft clay-shale environment. It is one of the four sites continuously monitored through a wide variety of geophysical and hydro-geological techniques in the framework of the OMIV French national landslide observatory. From early June to mid-July 2016, a temporary dense seismic array has been installed in the most active part of the landslide and at its surroundings. 50 different sites with an average inter-station distance of 50m have been instrumented with 150 miniaturized and autonomous seismic stations (Zland nodes), allowing a continuous record of the seismic signal at frequencies higher than 0.2Hz over an almost regular grid. Concurrently, a Ground-Based InSAR device allowed for a precise and continuous monitoring of the surface deformation. Overall, this experiment is intended to better characterize the spatio-temporal evolution of the deformation processes related to various type of forcing. We analyze the continuous records of ambient seismic noise recorded by the dense array. Using power spectral densities, we characterize the various types of natural and anthropogenic seismic sources, including the effect of water turbulence and bedload transport in the small nearby torrents. We also compute the correlation of the ambient diffuse seismic noise in various frequency bands for the 2448 station pairs to recover the empirical Green functions between them. The temporal evolution of the coda part of these noise correlation functions allows monitoring and localizing shear wave velocity variations in the sliding mass. Here we present some preliminary results of this analysis and compare the seismic variations to meteorological data and surface deformation.

Improving slowness estimate stability and visualization using limited sensor pair correlation on seismic arrays

NASA Astrophysics Data System (ADS)

Gibbons, Steven J.; Näsholm, S. P.; Ruigrok, E.; Kværna, T.

2018-04-01

Seismic arrays enhance signal detection and parameter estimation by exploiting the time-delays between arriving signals on sensors at nearby locations. Parameter estimates can suffer due to both signal incoherence, with diminished waveform similarity between sensors, and aberration, with time-delays between coherent waveforms poorly represented by the wave-front model. Sensor-to-sensor correlation approaches to parameter estimation have an advantage over direct beamforming approaches in that individual sensor-pairs can be omitted without necessarily omitting entirely the data from each of the sensors involved. Specifically, we can omit correlations between sensors for which signal coherence in an optimal frequency band is anticipated to be poor or for which anomalous time-delays are anticipated. In practice, this usually means omitting correlations between more distant sensors. We present examples from International Monitoring System seismic arrays with poor parameter estimates resulting when classical f-k analysis is performed over the full array aperture. We demonstrate improved estimates and slowness grid displays using correlation beamforming restricted to correlations between sufficiently closely spaced sensors. This limited sensor-pair correlation (LSPC) approach has lower slowness resolution than would ideally be obtained by considering all sensor-pairs. However, this ideal estimate may be unattainable due to incoherence and/or aberration and the LSPC estimate can often exploit all channels, with the associated noise-suppression, while mitigating the complications arising from correlations between very distant sensors. The greatest need for the method is for short-period signals on large aperture arrays although we also demonstrate significant improvement for secondary regional phases on a small aperture array. LSPC can also provide a robust and flexible approach to parameter estimation on three-component seismic arrays.

Seismic Imaging of a Prospective Geothermal Play, Using a Dense Geophone Array

NASA Astrophysics Data System (ADS)

Trow, A.; Pankow, K. L.; Wannamaker, P. E.; Lin, F. C.; Ward, K. M.

2017-12-01

In the summer of 2016 a dense array of 48 Nodal Seismic geophones was deployed near Beaver, Utah on the eastern flank of the Mineral Mountains. The array aperture was approximately 20 kilometers and recorded continuous seismic data for 30 days. Geophones were centered on a previously known shallow (5km depth) magnetolluric (MT) low-resistivity body. This region of low resistivity was interpreted to possibly contain hydrothermal/geothermal fluids and was targeted for further seismic investigation. The seismic array geometry was designed to optimize seismic event detection for small (magnitude of completeness zero) earthquakes and to facilitate seismic imaging at depths of 5 km and deeper. For the duration of the experiment, one ML 1 earthquake was detected underneath the array with 15 other earthquakes detected to the east and south in the more seismically active Pavant Range. Different passive imaging techniques, including ambient noise and earthquake tomography are being explored in order to produce a seismic velocity image. Understanding the subsurface, specifically the fracture network and fluid content of the bedrock is important for characterization of a geothermal prospect. If it is rich in fluids, it can be assumed that some fracture network is in place to accommodate such fluids. Both fractures and fluid content of the prospect will have an effect on the seismic velocities in the basement structure. These properties can help determine the viability of a geothermal system for power production.

Yearly report, Yucca Mountain project

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brune, J.N.

1992-09-30

We proposed to (1) Develop our data logging and analysis equipment and techniques for analyzing seismic data from the Southern Great Basin Seismic Network (SGBSN), (2) Investigate the SGBSN data for evidence of seismicity patterns, depth distribution patterns, and correlations with geologic features (3) Repair and maintain our three broad band downhole digital seismograph stations at Nelson, nevada, Troy Canyon, Nevada, and Deep Springs, California (4) Install, operate, and log data from a super sensitive microearthquake array at Yucca Mountain (5) Analyze data from micro-earthquakes relative to seismic hazard at Yucca Mountain.

Initial results from the Volcanic Risk in Saudi Arabia project: Microearthquakes in the northern Harrat Rahat monogenetic volcanic field, Madinah, Saudi Arabia

NASA Astrophysics Data System (ADS)

Kenedi, C. L.; Alvarez, M. G.; Abdelwahed, M. F.; Aboud, E.; Lindsay, J. M.; Mokhtar, T. A.; Moufti, M. R.

2012-12-01

An 8-station borehole seismic research array is recording microearthquake data in northern Harrat Rahat. This recently active monogenetic volcanic field lies southeast of the Islamic holy city of Madinah, Kingdom of Saudi Arabia. The VORiSA seismographs are operated in collaboration between King Abdulaziz University in Jeddah and the Institute of Earth Science and Engineering, University of Auckland, in New Zealand. The goal of the VORiSA project is to evaluate the seismic and volcanic hazard around Madinah. To this end, we will evaluate the local earthquake activity including the extent to which local earthquakes are tectonic or volcanic. We also will use seismicity to understand the subsurface structure. The analytical goals of the seismic research array are the following: (1) Calculate a new seismic velocity model, (2) Map subsurface structures using seismic tomography, and (3) Explore for fracture zones using shear wave splitting analysis. As compared to seismographs installed on the surface, borehole seismometers detect smaller and more numerous microearthquake signals. The sensitivity and location of the borehole sensors in the VORiSA array are designed to detect these weak signals. The array has a total aperture of 17 km with station spacing at 5 - 10 km. The seismometers are housed in IESE model S21g-2.0, two Hz, 3-component borehole sondes. Sensor depths range from 107 - 121 m. The data acquisition system at each stand-alone station consists of a Reftek 130-01, 6-channel, 24 bit data logger which records at 250 samples per second. The power source is a deep cycle battery with solar recharge. Local temperatures reach extremes of 0° to 50°C, so the battery and recorder are contained in a specially designed underground vault. The vault also provides security in the remote and sparsely populated volcanic field. Recording began on 31 March 2012. An average of one earthquake every three days suggests that currently this is not a highly seismic area. However, seismic swarms, likely related to magmatic intrusion, have occurred in 1999 in Harrat Rahat (~145 earthquakes, M1.4 to 2.3) (Moufti et al., 2010) and in 2009 in Harrat Lunayyir (~30,000 earthquakes up to M5.4) (Pallister et al., 2010). We can locate microearthquakes of Mm = -1 within the array, a significant advantage over the previous surface network. We have characterized instrument noise using power spectrum probability density functions (McNamara and Buland, 2004). All stations show a very high signal to noise ratio; for a near-source M-1 event S/N is ~5. The available data are still too sparse for advanced analysis and currently appear as a cloud of seismicity.

Seismicity in Oklahoma Before Prague

NASA Astrophysics Data System (ADS)

Delorey, A. A.; Johnson, P. A.

2017-12-01

The 2011 M5.7 Prague earthquake was the first large anthropogenically induced earthquake in Oklahoma. Since then, three more M5+ earthquakes followed it near Fairview, Pawnee, and Cushing. Oklahoma induced seismicity has garnered a lot of attention from both the media and the scientific community. But, little is known about seismicity in Oklahoma prior to the Prague earthquake due to a lack of instrumentation. We ask the question, "Was there any indication in the geophysical record prior to the Prague earthquake that bigger earthquakes were becoming more likely?" Fortunately, stations from Earthscope's Transportable Array were in Oklahoma during 2010 and 2011 providing a sparse, but still useful data set. Using our microseismicity detector called Interstation Seismic Coherence, we were able to catalog over 3000 earthquakes with a magnitude of completeness around 2.0 in northeastern Oklahoma over 17 months between June 2010 and the Prague earthquake in November 2011. During this period of time there are less than 200 earthquakes in the ANSS Comprehensive Catalog and 900 in the catalog produced by the Array Network Facility at the UCSD using Transportable Array stations. The M>5 earthquakes occurred in a region where stress conditions and seismicity rates were evolving much faster than they do in many natural systems presenting an opportunity to study the time dependence of upper crustal behavior. A clustering analysis shows that earthquakes occurring in northeastern Oklahoma during 2010-2011 are highly correlated with the magnitude of solid earth tides. Although some aftershocks and clusters were recorded following the Prague earthquake using temporary arrays, regional seismicity is not well recorded again until later in 2013. Of note, after 2013, we no longer observe tidal correlation suggesting the ensemble of fault criticality has evolved. One explanation for this change in earthquake behavior is a change in poroelastic conditions.

Characterizing Variability in Long Period Horizontal Tilt Noise Through Coherence Analysis

NASA Astrophysics Data System (ADS)

Rohde, M. D.; Ringler, A. T.; Hutt, C. R.; Wilson, D.; Holland, A. A.

2016-12-01

Tilt induced horizontal noise fundamentally limits a wide variety of seismological studies. This noise source is not well characterized or understood and the spatial variability has yet to be well constrained. Long-period (i.e., greater than 100 seconds period) horizontal seismic noise is generally known to be of greater magnitude than long-period vertical seismic noise due to tilt noise. As a result, many studies only make use of the vertical seismic wavefield as opposed to all three axes. The main source of long-period horizontal seismic noise is hypothesized to be tilt due to atmospheric pressure variation. Reducing horizontal tilt noise could lead to improved resolution of torsional earth modes and other long-period horizontal seismic signals that are often dominated by tilt noise, as well as better construction of seismic isolation systems for sensitive scientific experiments. We looked at a number of small aperture array configurations. For each array we installed eight Streckeisen STS-2 broadband seismometers in the Albuquerque Seismological Laboratory (ASL) underground vault. The data from these array configurations was used to characterize the long period horizontal tilt noise over a spatially small scale. Sensors were installed approximately 1 to 10 meters apart depending on the array configuration. Coherence as a function of frequency was calculated between sensors, of which we examine the frequency band between 10 and 500 seconds. We observed complexity in the pair-wise coherence with respect to frequency, seismometer axis, and time, even for spatially close sensors. We present some possible explanations for the large variability in our coherence observations and demonstrate how these results can be applied to find potentially low horizontal noise locations over small spatial scales, such as in stations with multiple co-located sensors within the Global Seismographic Network.

An Expedient but Fascinating Geophysical Chimera: The Pinyon Flat Seismic Strain Point Array

NASA Astrophysics Data System (ADS)

Langston, C. A.

2016-12-01

The combination of a borehole Gladwin Tensor Strain Meter (GTSM) and a co-located three component broadband seismometer (BB) can theoretically be used to determine the propagation attributes of P-SV waves in vertically inhomogeneous media such as horizontal phase velocity and azimuth of propagation through application of wave gradiometry. A major requirement for this to be successful is to have well-calibrated strain and seismic sensors to be able to rely on using absolute wave amplitude from both systems. A "point" seismic array is constructed using the PBO GTSM station B084 and co-located BB seismic stations from an open array experiment deployed by UCSD as well as PFO station at the Pinyon Flat facility. Site amplitude statics for all three ground motion components are found for the 14-element (13 PY stations + PFO), small aperture seismic array using data from 47 teleseisms recorded from 2014 until present. Precision of amplitude measurement at each site is better than 0.2% for vertical components, 0.5% for EW components, and 1% for NS components. Relative amplitudes among sites of the array are often better than 1% attesting to the high quality of the instrumentation and installation. The wavefield and related horizontal strains are computed for the location of B084 using a second order Taylor's expansion of observed waveforms from moderate ( M4) regional events. The computed seismic array areal, differential, and shear strains show excellent correlation in both phase and amplitude with those recorded by B084 when using the calibration matrix previously determined using teleseismic strains from the entire ANZA seismic network. Use of the GTSM-BB "point" array significantly extends the bandwidth of gradiometry calculations over the small-aperture seismic array by nearly two orders of magnitude from 0.5 Hz to 0.01 Hz. In principle, a seismic strain point array could be constructed from every PBO GTSM with a co-located seismometer to help serve earthquake early warning for large regional events on North America's west coast.

Moho Depth and Geometry in the Illinois Basin Region Based on Gravity and Seismic Data from an EarthScope FlexArray Experiment

NASA Astrophysics Data System (ADS)

Curcio, D. D.; Pavlis, G. L.; Yang, X.; Hamburger, M. W.; Zhang, H.; Ravat, D.

2017-12-01

We present results from a combined analysis of seismic and gravity in the Illinois Basin region that demonstrate the presence of an unusually deep and highly variable Moho discontinuity. We construct a new, high-resolution image of the Earth's crust beneath the Illinois Basin using teleseismic P-wave receiver functions from the EarthScope OIINK (Ozarks, Illinois, INdiana, Kentucky) Flexible Array and the USArray Transportable Array. Our seismic analyses involved data from 143 OIINK stations and 80 USArray stations, using 3D plane-wave migration and common conversion point (CCP) stacking of P-to-S conversion data. Seismic interpretation has been done using the seismic exploration software package Petrel. One of the most surprising results is the anomalous depth of the Moho in this area, ranging from 41 to 63 km, with an average depth of 50 km. This thickened crust is unexpected in the Illinois Basin area, which has not been subject to convergence and mountain building processes in the last 900 Ma. This anomalously thick crust in combination with the minimal topography requires abnormally dense lower crust or unusually light upper mantle in order to retain gravitational equilibrium. Combining gravity modeling with the seismically identified Moho and a ubiquitous lower crustal boundary, we solve for the density variation of the middle and lower crust. We test the hypothesis that the anomalously thick crust and its high lower crustal layer observed in most of the central and southeastern Illinois Basin predates the formation and development of the current Illinois Basin. Post-formation tectonic activity, such as late Precambrian rifting or underplating are inferred to have modified the crustal thickness as well. The combination of high-resolution seismic data analysis and gravity modeling promises to provide additional insight into the geometry and composition of the lower crust in the Illinois Basin area.

Multi-mode phase speed measurements with array-based analysis: Application to the North American continent

NASA Astrophysics Data System (ADS)

Matsuzawa, H.; Yoshizawa, K.

2017-12-01

Recent high-density broad-band seismic networks allow us to construct improved 3-D upper mantle models with unprecedented horizontal resolution using surface waves. Such dispersion measurements have been primarily based on the analysis of fundamental mode. Higher-mode information can be of help in enhancing vertical resolution of 3-D models, but their dispersion analysis is intrinsically difficult, since wave-packets of several modes are overlapped each other in an observed seismogram. In this study, we measure phase dispersion of multi-mode surface waves with an array-based analysis. Our method is modeled on a one-dimensional frequency-wavenumber method originally developed by Nolet (1975, GRL), which can be applied to a set of broadband seismic records observed in a linear array along a great circle path. Through this analysis, we can obtain a spectrogram in c-T (phase speed - period) domain, which is characterized by mode-branch dispersion curves and relative spectral powers for each mode. Synthetic experiments indicate that we can separate the modal contribution using a long linear array with typical array length of about 2000 to 4000 km. The method is applied to a large data set from USArray using nearly 400 seismic events in 2007 - 2014 with Mw 6.5 or greater. Our phase-speed maps for the fundamental-mode Love and Rayleigh waves and the first higher-mode Rayleigh waves match well with the earlier models. The phase speed maps reflect typical large-scale features of regional seismic structure in North America, but smaller-scale variations are less constrained in our model, since our measured phase speeds represent path-average features over a long path (about a few thousands kilometers). Our multi-mode dispersion measurements can also be used for the extraction of mode-branch waveforms for the first a few modes. This can be done by applying a narrow filter around the dispersion curves of a target mode in c-T spectrogram. The mode-branch waveforms can then be reconstructed based on a linear Radon transform (e.g., Luo et al., 2015, GJI). Synthetic experiments suggest that we can successfully retrieve the mode-branch waveforms for several mode branches, which can be used in the secondary analysis for constraining local-scale heterogeneity with enhanced depth resolution.

3-D Characterization of Seismic Properties at the Smart Weapons Test Range, YPG

DTIC Science & Technology

2001-10-01

confidence limits around each interpolated value. Ground truth was accomplished through cross-hole seismic measurements and borehole logs. Surface wave... seismic method, as well as estimating the optimal orientation and spacing of the seismic array . A variety of sources and receivers was evaluated...location within the array is partially related to at least two seismic lines. Either through good fortune or foresight by the designers of the SWTR site

Elastic-Waveform Inversion with Compressive Sensing for Sparse Seismic Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Youzuo; Huang, Lianjie

2015-01-28

Accurate velocity models of compressional- and shear-waves are essential for geothermal reservoir characterization and microseismic imaging. Elastic-waveform inversion of multi-component seismic data can provide high-resolution inversion results of subsurface geophysical properties. However, the method requires seismic data acquired using dense source and receiver arrays. In practice, seismic sources and/or geophones are often sparsely distributed on the surface and/or in a borehole, such as 3D vertical seismic profiling (VSP) surveys. We develop a novel elastic-waveform inversion method with compressive sensing for inversion of sparse seismic data. We employ an alternating-minimization algorithm to solve the optimization problem of our new waveform inversionmore » method. We validate our new method using synthetic VSP data for a geophysical model built using geologic features found at the Raft River enhanced-geothermal-system (EGS) field. We apply our method to synthetic VSP data with a sparse source array and compare the results with those obtained with a dense source array. Our numerical results demonstrate that the velocity models produced with our new method using a sparse source array are almost as accurate as those obtained using a dense source array.« less

Autonomous microexplosives subsurface tracing system final report.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Engler, Bruce Phillip; Nogan, John; Melof, Brian Matthew

The objective of the autonomous micro-explosive subsurface tracing system is to image the location and geometry of hydraulically induced fractures in subsurface petroleum reservoirs. This system is based on the insertion of a swarm of autonomous micro-explosive packages during the fracturing process, with subsequent triggering of the energetic material to create an array of micro-seismic sources that can be detected and analyzed using existing seismic receiver arrays and analysis software. The project included investigations of energetic mixtures, triggering systems, package size and shape, and seismic output. Given the current absence of any technology capable of such high resolution mapping ofmore » subsurface structures, this technology has the potential for major impact on petroleum industry, which spends approximately $1 billion dollar per year on hydraulic fracturing operations in the United States alone.« less

Exploring Seismic Noise with the USArray Transportable Array

NASA Astrophysics Data System (ADS)

Woodward, R.; Busby, R. W.; Simpson, D. W.

2009-12-01

The large number of seismic stations that comprise the EarthScope USArray Transportable Array (TA) seismic network provide an unparalleled opportunity for studying how seismic noise evolves with time over a large portion of the North American continent. Power spectra for every station in the TA data are computed automatically, for every hour of every station-day, by the Quality Analysis Control Kit (QUACK) system at the IRIS Data Management Center. The power spectra utilize hour-long data segments, with 50% overlap between segments, providing spectral values in the band between 20 Hz and 172 s. Thus, at any in-band frequency one can construct a continuous two-year time history of seismic noise for every TA station. When the time variation of the power spectra values across the array are rendered as individual movie frames one can examine the evolution of seismic noise across the full spatio-temporal extent of the TA. Overall, the background noise levels (especially at periods below 10 s) are remarkably uniform across the entire array. Numerous expected features are present, including diurnal and annual variations, enhanced noise levels at coastal stations, transients related to large storms, and episodes when the observations of background noise are dominated by earthquake energy. Upgrades to the TA station instrumentation will provide the capability to measure additional physical factors relevant to seismic noise. All TA stations deployed after August 2009 include MEMS barometers that can measure atmospheric pressure from DC to approximately 0.1 Hz. In additional, several stations have been temporarily equipped with infrasound sensors. Previous research has highlighted the direct effect of atmospheric pressure fluctuations on very long period vertical seismometers. The relationship to noise observed on horizontal seismometers is more complex. However, with a large number of uniform installations it may be possible to make further progress. We will present analyses of the spatio-temporal evolution of noise observed on the TA stations and present preliminary results from the barometers and infrasound sensors that have been deployed with TA stations so far. We will discuss opportunities for augmenting TA stations with additional sensors that may further elucidate seismic noise processes.

Towards a first design of a Newtonian-noise cancellation system for Advanced LIGO

NASA Astrophysics Data System (ADS)

Coughlin, M.; Mukund, N.; Harms, J.; Driggers, J.; Adhikari, R.; Mitra, S.

2016-12-01

Newtonian gravitational noise from seismic fields is predicted to be a limiting noise source at low frequency for second generation gravitational-wave detectors. Mitigation of this noise will be achieved by Wiener filtering using arrays of seismometers deployed in the vicinity of all test masses. In this work, we present optimized configurations of seismometer arrays using a variety of simplified models of the seismic field based on seismic observations at LIGO Hanford. The model that best fits the seismic measurements leads to noise reduction limited predominantly by seismometer self-noise. A first simplified design of seismic arrays for Newtonian-noise cancellation at the LIGO sites is presented, which suggests that it will be sufficient to monitor surface displacement inside the buildings.

Lateral variations of the Guerrero-Oaxaca subduction zone (Mexico) derived from weak seismicity (Mb3.5+) detected on a single array at teleseismic distance

NASA Astrophysics Data System (ADS)

Letort, Jean; Retailleau, Lise; Boué, Pierre; Radiguet, Mathilde; Gardonio, Blandine; Cotton, Fabrice; Campillo, Michel

2018-05-01

Detections of pP and sP phase arrivals (the so-called depth phases) at teleseismic distance provide one of the best ways to estimate earthquake focal depth, as the P-pP and the P-sP delays are strongly dependent on the depth. Based on a new processing workflow and using a single seismic array at teleseismic distance, we can estimate the depth of clusters of small events down to magnitude Mb 3.5. Our method provides a direct view of the relative variations of the seismicity depth from an active area. This study focuses on the application of this new methodology to study the lateral variations of the Guerrero subduction zone (Mexico) using the Eielson seismic array in Alaska (USA). After denoising the signals, 1232 Mb 3.5 + events were detected, with clear P, pP, sP and PcP arrivals. A high-resolution view of the lateral variations of the depth of the seismicity of the Guerero-Oaxaca area is thus obtained. The seismicity is shown to be mainly clustered along the interface, coherently following the geometry of the plate as constrained by the receiver-function analysis along the Meso America Subduction Experiment profile. From this study, the hypothesis of tears on the western part of Guerrero and the eastern part of Oaxaca are strongly confirmed by dramatic lateral changes in the depth of the earthquake clusters. The presence of these two tears might explain the observed lateral variations in seismicity, which is correlated with the boundaries of the slow slip events.

Submarine seismic monitoring of El Hierro volcanic eruption with a 3C-geophone string: applying new acquisition and data processing techniques to volcano monitoring

NASA Astrophysics Data System (ADS)

Jurado, Maria Jose; Ripepe, Maurizio; Lopez, Carmen; Blanco, Maria Jose; Crespo, Jose

2015-04-01

A submarine volcanic eruption took place near the southernmost emerged land of the El Hierro Island (Canary Islands, Spain), from October 2011 to February 2012. The Instituto Geografico Nacional (IGN) seismic stations network evidenced seismic unrest since July 2011 and was a reference also to follow the evolution of the seismic activity associated with the volcanic eruption. Right after the eruption onset, in October 2011 a geophone string was deployed by the CSIC-IGN to monitor seismic activity. Monitoring with the seismic array continued till May 2012. The array was installed less than 2 km away from the new vol¬cano, next to La Restinga village shore in the harbor from 6 to 12m deep into the water. Our purpose was to record seismic activity related to the volcanic activity, continuously and with special interest on high frequency events. The seismic array was endowed with 8, high frequency, 3 component, 250 Hz, geophone cable string with a separation of 6 m between them. Each geophone consists on a 3-component module based on 3 orthogonal independent sensors that measures ground velocity. Some of the geophones were placed directly on the seabed, some were buried. Due to different factors, as the irregular characteristics of the seafloor. The data was recorded on the surface with a seismometer and stored on a laptop computer. We show how acoustic data collected underwater show a great correlation with the seismic data recorded on land. Finally we compare our data analysis results with the observed sea surface activity (ash and lava emission and degassing). This evidence is disclosing new and innovative tecniques on monitoring submarine volcanic activity. Reference Instituto Geográfico Nacional (IGN), "Serie El Hierro." Internet: http://www.ign.es/ign/resources /volcanologia/HIERRO.html [May, 17. 2013

Quantitative analysis of seismic fault zone waves in the rupture zone of the 1992 Landers, California, earthquake: Evidence for a shallow trapping structure

USGS Publications Warehouse

Peng, Z.; Ben-Zion, Y.; Michael, A.J.; Zhu, L.

2003-01-01

We analyse quantitatively a waveform data set of 238 earthquakes recorded by a dense seismic array across and along the rupture zone of the 1992 Landers earthquake. A grid-search method with station delay corrections is used to locate events that do not have catalogue locations. The quality of fault zone trapped waves generated by each event is determined from the ratios of seismic energy in time windows corresponding to trapped waves and direct S waves at stations close to and off the fault zone. Approximately 70 per cent of the events with S-P times of less than 2 s, including many clearly off the fault, produce considerable trapped wave energy. This distribution is in marked contrast with previous claims that trapped waves are generated only by sources close to or inside the Landers rupture zone. The time difference between the S arrival and trapped waves group does not grow systematically with increasing hypocentral distance and depth. The dispersion measured from the trapped waves is weak. These results imply that the seismic trapping structure at the Landers rupture zone is shallow and does not extend continuously along-strike by more than a few kilometres. Synthetic waveform modelling indicates that the fault zone waveguide has depth of approximately 2-4 km, a width of approximately 200 m, an S-wave velocity reduction relative to the host rock of approximately 30-40 per cent and an S-wave attenuation coefficient of approximately 20-30. The fault zone waveguide north of the array appears to be shallower and weaker than that south of the array. The waveform modelling also indicates that the seismic trapping structure below the array is centred approximately 100 m east of the surface break.

A pilot study of the Earthquake Precursors in the Southwest Peloponnes, Greece

NASA Astrophysics Data System (ADS)

Velez, A. P.; Tsinganos, K.; Karastathis, V. K.; Kafatos, M.; Ouzounov, D.; Papadopoulos, G. A.; Tselentis, A.; Eleftheriou, G.; Mouzakiotis, E.; Gika, F.; Aspiotis, T.; Liakopoulos, S.; Voulgaris, N.

2016-12-01

A seismic array of the most contemporary technology has been recently installed in the area of Southwest Peloponnese, Greece, an area well known for its high seismic activity. The tectonic regime of the Hellenic arc was the reason for many lethal earthquakes with considerable damage to the broader area of East Mediterranean sea. The seismic array is based on nine 32-bit stations with broadband borehole seismometers. The seismogenic region, monitored by the array, is offshore. At this place the earthquake location suffers by poor azimuthal coverage and the stations of the national seismic network are very distant to this area. Therefore, the existing network cannot effectively monitor the microseismicity. The new array achieved a detailed monitoring of the small events dropping considerably the magnitude of completeness. The detectability of the microearthquakes has been drastically improved permitting so the statistical assessment of earthquake sequences in the area. In parallel the monitored seismicity is directly related with Radon measurement in the soil, taken at three stations in the area.. Radon measurements are performed indirectly by means γ-ray spectrometry of its radioactive progenies 214Pb and 214Bi (emitted at 351 keV and 609 keV, respectively). NaI(Tl) detectors have been installed at 1 m depth, at sites in vicinity of faults providing continuous real time data. Local meteorological records for atmospheric corrections are also continuously recorded. According to the Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model atmospheric thermal anomalies observed before strong events can be attributed to increased radon concentration. This is also supported by the statistical analysis of AVHRR/NOAA-18 satellite thermal infrared (TIR) daily records. A combined study of precursor's signals is expected to provide a reliable assessment of their ability on short-term forecasting.

Washington State Play Fairway Analysis - Passive Monitoring of St. Helens Shear Zone for Tomography and Precision Microseismic Event Detection

DOE Data Explorer

Swyer, Michael (ORCID:0000000309776975); Cladouhos, Trenton; Crosbie, Kayla; Ulberg, Carl (ORCID:000000016198809X)

2017-10-03

Data resources were derived from a passive seismic survey of the northern St. Helens Shear Zone on geothermal leases 12-24 km north of Mount St. Helens for phase 2 of the Geothermal Play-Fairway Analysis of Washington State Prospects. A 20 seismic station array of broadband seismometers was deployed with irregular spacing (1-4 km) over an area of 12 km to image seismogenic features and their damage zones in the shallow crust.

Deconvolution enhanced direction of arrival estimation using one- and three-component seismic arrays applied to ocean induced microseisms

NASA Astrophysics Data System (ADS)

Gal, M.; Reading, A. M.; Ellingsen, S. P.; Koper, K. D.; Burlacu, R.; Gibbons, S. J.

2016-07-01

Microseisms in the period of 2-10 s are generated in deep oceans and near coastal regions. It is common for microseisms from multiple sources to arrive at the same time at a given seismometer. It is therefore desirable to be able to measure multiple slowness vectors accurately. Popular ways to estimate the direction of arrival of ocean induced microseisms are the conventional (fk) or adaptive (Capon) beamformer. These techniques give robust estimates, but are limited in their resolution capabilities and hence do not always detect all arrivals. One of the limiting factors in determining direction of arrival with seismic arrays is the array response, which can strongly influence the estimation of weaker sources. In this work, we aim to improve the resolution for weaker sources and evaluate the performance of two deconvolution algorithms, Richardson-Lucy deconvolution and a new implementation of CLEAN-PSF. The algorithms are tested with three arrays of different aperture (ASAR, WRA and NORSAR) using 1 month of real data each and compared with the conventional approaches. We find an improvement over conventional methods from both algorithms and the best performance with CLEAN-PSF. We then extend the CLEAN-PSF framework to three components (3C) and evaluate 1 yr of data from the Pilbara Seismic Array in northwest Australia. The 3C CLEAN-PSF analysis is capable in resolving a previously undetected Sn phase.

South-Central Tibetan Seismicity from HiCLIMB Seismic Array Data

NASA Astrophysics Data System (ADS)

Carpenter, S.; Nabelek, J.; Braunmiller, J.

2010-12-01

The HiCLIMB broadband passive seismic experiment (2002-2005) operated 233 sites along a 800-km long north-south array extending from the Himalayan foreland into the Central Tibetan Plateau and a flanking 350x350 km lateral array in southern Tibet and eastern Nepal. We use data from the experiment’s second phase (June 2004 to August 2005), when stations operated in Tibet, to locate earthquakes in south-central Tibet, a region with no permanent seismic network where little is known about its seismicity. We used the Antelope software for automatic detection and arrival time picking, event-arrival association and event location. Requiring a low detection and event association threshold initially resulted in ~110,000 declared events. The large database size rendered manual inspection unfeasible and we developed automated post-processing modules to weed out spurious detections and erroneous phase and event associations, which stemmed, e.g., from multiple coincident earthquakes within the array or misplaced seismicity from the great 2004 Sumatra earthquake. The resulting database contains ~32,000 events within 5° distance from the closest station. We consider ~7,600 events defined by more than 30 P and S arrivals well located and discuss them here. Seismicity in the subset correlates well with mapped faults and structures seen on satellite imagery attesting to high location quality. This is confirmed by non-systematic, kilometer-scale differences between automatic and manual locations for selected events. Seismicity in south-central Tibet is intense north of the Yarlung-Tsangpo Suture. Almost 90% of events occurred in the Lhasa Terrane mainly along north-south trending rifts. Vigorous activity (>4,800 events) accompanied two M>6 earthquakes in the Payang Basin (84°E), ~100 km west of the linear array. The Tangra-Yum Co (86.5°E) and Pumqu-Xianza (88°E) rifts were very active (~1,000 events) without dominant main shocks indicating swarm like-behavior possibly related to shallow magmatic or geothermal activity. Seismicity in the Qiangtang Terrane accounts for less than 10% of activity; seismicity is distributed and, except for the Yibuk-Caka Rift (87°E), difficult to associate with known structures. Lower seismicity may be apparent and simply reflect a larger distance to the array. Fewer than 5% of events occurred south of the Yarlong Tsangpo Suture in the Tethyan Himalaya, the only region where in addition to shallow seismicity a significant number of deep (mantle) events was located. Hypocenter depth, particularly for shallow events, is usually not well constrained due to array geometry and large distances to closest sites. The nature of deep events inside the array, though, is resolved.

Search for Long Period Solar Normal Modes in Ambient Seismic Noise

NASA Astrophysics Data System (ADS)

Caton, R.; Pavlis, G. L.

2016-12-01

We search for evidence of solar free oscillations (normal modes) in long period seismic data through multitaper spectral analysis of array stacks. This analysis is similar to that of Thomson & Vernon (2015), who used data from the most quiet single stations of the global seismic network. Our approach is to use stacks of large arrays of noisier stations to reduce noise. Arrays have the added advantage of permitting the use of nonparametic statistics (jackknife errors) to provide objective error estimates. We used data from the Transportable Array, the broadband borehole array at Pinyon Flat, and the 3D broadband array in Homestake Mine in Lead, SD. The Homestake Mine array has 15 STS-2 sensors deployed in the mine that are extremely quiet at long periods due to stable temperatures and stable piers anchored to hard rock. The length of time series used ranged from 50 days to 85 days. We processed the data by low-pass filtering with a corner frequency of 10 mHz, followed by an autoregressive prewhitening filter and median stack. We elected to use the median instead of the mean in order to get a more robust stack. We then used G. Prieto's mtspec library to compute multitaper spectrum estimates on the data. We produce delete-one jackknife error estimates of the uncertainty at each frequency by computing median stacks of all data with one station removed. The results from the TA data show tentative evidence for several lines between 290 μHz and 400 μHz, including a recurring line near 379 μHz. This 379 μHz line is near the Earth mode 0T2 and the solar mode 5g5, suggesting that 5g5 could be coupling into the Earth mode. Current results suggest more statistically significant lines may be present in Pinyon Flat data, but additional processing of the data is underway to confirm this observation.

A tree fell in the forest, and SPREE heard it: seismic recording of the 2011 St. Croix Valley Blowdown

NASA Astrophysics Data System (ADS)

Wolin, E.; van der Lee, S.

2016-12-01

As part of the Superior Province Rifting Earthscope Experiment (SPREE), 82 broadband seismic stations from the EarthScope Flexible Array pool were deployed by the SPREE team from April 2011 through October 2013, to explore the deep structure of the Mid-Continent Rift System (Stein et al., 2011). The deployment included two crosslines with approximate station spacing of 10 km centered near the northern Minnesota-Wisconsin border. Analysis of long-period noise reveals strong seasonal and diurnal variations (Wolin et al., 2015). On 1 July 2011, a severe thunderstorm system swept over the St. Croix Valley, passing directly over the dense SPREE array. This storm system was accompanied by a series of downbursts that generated straight-line winds in excess of 100 km/hr, resulting in extensive damage to hundreds of thousands of acres of forest. Seven SPREE stations were located in the path of the storm, with two stations in the center of areas that were heavily damaged by downbursts. The stations remained in operation throughout this extreme weather event, capturing a unique record of ground noise generated by the storm system. We compare available radar reflectivity data with seismic noise power spectra throughout the event and show that storm cells generated significant broadband seismic signals as they passed over the region. Relative to typical background seismic noise levels, power between 0.05-10 Hz increased by 5-20 dB during the storm. Seismic noise levels can be compared to available wind speed data to provide a detailed record of wind speeds during the weather event. We also explore the long-period coherence of energy across the array, which is potentially useful to help constrain near-surface velocity structure at the array sites as well as to better characterize how atmospheric processes couple into the solid earth during severe weather events.

Application of the Spatial Auto-Correlation Method for Shear-Wave Velocity Studies Using Ambient Noise

NASA Astrophysics Data System (ADS)

Asten, M. W.; Hayashi, K.

2018-07-01

Ambient seismic noise or microtremor observations used in spatial auto-correlation (SPAC) array methods consist of a wide frequency range of surface waves from the frequency of about 0.1 Hz to several tens of Hz. The wavelengths (and hence depth sensitivity of such surface waves) allow determination of the site S-wave velocity model from a depth of 1 or 2 m down to a maximum of several kilometres; it is a passive seismic method using only ambient noise as the energy source. Application usually uses a 2D seismic array with a small number of seismometers (generally between 2 and 15) to estimate the phase velocity dispersion curve and hence the S-wave velocity depth profile for the site. A large number of methods have been proposed and used to estimate the dispersion curve; SPAC is the one of the oldest and the most commonly used methods due to its versatility and minimal instrumentation requirements. We show that direct fitting of observed and model SPAC spectra generally gives a superior bandwidth of useable data than does the more common approach of inversion after the intermediate step of constructing an observed dispersion curve. Current case histories demonstrate the method with a range of array types including two-station arrays, L-shaped multi-station arrays, triangular and circular arrays. Array sizes from a few metres to several-km in diameter have been successfully deployed in sites ranging from downtown urban settings to rural and remote desert sites. A fundamental requirement of the method is the ability to average wave propagation over a range of azimuths; this can be achieved with either or both of the wave sources being widely distributed in azimuth, and the use of a 2D array sampling the wave field over a range of azimuths. Several variants of the method extend its applicability to under-sampled data from sparse arrays, the complexity of multiple-mode propagation of energy, and the problem of precise estimation where array geometry departs from an ideal regular array. We find that sparse nested triangular arrays are generally sufficient, and the use of high-density circular arrays is unlikely to be cost-effective in routine applications. We recommend that passive seismic arrays should be the method of first choice when characterizing average S-wave velocity to a depth of 30 m ( V s30) and deeper, with active seismic methods such as multichannel analysis of surface waves (MASW) being a complementary method for use if and when conditions so require. The use of computer inversion methodology allows estimation of not only the S-wave velocity profile but also parameter uncertainties in terms of layer thickness and velocity. The coupling of SPAC methods with horizontal/vertical particle motion spectral ratio analysis generally allows use of lower frequency data, with consequent resolution of deeper layers than is possible with SPAC alone. Considering its non-invasive methodology, logistical flexibility, simplicity, applicability, and stability, the SPAC method and its various modified extensions will play an increasingly important role in site effect evaluation. The paper summarizes the fundamental theory of the SPAC method, reviews recent developments, and offers recommendations for future blind studies.

Application of the Spatial Auto-Correlation Method for Shear-Wave Velocity Studies Using Ambient Noise

NASA Astrophysics Data System (ADS)

Asten, M. W.; Hayashi, K.

2018-05-01

Ambient seismic noise or microtremor observations used in spatial auto-correlation (SPAC) array methods consist of a wide frequency range of surface waves from the frequency of about 0.1 Hz to several tens of Hz. The wavelengths (and hence depth sensitivity of such surface waves) allow determination of the site S-wave velocity model from a depth of 1 or 2 m down to a maximum of several kilometres; it is a passive seismic method using only ambient noise as the energy source. Application usually uses a 2D seismic array with a small number of seismometers (generally between 2 and 15) to estimate the phase velocity dispersion curve and hence the S-wave velocity depth profile for the site. A large number of methods have been proposed and used to estimate the dispersion curve; SPAC is the one of the oldest and the most commonly used methods due to its versatility and minimal instrumentation requirements. We show that direct fitting of observed and model SPAC spectra generally gives a superior bandwidth of useable data than does the more common approach of inversion after the intermediate step of constructing an observed dispersion curve. Current case histories demonstrate the method with a range of array types including two-station arrays, L-shaped multi-station arrays, triangular and circular arrays. Array sizes from a few metres to several-km in diameter have been successfully deployed in sites ranging from downtown urban settings to rural and remote desert sites. A fundamental requirement of the method is the ability to average wave propagation over a range of azimuths; this can be achieved with either or both of the wave sources being widely distributed in azimuth, and the use of a 2D array sampling the wave field over a range of azimuths. Several variants of the method extend its applicability to under-sampled data from sparse arrays, the complexity of multiple-mode propagation of energy, and the problem of precise estimation where array geometry departs from an ideal regular array. We find that sparse nested triangular arrays are generally sufficient, and the use of high-density circular arrays is unlikely to be cost-effective in routine applications. We recommend that passive seismic arrays should be the method of first choice when characterizing average S-wave velocity to a depth of 30 m (V s30) and deeper, with active seismic methods such as multichannel analysis of surface waves (MASW) being a complementary method for use if and when conditions so require. The use of computer inversion methodology allows estimation of not only the S-wave velocity profile but also parameter uncertainties in terms of layer thickness and velocity. The coupling of SPAC methods with horizontal/vertical particle motion spectral ratio analysis generally allows use of lower frequency data, with consequent resolution of deeper layers than is possible with SPAC alone. Considering its non-invasive methodology, logistical flexibility, simplicity, applicability, and stability, the SPAC method and its various modified extensions will play an increasingly important role in site effect evaluation. The paper summarizes the fundamental theory of the SPAC method, reviews recent developments, and offers recommendations for future blind studies.

Shear-wave velocity profile and seismic input derived from ambient vibration array measurements: the case study of downtown L'Aquila

NASA Astrophysics Data System (ADS)

Di Giulio, Giuseppe; Gaudiosi, Iolanda; Cara, Fabrizio; Milana, Giuliano; Tallini, Marco

2014-08-01

Downtown L'Aquila suffered severe damage (VIII-IX EMS98 intensity) during the 2009 April 6 Mw 6.3 earthquake. The city is settled on a top flat hill, with a shear-wave velocity profile characterized by a reversal of velocity at a depth of the order of 50-100 m, corresponding to the contact between calcareous breccia and lacustrine deposits. In the southern sector of downtown, a thin unit of superficial red soils causes a further shallow impedance contrast that may have influenced the damage distribution during the 2009 earthquake. In this paper, the main features of ambient seismic vibrations have been studied in the entire city centre by using array measurements. We deployed six 2-D arrays of seismic stations and 1-D array of vertical geophones. The 2-D arrays recorded ambient noise, whereas the 1-D array recorded signals produced by active sources. Surface-wave dispersion curves have been measured by array methods and have been inverted through a neighbourhood algorithm, jointly with the H/V ambient noise spectral ratios related to Rayleigh waves ellipticity. We obtained shear-wave velocity (Vs) profiles representative of the southern and northern sectors of downtown L'Aquila. The theoretical 1-D transfer functions for the estimated Vs profiles have been compared to the available empirical transfer functions computed from aftershock data analysis, revealing a general good agreement. Then, the Vs profiles have been used as input for a deconvolution analysis aimed at deriving the ground motion at bedrock level. The deconvolution has been performed by means of EERA and STRATA codes, two tools commonly employed in the geotechnical engineering community to perform equivalent-linear site response studies. The waveform at the bedrock level has been obtained deconvolving the 2009 main shock recorded at a strong motion station installed in downtown. Finally, this deconvolved waveform has been used as seismic input for evaluating synthetic time-histories in a strong-motion target site located in the middle Aterno river valley. As a target site, we selected the strong-motion station of AQV 5 km away from downtown L'Aquila. For this site, the record of the 2009 L'Aquila main shock is available and its surface stratigraphy is adequately known making possible to propagate the deconvolved bedrock motion back to the surface, and to compare recorded and synthetic waveforms.

Analysis of the Spatial and Temporal Distribution of the Seismicity of the Mid-Atlantic Ridge Using the SIRENA and the South Azores Autonomous Hydrophone Arrays

NASA Astrophysics Data System (ADS)

Simão, N.; Goslin, J.; Perrot, J.; Haxel, J.; Dziak, R.

2006-12-01

Acoustic data recorded by two Autonomous Hydrophone Arrays (AHA) were jointly processed in Brest (IUEM) and Newport (PMEL-VENTS) to monitor the seismicity of the Mid-Atlantic Ridge (MAR) over a ten month period, at a wide range of spatial scales. Over the deployment period, nearly 6000 T-phase generating earthquakes were localized using a semi-automatic algorithm. Our analysis of the temporal and spatial distribution of these events combined with their acoustic energy source levels provides important insights for the generation mechanisms and characteristic behavior of MAR seismicity. It shows for the AHA catalog a variation of the cumulative number of events with time almost linear. Taking in account the area inside the arrays, the section of the ridge north of the Azores is more seismically active than the southern part of it and the seismic activity occurs in large localized clusters. Our (AHA) catalog of acoustic events was used to compare locations, focal mechanisms and magnitude observations with correlated data from land-based stations of the NEIC global seismic network to establish completeness levels from both within and outside of the hydrophone array. The (AHA) catalog has a Source Level of Completeness (SLc) of 204dB, and a b-value of 0.0605. The NEIC catalog for this region during this period has a Magnitude of Completeness (Mc) of 4.6 and a b-value of 1.01. Regressing the AHA values onto the NEIC derived Mc/b-value relationship suggests a Mc of 3.2 for the AHA catalog. By restricting the events to the region inside the AHA, the NEIC catalog has an Mc of 4.7 with a b-value of 1.09, while the AHA catalog has a SLc of 205dB with a b-value of 0.0753. Comparing the b-values of the NEIC catalog with the AHA catalog, we obtain an improved Mc of 3.0 for the AHA inside the array. A time- and space-dependent Single-Link-Cluster algorithm was applied to the events localized inside the AHA. This allowed us to gather cluster sequences of earthquakes for higher temporal and spatial resolution Mc and b-value computations. The cumulative number of events and time series for several of these clusters were used in a Modified Omori Law simulation. Some of the identified sequences correlated well with a main-shock /aftershock mechanism associated with the older and colder crustal characteristics related to a tectonically dominated MAR regime.

Imaging 2015 Mw 7.8 Gorkha Earthquake and Its Aftershock Sequence Combining Multiple Calibrated Global Seismic Arrays

NASA Astrophysics Data System (ADS)

LI, B.; Ghosh, A.

2016-12-01

The 2015 Mw 7.8 Gorkha earthquake provides a good opportunity to study the tectonics and earthquake hazards in the Himalayas, one of the most seismically active plate boundaries. Details of the seismicity patterns and associated structures in the Himalayas are poorly understood mainly due to limited instrumentation. Here, we apply a back-projection method to study the mainshock rupture and the following aftershock sequence using four large aperture global seismic arrays. All the arrays show eastward rupture propagation of about 130 km and reveal similar evolution of seismic energy radiation, with strong high-frequency energy burst about 50 km north of Kathmandu. Each single array, however, is typically limited by large azimuthal gap, low resolution, and artifacts due to unmodeled velocity structures. Therefore, we use a self-consistent empirical calibration method to combine four different arrays to image the Gorkha event. It greatly improves the resolution, can better track rupture and reveal details that cannot be resolved by any individual array. In addition, we also use the same arrays at teleseismic distances and apply a back-projection technique to detect and locate the aftershocks immediately following the Gorkha earthquake. We detect about 2.5 times the aftershocks recorded by the Advance National Seismic System comprehensive earthquake catalog during the 19 days following the mainshock. The aftershocks detected by the arrays show an east-west trend in general, with majority of the aftershocks located at the eastern part of the rupture patch and surrounding the rupture zone of the largest Mw 7.3 aftershock. Overall spatiotemporal aftershock pattern agrees well with global catalog, with our catalog showing more details relative to the standard global catalog. The improved aftershock catalog enables us to better study the aftershock dynamics, stress evolution in this region. Moreover, rapid and better imaging of aftershock distribution may aid rapid response and hazard assessment after destructive large earthquakes. Existing multiple global seismic arrays, when properly calibrated and used in combinations, provide a high resolution image of rupture of large earthquakes and spatiotemporal distribution of aftershocks.

Ambient seismic noise study in Taiwan for two different scale arrays

NASA Astrophysics Data System (ADS)

Huang, Y.; Yao, H.; Liang, W.; Huang, B.; Wen, K.; Huang, W.; van der Hilst, R. D.

2008-12-01

It has been demonstrated that Time Domain Empirical Green's Function (TDEGF) from ambient seismic noise cross-correlation can be used to investigate crustal velocity structure from many studies around the world. For surface wave tomographic studies from ambient noise, the maximum exploring depth depends on the aperture of receiver array and the lateral resolution relies on the density of station-pair paths. To decipher subsurface structures in various scales, researchers can utilize some existing continuous-recording seismic stations and/or deploy a newly dense receiver array in the study region. In this study, we perform tomographic applications of ambient seismic noise analysis in Taiwan region for two arrays with very different scales. Taiwan is located at a complex convergent plate boundary zone where the Philippine Sea plate interacts with the Eurasian plate. As a result, the lateral velocity variations show dramatic patterns among different geologic provinces. In the past decade, many continuous-recording broadband stations have already been set up to monitor earthquake activities in the Taiwan region. The BATS (Broadband Array in Taiwan for Seismology) network is being operated by the Institute of Earth Sciences, Academia Sinica (IESAS) since 1994. Currently, there are 20 permanent stations covering approximately 350 km by 400 km area around Taiwan, including some remote islets. In this study we selected 7 years data (2000-2006) from BATS to get the TDEGFs which were then used to measure inter-station phase velocities in the period band 5-30s. Finally we then constructed 2D phase velocity maps. At shorter periods (5-10s), phase velocity distribution can compare well with surface geology. At longer periods (14-22s), there is a saxophone shape low velocity zone beneath the Taiwan Island. Taipei Basin is a high-level artificial noise metropolis with a nearly triangular shape basin located close to northern tip of Taiwan with area just around 20 km by 20 km, much smaller than the area BATS covers. Central Geological Survey (CGS) entrusted IESAS to monitor seismicity in this region from 2004. There were around 20 continuous-recording broadband stations with about 5km average inter-station distance. For this study we selected 3 months data, from mid July to mid October in 2005, to calculate TDEGFs. Finally we obtained 0.5-3s phase velocity maps, which can compare well with surface geologic structure. The days with typhoon warnings were excluded from ambient seismic noise analysis due to the fact that TDEGFs are affected by temporarily close and massive moving sources like typhoons. We also found that the source direction of ambient seismic noise in typhoon days had close relationship with typhoon location.

Mechanism of the 2015 volcanic tsunami earthquake near Torishima, Japan

PubMed Central

Satake, Kenji

2018-01-01

Tsunami earthquakes are a group of enigmatic earthquakes generating disproportionally large tsunamis relative to seismic magnitude. These events occur most typically near deep-sea trenches. Tsunami earthquakes occurring approximately every 10 years near Torishima on the Izu-Bonin arc are another example. Seismic and tsunami waves from the 2015 event [Mw (moment magnitude) = 5.7] were recorded by an offshore seafloor array of 10 pressure gauges, ~100 km away from the epicenter. We made an array analysis of dispersive tsunamis to locate the tsunami source within the submarine Smith Caldera. The tsunami simulation from a large caldera-floor uplift of ~1.5 m with a small peripheral depression yielded waveforms remarkably similar to the observations. The estimated central uplift, 1.5 m, is ~20 times larger than that inferred from the seismologically determined non–double-couple source. Thus, the tsunami observation is not compatible with the published seismic source model taken at face value. However, given the indeterminacy of Mzx, Mzy, and M{tensile} of a shallow moment tensor source, it may be possible to find a source mechanism with efficient tsunami but inefficient seismic radiation that can satisfactorily explain both the tsunami and seismic observations, but this question remains unresolved. PMID:29740604

Mechanism of the 2015 volcanic tsunami earthquake near Torishima, Japan.

PubMed

Fukao, Yoshio; Sandanbata, Osamu; Sugioka, Hiroko; Ito, Aki; Shiobara, Hajime; Watada, Shingo; Satake, Kenji

2018-04-01

Tsunami earthquakes are a group of enigmatic earthquakes generating disproportionally large tsunamis relative to seismic magnitude. These events occur most typically near deep-sea trenches. Tsunami earthquakes occurring approximately every 10 years near Torishima on the Izu-Bonin arc are another example. Seismic and tsunami waves from the 2015 event [ M w (moment magnitude) = 5.7] were recorded by an offshore seafloor array of 10 pressure gauges, ~100 km away from the epicenter. We made an array analysis of dispersive tsunamis to locate the tsunami source within the submarine Smith Caldera. The tsunami simulation from a large caldera-floor uplift of ~1.5 m with a small peripheral depression yielded waveforms remarkably similar to the observations. The estimated central uplift, 1.5 m, is ~20 times larger than that inferred from the seismologically determined non-double-couple source. Thus, the tsunami observation is not compatible with the published seismic source model taken at face value. However, given the indeterminacy of M zx , M zy , and M {tensile} of a shallow moment tensor source, it may be possible to find a source mechanism with efficient tsunami but inefficient seismic radiation that can satisfactorily explain both the tsunami and seismic observations, but this question remains unresolved.

The Use of Signal Dimensionality for Automatic QC of Seismic Array Data

NASA Astrophysics Data System (ADS)

Rowe, C. A.; Stead, R. J.; Begnaud, M. L.; Draganov, D.; Maceira, M.; Gomez, M.

2014-12-01

A significant problem in seismic array analysis is the inclusion of bad sensor channels in the beam-forming process. We are testing an approach to automated, on-the-fly quality control (QC) to aid in the identification of poorly performing sensor channels prior to beam-forming in routine event detection or location processing. The idea stems from methods used for large computer servers, when monitoring traffic at enormous numbers of nodes is impractical on a node-by-node basis, so the dimensionality of the node traffic is instead monitored for anomalies that could represent malware, cyber-attacks or other problems. The technique relies upon the use of subspace dimensionality or principal components of the overall system traffic. The subspace technique is not new to seismology, but its most common application has been limited to comparing waveforms to an a priori collection of templates for detecting highly similar events in a swarm or seismic cluster. We examine the signal dimension in similar way to the method addressing node traffic anomalies in large computer systems. We explore the effects of malfunctioning channels on the dimension of the data and its derivatives, and how to leverage this effect for identifying bad array elements. We show preliminary results applied to arrays in Kazakhstan (Makanchi) and Argentina (Malargue).

The Green Canyon Event as Recorded by the Atlantis OBS Node Survey

NASA Astrophysics Data System (ADS)

Dellinger, J. A.; Ehlers, J.; Clarke, R.

2006-12-01

On 10 February, 2006, a magnitude 5.2 earthquake occurred 260~km South of New Orleans, Louisiana, in the Green Canyon area of the United States Gulf of Mexico. Fortuitously, at the time of the earthquake an array of nearly 500 ocean-bottom-seismic nodes happened to be recording about 40~km SouthEast of the epicenter. These nodes were part of an ongoing oil-exploration 3D-seismic survey ("Atlantis patch 2"), and were designed to record oil-exploration air-gun seismic signals (with a dominant frequency of about 15~Hz), not low-frequency earthquake signals (1~Hz). The survey's own air guns, located about 7~km to the SouthEast of the array at the time of the event, were also repeatedly firing, generating large amounts of "noise" (at least for the purposes of analyzing the earthquake signal). Not surprisingly, when the data are plotted at their original sample rate they are dominated by the Atlantis survey's air-gun signal. When low passed with an upper cutoff of 2~Hz, however, the air-gun signals essentially vanish and underlying natural signals are clearly revealed. In land-seismic exploration dense 3D arrays of single geophones are used to characterize unwanted surface-wave energy. Beam forming the dense array allows the directions and phase velocities of wavefronts propagating across the array to be identified and localized so that receiver arrays can be designed that best attenuate the surface-wave noise. The 400-meter spacing of the Atlantis node array was designed to be optimally sparse for reflection-seismic processing. At 1~Hz, however, a 400-meter spacing becomes "dense" and we were able to use the same toolkit of programs originally developed for analyzing surface waves in land-seismic data to analyze the earthquake waves. The analysis reveals a complex and protracted series of arrivals spanning nearly 20~minutes of time. The expected sequence of earthquake arrivals from the North-NorthWest are followed by weaker sequences of arrivals of unknown origin from first the SouthEast and then from the East. It is hoped that these data can be used to help constrain the location, depth, and mechanism of the Green Canyon event. The authors wish to thank BP and BHPB for their permission to present this work, Fairfield for their enthusiasm in preserving the data, and CGG, WesternGeco, and Fugro for their cooperation in identifying other sources of man-made signals in the data.

Calibration of the R/V Marcus G. Langseth Seismic Array in shallow Cascadia waters using the Multi-Channel Streamer

NASA Astrophysics Data System (ADS)

Crone, T. J.; Tolstoy, M.; Carton, H. D.

2013-12-01

In the summer of 2012, two multi-channel seismic (MCS) experiments, Cascadia Open-Access Seismic Transects (COAST) and Ridge2Trench, were conducted in the offshore Cascadia region. An area of growing environmental concern with active source seismic experiments is the potential impact of the received sound on marine mammals, but data relating to this issue is limited. For these surveys sound level 'mitigation radii' are established for the protection of marine mammals, based on direct arrival modeling and previous calibration experiments. Propagation of sound from seismic arrays can be accurately modeled in deep-water environments, but in shallow and sloped environments the complexity of local geology and bathymetry can make it difficult to predict sound levels as a function of distance from the source array. One potential solution to this problem is to measure the received levels in real-time using the ship's streamer (Diebold et al., 2010), which would allow the dynamic determination of suitable mitigation radii. We analyzed R/V Langseth streamer data collected on the shelf and slope off the Washington coast during the COAST experiment to measure received levels in situ up to 8 km away from the ship. Our analysis shows that water depth and bathymetric features can affect received levels in shallow water environments. The establishment of dynamic mitigation radii based on local conditions may help maximize the safety of marine mammals while also maximizing the ability of scientists to conduct seismic research. With increasing scientific and societal focus on subduction zone environments, a better understanding of shallow water sound propagation is essential for allowing seismic exploration of these hazardous environments to continue. Diebold, J. M., M. Tolstoy, L. Doermann, S. Nooner, S. Webb, and T. J. Crone (2010) R/V Marcus G. Langseth Seismic Source: Modeling and Calibration. Geochemistry, Geophysics, Geosystems, 11, Q12012, doi:10.1029/2010GC003216.

Digital processing of array seismic recordings

USGS Publications Warehouse

Ryall, Alan; Birtill, John

1962-01-01

This technical letter contains a brief review of the operations which are involved in digital processing of array seismic recordings by the methods of velocity filtering, summation, cross-multiplication and integration, and by combinations of these operations (the "UK Method" and multiple correlation). Examples are presented of analyses by the several techniques on array recordings which were obtained by the U.S. Geological Survey during chemical and nuclear explosions in the western United States. Seismograms are synthesized using actual noise and Pn-signal recordings, such that the signal-to-noise ratio, onset time and velocity of the signal are predetermined for the synthetic record. These records are then analyzed by summation, cross-multiplication, multiple correlation and the UK technique, and the results are compared. For all of the examples presented, analysis by the non-linear techniques of multiple correlation and cross-multiplication of the traces on an array recording are preferred to analyses by the linear operations involved in summation and the UK Method.

Influence of Spatial Variation in Ground Motion Peak Acceleration on Local Site Effects Estimation at Bucovina Seismic Array (BURAR) Romania

NASA Astrophysics Data System (ADS)

Ghica, D. V.; Radulian, M.; Popa, M.; Grecu, B.

2006-05-01

Basically, array processing techniques require a high signal coherency across the seismic site; therefore the local crustal velocities below the station, signal amplitude differences between array elements and local noise conditions, resulting in local site effects will affect calculation of phase arrival times, propagation velocities and ground motion amplitudes. In general, array techniques assume a homogenous structure for all sites, and a simple relief correction is taking in account for the data analysis. To increase the results accuracy, individual element corrections must be applied, based on the biases factors systematically observed. This study aims at identifying the anomalous amplitude variations recorded at the Bucovina Seismic Array (BURAR) and at explaining their influence on site effects estimation. Maximum amplitudes for the teleseismic and regional phases in four narrow frequency bands (0.25-0.5Hz; 0.5-1Hz; 1-2Hz; 1.5-3Hz) are measured. Spatial distribution of ground motion peak acceleration in BURAR site, for each band, is plotted; a different behavior was observed at frequencies below 2Hz. The most important aspect observed is the largest amplitude exhibited by BUR07 across the whole array at high frequencies (an amplification factor of about two). This can be explained by the different geology at BUR07 site (mica schist outcrops), comparing with the rest of elements (green schist outcrops). At the lowest frequencies (0.25-0.5Hz), BUR09 peak amplitudes dominate the other sites. Considering BUR07 as reference site, peak acceleration ratios were investigated. The largest scattering of these ratios appears at the highest frequencies (1.5-3Hz), when the weight of over unit values is about 90 %. No azimuth and distance dependence was found for these effects, suggesting the absence of the dipping layer structures. Although an increase of the ratio values is noticed for epicentral distance between 8000 and 10000 km, for frequencies over 1 Hz. The results of this study are essential to further develop the calibration technique for seismic monitoring with BURAR array, in order to improve the detection and single-array location capabilities of the system.

Using the ENTLN lightning catalog to identify thunder signals in the USArray Transportable Array

NASA Astrophysics Data System (ADS)

Tytell, J. E.; Reyes, J. C.; Vernon, F.; Sloop, C.; Heckman, S.

2013-12-01

Severe weather events can pose a challenge for seismic analysts who regularly see non-seismic signals recorded at the stations. Sometimes, the noise from thunder can be confused with signals from seismic events such as quarry blasts or earthquakes depending on where and when the noise is observed. Automatic analysis of data is also severely affected by big amplitude arrivals that we could safely ignore. A comprehensive lightning catalog for the continental US in conjunction with a travel time model for thunder arrivals can help analysts identify some of these unknown sources. Researchers from Earthscope's USArray Transportable Array (TA) have partnered with the Earth Networks Total Lightning Network (ENTLN) in an effort to create such a catalog. Predicted thunder arrivals from some powerful meteorological systems affecting the main TA footprint will undergo extensive evaluation. We will examine the veracity of the predicted arrivals at different distances and azimuths and the time accuracy of the model. A combination of barometric pressure and seismic signals will be use to verify these arrivals.

Seismic monitoring at Deception Island volcano (Antarctica): Recent advances

NASA Astrophysics Data System (ADS)

Carmona, E.; Almendros, J.; Martín, R.; Cortés, G.; Alguacil, G.; Moreno, J.; Martín, B.; Martos, A.; Serrano, I.; Stich, D.; Ibáñez, J. M.

2012-04-01

Deception Island (South Shetland Island, Antarctica) is an active volcano with recent eruptions (e.g. 1967, 1969 and 1970). It is also among the Antarctic sites most visited by tourists. Besides, there are currently two scientific bases operating during the austral summers, usually from late November to early March. For these reasons it is necessary to deploy a volcano monitoring system as complete as possible, designed specifically to endure the extreme conditions of the volcanic environment and the Antarctic climate. The Instituto Andaluz de Geofísica of University of Granada, Spain (IAG-UGR) performs seismic monitoring on Deception Island since 1994 during austral summer surveys. The seismicity basically includes volcano-tectonic earthquakes, long-period events and volcanic tremor, among other signals. The level of seismicity is moderate, except for a seismo-volcanic crisis in 1999. The seismic monitoring system has evolved during these years, following the trends of the technological developments and software improvements. Recent advances have been mainly focused on: (1) the improvement of the seismic network introducing broadband stations and 24-bit data acquisition systems; (2) the development of a short-period seismic array, with a 12-channel, 24-bit data acquisition system; (3) the implementation of wireless data transmission from the network stations and also from the seismic array to a recording center, allowing for real-time monitoring; (4) the efficiency of the power supply systems and the monitoring of the battery levels and power consumption; (5) the optimization of data analysis procedures, including database management, automated event recognition tools for the identification and classification of seismo-volcanic signals, and apparent slowness vector estimates using seismic array data; (6) the deployment of permanent seismic stations and the transmission of data during the winter using a satellite connection. A single permanent station is operating at Deception Island since 2008. In the current survey we collaborate with the Spanish Army to add another permanent station that will be able to send to the IAG-UGR seismic information about the activity of the volcano during the winter, using a communications satellite (SPAINSAT). These advances simplify the field work and the data acquisition procedures, and allow us to obtain high-quality seismic data in real-time. These improvements have a very important significance for a better and faster interpretation of the seismo-volcanic activity and assessment of the volcanic hazards at Deception Island volcano.

Improved Phase Characterization of Far-Regional Body Wave Arrivals in Central Asia

DTIC Science & Technology

2009-09-30

array processing techniques. The regional seismic arrays that have been built in the last fifteen years should be a rich data source for the study of...far-regional phase behavior. The arrays are composed of high-quality borehole seismometers that make high fidelity, low-noise recordings. However...that propagate from the different seismic regions of South-Central Asia, utilizing recordings from the Makanchi (MKAR) and Karatau (KKAR) arrays in

Small-aperture seismic array data processing using a representation of seismograms at zero-crossing points

NASA Astrophysics Data System (ADS)

Brokešová, Johana; Málek, Jiří

2018-07-01

A new method for representing seismograms by using zero-crossing points is described. This method is based on decomposing a seismogram into a set of quasi-harmonic components and, subsequently, on determining the precise zero-crossing times of these components. An analogous approach can be applied to determine extreme points that represent the zero-crossings of the first time derivative of the quasi-harmonics. Such zero-crossing and/or extreme point seismogram representation can be used successfully to reconstruct single-station seismograms, but the main application is to small-aperture array data analysis to which standard methods cannot be applied. The precise times of the zero-crossing and/or extreme points make it possible to determine precise time differences across the array used to retrieve the parameters of a plane wave propagating across the array, namely, its backazimuth and apparent phase velocity along the Earth's surface. The applicability of this method is demonstrated using two synthetic examples. In the real-data example from the Příbram-Háje array in central Bohemia (Czech Republic) for the Mw 6.4 Crete earthquake of October 12, 2013, this method is used to determine the phase velocity dispersion of both Rayleigh and Love waves. The resulting phase velocities are compared with those obtained by employing the seismic plane-wave rotation-to-translation relations. In this approach, the phase velocity is calculated by obtaining the amplitude ratios between the rotation and translation components. Seismic rotations are derived from the array data, for which the small aperture is not only an advantage but also an applicability condition.

The underground seismic array of Gran Sasso (UNDERSEIS), central Italy

NASA Astrophysics Data System (ADS)

Scarpa, R.; Muscente, R.; Tronca, F.; Fischione, C.; Rotella, P.; Abril, M.; Alguacil, G.; Martini, M.; de Cesare, W.

2003-04-01

Since early May, 2002, a small aperture seismic array has been installed in the underground Physics Laboratories of Gran Sasso, located near seismic active faults of central Apennines, Italy. This array is presently composed by 21 three-component short period seismic stations (Mark L4C-3D), with average distance 90 m and semi-circular aperture of 400 m x 600 m. It is intersecting a main seismogenic fault where the presence of slow earthquakes has been recently detected through two wide band geodetic laser interferometers. The underground Laboratories are shielded by a limestone rock layer having 1400 m thickness. Each seismometer is linked, through a 24 bits A/D board, to a set of 6 industrial PC via a serial RS-485 standard. The six PC transmit data to a server through an ethernet network. Time syncronization is provided by a Master Oscillator controlled by an atomic clock. Earthworm package is used for data selection and transmission. High quality data have been recorded since May 2002, including local and regional earthquakes. In particular the 31 October, 2002, Molise (Mw=5.8 earthquake) and its aftershocks have been recorded at this array. Array techniques such as polarisation and frequency-slowness analyses with the MUSIC noise algorithm indicate the high performance of this array, as compared to the national seismic network, for identifying the basic source parameters for earthquakes located at distance of few hundreds of km.

Data Quality Control Tools Applied to Seismo-Acoustic Arrays in Korea

NASA Astrophysics Data System (ADS)

Park, J.; Hayward, C.; Stump, B. W.

2017-12-01

We assess data quality (data gap, seismometer orientation, timing error, noise level and coherence between co-located sensors) for seismic and infrasound data in South Korea using six seismo-acoustic arrays, BRDAR, CHNAR, KSGAR, KMPAR, TJIAR, and YPDAR, cooperatively operated by Southern Methodist University and Korea Institute for Geosciences and Mineral Resources. Timing errors associated with seismometers can be found based on estimated changes in instrument orientation calculated from RMS errors between the reference array and each array seismometer using waveforms filtered from 0.1 to 0.35 Hz. Noise levels of seismic and infrasound data are analyzed to investigate local environmental effects and seasonal noise variation. In order to examine the spectral properties of the noise, the waveform are analyzed using Welch's method (Welch, 1967) that produces a single power spectral estimate from an average of spectra taken at regular intervals over a specific time period. This analysis quantifies the range of noise conditions found at each of the arrays over the given time period. We take an advantage of the fact that infrasound sensors are co-located or closely located to one another, which allows for a direct comparison of sensors, following the method by Ringler et al. (2010). The power level differences between two sensors at the same array in the frequency band of interest are used to monitor temporal changes in data quality and instrument conditions. A data quality factor is assigned to stations based on the average values of temporal changes estimated in the frequency and time domains. These monitoring tools enable us to automatically assess technical issue related to the instruments and data quality at each seismo-acoustic array as well as to investigate local environmental effects and seasonal variations in both seismic and infrasound data.

SeisCORK Engineering Design Study

DTIC Science & Technology

2006-05-01

Stephen, R. A., et al. (1994a), The seafloor borehole array seismic system (SEABASS) and VLF ambient noise, Marine Geophysical Researches, 16, 243...286. Stephen, R. A., et al. (1994b), The Seafloor Borehole Array Seismic System (SEABASS) and VLF Ambient Noise, Marine Geophysical Researches, 16, 243...Contents Executive Summary 4 Introduction 5 General Science Goals and Justification for Borehole Seismology in the Seafloor 6 Validating Surface Seismic

Detecting Noisy Events Using Waveform Cross-Correlation at Superarrays of Seismic Stations

NASA Astrophysics Data System (ADS)

von Seggern, D. H.; Tibuleac, I. M.

2007-12-01

Cross-correlation using master events, followed by stacking of the correlation series, has been shown to dramatically improve detection thresholds of small-to-medium seismic arrays. With the goal of lowering the detection threshold, determining relative magnitudes or moments, and characterizing sources by empirical Green's functions, we extend the cross-correlation methodology to include "superarrays" of seismic stations. The superarray concept naturally brings further benefits over conventional arrays and single-stations due to the fact that many distances and azimuths can be sampled. This extension is straightforward given the ease with which regional or global data from various stations or arrays can be currently accessed and combined into a single database. We demonstrate the capability of superarrays to detect and analyze events which lie below the detection threshold. This is aided by applying an F-statistic detector to the superarray cross-correlation stack and its components. Our first example illustrates the use of a superarray consisting of the Southern Great Basin Digital Seismic Network, a small-aperture array (NVAR) in Mina, Nevada and the Earthscope Transportable Array to detect events in California-Nevada areas. In our second example, we use a combination of small-to-medium arrays and single stations to study the rupture of the great Sumatra earthquake of 26 December 2004 and to detect its early aftershocks. The location and times of "detected" events are confirmed using a frequency- wavenumber method at the small-to-medium arrays. We propose that ad hoc superarrays can be used in many studies where conventional approaches previously used only single arrays or groups of single stations. The availability of near-real-time data from many networks and of archived data from, for instance, IRIS makes possible the easy assembly of superarrays. Furthermore, the continued improvement of seismic data availability and the continued growth in the number of world-wide seismic sensors will increasingly make superarrays an attractive choice for many studies.

Goal-seismic computer programs in BASIC: Part I; Store, plot, and edit array data

USGS Publications Warehouse

Hasbrouck, Wilfred P.

1979-01-01

Processing of geophysical data taken with the U.S. Geological Survey's coal-seismic system is done with a desk-top, stand-alone computer. Programs for this computer are written in an extended BASIC language specially augmented for acceptance by the Tektronix 4051 Graphic System. This report presents five computer programs used to store, plot, and edit array data for the line, cross, and triangle arrays commonly employed in our coal-seismic investigations. * Use of brand names in this report is for descriptive purposes only and does not constitute endorsement by the U.S. Geological Survey.

Imaging San Jacinto Fault damage zone structure using dense linear arrays: application of ambient noise tomography, Rayleigh wave ellipticity, and site amplification

NASA Astrophysics Data System (ADS)

Wang, Y.; Lin, F. C.; Allam, A. A.; Ben-Zion, Y.

2017-12-01

The San Jacinto fault is presently the most seismically active component of the San Andreas Transform system in Southern California. To study the damage zone structure, two dense linear geophone arrays (BS and RR) were deployed across the Clark segment of the San Jacinto Fault between Anza and Hemet during winter 2015 and Fall 2016, respectively. Both arrays were 2 km long with 20 m station spacing. Month-long three-component ambient seismic noise data were recorded and used to calculate multi-channel cross-correlation functions. All three-component noise records of each array were normalized simultaneously to retain relative amplitude information between different stations and different components. We observed clear Rayleigh waves and Love waves on the cross-correlations of both arrays at 0.3 - 1 s period. The phase travel times of the Rayleigh waves on both arrays were measured by frequency-time analysis (FTAN), and inverted for Rayleigh wave phase velocity profiles of the upper 500 m depth. For both arrays, we observe prominent asymmetric low velocity zones which narrow with depth. At the BS array near the Hemet Stepover, an approximately 250m wide slow zone is observed to be offset by 75m to the northeast of the surface fault trace. At the RR array near the Anza segment of the fault, a similar low velocity zone width and offset are observed, along with a 10% across-fault velocity contrast. Analyses of Rayleigh wave ellipticity (H/V ratio), Love wave phase travel times, and site amplification are in progress. By using multiple measurements from ambient noise cross-correlations, we can obtain strong constraints on the local damage zone structure of the San Jacinto Fault. The results contribute to improved understanding of rupture directivity, maximum earthquake magnitude and more generally seismic hazard associated with the San Jacinto fault zone.

High-resolution lithospheric imaging with seismic interferometry

NASA Astrophysics Data System (ADS)

Ruigrok, Elmer; Campman, Xander; Draganov, Deyan; Wapenaar, Kees

2010-10-01

In recent years, there has been an increase in the deployment of relatively dense arrays of seismic stations. The availability of spatially densely sampled global and regional seismic data has stimulated the adoption of industry-style imaging algorithms applied to converted- and scattered-wave energy from distant earthquakes, leading to relatively high-resolution images of the lower crust and upper mantle. We use seismic interferometry to extract reflection responses from the coda of transmitted energy from distant earthquakes. In theory, higher-resolution images can be obtained when migrating reflections obtained with seismic interferometry rather than with conversions, traditionally used in lithospheric imaging methods. Moreover, reflection data allow the straightforward application of algorithms previously developed in exploration seismology. In particular, the availability of reflection data allows us to extract from it a velocity model using standard multichannel data-processing methods. However, the success of our approach relies mainly on a favourable distribution of earthquakes. In this paper, we investigate how the quality of the reflection response obtained with interferometry is influenced by the distribution of earthquakes and the complexity of the transmitted wavefields. Our analysis shows that a reasonable reflection response could be extracted if (1) the array is approximately aligned with an active zone of earthquakes, (2) different phase responses are used to gather adequate angular illumination of the array and (3) the illumination directions are properly accounted for during processing. We illustrate our analysis using a synthetic data set with similar illumination and source-side reverberation characteristics as field data recorded during the 2000-2001 Laramie broad-band experiment. Finally, we apply our method to the Laramie data, retrieving reflection data. We extract a 2-D velocity model from the reflections and use this model to migrate the data. On the final reflectivity image, we observe a discontinuity in the reflections. We interpret this discontinuity as the Cheyenne Belt, a suture zone between Archean and Proterozoic terranes.

Aftershock distribution and heterogeneous structure in and around the source area of the 2014 northern Nagano Prefecture earthquake (Mw 6.2) , central Japan, revealed by dense seismic array observation

NASA Astrophysics Data System (ADS)

Kurashimo, E.; Hirata, N.; Iwasaki, T.; Sakai, S.; Obara, K.; Ishiyama, T.; Sato, H.

2015-12-01

A shallow earthquake (Mw 6.2) occurred on November 22 in the northern Nagano Prefecture, central Japan. Aftershock area is located near the Kamishiro fault, which is a part of the Itoigawa-Shizuoka Tectonic Line (ISTL). ISTL is one of the major tectonic boundaries in Japan. Precise aftershock distribution and heterogeneous structure in and around the source region of this earthquake is important to constrain the process of earthquake occurrence. We conducted a high-density seismic array observation in and around source area to investigate aftershock distribution and crustal structure. One hundred sixty-three seismic stations, approximately 1 km apart, were deployed during the period from December 3, 2014 to December 21, 2014. Each seismograph consisted of a 4.5 Hz 3-component seismometer and a digital data recorder (GSX-3). Furthermore, the seismic data at 40 permanent stations were incorporated in our analysis. During the seismic array observation, the Japan Meteorological Agency located 977 earthquakes in a latitude range of 35.5°-37.1°N and a longitude range of 136.7°-139.0°E, from which we selected 500 local events distributed uniformly in the study area. To investigate the aftershock distribution and the crustal structure, the double-difference tomography method [Zhang and Thurber, 2003] was applied to the P- and S-wave arrival time data obtained from 500 local earthquakes. The relocated aftershock distribution shows a concentration on a plane dipping eastward in the vicinity of the mainshock hypocenter. The large slip region (asperity) estimated from InSAR analysis [GSI, 2014] corresponds to the low-activity region of the aftershocks. The depth section of Vp structure shows that the high Vp zone corresponds to the large slip region. These results suggest that structural heterogeneities in and around the fault plane may have controlled the rupture process of the 2014 northern Nagano Prefecture earthquake.

Asymmetric radiation of seismic waves from an atoll: nuclear tests in French Polynesia

USGS Publications Warehouse

Weber, Michael J.; Wicks, Charles W.; Krüger, Frank; Jahnke, Gunnar; Schlittenhardt, Jörg

1998-01-01

Seismic records of nuclear tests detonated in the Mururoa Atoll in French Polynesia show large unpredicted arrivals 2.2 and 4.5 seconds (X1 and X2) after the P-wave at the Australian Warramunga Array. These arrivals are not observed at the Canadian Yellowknife Array. X1 and X2 are also absent on Warramunga Array recordings of tests carried out at the Fangataufa Atoll situated 40 km SSE of Mururoa. Array analysis shows that X1 and X2 are produced within the source area. The layered crustal structure of the atoll, significant local inhomogeneities, and focusing effects due to the elongated shape and the steep flanks of the Mururoa Atoll are most likely responsible for X1 and X2. The form of Mururoa (28 × 10 km) and its East-West orientation is due to its location on the Austral Fracture Zone (AFZ). The Fangataufa Atoll on the other hand is almost circular (10 km diameter) and is unaffected by the dynamics along the AFZ. Our observations demonstrate that complicated structures in the source area can significantly alter the wave field at teleseismic distances and produce a large magnitude (mb) bias. A better understanding of the exact cause of these unusual seismic observations will only become possible, if the coordinates of the tests and information on the detailed 3-D structure of the atolls are released.

Porosity, Fracturing and Alteration of Young Oceanic Crust: New Seismic Analyses at Borehole 504B

NASA Astrophysics Data System (ADS)

Gregory, E. P. M.; Hobbs, R. W.; Peirce, C.; Wilson, D. J.

2017-12-01

DSDP/ODP borehole 504B, drilled 2111 m into 6.9 Ma oceanic crust, provides in-situ core and logging measurements of the lithology, fracturing and porosity of crust originally formed at the Costa Rica Rift and its subsequent alteration by hydrothermal fluids. A recent active seismic survey over the borehole and surrounding area reveals wider spatial variations in velocity that can be related to this porosity and fracturing. Over 10,000 airgun shots were fired in a 30 x 30 km grid over the borehole region, using both high-frequency and low-frequency airgun arrays. The shots were recorded on a 4.5 km-long streamer and 24 ocean-bottom seismographs, each equipped with a three-component geophone and an hydrophone. A vertical hydrophone array recorded the downgoing source wavelet, and underway gravity, magnetic field and multibeam bathymetry data were also recorded. This combined dataset enables the most comprehensive geophysical analysis of this area of crust to date, while the ground-truthing provided by 504B enables us to address the questions of what do the seismic oceanic crustal layers represent and what controls their characteristics as the crust ages? Wide-angle seismic modelling with a Monte Carlo based uncertainty analysis reveals new 2D and 3D Vp and Vs models of the area, which show relatively homogeneous crust around borehole 504B, and place the seismic layer 2B/2C, and seismic layer 2/3 boundaries coincident with fracturing and alteration fronts rather than the lithological boundaries between lavas and dykes, and dykes and gabbros, respectively. Analysis of Poisson's ratio, seismic anisotropy and particle motions reveal patterns in fracturing and porosity across the survey area, and locate possible fossilised hydrothermal circulation cells. These cells appear to have influenced the porosity of the crust through alteration and mineralisation processes, with faults inherited from initial crustal accretion influencing basement topographic highs and providing conduits for mineralising fluids to flow. This research is part of a major, interdisciplinary NERC-funded research collaboration entitled: Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR).

Celebrating 10 Years of Delivering EarthScope USArray Transportable Array Data from the Array Network Facility (ANF)

NASA Astrophysics Data System (ADS)

Eakins, J. A.; Vernon, F.; Astiz, L.; Davis, G. A.; Reyes, J. C.; Martynov, V. G.; Tytell, J.; Cox, T. A.; Meyer, J.

2013-12-01

Since 2004, the Array Network Facility (ANF) has been responsible for generation and delivery of the metadata as well as collection and initial quality control and the transmission of the seismic, and more recently infrasound and meteorological data, for the Earthscope USArray Transportable Array. As of August 2013, we have managed data from over 1600 stations. Personnel at the ANF provide immediate eyes on the data to improve quality control as well as interact with the individual stations via calibrations, mass recentering, baler data retrieval and event analysis. Web-based tools have been developed, and rewritten over the years, to serve the needs of both station engineers and the public. Many lessons on the needs for scalability have been learned. Analysts continue to review all seismic events recorded on 7 or more TA stations making associations against externally available bulletins and/or generating ANF authored locations which are available at both the ANF and IRIS-DMC. The US Array pressure data have several unique characteristics that are allowing us to conduct a rigorous analysis of the spatio-temporal variations in the pressure field on time scales of less than an hour across the eastern United States. With the installation of the infrasound and atmospheric pressure sensors, starting in 2010, observations of gust fronts, near misses of tornados at individual stations, and of the mesoscale gravity waves showing the value and utility of the US Array pressure data will be presented.

Explosion Source Location Study Using Collocated Acoustic and Seismic Networks in Israel

NASA Astrophysics Data System (ADS)

Pinsky, V.; Gitterman, Y.; Arrowsmith, S.; Ben-Horin, Y.

2013-12-01

We explore a joined analysis of seismic and infrasonic signals for improvement in automatic monitoring of small local/regional events, such as construction and quarry blasts, military chemical explosions, sonic booms, etc. using collocated seismic and infrasonic networks recently build in Israel (ISIN) in the frame of the project sponsored by the Bi-national USA-Israel Science Foundation (BSF). The general target is to create an automatic system, which will provide detection, location and identification of explosions in real-time or close-to-real time manner. At the moment the network comprises 15 stations hosting a microphone and seismometer (or accelerometer), operated by the Geophysical Institute of Israel (GII), plus two infrasonic arrays, operated by the National Data Center, Soreq: IOB in the South (Negev desert) and IMA in the North of Israel (Upper Galilee),collocated with the IMS seismic array MMAI. The study utilizes a ground-truth data-base of numerous Rotem phosphate quarry blasts, a number of controlled explosions for demolition of outdated ammunitions and experimental surface explosions for a structure protection research, at the Sayarim Military Range. A special event, comprising four military explosions in a neighboring country, that provided both strong seismic (up to 400 km) and infrasound waves (up to 300 km), is also analyzed. For all of these events the ground-truth coordinates and/or the results of seismic location by the Israel Seismic Network (ISN) have been provided. For automatic event detection and phase picking we tested the new recursive picker, based on Statistically optimal detector. The results were compared to the manual picks. Several location techniques have been tested using the ground-truth event recordings and the preliminary results obtained have been compared to the ground-truth locations: 1) a number of events have been located as intersection of azimuths estimated using the wide-band F-K analysis technique applied to the infrasonic phases of the two distant arrays; 2) a standard robust grid-search location procedure based on phase picks and a constant celerity for a phase (tropospheric or stratospheric) was applied; 3) a joint coordinate grid-search procedure using array waveforms and phase picks was tested, 4) the Bayesian Infrasonic Source Localization (BISL) method, incorporating semi-empirical model-based prior information, was modified for array+network configuration and applied to the ground-truth events. For this purpose we accumulated data of the former observations of the air-to-ground infrasonic phases to compute station specific ground-truth Celerity-Range Histograms (ssgtCRH) and/or model-based CRH (mbCRH), which allow to essentially improve the location results. For building the mbCRH the local meteo-data and the ray-tracing modeling in 3 available azimuth ranges, accounting seasonal variations of winds directivity (quadrants North:315-45, South: 135-225, East 45-135) have been used.

Polarization Analysis of the September 2005 Northern Cascadia Episodic Tremor and Slip Event

NASA Astrophysics Data System (ADS)

Wech, A. G.; Creager, K. C.

2006-12-01

The region of Northern Cascadia, extending from the Olympic Mountains and Puget Sound to southern Vancouver Island, down-dip of the subduction "locked" zone has repeatedly experienced episodes of slow slip. This episodic slip, observed to take place over a period of two to several weeks, is accompanied by a seismic tremor signal. Based on the average recurrence interval of 14 months, the last episodic tremor and slip (ETS) event was expected to occur in September, 2005. Indeed, it began on September 3. In order to record this event, we deployed an array of 11 three-component seismometers on the northern side of the Olympic Peninsula augmenting Pacific Northwest Seismographic Network stations as well as the first few EarthScope BigFoot stations and Plate Boundary Observatory borehole seismometers. This seismic array was comprised of six short-period and five broadband instruments with average spacings of 500 m and 2200 m respectively. In conjunction with this Earthscope seismic deployment, we also installed a dense network of 29 temporary, continuous GPS stations across the entire Olympic Peninsula to integrate seismic and geodetic observations. Based on past geodetic observations, a dominant assumption for the source of tremor is fault-slip in the direction of subduction, which can be tested using polarization of the seismic tremor. Using waveform cross- correlation to invert for the direction of slowness, we observed the tremor signal to migrate directly under our array. As the source passed beneath the array, tremor polarization stabilized to coincide with the direction of subduction. During a four day period starting September 8, the normalized eigenvalue associated with the dominant linear polarization jumped from ~0.7 to a stable 0.9 value. Also during this time, the polarization azimuth stabilized to a value of 57 +/- 8 degrees, close to the angle of subduction (56 degrees) suggesting that the tremor is caused by slip in the direction of relative plate motion on one or more faults.

Velocity and Attenuation Structure of the Tibetan Lithosphere using Seismic Attributes of P-waves from Regional Earthquakes Recorded by the Hi-CLIMB Array

NASA Astrophysics Data System (ADS)

Nowack, R. L.; Bakir, A. C.; Griffin, J.; Chen, W.; Tseng, T.

2010-12-01

Using data from regional earthquakes recorded by the Hi-CLIMB array in Tibet, we utilize seismic attributes from crustal and Pn arrivals to constrain the velocity and attenuation structure in the crust and the upper mantle in central and western Tibet. The seismic attributes considered include arrival times, Hilbert envelope amplitudes, and instantaneous as well as spectral frequencies. We have constructed more than 30 high-quality regional seismic profiles, and of these, 10 events have been selected with excellent crustal and Pn arrivals for further analysis. Travel-times recorded by the Hi-CLIMB array are used to estimate the large-scale velocity structure in the region, with four near regional events to the array used to constrain the crustal structure. The travel times from the far regional events indicate that the Moho beneath the southern Lhasa terrane is up to 75 km thick, with Pn velocities greater than 8 km/s. In contrast, the data sampling the Qiangtang terrane north of the Bangong-Nujiang (BNS) suture shows thinner crust with Pn velocities less than 8 km/s. Seismic amplitude and frequency attributes have been extracted from the crustal and Pn wave trains, and these data are compared with numerical results for models with upper-mantle velocity gradients and attenuation, which can strongly affect Pn amplitudes and pulse frequencies. The numerical modeling is performed using the complete spectral element method (SEM), where the results from the SEM method are in good agreement with analytical and reflectivity results for different models with upper-mantle velocity gradients. The results for the attenuation modeling in Tibet imply lower upper mantle Q values in the Qiangtang terrane to the north of the BNS compared to the less attenuative upper mantle beneath the Lhasa terrane to the south of the BNS.

Structure of the North Anatolian Fault Zone from the Auto-Correlation of Ambient Seismic Noise Recorded at a Dense Seismometer Array

NASA Astrophysics Data System (ADS)

Taylor, D. G.; Rost, S.; Houseman, G.

2015-12-01

In recent years the technique of cross-correlating the ambient seismic noise wavefield at two seismometers to reconstruct empirical Green's Functions for the determination of Earth structure has been a powerful tool to study the Earth's interior without earthquake or man-made sources. However, far less attention has been paid to using auto-correlations of seismic noise to reveal body wave reflections from interfaces in the subsurface. In principle, the Green's functions thus derived should be comparable to the Earth's impulse response to a co-located source and receiver. We use data from a dense seismic array (Dense Array for Northern Anatolia - DANA) deployed across the northern branch of the North Anatolian Fault Zone (NAFZ) in the region of the 1999 magnitude 7.6 Izmit earthquake in western Turkey. The NAFZ is a major strike-slip system that extends ~1200 km across northern Turkey and continues to pose a high level of seismic hazard, in particular to the mega-city of Istanbul. We construct reflection images for the entire crust and upper mantle over the ~35 km by 70 km footprint of the 70-station DANA array. Using auto-correlations of vertical and horizontal components of ground motion, both P- and S-wave velocity information can be retrieved from the wavefield to constrain crustal structure further to established methods. We show that clear P-wave reflections from the crust-mantle boundary (Moho) can be retrieved using the autocorrelation technique, indicating topography on the Moho on horizontal scales of less than 10 km. Offsets in crustal structure can be identified that seem to be correlated with the surface expression of the fault zone in the region. The combined analysis of auto-correlations using vertical and horizontal components will lead to further insight into the fault zone structure throughout the crust and upper mantle.

Studies of infrasound propagation using the USArray seismic network (Invited)

NASA Astrophysics Data System (ADS)

Hedlin, M. A.; Degroot-Hedlin, C. D.; Walker, K. T.

2010-12-01

Although there are currently ~ 100 infrasound arrays worldwide, more than ever before, the station density is still insufficient to provide validation for detailed propagation modeling. Much structure in the atmosphere is short-lived and occurs at spatial scales much smaller than the average distance between infrasound stations. Relatively large infrasound signals can be observed on seismic channels due to coupling at the Earth's surface. Recent research, using data from the 70-km spaced 400-station USArray and other seismic network deployments, has shown the value of dense seismic network data for filling in the gaps between infrasound arrays. The dense sampling of the infrasound wavefield has allowed us to observe complete travel-time branches of infrasound signals and shed more light on the nature of infrasound propagation. We present early results from our studies of impulsive atmospheric sources, such as series of UTTR rocket motor detonations in Utah. The Utah blasts have been well recorded by USArray seismic stations and infrasound arrays in Nevada and Washington State. Recordings of seismic signals from a series of six events in 2007 are used to pinpoint the shot times to < 1 second. Variations in the acoustic branches and signal arrival times at the arrays are used to probe variations in atmospheric structure. Although we currently use coupled signals we anticipate studying dense acoustic network recordings as the USArray is currently being upgraded with infrasound microphones. These new sensors will allow us to make semi-continental scale network recordings of infrasound signals free of concerns about how the signals observed on seismic channels were modified when being coupled to seismic.

Earthquake Monitoring with the MyShake Global Smartphone Seismic Network

NASA Astrophysics Data System (ADS)

Inbal, A.; Kong, Q.; Allen, R. M.; Savran, W. H.

2017-12-01

Smartphone arrays have the potential for significantly improving seismic monitoring in sparsely instrumented urban areas. This approach benefits from the dense spatial coverage of users, as well as from communication and computational capabilities built into smartphones, which facilitate big seismic data transfer and analysis. Advantages in data acquisition with smartphones trade-off with factors such as the low-quality sensors installed in phones, high noise levels, and strong network heterogeneity, all of which limit effective seismic monitoring. Here we utilize network and array-processing schemes to asses event detectability with the MyShake global smartphone network. We examine the benefits of using this network in either triggered or continuous modes of operation. A global database of ground motions measured on stationary phones triggered by M2-6 events is used to establish detection probabilities. We find that the probability of detecting an M=3 event with a single phone located <10 km from the epicenter exceeds 70%. Due to the sensor's self-noise, smaller magnitude events at short epicentral distances are very difficult to detect. To increase the signal-to-noise ratio, we employ array back-projection techniques on continuous data recorded by thousands of phones. In this class of methods, the array is used as a spatial filter that suppresses signals emitted from shallow noise sources. Filtered traces are stacked to further enhance seismic signals from deep sources. We benchmark our technique against traditional location algorithms using recordings from California, a region with large MyShake user database. We find that locations derived from back-projection images of M 3 events recorded by >20 nearby phones closely match the regional catalog locations. We use simulated broadband seismic data to examine how location uncertainties vary with user distribution and noise levels. To this end, we have developed an empirical noise model for the metropolitan Los-Angeles (LA) area. We find that densities larger than 100 stationary phones/km2 are required to accurately locate M 2 events in the LA basin. Given the projected MyShake user distribution, that condition may be met within the next few years.

Noise-Based Seismic Measurements of Tidal-Induced Velocity Changes from Large-N Arrays at the Piton de la Fournaise Volcano

NASA Astrophysics Data System (ADS)

Mao, S.; Campillo, M.; van der Hilst, R. D.; Brenguier, F.; Stehly, L.; Hillers, G.

2016-12-01

We measure the relative seismic velocity changes due to the periodic tidal deformation of the crust at Piton de la Fournaise (PdF) Volcano, La Réunion, where the velocity is expected to be highly sensitive to stress changes because of the low effective pressure resulting from volcanic fluids. We use ambient noise data from the VolcArray experiment at PdF [Brenguier et al, 2016], which includes continuous records of three dense arrays for 30 days in July 2014. Each array consists of 7 x 7 grid points of vertical-component geophones with spacing of about 80 m. We compute hourly cross-correlations of the ambient seismic wavefield to recover the Green's functions, and apply the curvelet filter to improve the signal to noise ratio at high frequency. The travel time variations of multiple-scattered body waves are calculated by the doublet analysis. Taking advantage of the stack of over 1200 station pairs for each array, the relative velocity changes are obtained with a time resolution of up to 1 hour. We remove the long period velocity variations associated with precipitation and deformation related to magma migration using a polynomial interpolation. The remaining velocity fluctuations are of the order of 0.01%. We compare the temporal changes to the vertical accelerations recorded by the nearby very long period seismic station RER, and the simulations of the volumetric tidal strain by SPOTL [Agnew, 2012]. Dominant peaks at around 12 hours and 24 hours are found very consistent in the spectrums of all three series, while small peaks at higher frequency also appear. The phases of dv/v temporal variations match well with the tidal signals during periods of large amplitudes. This experiment shows the feasibility of continuous noise-based measurements of tidal-induced seismic velocity changes with hourly resolution. REFERENCE: [1] Brenguier, F., et al. (2016), Towards 4-D noise-based seismology: First results of a Large-N array experiment on Piton de la Fournaise volcano, Seismol. Res. Lett., 87(1), 15-25, doi:10.1785/0220150173. [2] Agnew, D. C. (2012). SPOTL: Some Programs for Ocean-Tide Loading, SIO Technical Report, Scripps Institution of Oceanography

Analysis of the seismic wavefield in the Moesian Platform (Bucharest area) for hazard assessment purposes

NASA Astrophysics Data System (ADS)

Manea, Elena Florinela; Michel, Clotaire; Hobiger, Manuel; Fäh, Donat; Cioflan, Carmen Ortanza; Radulian, Mircea

2017-09-01

During large earthquakes generated at intermediate depth in the Vrancea seismic zone, the ground motion recorded in Bucharest (Romania) is characterized by predominant long periods with strong amplification. Time-frequency analysis highlights the generation of low frequency surface waves (<1 Hz) for sufficiently strong and superficial events. This phenomenon has been explained by the influence of both source mechanism (radiation pattern, directivity effects) and mechanical properties of the local geological structure (geological layering and geometry). The main goal of our study is to better characterize and understand the seismic wavefield produced by earthquakes in the area of Bucharest, taking into account its location in the centre of the Moesian Platform, a large sedimentary basin (450 km long, 300 km wide and up to 20 km deep). To this aim, we identify the contribution of different seismic surface waves, such as the ones produced at the edges of this large sedimentary basin or multipath interference waves (Airy phases of Love and Rayleigh waves), on ground motion. The data from a 35 km diameter array (URS experiment) were used. The array was installed by the National Institute for Earth Physics in cooperation with the Karlsruhe Institute for Technology and operated during 10 months in 2003 and 2004 in the urban area of Bucharest and adjacent zones. The earthquake wavefield recorded by the URS array was analysed using the MUSIQUE technique. This technique analyses the three-component signals of all sensors of a seismic array together. The analysis includes 19 earthquakes with epicentral distances from 100 to 1560 km and with various backazimuths with enough energy at low frequencies (0.1-1 Hz), within the resolution range of the array. For all events, the largest portion of energy is arriving from the source direction and the wavefield is dominated by Love waves. The results of the array analyses clearly indicate a significant scattering corresponding to 2-D or 3-D effects of the Moesian Platform. The azimuthal distribution shows that the scattering comes primarily from the southern and northern edges of the basin. The Airy phase of Love waves was clearly identified as the main contributor in the range of the fundamental frequency of resonance of the basin (0.15-0.25 Hz), with directionality along the backazimuth and its opposite direction. Moreover, two further distinct frequency bands around 0.4 and 0.7 Hz with higher amplitudes were identified. Their complex nature is a combination of the higher modes of Rayleigh waves, Airy phases of Love waves and SH waves. Love and Rayleigh wave dispersion curves were successfully retrieved by combining the information of all events and show a good match with the ones obtained using ambient vibrations. Additionally, the first higher mode of Rayleigh waves could be retrieved using data from earthquakes. Also, the prograde and retrograde Rayleigh wave ellipticity was computed.

Large-N Nodal Seismic Deployment at Mount St Helens

NASA Astrophysics Data System (ADS)

Hansen, S. M.; Schmandt, B.; Vidale, J. E.; Creager, K. C.; Levander, A.; Kiser, E.; Barklage, M.; Hollis, D.

2014-12-01

In late July of 2014 over 900 autonomous short period seismometers were deployed within 12 km of the summit crater at Mount St Helens. In concert with the larger iMUSH experiment, these data constitute the largest seismic interrogation of an active volcano ever conducted. The array was deployed along the road and trail system of the national volcanic monument and adjacent regions with an average station spacing of 250 meters and included several station clusters with increased sampling density. The 10 Hz phones recorded the vertical component wavefield continuously at 250 Hz sampling rate over a period of approximately two weeks. During the recording time, the Pacific Northwest Seismic Network detected ~65 earthquakes within the array footprint ranging in magnitude from -0.9 to 1.1, the majority of which were located beneath the crater at less than 10 km depth. In addition to the natural seismicity, 23 explosion sources from the iMUSH active source experiment were recorded, several of which exceeded magnitude 2. Preliminary results for this project will include an expanded event catalog as the array should significantly reduce the detection threshold. The sheer number of instruments allows for stacking of station clusters producing high signal-to-noise beam traces which can be used for event triggering and for creating waveform templates to measure relative travel-times across the array via cross-correlation. The ability of the array to estimate focal mechanisms from event radiation patterns and delineate complex path effects will also be investigated. The density and azimuthal coverage provide by this array offers an excellent opportunity to investigate short-wavelength variations of the seismic wavefield in a complex geologic environment. Previous seismic tomography results suggest the presence of a shallow magma chamber at 1-3 km depth near the region of shallow seismicity as evidenced by a P wave low-velocity anomaly of at least -5.5% [Waite and Moran, 2009]. The proximity of the array as well as the event distribution make it possible to investigate wavefield distortion and scattering due to the potential magma chamber, including s-wave blockage as has been observed in other systems.

An Evaluation of North Korea’s Nuclear Test by Belbasi Nuclear Tests Monitoring Center-KOERI

NASA Astrophysics Data System (ADS)

Necmioglu, O.; Meral Ozel, N.; Semin, K.

2009-12-01

Bogazici University and Kandilli Observatory and Earthquake Research Institute (KOERI) is acting as the Turkish National Data Center (NDC) and responsible for the operation of the International Monitoring System (IMS) Primary Seismic Station (PS-43) under Belbasi Nuclear Tests Monitoring Center for the verification of compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) since February 2000. The NDC is responsible for operating two arrays which are part of the IMS, as well as for transmitting data from these stations to the International Data Centre (IDC) in Vienna. The Belbasi array was established in 1951, as a four-element (Benioff 1051) seismic array as part of the United States Atomic Energy Detection System (USAEDS). Turkish General Staff (TGS) and U.S. Air Force Technical Application Center (AFTAC) under the Defense and Economic Cooperation Agreement (DECA) jointly operated this short period array. The station was upgraded and several seismometers were added to array during 1951 and 1994 and the station code was changed from BSRS (Belbasi Seismic Research Station) to BRTR-PS43 later on. PS-43 is composed of two sub-arrays (Ankara and Keskin): the medium-period array with a ~40 km radius located in Ankara and the short-period array with a ~3 km radius located in Keskin. Each array has a broadband element located at the middle of the circular geometry. Short period instruments are installed at depth 30 meters from the surface while medium and broadband instruments are installed at depth 60 meters from surface. On 25 May 2009, The Democratic People’s Republic of Korea (DPRK) claimed that it had conducted a nuclear test. Corresponding seismic event was recorded by IMS and IDC released first automatic estimation of time (00:54:43 GMT), location (41.2896°N and 129.0480°E) and the magnitude (4.52 mb) of the event in less than two hours time (USGS: 00:54:43 GMT; 41.306°N, 129.029°E; 4.7 mb) During our preliminary analysis of the 25th May 2009 DPRK event, we saw a very clear P arrival at 01:05:47 (GMT) at BRTR SP array. The result of the f-k analysis performed in Geotool software, installed at NDC facilities in 2008 and is in full use currently, was also indicating that the arrival belongs to the DPRK event. When comparing our f-k results (calculated at 1-2 Hz) with IDC-REB, however, we have noticed that our calculation and therefore corresponding residuals (calculated with reference to REB residuals) are much better in comparison to REB. The reasons of this ambiguity have been explored and for the first time a comprehensive seismological analysis of a Nuclear Test has been conducted in Turkey. CTBT has an important role for the implementation of the non-proliferation of nuclear weapons and it is a key element for the pursuit of nuclear disarmament. In this study, we would like to reflect the technical and scientific aspects of the 25 May 2009 DPRK event analysis, together with our involvement in CTBT(O) affairs, which we believe it brings new dimensions to Turkey especially in the area of Geophysics.

Armored umbilical apparatus for towing a marine seismic air gun sub array

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burrage, E.C.

1985-06-25

An armored umbilical and termination housing is disclosed for towing a sub-array of seismic air guns used in marine seismic surveying comprising a single air hose for supplying all the high pressure air to the individual air guns surrounded by all the electrical control cables needed to operate the air guns in the sub-array. Protective coatings are applied around the electrical control cables and stress members for carrying the load of towing the sub-array are incorporated within the umbilical. A termination housing is provided on the end of the umbilical for terminating the single air hose and all the electricalmore » control lines to common connectors so that individual electrical control lines and air hoses can run from the termination housing to each individual air gun in the sub-array. Air shut off valves are provided so that the high pressure air can be shut off to the individual air guns within the sub-array remotely from the survey vessel.« less

Identifying regions of strong scattering at the core-mantle boundary from analysis of PKKP precursor energy

USGS Publications Warehouse

Rost, S.; Earle, P.S.

2010-01-01

We detect seismic scattering from the core-mantle boundary related to the phase PKKP (PK. KP) in data from small aperture seismic arrays in India and Canada. The detection of these scattered waves in data from small aperture arrays is new and allows a better characterization of the fine-scale structure of the deep Earth especially in the southern hemisphere. Their slowness vector is determined from array processing allowing location of the heterogeneities at the core-mantle boundary using back-projection techniques through 1D Earth models. We identify strong scattering at the core-mantle boundary (CMB) beneath the Caribbean, Patagonia and the Antarctic Peninsula as well as beneath southern Africa. An analysis of the scattering regions relative to sources and receivers indicates that these regions represent areas of increased scattering likely due to increased heterogeneities close to the CMB. The 1. Hz array data used in this study is most sensitive to heterogeneity with scale lengths of about 10. km. Given the small size of the scatterers, a chemical origin of the heterogeneities is likely. By comparing the location of the fine-scale heterogeneity to geodynamical models and tomographic images, we identify different scattering mechanisms in regions related to subduction (Caribbean and Patagonia) and dense thermo chemical piles (Southern Africa). ?? 2010 Elsevier B.V.

Seismo-volcano source localization with triaxial broad-band seismic array

NASA Astrophysics Data System (ADS)

Inza, L. A.; Mars, J. I.; Métaxian, J. P.; O'Brien, G. S.; Macedo, O.

2011-10-01

Seismo-volcano source localization is essential to improve our understanding of eruptive dynamics and of magmatic systems. The lack of clear seismic wave phases prohibits the use of classical location methods. Seismic antennas composed of one-component (1C) seismometers provide a good estimate of the backazimuth of the wavefield. The depth estimation, on the other hand, is difficult or impossible to determine. As in classical seismology, the use of three-component (3C) seismometers is now common in volcano studies. To determine the source location parameters (backazimuth and depth), we extend the 1C seismic antenna approach to 3Cs. This paper discusses a high-resolution location method using a 3C array survey (3C-MUSIC algorithm) with data from two seismic antennas installed on an andesitic volcano in Peru (Ubinas volcano). One of the main scientific questions related to the eruptive process of Ubinas volcano is the relationship between the magmatic explosions and long-period (LP) swarms. After introducing the 3C array theory, we evaluate the robustness of the location method on a full wavefield 3-D synthetic data set generated using a digital elevation model of Ubinas volcano and an homogeneous velocity model. Results show that the backazimuth determined using the 3C array has a smaller error than a 1C array. Only the 3C method allows the recovery of the source depths. Finally, we applied the 3C approach to two seismic events recorded in 2009. Crossing the estimated backazimuth and incidence angles, we find sources located 1000 ± 660 m and 3000 ± 730 m below the bottom of the active crater for the explosion and the LP event, respectively. Therefore, extending 1C arrays to 3C arrays in volcano monitoring allows a more accurate determination of the source epicentre and now an estimate for the depth.

Velocity Model Using the Large-N Seismic Array from the Source Physics Experiment (SPE)

NASA Astrophysics Data System (ADS)

Chen, T.; Snelson, C. M.

2016-12-01

The Source Physics Experiment (SPE) is a multi-institutional, multi-disciplinary project that consists of a series of chemical explosions conducted at the Nevada National Security Site (NNSS). The goal of SPE is to understand the complicated effect of geological structures on seismic wave propagation and source energy partitioning, develop and validate physics-based modeling, and ultimately better monitor low-yield nuclear explosions. A Large-N seismic array was deployed at the SPE site to image the full 3D wavefield from the most recent SPE-5 explosion on April 26, 2016. The Large-N seismic array consists of 996 geophones (half three-component and half vertical-component sensors), and operated for one month, recording the SPE-5 shot, ambient noise, and additional controlled-sources (a large hammer). This study uses Large-N array recordings of the SPE-5 chemical explosion to develop high resolution images of local geologic structures. We analyze different phases of recorded seismic data and construct a velocity model based on arrival times. The results of this study will be incorporated into the large modeling and simulation efforts as ground-truth further validating the models.

Virtual source reflection imaging of the Socorro Magma Body, New Mexico, using a dense seismic array

NASA Astrophysics Data System (ADS)

Finlay, T. S.; Worthington, L. L.; Schmandt, B.; Hansen, S. M.; Bilek, S. L.; Aster, R. C.; Ranasinghe, N. R.

2017-12-01

The Socorro Magma Body (SMB) is one of the largest known actively inflating continental magmatic intrusions. Previous studies have relied on sparse instrument coverage to determine its spatial extent, depth, and seismic signature, which characterized the body as a thin sill with a surface at 19 km below the Earth's surface. However, over the last two decades, InSAR and magneto-telluric (MT) studies have shed new light on the SMB and invigorated the scientific debate of the spatial distribution and uplift rate of the SMB. We return to seismic imaging of the SMB with the Sevilleta Array, a 12-day deployment of approximately 800 vertical component, 10-Hz geophones north of Socorro, New Mexico above and around the estimated northern half of the SMB. Teleseismic virtual source reflection profiling (TVR) employs the free surface reflection off of a teleseismic P as a virtual source in dense arrays, and has been used successfully to image basin structure and the Moho in multiple tectonic environments. The Sevilleta Array recorded 62 teleseismic events greater than M5. Applying TVR to the data collected by the Sevilleta Array, we present stacks from four events that produced the with high signal-to-noise ratios and simple source-time functions: the February 11, 2015 M6.7 in northern Argentina, the February 19, 2015 M5.4 in Kamchatka, Russia, and the February 21, 2015 M5.1 and February 22, 2015 M5.5 in western Colombia. Preliminary results suggest eastward-dipping reflectors at approximately 5 km depth near the Sierra Ladrones range in the northwestern corner of the array. Further analysis will focus on creating profiles across the area of maximum SMB uplift and constraining basin geometry.

Static Corrections to Improve Seismic Monitoring of the North Korean Nuclear Test Site with Regional Arrays

NASA Astrophysics Data System (ADS)

Wilkins, N.; Wookey, J. M.; Selby, N. D.

2017-12-01

Seismology is an important part of the International Monitoring System (IMS) installed to detect, identify, and locate nuclear detonations in breach of the Comprehensive nuclear Test Ban Treaty (CTBT) prior to and after its entry into force. Seismic arrays in particular provide not only a means of detecting and locating underground nuclear explosions, but in discriminating them from naturally occurring earthquakes of similar magnitude. One potential discriminant is the amplitude ratio of high frequency (> 2 Hz) P waves to S waves (P/S) measured at regional distances (3 - 17 °). Accurate measurement of such discriminants, and the ability to detect low-magnitude seismicity from a suspicious event relies on high signal-to-noise ratio (SNR) data. A correction to the slowness vector of the incident seismic wavefield, and static corrections applied to the waveforms recorded at each receiver within the array can be shown to improve the SNR. We apply codes we have developed to calculate slowness-azimuth station corrections (SASCs) and static corrections to the arrival time and amplitude of the seismic waveform to seismic arrays regional to the DPRK nuclear test site at Punggye-ri, North Korea. We use the F-statistic to demonstrate the SNR improvement to data from the nuclear tests and other seismic events in the vicinity of the test site. We also make new measurements of P/S with the corrected waveforms and compare these with existing measurements.

Adaptive Waveform Correlation Detectors for Arrays: Algorithms for Autonomous Calibration

DTIC Science & Technology

2007-09-01

March 17, 2005. The seismic signals from both master and detected events are followed by infrasound arrivals. Note the long duration of the...correlation coefficient traces with a significant array -gain. A detected event that is co-located with the master event will record the same time-difference...estimating the detection threshold reduction for a range of highly repeating seismic sources using arrays of different configurations and at different

Towards marine seismological Network: real time small aperture seismic array

NASA Astrophysics Data System (ADS)

Ilinskiy, Dmitry

2017-04-01

Most powerful and dangerous seismic events are generated in underwater subduction zones. Existing seismological networks are based on land seismological stations. Increased demands for accuracy of location, magnitude, rupture process of coming earthquakes and at the same time reduction of data processing time require information from seabed seismic stations located near the earthquake generation area. Marine stations provide important contribution for clarification of the tectonic settings in most active subduction zones of the world. Early warning system for subduction zone area is based on marine seabed array which located near the area of most hazardous seismic zone in the region. Fast track processing for location of the earthquake hypocenter and energy takes place in buoy surface unit. Information about detected and located earthquake reaches the onshore seismological center earlier than the first break waves from the same earthquake will reach the nearest onshore seismological station. Implementation of small aperture array is based on existed and shown a good proven performance and costs effective solutions such as weather moored buoy and self-pop up autonomous seabed seismic nodes. Permanent seabed system for real-time operation has to be installed in deep sea waters far from the coast. Seabed array consists of several self-popup seismological stations which continuously acquire the data, detect the events of certain energy class and send detected event parameters to the surface buoy via acoustic link. Surface buoy unit determine the earthquake location by receiving the event parameters from seabed units and send such information in semi-real time to the onshore seismological center via narrow band satellite link. Upon the request from the cost the system could send wave form of events of certain energy class, bottom seismic station battery status and other environmental parameters. When the battery life of particular seabed unit is close to became empty, the seabed unit is switching into sleep mode and send that information to surface buoy and father to the onshore data center. Then seabed unit can wait for the vessel of opportunity for recovery of seabed unit to sea surface and replacing seabed station to another one with fresh batteries. All collected permanent seismic data by seabed unit could than downloaded for father processing and analysis. In our presentation we will demonstrate the several working prototypes of proposed system such as real time cable broad band seismological station and real time buoy seabed seismological station.

Array analysis of electromagnetic radiation from radio transmitters for submarine communication

NASA Astrophysics Data System (ADS)

Füllekrug, Martin; Mezentsev, Andrew; Watson, Robert; Gaffet, Stéphane; Astin, Ivan; Evans, Adrian

2014-12-01

The array analyses used for seismic and infrasound research are adapted and applied here to the electromagnetic radiation from radio transmitters for submarine communication. It is found that the array analysis enables a determination of the slowness and the arrival azimuth of the wave number vectors associated with the electromagnetic radiation. The array analysis is applied to measurements of ˜20-24 kHz radio waves from transmitters for submarine communication with an array of 10 radio receivers distributed over an area of ˜1 km ×1 km. The observed slowness of the observed wave number vectors range from ˜2.7 ns/m to ˜4.1 ns/m, and the deviations between the expected arrival azimuths and the observed arrival azimuths range from ˜-9.7° to ˜14.5°. The experimental results suggest that it is possible to determine the locations of radio sources from transient luminous events above thunderclouds with an array of radio receivers toward detailed investigations of the electromagnetic radiation from sprites.

Quantifying the similarity of seismic polarizations

NASA Astrophysics Data System (ADS)

Jones, Joshua P.; Eaton, David W.; Caffagni, Enrico

2016-02-01

Assessing the similarities of seismic attributes can help identify tremor, low signal-to-noise (S/N) signals and converted or reflected phases, in addition to diagnosing site noise and sensor misalignment in arrays. Polarization analysis is a widely accepted method for studying the orientation and directional characteristics of seismic phases via computed attributes, but similarity is ordinarily discussed using qualitative comparisons with reference values or known seismic sources. Here we introduce a technique for quantitative polarization similarity that uses weighted histograms computed in short, overlapping time windows, drawing on methods adapted from the image processing and computer vision literature. Our method accounts for ambiguity in azimuth and incidence angle and variations in S/N ratio. Measuring polarization similarity allows easy identification of site noise and sensor misalignment and can help identify coherent noise and emergent or low S/N phase arrivals. Dissimilar azimuths during phase arrivals indicate misaligned horizontal components, dissimilar incidence angles during phase arrivals indicate misaligned vertical components and dissimilar linear polarization may indicate a secondary noise source. Using records of the Mw = 8.3 Sea of Okhotsk earthquake, from Canadian National Seismic Network broad-band sensors in British Columbia and Yukon Territory, Canada, and a vertical borehole array at Hoadley gas field, central Alberta, Canada, we demonstrate that our method is robust to station spacing. Discrete wavelet analysis extends polarization similarity to the time-frequency domain in a straightforward way. Time-frequency polarization similarities of borehole data suggest that a coherent noise source may have persisted above 8 Hz several months after peak resource extraction from a `flowback' type hydraulic fracture.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bame, D.

To determine if seismic signals at frequencies up to 50 Hz are useful for detecting events and discriminating between earthquakes and explosions, approximately 180 events from the three-component high-frequency seismic element (HFSE) installed at the center of the Norwegian Regional Seismic Array (NRSA) have been analyzed. The attenuation of high-frequency signals in Scandinavia varies with distance, azimuth, magnitude, and source effects. Most of the events were detected with HFSE, although detections were better on the NRSA where signal processing techniques were used. Based on a preliminary analysis, high-frequency data do not appear to be a useful discriminant in Scandinavia. 21more » refs., 29 figs., 3 tabs.« less

A Two-Radius Circular Array Method: Extracting Independent Information on Phase Velocities of Love Waves From Microtremor Records From a Simple Seismic Array

NASA Astrophysics Data System (ADS)

Tada, T.; Cho, I.; Shinozaki, Y.

2005-12-01

We have invented a Two-Radius (TR) circular array method of microtremor exploration, an algorithm that enables to estimate phase velocities of Love waves by analyzing horizontal-component records of microtremors that are obtained with an array of seismic sensors placed around circumferences of two different radii. The data recording may be done either simultaneously around the two circles or in two separate sessions with sensors distributed around each circle. Both Rayleigh and Love waves are present in the horizontal components of microtremors, but in the data processing of our TR method, all information on the Rayleigh waves ends up cancelled out, and information on the Love waves alone are left to be analyzed. Also, unlike the popularly used frequency-wavenumber spectral (F-K) method, our TR method does not resolve individual plane-wave components arriving from different directions and analyze their "vector" phase velocities, but instead directly evaluates their "scalar" phase velocities --- phase velocities that contain no information on the arrival direction of waves --- through a mathematical procedure which involves azimuthal averaging. The latter feature leads us to expect that, with our TR method, it is possible to conduct phase velocity analysis with smaller numbers of sensors, with higher stability, and up to longer-wavelength ranges than with the F-K method. With a view to investigating the capabilities and limitations of our TR method in practical implementation to real data, we have deployed circular seismic arrays of different sizes at a test site in Japan where the underground structure is well documented through geophysical exploration. Ten seismic sensors were placed equidistantly around two circumferences, five around each circle, with varying combinations of radii ranging from several meters to several tens of meters, and simultaneous records of microtremors around circles of two different radii were analyzed with our TR method to produce estimates for the phase velocities of Love waves. The estimates were then checked against "model" phase velocities that are derived from theoretical calculations. We have also conducted a check of the estimated spectral ratios against the "model" spectral ratios, where we mean by "spectral ratio" an intermediary quantity that is calculated from observed records prior to the estimation of the phase velocity in the data analysis procedure of our TR method. In most cases, the estimated phase velocities coincided well with the model phase velocities within a wavelength range extending roughly from 3r to 6r (r: array radius). It was found out that, outside the upper and lower resolution limits of the TR method, the discrepancy between the estimated and model phase velocities, as well as the discrepancy between the estimated and model spectral ratios, were accounted for satisfactorily by theoretical consideration of three factors: the presence of higher surface-wave modes, directional aliasing effects related to the finite number of sensors in the seismic array, and the presence of incoherent noise.

Basic Research on Seismic and Infrasonic Monitoring of the European Arctic

DTIC Science & Technology

2007-09-01

detected with a high signal -to-noise ratio (SNR) on the ARCES array ; secondly they register very stable azimuth estimates on the detection lists; and...exploiting the data from the Swedish infrasound array network, which provides a useful supplement to the seismic and infrasonic arrays in Norway and NW...infrasonic phase associations. Furthermore, we plan to generate an infrasonic event bulletin using only the estimated azimuths and detection times of

Improved Phase Characterization of Far-Regional Body Wave Arrivals in Central Asia

DTIC Science & Technology

2008-09-30

developing array -based methods that can more accurately characterize far-regional (14*-29*) seismic wavefield structure. Far- regional (14*-29*) seismograms...arrivals with the primary arrivals. These complexities can be region and earthquake specific. The regional seismic arrays that have been built in the last...fifteen years should be a rich data source for the study of far-regional phase behavior. The arrays are composed of high-quality borehole seismometers

Stress and structure analysis of the Seismic Gap between the Wenchuan and Lushan Earthquakes

NASA Astrophysics Data System (ADS)

Liang, Chuntao

2017-04-01

An array of 20 short-period and 15 broadband seismometers were deployed to monitor the seismic gap between the 2008 Ms8.0 Wenchuan earthquake and the 2013 Ms7.0 Lushan earthquake. The Wenchuan earthquake ruptured from epicenter at (31.01°N, 103.42°E) largely northeastward while the Lushan earthquake ruptured from epicenter at (30.3°N, 103.0°E) largely southwestward. The region between the two earthquakes has recorded very few aftershocks and cataloged seismicity before and after the two big earthquakes compared to neighboring segments. As one small segment of the 500KM long Longmen Shan fault system, its absence of seismicity draws hot debate on whether a big one is still in brewing or steady creeping is in control of the strain energy release. The dense array is deployed primarily aimed to detect events that are much smaller than cataloged events and to determine if the segment is experiencing constantly creeping. The preliminary findings include: (1) source mechanisms show that the seismic gap appears to be a transitional zone between north and south segment. The events to the south are primarily thrust while events to north have more or less striking-slip components. This is also the case for both Lushan and Wenchuan earthquake; (2) The receiver function analysis shows that the Moho beneath the seismic Gap is less defined than its adjacent region with relatively weaker Ps conversion phases; (3) Both receiver function and ambient noise tomography show that the velocities in the upper crust is relatively lower in the Gap region than surrounding regions; (4) significant number of small earthquakes are located near surface in the gap region. Further examinations should be conducted before we can make a sounding conclusion on what mechanism is in control of the seismicity in this region.

Newberry Volcano EGS Demonstration - Phase I Results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osborn, William L.; Petty, Susan; Cladouhos, Trenton T.

Phase I of the Newberry Volcano Enhanced Geothermal System (EGS) Demonstration included permitting, community outreach, seismic hazards analysis, initial microseismic array deployment and calibration, final MSA design, site characterization, and stimulation planning. The multi-disciplinary Phase I site characterization supports stimulation planning and regulatory permitting, as well as addressing public concerns including water usage and induced seismicity. A review of the project's water usage plan by an independent hydrology consultant found no expected impacts to local stakeholders, and recommended additional monitoring procedures. The IEA Protocol for Induced Seismicity Associated with Enhanced Geothermal Systems was applied to assess site conditions, properly informmore » stakeholders, and develop a comprehensive mitigation plan. Analysis of precision LiDAR elevation maps has concluded that there is no evidence of recent faulting near the target well. A borehole televiewer image log of the well bore revealed over three hundred fractures and predicted stress orientations. No natural, background seismicity has been identified in a review of historic data, or in more than seven months of seismic data recorded on an array of seven seismometers operating around the target well. A seismic hazards and induced seismicity risk assessment by an independent consultant concluded that the Demonstration would contribute no additional risk to residents of the nearest town of La Pine, Oregon. In Phase II of the demonstration, an existing deep hot well, NWG 55-29, will be stimulated using hydroshearing techniques to create an EGS reservoir. The Newberry Volcano EGS Demonstration is allowing geothermal industry and academic experts to develop, validate and enhance geoscience and engineering techniques, and other procedures essential to the expansion of EGS throughout the country. Successful development will demonstrate to the American public that EGS can play a significant role in reducing foreign energy dependence, and provide clean, renewable, baseload geothermal power generation in the State of Oregon.« less

Analysis and Simulation of Near-Field Wave Motion Data from the Source Physics Experiment Explosions

DTIC Science & Technology

2011-09-01

understanding and ability to model explosively generated seismic waves, particularly S-waves. The first SPE explosion (SPE1) consisted of a 100 kg shot at a...depth of 60 meters in granite (Climax Stock). The shot was well- recorded by an array of over 150 instruments, including both near-field wave motion...measurements as well as far- field seismic measurements. This paper focuses on measurements and modeling of the near-field data. A complimentary

Determination of Rayleigh wave ellipticity across the Earthscope Transportable Array using single-station and array-based processing of ambient seismic noise

NASA Astrophysics Data System (ADS)

Workman, Eli; Lin, Fan-Chi; Koper, Keith D.

2017-01-01

We present a single station method for the determination of Rayleigh wave ellipticity, or Rayleigh wave horizontal to vertical amplitude ratio (H/V) using Frequency Dependent Polarization Analysis (FDPA). This procedure uses singular value decomposition of 3-by-3 spectral covariance matrices over 1-hr time windows to determine properties of the ambient seismic noise field such as particle motion and dominant wave-type. In FPDA, if the noise is mostly dominated by a primary singular value and the phase difference is roughly 90° between the major horizontal axis and the vertical axis of the corresponding singular vector, we infer that Rayleigh waves are dominant and measure an H/V ratio for that hour and frequency bin. We perform this analysis for all available data from the Earthscope Transportable Array between 2004 and 2014. We compare the observed Rayleigh wave H/V ratios with those previously measured by multicomponent, multistation noise cross-correlation (NCC), as well as classical noise spectrum H/V ratio analysis (NSHV). At 8 s the results from all three methods agree, suggesting that the ambient seismic noise field is Rayleigh wave dominated. Between 10 and 30 s, while the general pattern agrees well, the results from FDPA and NSHV are persistently slightly higher (˜2 per cent) and significantly higher (>20 per cent), respectively, than results from the array-based NCC. This is likely caused by contamination from other wave types (i.e. Love waves, body waves, and tilt noise) in the single station methods, but it could also reflect a small, persistent error in NCC. Additionally, we find that the single station method has difficulty retrieving robust Rayleigh wave H/V ratios within major sedimentary basins, such as the Williston Basin and Mississippi Embayment, where the noise field is likely dominated by reverberating Love waves and tilt noise.

Bedload transport from spectral analysis of seismic noise near rivers

NASA Astrophysics Data System (ADS)

Hsu, L.; Finnegan, N. J.; Brodsky, E. E.

2010-12-01

Channel change in rivers is driven by bedload sediment transport. However, the nonlinear nature of sediment transport combined with the difficulty of making direct observations in rivers at flood hinder prediction of the timing and magnitude of bedload movement. Recent studies have shown that spectral analysis of seismic noise from seismometers near rivers illustrate a correlation between the relative amplitude of high frequency (>1 Hz) seismic noise and conditions for bedload transport, presumably from the energy transferred from clast collisions with the channel. However, a previous study in the Himalayas did not contain extensive bedload transport or discharge measurements, and the correspondence of seismic noise with proxy variables such as regional hydrologic and meteorologic data was not exact. A more complete understanding of the relationship between bedload transport and seismic noise would be valuable for extending the spatial and temporal extent of bedload data. To explore the direct relationship between bedload transport and seismic noise, we examine data from several seismic stations near the Trinity River in California, where the fluvial morphodynamics and bedload rating curves have been studied extensively. We compare the relative amplitude of the ambient seismic noise with records of water discharge and sediment transport. We also examine the noise at hourly, daily, and seasonal timescales to determine other possible sources of noise. We report the influence of variables such as local river slope, adjacent geology, anthropogenic noise, and distance from the river. The results illustrate the feasibility of using existing seismic arrays to sense radiated energy from processes of bedload transport. In addition, the results can be used to design future seismic array campaigns to optimize information about bedload transport. This technique provides great spatial and temporal coverage, and can be performed where direct bedload measurements are difficult or impossible. In addition to supplying information about sediment transport, the measure of energy transfer to the bed is useful for other applications such as potential for channel bed scour and erosion. Preliminary calculations indicate that the radiated energy sensed by a seismometer 1 km from a large mountain stream is of order 10^2 joules/s. This is similar in magnitude to the gravitational potential energy supply per time of the river, and therefore suggests that in these steep landscapes, a significant fraction of the energy from rivers is transmitted to the bed and can be documented by seismic noise.

Vertical Seismic Profiling at riser drilling site in the rupture area of the 1944 Tonankai Earthquake, Japan (Invited)

NASA Astrophysics Data System (ADS)

Hino, R.; Kinoshita, M.; Araki, E.; Byrne, T. B.; McNeill, L. C.; Saffer, D. M.; Eguchi, N. O.; Takahashi, K.; Toczko, S.

2009-12-01

A series of scientific drilling expeditions is in operation in the Nankai Trough to reveal the faulting mechanism of the magathrust earthquakes, through clarifying composition, fine structure, mechanical behavior, and environmental variables of the seismogenic faults. In the studied area, extensive seismic surveys for site characterization have been made to image detailed geometry of the fault complex in the accretionary prism as well as Vp distribution around the faults. Although these previous surveys provided invaluable information for understanding seismotectonic processes in this subduction zone, more complete knowledge is needed to be acquired to predict dynamic behavior of the faults, such as geometrical irregularities in short wavelength, Vs and seismic attenuation which are sensitive to fluid distribution in and around fault zones. It is expected that estimation of these parameters would be improved considerably by a seismic exploration using a vertical array of seismographs installed in a deep borehole (VSP: vertical seismic profiling). In July 2009, we made a VSP at one of the drilling sites located just above the rupture area of the 1994 Tonankai Earthquake (M 8.1), during the IODP Exp.319. The well site of our VSP was made by the riser drilling of D/V Chikyu. The seismic array, lowered from Chikyu into the hole, was composed of a three-component accelerometer and vertical separation of the array elements was 15.12 m. The VSP was composed of offset VSP and zero-offset VSP. In the offset VSP, a tuned airgun array towed by R/V Kairei was shot along one straight line (walk-away VSP) and another circular line (walk-around VSP) and seismic signals were recorded by an array consisting of 16 elements installed from 907 to 1,135 m in depth from seafloor. The object of the walk-away VSP is to obtain fine image of the faults using reflection arrivals with less attenuation. It is also expected to obtain spatial variation of Vs from arrival time tomography of refracted S waves. For this purpose, we preferred extraordinarily longer (~ 30 km) offset shooting than usual industrial VSPs. Shot spacing was 60 m along the same line as the previous 3D reflection and OBS wide angle surveys. The radius of circle of the walk-around VSP was 3.5 km to detect azimuthal anisotropy of downgoing P and S waves, correlated to stress state around the site. In zero-offset VSP, shots just above the hole were recorded by the 8 element array moving from 0 to 1,135 mbsf along the hole so that seismic structure with comparable vertical resolution as core-log information would be obtained. In the records of the walk-away VSP, clear first arrivals as well as several evident later arrivals were clearly identified. The later phases contain the reflection from the megasplay fault and the refracted S wave through the accretional prism, on both of which we have significant interest. The walk-around VSP also provided us with high S/N records but detailed data reduction, such as velocity analysis using vertical array, are required to derive anisotropic nature of the formation around the hole.

Local Earthquake P-wave Tomography at Mount St. Helens with the iMUSH Broadband Array

NASA Astrophysics Data System (ADS)

Ulberg, C. W.; Creager, K. C.; Moran, S. C.; Abers, G. A.; Crosbie, K.; Crosson, R. S.; Denlinger, R. P.; Thelen, W. A.; Hansen, S. M.; Schmandt, B.; Kiser, E.; Levander, A.; Bachmann, O.

2016-12-01

We deployed 70 broadband seismometers in the summer of 2014 to image the seismic velocity structure beneath Mount St. Helens (MSH), Washington, as part of the collaborative imaging Magma Under St. Helens (iMUSH) project. Our goal is to illuminate the MSH magmatic system by integrating all portions of the iMUSH experiment, including active- and passive-source tomography, ambient-noise tomography, seismicity, receiver functions, magnetotellurics, and petrology. The broadband array has a diameter of 100 km centered on MSH with an average station spacing of 10 km, and was deployed through summer 2016. It is augmented by dozens of permanent stations in the area. We determine P-wave arrival times and also incorporate picks from the permanent network. There were more than 250 local events during the first year of iMUSH broadband recording, which have provided over 11,000 high-quality arrival times. The iMUSH experiment included 23 active shots in 2014 that were recorded with good signal-to-noise ratios across the entire array. Direct raypaths from local earthquakes and active shots reach 15-20 km depth beneath MSH. We use the program struct3DP to iteratively invert travel times to obtain a 3-D seismic velocity model and relocate hypocenters. Travel times are computed using a 3-D eikonal-equation solver. We are expanding our analysis to include S-wave arrivals from local events. The preliminary 3-D model shows low P-wave speeds along the St. Helens seismic zone, striking NNW-SSE of MSH from near the surface to where we lose resolution at 15-20km depth. This seismic zone coincides with a sharp boundary in Moho reflectivity that has been interpreted as the eastern boundary of a serpentinized mantle wedge (Hansen et al, 2016, submitted). We speculate that the seismic zone and low wave speeds are related to fluids rising from the eastern boundary of the wedge.

Seismic and hydroacoustic analysis relevant to MH370

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stead, Richard J.

2014-07-03

The vicinity of the Indian Ocean is searched for open and readily available seismic and/or hydroacoustic stations that might have recorded a possible impact of MH370 with the ocean surface. Only three stations are identified: the IMS hydrophone arrays H01 and H08, and the Geoscope seismic station AIS. Analysis of the data from these stations shows an interesting arrival on H01 that has some interference from an Antarctic ice event, large amplitude repeating signals at H08 that obscure any possible arrivals, and large amplitude chaotic noise at AIS precludes any analysis at higher frequencies of interest. The results are thereforemore » rather inconclusive but may point to a more southerly impact location within the overall Indian Ocean search region. The results would be more useful if they can be combined with any other data that are not readily available.« less

Array seismological investigation of the South Atlantic 'Superplume'

NASA Astrophysics Data System (ADS)

Hempel, Stefanie; Gassmöller, Rene; Thomas, Christine

2015-04-01

We apply the axisymmetric, spherical Earth spectral elements code AxiSEM to model seismic compressional waves which sample complex `superplume' structures in the lower mantle. High-resolution array seismological stacking techniques are evaluated regarding their capability to resolve large-scale high-density low-velocity bodies including interior structure such as inner upwellings, high density lenses, ultra-low velocity zones (ULVZs), neighboring remnant slabs and adjacent small-scale uprisings. Synthetic seismograms are also computed and processed for models of the Earth resulting from geodynamic modelling of the South Atlantic mantle including plate reconstruction. We discuss the interference and suppression of the resulting seismic signals and implications for a seismic data study in terms of visibility of the South Atlantic `superplume' structure. This knowledge is used to process, invert and interpret our data set of seismic sources from the Andes and the South Sandwich Islands detected at seismic arrays spanning from Ethiopia over Cameroon to South Africa mapping the South Atlantic `superplume' structure including its interior structure. In order too present the model of the South Atlantic `superplume' structure that best fits the seismic data set, we iteratively compute synthetic seismograms while adjusting the model according to the dependencies found in the parameter study.

Slow Earthquakes in the Alaska-Aleutian Subduction Zone Detected by Multiple Mini Seismic Arrays

NASA Astrophysics Data System (ADS)

LI, B.; Ghosh, A.; Thurber, C. H.; Lanza, F.

2017-12-01

The Alaska-Aleutian subduction zone is one of the most seismically and volcanically active plate boundaries on earth. Compared to other subduction zones, the slow earthquakes, such as tectonic tremors (TTs) and low frequency earthquakes (LFEs), are relatively poorly studied due to the limited data availability and difficult logistics. The analysis of two-months of continuous data from a mini array deployed in 2012 shows abundant tremor and LFE activities under Unalaska Island that is heterogeneously distributed [Li & Ghosh, 2017]. To better study slow earthquakes and understand their physical characteristics in the study region, we deployed a hybrid array of arrays, consisting of three well-designed mini seismic arrays and five stand alone stations, in the Unalaska Island in 2014. They were operational for between one and two years. Using the beam back-projection method [Ghosh et al., 2009, 2012], we detect continuous tremor activities for over a year when all three arrays are running. The sources of tremors are located south of the Unalaska and Akutan Islands, at the eastern and down-dip edge of the rupture zone of the 1957 Mw 8.6 earthquake, and they are clustered in several patches, with a gap between the two major clusters. Tremors show multiple migration patterns with propagation in both along-strike and dip directions and a wide range of velocities. We also identify tens of LFE families and use them as templates to search for repeating LFE events with the matched-filter method. Hundreds to thousands of LFEs for each family are detected and their activities are spatiotemporally consistent with tremor activities. The array techniques are revealing a near-continuous tremor activity in this area with remarkable spatiotemporal details. It helps us to better recognize the physical properties of the transition zone, provides new insights into the slow earthquake activities in this area, and explores their relation with the local earthquakes and the potential slow slip events.

Imaging Critical Zone Using High Frequency Rayleigh Wave Group Velocity Measurements Extracted from Ambient Seismic Fields Gathered With 2400 Seismic Nodes in Southeastern Wyoming.

NASA Astrophysics Data System (ADS)

Keifer, I. S.; Dueker, K. G.

2016-12-01

In an effort to characterize critical zone development in varying regions, seismologist conduct seismic surveys to assist in the realization of critical zone properties e.g. porosity and regolith thickness. A limitation of traditional critical zone seismology is that data is normally collected along lines, to generate two dimensional transects of the subsurface seismic velocity, even though the critical zone structure is 3D. Hence, we deployed six seismic 2D arrays in southeastern Wyoming to gather ambient seismic fields so that 3D shear velocity models could be produced. The arrays were made up of nominally 400 seismic stations arranged in a 200-meter square grid layout. Each array produced a half Terabyte data volume, so a premium was placed on computational efficiency throughout this study, to handle the roughly 65 billion samples recorded by each array. The ambient fields were cross-correlated on the Yellowstone Super-Computer using the pSIN code (Chen et al., 2016), which decreased correlation run times by a factor of 300 with respect to workstation computers. Group delay times extracted from cross-correlations using 8 Hz frequency bands from 10 Hz to 100 Hz show frequency dispersion at sites with shallow regolith underlain by granite bedrock. Dimensionally, the group velocity map inversion is overdetermined, even after extensive culling of spurious group delay times. Model Resolution matrices for our six arrays show values > 0.7 for most of the modal domain, approaching unity at the center of the model domain; we are then confident that we have an adequate number of rays covering our array space, and should experience minimal smearing of our resultant model due to application of inverse solution on the data. After inverting for the group velocity maps, a second inversion is performed of the group velocity maps for the 3D shear velocity model. This inversion is underdetermined and a second order Tikhonov regularization is used to obtain stable inverse images. Results will be presented.

Site response, shallow shear-wave velocity, and wave propagation at the San Jose, California, dense seismic array

USGS Publications Warehouse

Hartzell, S.; Carver, D.; Williams, R.A.; Harmsen, S.; Zerva, A.

2003-01-01

Ground-motion records from a 52-element dense seismic array near San Jose, California, are analyzed to obtain site response, shallow shear-wave velocity, and plane-wave propagation characteristics. The array, located on the eastern side of the Santa Clara Valley south of the San Francisco Bay, is sited over the Evergreen basin, a 7-km-deep depression with Miocene and younger deposits. Site response values below 4 Hz are up to a factor of 2 greater when larger, regional records are included in the analysis, due to strong surface-wave development within the Santa Clara Valley. The pattern of site amplification is the same, however, with local or regional events. Site amplification increases away from the eastern edge of the Santa Clara Valley, reaching a maximum over the western edge of the Evergreen basin, where the pre-Cenozoic basement shallows rapidly. Amplification then decreases further to the west. This pattern may be caused by lower shallow shear-wave velocities and thicker Quaternary deposits further from the edge of the Santa Clara Valley and generation/trapping of surface waves above the shallowing basement of the western Evergreen basin. Shear-wave velocities from the inversion of site response spectra based on smaller, local earthquakes compare well with those obtained independently from our seismic reflection/refraction measurements. Velocities from the inversion of site spectra that include larger, regional records do not compare well with these measurements. A mix of local and regional events, however, is appropriate for determination of site response to be used in seismic hazard evaluation, since large damaging events would excite both body and surface waves with a wide range in ray parameters. Frequency-wavenumber, plane-wave analysis is used to determine the backazimuth and apparent velocity of coherent phases at the array. Conventional, high-resolution, and multiple signal characterization f-k power spectra and stacked slowness power spectra are compared. These spectra show surface waves generated/ scattered at the edges of the Santa Clara Valley and possibly within the valley at the western edge of the Evergreen basin.

Monitoring the development of volcanic eruptions through volcanic lightning - Using a lightning mapping array, seismic and infrasound array, and visual plume analysis

NASA Astrophysics Data System (ADS)

Smith, C. M.; Thompson, G.; McNutt, S. R.; Behnke, S. A.; Edens, H. E.; Van Eaton, A. R.; Gaudin, D.; Thomas, R. J.

2017-12-01

The period of 28 May - 7 June 2015 at Sakurajima Volcano, Japan witnessed a multitude of Vulcanian eruptive events, which resulted in plumes reaching 500-3000m above the vent. These plumes varied from white, gas-rich plumes to dark grey and black ash-rich plumes, and were recorded on lowlight and infrared cameras. A nine-station lightning mapping array (LMA) was deployed to locate sources of VHF (67-73 MHz) radiation produced by lightning flashes and other types of electrical activity such as `continuous RF (radio frequency)'. Two Nanometrics Trillium broadband seismometers and six BSU infrasound sensors were deployed. Over this ten day period we recorded 1556 events that consisted of both seismic and infrasound signals, indicating explosive activity. There are an additional 1222 events that were recorded as only seismic or infrasound signals, which may be a result of precursory seismic signals or noise contamination. Plume discharge types included both distinct lightning flashes and `continuous RF'. The LMA ran continuously for the duration of the experiment. On 30 May 2015 at least seven lightning flashes were also detected by the Vaisala Global Lightning Detection 360 network, which detects VLF (3-30 kHz) radiation. However the University of Washington's World Wide Lightning Location Network, which also detects VLF radiation, detected no volcanic lightning flashes in this time period. This indicates that the electrical activity in Sakurajima's plume occurs near the lower limits of the VLF detection threshold. We investigate relationships between the plume dynamics, the geophysical signal and the corresponding electrical activity through: plume velocity and height; event waveform cross-correlation; volcano acoustic-seismic ratios; overall geophysical energy; RSAM records; and VHF sources detected by the LMA. By investigating these relationships we hope to determine the seismic/infrasound energy threshold required to generate measurable electrical activity. Seismic and infrasound are two of the most common volcanic monitoring methods. By developing the relationships between plume electrification and these geophysical methods we hope to expand the use of lightning for active volcano monitoring.

Laboratory simulation of volcano seismicity.

PubMed

Benson, Philip M; Vinciguerra, Sergio; Meredith, Philip G; Young, R Paul

2008-10-10

The physical processes generating seismicity within volcanic edifices are highly complex and not fully understood. We report results from a laboratory experiment in which basalt from Mount Etna volcano (Italy) was deformed and fractured. The experiment was monitored with an array of transducers around the sample to permit full-waveform capture, location, and analysis of microseismic events. Rapid post-failure decompression of the water-filled pore volume and damage zone triggered many low-frequency events, analogous to volcanic long-period seismicity. The low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample; these events exhibited a weak component of shear (double-couple) slip, consistent with fluid-driven events occurring beneath active volcanoes.

Seismic anisotropy across the east African plateau from shear wave splitting analysis

NASA Astrophysics Data System (ADS)

Bagley, B. C.; Nyblade, A.; Mulibo, G.; Tugume, F.

2011-12-01

Previous studies of the east African plateau reveal complicated patterns of seismic anisotropy that are not easily explained by a single mechanism. The pattern is defined by rift-parallel fast directions for stations within or near Cenozoic rift valleys, and near-null results in Precambrian terrains away from the rift. Data from 65 temporary Africa Array stations deployed between 2007 and 2011 are being used to make new shear wave splitting measurements. The stations span the east African plateau and cover both the eastern and western branches of the east African rift system, as well as unrifted Proterozoic and Archean terrains in Uganda, Kenya, Tanzania, and Zambia. Through analysis of shear wave splitting we will better constrain the distribution of seismic anisotropy, and and from it gain new insight into the tectonic evolution of east Africa.

A Suite of Discriminants for Ground-Truth Mining Events in the Western U.S. and Its Implications for Discrimination Capability in Russia

DTIC Science & Technology

2008-09-01

of up to 1000 individual boreholes is filled with 5000 to 10,000 lbs of material and delay fired over several seconds. The explosive array is...delay-fired mining events using seismic arrays : Application to the PDAR array in Wyoming, USA, Bull. Seism. Soc. Am. 97: pp .989–1001. Arrowsmith...regional seismic stations in monitoring areas of interest, particularly in countries where mining efforts are significant to the economy. As with other

New constraints on micro-seismicity and stress state in the western part of the North Anatolian Fault Zone: Observations from a dense seismic array

NASA Astrophysics Data System (ADS)

Altuncu Poyraz, Selda; Teoman, M. Uğur; Türkelli, Niyazi; Kahraman, Metin; Cambaz, Didem; Mutlu, Ahu; Rost, Sebastian; Houseman, Gregory A.; Thompson, David A.; Cornwell, David; Utkucu, Murat; Gülen, Levent

2015-08-01

With the aim of extensively investigating the crustal structure beneath the western segment of the North Anatolian Fault Zone where it splays into northern and southern branches, a temporary seismic network (dense array for North Anatolia-DANA) consisting of 70 stations was deployed in early May 2012 and operated for 18 months in the Sakarya region during the FaultLab experiment. Out of 2437 events contaminated by explosions, we extracted 1371 well located earthquakes. The enhanced station coverage having a nominal station spacing of 7 km, lead to a minimum magnitude calculation of 0.1. Horizontal and vertical location uncertainties within the array do not exceed 0.8 km and 0.9 km, respectively. We observe considerable seismic activity along both branches of the fault where the depth of the seismogenic zone was mostly confined to 15 km. Using our current earthquake catalog we obtained a b-value of 1. We also mapped the b-value variation with depth and observed a gradual decrease. Furthermore, we determined the source parameters of 41 earthquakes with magnitudes greater than 1.8 using P-wave first motion polarity method. Regional Moment Tensor Inversion method was also applied to earthquakes with magnitudes greater than 3.0. Focal mechanism solutions confirm that Sakarya and its vicinity is stressed by a compressional regime showing a primarily oblique-slip motion character. Stress tensor analysis indicates that the maximum principal stress is aligned in WNW-ESE direction and the tensional axis is aligned in NNE-SSW direction.

Performance of the Broadband Golay 3x6 Array Associated with the 2016 IRIS Community Wavefields Experiment

NASA Astrophysics Data System (ADS)

Bolarinwa, O. J.; Langston, C. A.; Sweet, J. R.; Anderson, K. R.; Woodward, R.

2017-12-01

A 6 km aperture regional array in the Golay 3x6 configuration was fielded as part of the IRIS Community Wavefields Experiment near Enid, Oklahoma from June 26 through November 12, 2016. The array consisted of 18 broadband CMG-3T seismometers deployed using a PASSCAL insulated vault design and RT130 data recorders. The Golay geometry is unusual in that it features 6 tripartite arrays in an open arrangement. Spacing and orientation of each tripartite array is such that the array uniformly samples the wavefield in space as determined from the co-array diagram even though the interior of the array configuration contains no seismic stations. The short wavelength performance of this array requires a high degree of phase correlation across its entire aperture, a characteristic that has been difficult to achieve for other regional array designs because of velocity heterogeneity in the earth. Located within an area of high regional seismicity, the IRIS experiment offered an opportunity to examine the slowness-frequency performance of a real-world Golay 3x6 array that was subject to constraints on land usage during deployment. Individual tripartite arrays fit well within a land survey quarter section but it proved difficult to match the ideal spacing between each subarray because of permitting problems. Nevertheless, these unavoidable geometry perturbations caused only minor changes to the theoretical array response. More surprisingly, observations of high frequency regional P and S phases show very high correlation over the array aperture that gives rise to precise array responses that are close to theoretical. Both the array geometry and relatively homogeneous structure under the array produces an exceptional facility that can be used for high-resolution studies of regional seismic waves.

Discriminating different type waves from pressure and ground motion observation in the seafloor by DONET cabled observation network.

NASA Astrophysics Data System (ADS)

Araki, E.; Kawaguchi, K.; Kaneda, Y.

2011-12-01

We developed and deployed seafloor cabled observatory called "Dense Ocean-floor Network for Earthquake and Tsunamis (DONET)" in the Nankai Trough, south of Japan. The main purpose of the DONET network is to observe large earthquake such as Tonankai earthquake in the deployed seafloor and associate Tsunamis in real-time to help disaster mitigation, and as well to monitor inter-seismic crustal activities such as micro earthquakes, very low frequency earthquakes, and slower crustal deformation. In each DONET seafloor observatory, high-sensitive broadband set of instruments for seismic and seafloor pressure monitoring, consisted from Guralp CMG3T broadband seismometer, Metrozet TSA100S accelerometer, Paroscientific 8B7000-2 pressure gauge, a deep-sea differential pressure gauge, a hydrophone, and a seawater thermometer, are installed. The density of seafloor observatories are 20 observatories distributed in 15-30 km interval which is optimized for monitoring of events in the plate boundary beneath the network. DONET may be regarded as a large-scale, high sensitive high density seismic array for monitoring teleseismic events in the Philippine Sea and the Pacific Ocean. The DONET seafloor observatories are situated in wide range of seafloor depth between 1800m and 4500m, from the seafloor basin about 50 km off Japanese Island through the slope of accerecionary prism to the deep trench axis 150 km off the coast, that may also regarded as a vertical array in the 4.5km thick ocean. This variation of depths helps identify T-phases from the array record. In data analysis, it is necessary to identify propagation mode of each observed wave which may often be mixed together. In our design of DONET observation system, we took care to help identification of seismic phase by obtaining both ground motion and seafloor pressure in the same location. This is simply achieved by combining seafloor pressure gauges and seismometer in a single observatory package, but care was taken to observe both in the similar level of sensitivity and dynamic range in wide frequencies from near DC to over 100 Hz. In the case of DONET, the broadband seismometer and the differential pressure gauge have similar level of sensitivity in 0.005 - 10 Hz, and similarly the accelerometer and the hydrophone cover between 1-100Hz, in total covering most frequencies of our interest, 0.005 Hz to 100 Hz. With both ground motion and seafloor pressure measurement, we may distinguish types of waves relatively easily, and it is also possible to filter particular types of waves from the array dataset to help our data analysis. For example, it has been commonly practiced to distinguish up-going and down-going seismic phases from pressure and ground motion, but this is relatively difficult only with sparse seismometer array. This technique may also be applied to correct teleseismic record with sea surface reflection in receiver function analysis for exploring deep crustal structure.

Broadband spectra of seismic survey air-gun emissions, with reference to dolphin auditory thresholds.

PubMed

Goold, J C; Fish, P J

1998-04-01

Acoustic emissions from a 2120 cubic in air-gun array were recorded through a towed hydrophone assembly during an oil industry 2-D seismic survey off the West Wales Coast of the British Isles. Recorded seismic pulses were sampled, calibrated, and analyzed post-survey to investigate power levels of the pulses in the band 200 Hz-22 kHz at 750-m, 1-km, 2.2-km, and 8-km range from source. At 750-m range from source, seismic pulse power at the 200-Hz end of the spectrum was 140 dB re: 1 microPa2/Hz, and at the 20-kHz end of the spectrum seismic pulse power was 90 dB re: 1 microPa2/Hz. Although the background noise levels of the seismic recordings were far in excess of ambient, due to the proximity of engine, propeller, and flow sources of the ship towing the hydrophone, seismic power dominated the entire recorded bandwidth of 200 Hz-22 kHz at ranges of up to 2 km from the air-gun source. Even at 8-km range seismic power was still clearly in excess of the high background noise levels up to 8 kHz. Acoustic observations of common dolphins during preceding seismic surveys suggest that these animals avoided the immediate vicinity of the air-gun array while firing was in progress, i.e., localized disturbance occurred during seismic surveying. Although a general pattern of localized disturbance is suggested, one specific observation revealed that common dolphins were able to tolerate the seismic pulses at 1-km range from the air-gun array. Given the high broadband seismic pulse power levels across the entire recorded bandwidth, and known auditory thresholds for several dolphin species, we consider such seismic emissions to be clearly audible to dolphins across a bandwidth of tens on kilohertz, and at least out to 8-km range.

Finite-Difference Numerical Simulation of Seismic Gradiometry

NASA Astrophysics Data System (ADS)

Aldridge, D. F.; Symons, N. P.; Haney, M. M.

2006-12-01

We use the phrase seismic gradiometry to refer to the developing research area involving measurement, modeling, analysis, and interpretation of spatial derivatives (or differences) of a seismic wavefield. In analogy with gradiometric methods used in gravity and magnetic exploration, seismic gradiometry offers the potential for enhancing resolution, and revealing new (or hitherto obscure) information about the subsurface. For example, measurement of pressure and rotation enables the decomposition of recorded seismic data into compressional (P) and shear (S) components. Additionally, a complete observation of the total seismic wavefield at a single receiver (including both rectilinear and rotational motions) offers the possibility of inferring the type, speed, and direction of an incident seismic wave. Spatially extended receiver arrays, conventionally used for such directional and phase speed determinations, may be dispensed with. Seismic wave propagation algorithms based on the explicit, time-domain, finite-difference (FD) numerical method are well-suited for investigating gradiometric effects. We have implemented in our acoustic, elastic, and poroelastic algorithms a point receiver that records the 9 components of the particle velocity gradient tensor. Pressure and particle rotation are obtained by forming particular linear combinations of these tensor components, and integrating with respect to time. All algorithms entail 3D O(2,4) FD solutions of coupled, first- order systems of partial differential equations on uniformly-spaced staggered spatial and temporal grids. Numerical tests with a 1D model composed of homogeneous and isotropic elastic layers show isolation of P, SV, and SH phases recorded in a multiple borehole configuration, even in the case of interfering events. Synthetic traces recorded by geophones and rotation receivers in a shallow crosswell geometry with randomly heterogeneous poroelastic models also illustrate clear P (fast and slow) and S separation. Finally, numerical tests of the "point seismic array" concept are oriented toward understanding its potential and limitations. Sandia National Laboratories is a multiprogram science and engineering facility operated by Sandia Corporation, a Lockheed-Martin company, for the United States Department of Energy under contract DE- AC04-94AL85000.

Depth-Dependent Earthquake Properties Beneath Long-Beach, CA: Implications for the Rheology at the Brittle-Ductile Transition Zone

NASA Astrophysics Data System (ADS)

Inbal, A.; Clayton, R. W.; Ampuero, J. P.

2015-12-01

Except for a few localities, seismicity along faults in southern California is generally confined to depths shallower than 15 km. Among faults hosting deep seismicity, the Newport-Inglewood Fault (NIF), which traverses the Los-Angeles basin, has an exceptionally mild surface expression and low deformation rates. Moreover, the NIF structure is not as well resolved as other, less well instrumented faults because of poor signal-to-noise ratio. Here we use data from three temporary dense seismic arrays, which were deployed for exploration purposes and contain up to several thousands of vertical geophones, to investigate the properties of deep seismicity beneath Long-Beach (LB), Compton and Santa-Fe Springs (SFS). The latter is located 15 km northeast of the NIF, presumably above a major detachment fault underthrusting the basin.Event detection is carried out using a new approach for microseismic multi-channel picking, in which downward-continued data are back-projected onto the volume beneath the arrays, and locations are derived from statistical analysis of back-projection images. Our technique reveals numerous, previously undetected events along the NIF, and confirms the presence of an active shallow structure gently dipping to the north beneath SFS. Seismicity characteristics vary along the NIF strike and dip. While LB seismicity is uncorrelated with the mapped trace of the NIF, Compton seismicity illuminates a sub-vertical fault that extends down to about 20 km. This result, along with the reported high flux of mantle Helium along the NIF (Boles et al., 2015), suggests that the NIF is deeply rooted and acts as a major conduit for mantle fluids. We find that the LB size distribution obeys the typical power-law at shallow depths, but falls off exponentially for events occurring below 20 km. Because deep seismicity occurs uniformly beneath LB, this transition is attributed to a reduction in seismic asperity density with increasing depth, consistent with a transition to a diffuse deformation regime.

Seismic array processing and computational infrastructure for improved monitoring of Alaskan and Aleutian seismicity and volcanoes

NASA Astrophysics Data System (ADS)

Lindquist, Kent Gordon

We constructed a near-real-time system, called Iceworm, to automate seismic data collection, processing, storage, and distribution at the Alaska Earthquake Information Center (AEIC). Phase-picking, phase association, and interprocess communication components come from Earthworm (U.S. Geological Survey). A new generic, internal format for digital data supports unified handling of data from diverse sources. A new infrastructure for applying processing algorithms to near-real-time data streams supports automated information extraction from seismic wavefields. Integration of Datascope (U. of Colorado) provides relational database management of all automated measurements, parametric information for located hypocenters, and waveform data from Iceworm. Data from 1997 yield 329 earthquakes located by both Iceworm and the AEIC. Of these, 203 have location residuals under 22 km, sufficient for hazard response. Regionalized inversions for local magnitude in Alaska yield Msb{L} calibration curves (logAsb0) that differ from the Californian Richter magnitude. The new curve is 0.2\\ Msb{L} units more attenuative than the Californian curve at 400 km for earthquakes north of the Denali fault. South of the fault, and for a region north of Cook Inlet, the difference is 0.4\\ Msb{L}. A curve for deep events differs by 0.6\\ Msb{L} at 650 km. We expand geographic coverage of Alaskan regional seismic monitoring to the Aleutians, the Bering Sea, and the entire Arctic by initiating the processing of four short-period, Alaskan seismic arrays. To show the array stations' sensitivity, we detect and locate two microearthquakes that were missed by the AEIC. An empirical study of the location sensitivity of the arrays predicts improvements over the Alaskan regional network that are shown as map-view contour plots. We verify these predictions by detecting an Msb{L} 3.2 event near Unimak Island with one array. The detection and location of four representative earthquakes illustrates the expansion of geographic coverage from array processing. Measurements at the arrays of systematic azimuth residuals, between 5sp° and 50sp° from 203 Aleutian events, reveal significant effects of heterogeneous structure on wavefields. Finally, algorithms to automatically detect earthquakes in continuous array data are demonstrated with the detection of an Aleutian earthquake.

CAFE: a seismic investigation of water percolation in the Cascadia subduction zone

NASA Astrophysics Data System (ADS)

Rondenay, S.; Abers, G. A.; Creager, K. C.; Malone, S. D.; MacKenzie, L.; Zhang, Z.; van Keken, P. E.; Wech, A. G.; Sweet, J. R.; Melbourne, T. I.; Hacker, B. R.

2008-12-01

Subduction zones transport water into the Earth's interior. The subsequent release of this water through dehydration reactions may trigger intraslab earthquakes and arc volcanism, regulate slip on the plate interface, control plate buoyancy, and regulate the long-term budget of water on the planet's surface. As part of Earthscope, we have undertaken an experiment named CAFE (Cascadia Arrays for Earthscope) seeking to better constrain these effects in the Cascadia subduction zone. The basic experiment has four components: (1) a 47-element broadband imaging array of Flexible Array instruments integrated with Bigfoot; (2) three small-aperture seismic arrays with 15 additional short-period instruments near known sources of Episodic Tremor and Slip (ETS) events; (3) analysis of the PBO and PANGA GPS data sets to define the details of episodic slip events; and (4) integrative modeling with complementary constraints from petrology and geodynamics. Here, we present a summary of the results that have been obtained to date by CAFE, with a focus on high-resolution seismic imaging. A 250 km-long by 120 km-deep seismic profile extending eastward from the Washington coast was generated by 2-D Generalized Radon Transform Inversion of the broadband data. It images the subducted crust as a shallow-dipping, low-velocity layer from 20km depth beneath the coast to 40km depth beneath the forearc. The termination of the low-velocity layer is consistent with the depth at which hydrated metabasalts of the subducted crust are expected to undergo eclogitization, a reaction that is accompanied by the release of water and an increase in seismic velocities. Slab earthquakes are located in both the oceanic crust and mantle at depths <40 km, and exclusively in the oceanic mantle at greater depth, as would be expected if they are related to slab dehydration. Two ETS events have occurred during the course of the deployment. They were precisely located and are confined to the region above which the crust exhibits low-velocities and is believed to undergo progressive dehydration, further supporting the proposition that water plays a role in ETS.

Wind seismic noise introduced by external infrastructure: field data and transfer mechanism

NASA Astrophysics Data System (ADS)

Martysevich, Pavel; Starovoyt, Yuri

2017-04-01

Background seismic noise generated by wind was analyzed at six co-located seismic and infrasound arrays with the use of the wind speed data. The main factors affecting the noise level were identified as (a) external structures as antenna towers for intrasite communication, vegetation and heavy solar panels fixtures, (b) borehole casing and (c) local lithology. The wind-induced seismic noise peaks in the spectra can be predicted by combination of inverted pendulum model for antenna towers and structures used to support solar panels, free- or clamped-tube resonance of the borehole casing and is dependent on the type of sedimentary upper layer. Observed resonance frequencies are in agreement with calculated clamped / free tube modes for towers and borehole casings. Improvement of the seismic data quality can be achieved by minimizing the impact of surrounding structures close to seismic boreholes. The need and the advantage of the borehole installation may vanish and appear to be even not necessary at locations with non-consolidated sediments because the impact of surrounding structures on seismic background may significantly deteriorate the installation quality and therefore the detection capability of the array. Several IMS arrays where the radio telemetry antennas are used for data delivery to the central site may benefit from the redesign of the intrasite communication system by its substitute with the fiber-optic net as less harmful engineering solution.

Seismic Monitoring of Permafrost During Controlled Thaw: An Active-Source Experiment Using a Surface Orbital Vibrator and Fiber-Optic DAS Arrays

NASA Astrophysics Data System (ADS)

Dou, S.; Wood, T.; Lindsey, N.; Ajo Franklin, J. B.; Freifeld, B. M.; Gelvin, A.; Morales, A.; Saari, S.; Ekblaw, I.; Wagner, A. M.; Daley, T. M.; Robertson, M.; Martin, E. R.; Ulrich, C.; Bjella, K.

2016-12-01

Thawing of permafrost can cause ground deformations that threaten the integrity of civil infrastructure. It is essential to develop early warning systems that can identify critically warmed permafrost and issue warnings for hazard prevention and control. Seismic methods can play a pivotal role in such systems for at least two reasons: First, seismic velocities are indicative of mechanical strength of the subsurface and thus are directly relevant to engineering properties; Second, seismic velocities in permafrost systems are sensitive to pre-thaw warming, which makes it possible to issue early warnings before the occurrence of hazardous subsidence events. However, several questions remain: What are the seismic signatures that can be effectively used for early warning of permafrost thaw? Can seismic methods provide enough warning times for hazard prevention and control? In this study, we investigate the feasibility of using permanently installed seismic networks for early warnings of permafrost thaw. We conducted continuous active-source seismic monitoring of permafrost that was under controlled heating at CRREL's Fairbanks permafrost experiment station. We used a permanently installed surface orbital vibrator (SOV) as source and surface-trenched DAS arrays as receivers. The SOV is characterized by its excellent repeatability, automated operation, high energy level, and the rich frequency content (10-100 Hz) of the generated wavefields. The fiber-optic DAS arrays allow continuous recording of seismic data with dense spatial sampling (1-meter channel spacing), low cost, and low maintenance. This combination of SOV-DAS provides unique seismic datasets for observing time-lapse changes of warming permafrost at the field scale, hence providing an observational basis for design and development of early warning systems for permafrost thaw.

Spatial Distribution of Seismic Anisotropy in the Crust in the Northeast Front Zone of Tibetan Plateau

NASA Astrophysics Data System (ADS)

Gao, Y.; Wang, Q.; SHI, Y.

2017-12-01

There are orogenic belts and strong deformation in northeastern zone of Tibetan Plateau. The media in crust and in the upper mantle are seismic anisotropic there. This study uses seismic records by permanent seismic stations and portable seismic arrays, and adopts analysis techniques on body waves to obtain spatial anisotropic distribution in northeastern front zone of Tibetan Plateau. With seismic records of small local earthquakes, we study shear-wave splitting in the upper crust. The polarization of fast shear wave (PFS) can be obtained, and PFS is considered parallel to the strike of the cracks, as well as the direction of maximum horizontal compressive stress. However, the result shows the strong influence from tectonics, such as faults. It suggests multiple-influence including stress and fault. Spatial distribution of seismic anisotropy in study zone presents the effect in short range. PFS at the station on the strike-slip fault is quite different to PFS at station just hundreds of meters away from the fault. With seismic records of teleseismic waveforms, we obtained seismic anisotropy in the whole crust by receiver functions. The PFS directions from Pms receiver functions show consistency, generally in WNW. The time-delay of slow S phases is significant. With seismic records of SKS, PKS and SKKS phases, we can detect seismic anisotropy in the upper mantle by splitting analysis. The fast directions of these phases also show consistency, generally in WNW, similar to those of receiver functions, but larger time-delays. It suggests significant seismic anisotropy in the crust and crustal deformation is coherent to that in the upper mantle.Seismic anisotropy in the upper crust, in the whole crust and in the upper mantle are discussed both in difference and tectonic implications [Grateful to the support by NSFC Project 41474032].

Analysis of the seismic wavefield in the Moesian Platform (Bucharest area)

NASA Astrophysics Data System (ADS)

-Florinela Manea, Elena; Hobiger, Manuel-Thomas; Michel, Clotaire; Fäh, Donat; -Ortanza Cioflan, Carmen

2016-04-01

Bucharest is located in the center of the Moesian platform, in a large and deep sedimentary basin (450 km long, 300 km wide and in some places up to 20 km depth). During large earthquakes generated by the Vrancea seismic zone, located approximately 140 km to the North, the ground motion recorded in Bucharest area is characterized by predominant long periods and large amplification. This phenomenon has been explained by the influence of both source mechanism (azimuth and type of incident waves) and mechanical properties of the local structure (geological layering and geometry). The main goal of our study is to better characterize and understand the seismic wave field produced by earthquakes in the area of Bucharest. We want to identify the contribution of different seismic surface waves, such as the ones produced at the edges of the large sedimentary basin or multipath interference waves (Airy phases of Love and Rayleigh waves) to the ground motion. The data from a 35 km diameter array (URS experiment) installed by the National Institute for Earth Physics during 10 months in 2003 and 2004 in the urban area of Bucharest and adjacent zones was used. In order to perform the wave field characterization of the URS array, the MUSIQUE technique was used. This technique consists in a combination of the classical MUSIC and the quaternion-MUSIC algorithms and analyzes the three-component signals of all sensors of a seismic array together in order to analyze the Love and Rayleigh wave dispersion curves as well as the Rayleigh wave ellipticity curve. The analysis includes 20 regional earthquakes with Mw >3 and 5 teleseismic events with Mw> 7 that have enough energy at low frequency (0.1 - 1 Hz), i.e. in the resolution range of the array. For all events, the greatest energy is coming from the backazimuth of the source and the wave field is dominated by Love waves. The results of the array analyses clearly indicate a significant scattering corresponding to 2D or 3D effects in the Moesian Platform. The backazimuth distribution of energy shows that the scattering comes primarily from the southern and northern edges of the basin. The Airy phases of Love waves were identified in the direction of the backazimuth and its reflection around the fundamental frequency (0.15 - 0.25 Hz). Love and Rayleigh wave dispersion curves are successfully retrieved after combining the records of all events, and show a good match with the ones obtained in previous studies using ambient vibration measurements. Additionally, the first higher mode of Rayleigh waves was retrieved using earthquakes records. We could also identify the Rayleigh wave ellipticity curves, distinguishing between prograde and retrograde particle motion.

Volcanic tremor and local earthquakes at Copahue volcanic complex, Southern Andes, Argentina

NASA Astrophysics Data System (ADS)

Ibáñez, J. M.; Del Pezzo, E.; Bengoa, C.; Caselli, A.; Badi, G.; Almendros, J.

2008-07-01

In the present paper we describe the results of a seismic field survey carried out at Copahue Volcano, Southern Andes, Argentina, using a small-aperture, dense seismic antenna. Copahue Volcano is an active volcano that exhibited a few phreatic eruptions in the last 20 years. The aim of this experiment was to record and classify the background seismic activity of this volcanic area, and locate the sources of local earthquakes and volcanic tremor. Data consist of several volcano-tectonic (VT) earthquakes, and many samples of back-ground seismic noise. We use both ordinary spectral, and multi-spectral techniques to measure the spectral content, and an array technique [Zero Lag Cross Correlation technique] to measure the back-azimuth and apparent slowness of the signals propagating across the array. We locate VT earthquakes using a procedure based on the estimate of slowness vector components and S-P time. VT events are located mainly along the border of the Caviahue caldera lake, positioned at the South-East of Copahue volcano, in a depth interval of 1-3 km below the surface. The background noise shows the presence of many transients with high correlation among the array stations in the frequency band centered at 2.5 Hz. These transients are superimposed to an uncorrelated background seismic signal. Array solutions for these transients show a predominant slowness vector pointing to the exploited geothermal field of "Las Maquinitas" and "Copahue Village", located about 6 km north of the array site. We interpret this coherent signal as a tremor generated by the activity of the geothermal field.

The AlpArray Seismic Network: A Large-Scale European Experiment to Image the Alpine Orogen

NASA Astrophysics Data System (ADS)

Hetényi, György; Molinari, Irene; Clinton, John; Bokelmann, Götz; Bondár, István; Crawford, Wayne C.; Dessa, Jean-Xavier; Doubre, Cécile; Friederich, Wolfgang; Fuchs, Florian; Giardini, Domenico; Gráczer, Zoltán; Handy, Mark R.; Herak, Marijan; Jia, Yan; Kissling, Edi; Kopp, Heidrun; Korn, Michael; Margheriti, Lucia; Meier, Thomas; Mucciarelli, Marco; Paul, Anne; Pesaresi, Damiano; Piromallo, Claudia; Plenefisch, Thomas; Plomerová, Jaroslava; Ritter, Joachim; Rümpker, Georg; Šipka, Vesna; Spallarossa, Daniele; Thomas, Christine; Tilmann, Frederik; Wassermann, Joachim; Weber, Michael; Wéber, Zoltán; Wesztergom, Viktor; Živčić, Mladen

2018-04-01

The AlpArray programme is a multinational, European consortium to advance our understanding of orogenesis and its relationship to mantle dynamics, plate reorganizations, surface processes and seismic hazard in the Alps-Apennines-Carpathians-Dinarides orogenic system. The AlpArray Seismic Network has been deployed with contributions from 36 institutions from 11 countries to map physical properties of the lithosphere and asthenosphere in 3D and thus to obtain new, high-resolution geophysical images of structures from the surface down to the base of the mantle transition zone. With over 600 broadband stations operated for 2 years, this seismic experiment is one of the largest simultaneously operated seismological networks in the academic domain, employing hexagonal coverage with station spacing at less than 52 km. This dense and regularly spaced experiment is made possible by the coordinated coeval deployment of temporary stations from numerous national pools, including ocean-bottom seismometers, which were funded by different national agencies. They combine with permanent networks, which also required the cooperation of many different operators. Together these stations ultimately fill coverage gaps. Following a short overview of previous large-scale seismological experiments in the Alpine region, we here present the goals, construction, deployment, characteristics and data management of the AlpArray Seismic Network, which will provide data that is expected to be unprecedented in quality to image the complex Alpine mountains at depth.

Berkeley Seismological Laboratory Seismic Moment Tensor Report for the August 6, 2007 M3.9 Seismic event in central Utah

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ford, S; Dreger, D; Hellweg, P

2007-08-08

We have performed a complete moment tensor analysis of the seismic event, which occurred on Monday August 6, 2007 at 08:48:40 UTC 21 km from Mt.Pleasant, Utah. In our analysis we utilized complete three-component seismic records recorded by the USArray, University of Utah, and EarthScope seismic arrays. The seismic waveform data was integrated to displacement and filtered between 0.02 to 0.10 Hz following instrument removal. We used the Song et al. (1996) velocity model to compute Green's functions used in the moment tensor inversion. A map of the stations we used and the location of the event is shown inmore » Figure 1. In our moment tensor analysis we assumed a shallow source depth of 1 km consistent with the shallow depth reported for this event. As shown in Figure 2 the results point to a source mechanism with negligible double-couple radiation and is composed of dominant CLVD and implosive isotropic components. The total scalar seismic moment is 2.12e22 dyne cm corresponding to a moment magnitude (Mw) of 4.2. The long-period records are very well matched by the model (Figure 2) with a variance reduction of 73.4%. An all dilational (down) first motion radiation pattern is predicted by the moment tensor solution, and observations of first motions are in agreement.« less

Improved earthquake monitoring in the central and eastern United States in support of seismic assessments for critical facilities

USGS Publications Warehouse

Leith, William S.; Benz, Harley M.; Herrmann, Robert B.

2011-01-01

Evaluation of seismic monitoring capabilities in the central and eastern United States for critical facilities - including nuclear powerplants - focused on specific improvements to understand better the seismic hazards in the region. The report is not an assessment of seismic safety at nuclear plants. To accomplish the evaluation and to provide suggestions for improvements using funding from the American Recovery and Reinvestment Act of 2009, the U.S. Geological Survey examined addition of new strong-motion seismic stations in areas of seismic activity and addition of new seismic stations near nuclear power-plant locations, along with integration of data from the Transportable Array of some 400 mobile seismic stations. Some 38 and 68 stations, respectively, were suggested for addition in active seismic zones and near-power-plant locations. Expansion of databases for strong-motion and other earthquake source-characterization data also was evaluated. Recognizing pragmatic limitations of station deployment, augmentation of existing deployments provides improvements in source characterization by quantification of near-source attenuation in regions where larger earthquakes are expected. That augmentation also supports systematic data collection from existing networks. The report further utilizes the application of modeling procedures and processing algorithms, with the additional stations and the improved seismic databases, to leverage the capabilities of existing and expanded seismic arrays.

The behavioural response of migrating humpback whales to a full seismic airgun array.

PubMed

Dunlop, Rebecca A; Noad, Michael J; McCauley, Robert D; Kniest, Eric; Slade, Robert; Paton, David; Cato, Douglas H

2017-12-20

Despite concerns on the effects of noise from seismic survey airguns on marine organisms, there remains uncertainty as to the biological significance of any response. This study quantifies and interprets the response of migrating humpback whales ( Megaptera novaeangliae ) to a 3130 in 3 (51.3l) commercial airgun array. We compare the behavioural responses to active trials (array operational; n = 34 whale groups), with responses to control trials (source vessel towing the array while silent; n = 33) and baseline studies of normal behaviour in the absence of the vessel ( n = 85). No abnormal behaviours were recorded during the trials. However, in response to the active seismic array and the controls , the whales displayed changes in behaviour. Changes in respiration rate were of a similar magnitude to changes in baseline groups being joined by other animals suggesting any change group energetics was within their behavioural repertoire. However, the reduced progression southwards in response to the active treatments, for some cohorts, was below typical migratory speeds. This response was more likely to occur within 4 km from the array at received levels over 135 dB re 1 µPa 2 s. © 2017 The Author(s).

Preliminary Seismic Velocity Structure Results from Ambient Noise and Teleseismic Tomography: Laguna del Maule Volcanic Field, Chile

NASA Astrophysics Data System (ADS)

Wespestad, C.; Thurber, C. H.; Zeng, X.; Bennington, N. L.; Cardona, C.; Singer, B. S.

2016-12-01

Laguna del Maule Volcanic Field is a large, restless, rhyolitic system in the Southern Andes that is being heavily studied through several methods, including seismology, by a collaborative team of research institutions. A temporary array of 52 seismometers from OVDAS (the Southern Andean Volcano Observatory), PASSCAL (Portable Array Seismic Studies of the Continental Lithosphere), and the University of Wisconsin-Madison was used to collect the 1.3 years worth of data for this preliminary study. Ambient noise tomography uses surface wave dispersion data obtained from noise correlation functions (NCFs) between pairs of seismic stations, with one of each pair acting as a virtual source, in order to image the velocity structure in 3-D. NCFs were computed for hour-long time windows, and the final NCFs were obtained with phase-weighted stacking. The Frequency-Time Analysis technique was then utilized to measure group velocity between station pairs. NCFs were also analyzed to detect temporal changes in seismic velocity related to magmatic activity at the volcano. With the surface wave data from ambient noise, our small array aperture limits our modeling to the upper crust, so we employed teleseismic tomography to study deeper structures. For picking teleseismic arrivals, we tested two different correlation and stacking programs, which utilize adaptive stacking and multi-channel cross-correlation, to get relative arrival time data for a set of high quality events. Selected earthquakes were larger than magnitude 5 and between 30 and 95 degrees away from the center of the array. Stations that consistently show late arrivals may have a low velocity body beneath them, more clearly visualized via a 3-D tomographic model. Initial results from the two tomography methods indicate the presence of low-velocity zones at several depths. Better resolved velocity models will be developed as more data are acquired.

Monitoring hydrofrac-induced seismicity by surface arrays - the DHM-Project Basel case study

NASA Astrophysics Data System (ADS)

Blascheck, P.; Häge, M.; Joswig, M.

2012-04-01

The method "nanoseismic monitoring" was applied during the hydraulic stimulation at the Deep-Heat-Mining-Project (DHM-Project) Basel. Two small arrays in a distance of 2.1 km and 4.8 km to the borehole recorded continuously for two days. During this time more than 2500 seismic events were detected. The method of the surface monitoring of induced seismicity was compared to the reference which the hydrofrac monitoring presented. The latter was conducted by a network of borehole seismometers by Geothermal Explorers Limited. Array processing provides a outlier resistant, graphical jack-knifing localization method which resulted in a average deviation towards the reference of 850 m. Additionally, by applying the relative localization master-event method, the NNW-SSE strike direction of the reference was confirmed. It was shown that, in order to successfully estimate the magnitude of completeness as well as the b-value at the event rate and detection sensibility present, 3 h segments of data are sufficient. This is supported by two segment out of over 13 h of evaluated data. These segments were chosen so that they represent a time during the high seismic noise during normal working hours in daytime as well as the minimum anthropogenic noise at night. The low signal-to-noise ratio was compensated by the application of a sonogram event detection as well as a coincidence analysis within each array. Sonograms allow by autoadaptive, non-linear filtering to enhance signals whose amplitudes are just above noise level. For these events the magnitude was determined by the master-event method, allowing to compute the magnitude of completeness by the entire-magnitude-range method provided by the ZMAP toolbox. Additionally, the b-values were determined and compared to the reference values. An introduction to the method of "nanoseismic monitoring" will be given as well as the comparison to reference data in the Basel case study.

Considerations in Phase Estimation and Event Location Using Small-aperture Regional Seismic Arrays

NASA Astrophysics Data System (ADS)

Gibbons, Steven J.; Kværna, Tormod; Ringdal, Frode

2010-05-01

The global monitoring of earthquakes and explosions at decreasing magnitudes necessitates the fully automatic detection, location and classification of an ever increasing number of seismic events. Many seismic stations of the International Monitoring System are small-aperture arrays designed to optimize the detection and measurement of regional phases. Collaboration with operators of mines within regional distances of the ARCES array, together with waveform correlation techniques, has provided an unparalleled opportunity to assess the ability of a small-aperture array to provide robust and accurate direction and slowness estimates for phase arrivals resulting from well-constrained events at sites of repeating seismicity. A significant reason for the inaccuracy of current fully-automatic event location estimates is the use of f- k slowness estimates measured in variable frequency bands. The variability of slowness and azimuth measurements for a given phase from a given source region is reduced by the application of almost any constant frequency band. However, the frequency band resulting in the most stable estimates varies greatly from site to site. Situations are observed in which regional P- arrivals from two sites, far closer than the theoretical resolution of the array, result in highly distinct populations in slowness space. This means that the f- k estimates, even at relatively low frequencies, can be sensitive to source and path-specific characteristics of the wavefield and should be treated with caution when inferring a geographical backazimuth under the assumption of a planar wavefront arriving along the great-circle path. Moreover, different frequency bands are associated with different biases meaning that slowness and azimuth station corrections (commonly denoted SASCs) cannot be calibrated, and should not be used, without reference to the frequency band employed. We demonstrate an example where fully-automatic locations based on a source-region specific fixed-parameter template are more stable than the corresponding analyst reviewed estimates. The reason is that the analyst selects a frequency band and analysis window which appears optimal for each event. In this case, the frequency band which produces the most consistent direction estimates has neither the best SNR or the greatest beam-gain, and is therefore unlikely to be chosen by an analyst without calibration data.

Background Lamb waves in the Earth's atmosphere

NASA Astrophysics Data System (ADS)

Nishida, K.; Kobayashi, N.; Fukao, Y.

2013-12-01

Lamb waves of the Earth's atmosphere in the millihertz band have been considered as transient phenomena excited only by large events [e.g. the major volcanic eruption of Krakatoa in 1833, the impact of Siberian meteorite in 1908, the testing of large nuclear tests and the huge earthquakes, Garrett1969]. In a case of the solid Earth, observation of background free oscillations in the millihertz band-now known as Earth's background free oscillations or seismic hum, has been firmly established. Above 5 mHz, their dominant excitation sources are oceanic infragravity waves. At 3.7 and 4.4 mHz an elasto-acoustic resonance between the solid Earth and the atmosphere was observed [Nishida et al., 2000]. These seismic observations show that the contribution of atmospheric disturbances to the seismic hum is dominant below 5 mHz. Such contribution implies background excitations of acoustic-gravity waves in this frequency range. For direct detection of the background acoustic-gravity waves, our group conducted observations using an array of barometers [Nishida et al. 2005]. However, the spatial scale of the array of about 10 km was too small to detect acoustic modes below 10 mHz. Since then, no direct observations of these waves have been reported. In 2011, 337 high-resolution microbarometers were installed on a continental scale at USArray Transportable Array. The large and dense array enables us to detect the background atmospheric waves. Here, we show the first evidence of background Lamb waves in the Earth's atmosphere from 0.2 to 10 mHz, based on the array analysis of microbarometer data from the USArray in 2012. The observations suggest that the excitation sources are atmospheric disturbances in the troposphere. Theoretically, their energy in the troposphere tunnels into the thermosphere at a resonant frequency via thermospheric gravity wave, where the observed amplitudes indeed take a local minimum. The energy leak through the frequency window could partly contribute to thermospheric wave activity. Tropospheric disturbances exciting background Lamb waves may also be responsible for seismic hum at frequencies below 5 mHz.

Passive Seismic Monitoring for Rockfall at Yucca Mountain: Concept Tests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, J; Twilley, K; Murvosh, H

2003-03-03

For the purpose of proof-testing a system intended to remotely monitor rockfall inside a potential radioactive waste repository at Yucca Mountain, a system of seismic sub-arrays will be deployed and tested on the surface of the mountain. The goal is to identify and locate rockfall events remotely using automated data collecting and processing techniques. We install seismometers on the ground surface, generate seismic energy to simulate rockfall in underground space beneath the array, and interpret the surface response to discriminate and locate the event. Data will be analyzed using matched-field processing, a generalized beam forming method for localizing discrete signals.more » Software is being developed to facilitate the processing. To date, a three-component sub-array has been installed and successfully tested.« less

Studies Of Infrasonic Propagation Using Dense Seismic Networks

NASA Astrophysics Data System (ADS)

Hedlin, M. A.; deGroot-Hedlin, C. D.; Drob, D. P.

2011-12-01

Although there are approximately 100 infrasonic arrays worldwide, more than ever before, the station density is still insufficient to provide validation for detailed propagation modeling. Relatively large infrasonic signals can be observed on seismic channels due to coupling at the Earth's surface. Recent research, using data from the 70-km spaced 400-station USArray and other seismic network deployments, has shown the value of dense seismic network data for filling in the gaps between infrasonic arrays. The dense sampling of the infrasonic wavefield has allowed us to observe complete travel-time branches of infrasound and address important research problems in infrasonic propagation. We present our analysis of infrasound created by a series of rocket motor detonations that occurred at the UTTR facility in Utah in 2007. These data were well recorded by the USArray seismometers. We use the precisely located blasts to assess the utility of G2S mesoscale models and methods to synthesize infrasonic propagation. We model the travel times of the branches using a ray-based approach and the complete wavefield using a FDTD algorithm. Although results from both rays and FDTD approaches predict the travel times to within several seconds, only about 40% of signals are predicted using rays largely due to penetration of sound into shadow zones. FDTD predicts some sound penetration into the shadow zone, but the observed shadow zones, as defined by the seismic data, have considerably narrower spatial extent than either method predicts, perhaps due to un-modeled small-scale structure in the atmosphere.

Studies of the seismic coda using an earthquake cluster as a deeply buried seismograph array

NASA Astrophysics Data System (ADS)

Spudich, Paul; Bostwick, Todd

1987-09-01

Loosely speaking, the principle of Green's function reciprocity means that the source and receiver positions in a seismic experiment can be exchanged without affecting the observed seismograms. Consequently, the seismograms observed at a single observation location o and caused by a cluster of microearthquakes at locations {ei} are identical to the time series that would be measured by an array of stress meters emplaced at positions {ei}, recording waves generated by a source acting at o. By applying array analysis techniques like slant stacking and frequency-wave number analysis to these seismograms, we can determine the directions and velocities of the component waves as they travel in the earthquake focal region rather than at the surface. We have developed a computationally rapid plane-wave decomposition which we have applied to single-station recordings of aftershocks of the 1984 Morgan Hill, California, earthquake. The analysis is applied to data from three seismic stations having considerably different site geologies. One is a relatively hard rock station situated on Franciscan metamorphics, one is within the Calaveras fault zone, and one is on semiconsolidated sand and gravels. We define the early coda to be the part of the coda initiating immediately after the direct S wave and ending at twice the S wave lapse time. The character of the S wave and early coda varies from being impulsive at the first station to highly reverberative at the last. We examine waves in sequential time windows starting at the S wave and continuing through the early part of the coda. At all seismic stations the early coda is dominated by a persistent signal that must be caused by multiple scattering, probably within 2 km of each seismic station. Despite clear station-to-station differences in the character of the early coda, coda Q values measured in the late coda (greater than twice the S lapse time) agree well among stations, implying that the mechanisms causing the varying behavior of the early coda do not control the coda decay rate at the stations we have considered. Coda Q values measured on horizontal components of motion agree within a factor of 2 with those measured on vertical components. We have not been able to determine the composition of the late coda because of a low signal-to-noise ratio. Our analysis technique, however, is quite appropriate for such a task.

Seismic gradiometry using ambient seismic noise in an anisotropic Earth

NASA Astrophysics Data System (ADS)

de Ridder, S. A. L.; Curtis, A.

2017-05-01

We introduce a wavefield gradiometry technique to estimate both isotropic and anisotropic local medium characteristics from short recordings of seismic signals by inverting a wave equation. The method exploits the information in the spatial gradients of a seismic wavefield that are calculated using dense deployments of seismic arrays. The application of the method uses the surface wave energy in the ambient seismic field. To estimate isotropic and anisotropic medium properties we invert an elliptically anisotropic wave equation. The spatial derivatives of the recorded wavefield are evaluated by calculating finite differences over nearby recordings, which introduces a systematic anisotropic error. A two-step approach corrects this error: finite difference stencils are first calibrated, then the output of the wave-equation inversion is corrected using the linearized impulse response to the inverted velocity anomaly. We test the procedure on ambient seismic noise recorded in a large and dense ocean bottom cable array installed over Ekofisk field. The estimated azimuthal anisotropy forms a circular geometry around the production-induced subsidence bowl. This conforms with results from studies employing controlled sources, and with interferometry correlating long records of seismic noise. Yet in this example, the results were obtained using only a few minutes of ambient seismic noise.

Post-processing of seismic parameter data based on valid seismic event determination

DOEpatents

McEvilly, Thomas V.

1985-01-01

An automated seismic processing system and method are disclosed, including an array of CMOS microprocessors for unattended battery-powered processing of a multi-station network. According to a characterizing feature of the invention, each channel of the network is independently operable to automatically detect, measure times and amplitudes, and compute and fit Fast Fourier transforms (FFT's) for both P- and S- waves on analog seismic data after it has been sampled at a given rate. The measured parameter data from each channel are then reviewed for event validity by a central controlling microprocessor and if determined by preset criteria to constitute a valid event, the parameter data are passed to an analysis computer for calculation of hypocenter location, running b-values, source parameters, event count, P- wave polarities, moment-tensor inversion, and Vp/Vs ratios. The in-field real-time analysis of data maximizes the efficiency of microearthquake surveys allowing flexibility in experimental procedures, with a minimum of traditional labor-intensive postprocessing. A unique consequence of the system is that none of the original data (i.e., the sensor analog output signals) are necessarily saved after computation, but rather, the numerical parameters generated by the automatic analysis are the sole output of the automated seismic processor.

High lateral resolution exploration using surface waves from noise records

NASA Astrophysics Data System (ADS)

Chávez-García, Francisco José Yokoi, Toshiaki

2016-04-01

Determination of the shear-wave velocity structure at shallow depths is a constant necessity in engineering or environmental projects. Given the sensitivity of Rayleigh waves to shear-wave velocity, subsoil structure exploration using surface waves is frequently used. Methods such as the spectral analysis of surface waves (SASW) or multi-channel analysis of surface waves (MASW) determine phase velocity dispersion from surface waves generated by an active source recorded on a line of geophones. Using MASW, it is important that the receiver array be as long as possible to increase the precision at low frequencies. However, this implies that possible lateral variations are discarded. Hayashi and Suzuki (2004) proposed a different way of stacking shot gathers to increase lateral resolution. They combined strategies used in MASW with the common mid-point (CMP) summation currently used in reflection seismology. In their common mid-point with cross-correlation method (CMPCC), they cross-correlate traces sharing CMP locations before determining phase velocity dispersion. Another recent approach to subsoil structure exploration is based on seismic interferometry. It has been shown that cross-correlation of a diffuse field, such as seismic noise, allows the estimation of the Green's Function between two receivers. Thus, a virtual-source seismic section may be constructed from the cross-correlation of seismic noise records obtained in a line of receivers. In this paper, we use the seismic interferometry method to process seismic noise records obtained in seismic refraction lines of 24 geophones, and analyse the results using CMPCC to increase the lateral resolution of the results. Cross-correlation of the noise records allows reconstructing seismic sections with virtual sources at each receiver location. The Rayleigh wave component of the Green's Functions is obtained with a high signal-to-noise ratio. Using CMPCC analysis of the virtual-source seismic lines, we are able to identify lateral variations of phase velocity inside the seismic line, and increase the lateral resolution compared with results of conventional analysis.

76 FR 26255 - Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey in the...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-06

..., the R/V Marcus G. Langseth (Langseth) and a seismic airgun array to collect seismic reflection and... possible, depending on logistics and weather. The proposed seismic survey will collect seismic reflection... Shillington, Spahr Webb, and Mladen Nedimovic, all of L-DEO. The vessel will be self-contained, and the crew...

Shallow velocity structure above the Socorro Magma Body from ambient noise tomography using the large-N Sevilleta array, central Rio Grande Rift, New Mexico

NASA Astrophysics Data System (ADS)

Worthington, L. L.; Ranasinghe, N. R.; Schmandt, B.; Jiang, C.; Finlay, T. S.; Bilek, S. L.; Aster, R. C.

2017-12-01

The Socorro Magma Body (SMB) is one of the largest recognized active mid-crustal magma intrusions globally. Inflation of the SMB drives sporadically seismogenic uplift at rates of up to of few millimeters per year. We examine the upper crustal structure of the northern section of the SMB region using ambient noise seismic data collected from the Sevilleta Array and New Mexico Tech (NMT) seismic network to constrain basin structure and identify possible upper crustal heterogeneities caused by heat flow and/or fluid or magma migration to shallower depths. The Sevilleta Array comprised 801 vertical-component Nodal seismic stations with 10-Hz seismometers deployed within the Sevilleta National Wildlife Refuge in the central Rio Grande rift north of Socorro, New Mexico, for a period of 12 days during February 2015. Five short period seismic stations from the NMT network located south of the Sevilleta array are also used to improve the raypath coverage outside the Sevilleta array. Inter-station ambient noise cross-correlations were computed from all available 20-minute time windows and stacked to obtain estimates of the vertical component Green's function. Clear fundamental mode Rayleigh wave energy is observed from 3 to 6 s period. Beamforming indicates prominent noise sources from the southwest, near Baja California, and the southeast, in the Gulf of Mexico. The frequency-time analysis method was implemented to measure fundamental mode Rayleigh wave phase velocities and the resulting inter-station travel times were inverted to obtain 2-D phase velocity maps. One-dimensional sensitivity kernels indicate that the Rayleigh wave phase velocity maps are sensitive to a depth interval of 1 to 8 km, depending on wave period. The maps show (up to 40%) variations in phase velocity within the Sevilleta Array, with the largest variations found for periods of 5-6 seconds. Holocene to upper Pleistocene, alluvial sediments found in the Socorro Basin consistently show lower phase velocities than the basin-bounding ranges. Two areas of localized low velocities will be the focus of future work and interpretation. One low velocity zone appears to be co-located with the area of maximum InSAR-observed uplift related to the SMB. A second low velocity zone surrounds the Paleogene-aged Black Butte Volcano.

New seismic array solution for earthquake observations and hydropower plant health monitoring

NASA Astrophysics Data System (ADS)

Antonovskaya, Galina N.; Kapustian, Natalya K.; Moshkunov, Alexander I.; Danilov, Alexey V.; Moshkunov, Konstantin A.

2017-09-01

We present the novel fusion of seismic safety monitoring data of the hydropower plant in Chirkey (Caucasus Mountains, Russia). This includes new hardware solutions and observation methods, along with technical limitations for three types of applications: (a) seismic monitoring of the Chirkey reservoir area, (b) structure monitoring of the dam, and (c) monitoring of turbine vibrations. Previous observations and data processing for health monitoring do not include complex data analysis, while the new system is more rational and less expensive. The key new feature of the new system is remote monitoring of turbine vibration. A comparison of the data obtained at the test facilities and by hydropower plant inspection with remote sensors enables early detection of hazardous hydrodynamic phenomena.

Characterization of a complex near-surface structure using well logging and passive seismic measurements

NASA Astrophysics Data System (ADS)

Benjumea, Beatriz; Macau, Albert; Gabàs, Anna; Figueras, Sara

2016-04-01

We combine geophysical well logging and passive seismic measurements to characterize the near-surface geology of an area located in Hontomin, Burgos (Spain). This area has some near-surface challenges for a geophysical study. The irregular topography is characterized by limestone outcrops and unconsolidated sediments areas. Additionally, the near-surface geology includes an upper layer of pure limestones overlying marly limestones and marls (Upper Cretaceous). These materials lie on top of Low Cretaceous siliciclastic sediments (sandstones, clays, gravels). In any case, a layer with reduced velocity is expected. The geophysical data sets used in this study include sonic and gamma-ray logs at two boreholes and passive seismic measurements: three arrays and 224 seismic stations for applying the horizontal-to-vertical amplitude spectra ratio method (H/V). Well-logging data define two significant changes in the P-wave-velocity log within the Upper Cretaceous layer and one more at the Upper to Lower Cretaceous contact. This technique has also been used for refining the geological interpretation. The passive seismic measurements provide a map of sediment thickness with a maximum of around 40 m and shear-wave velocity profiles from the array technique. A comparison between seismic velocity coming from well logging and array measurements defines the resolution limits of the passive seismic techniques and helps it to be interpreted. This study shows how these low-cost techniques can provide useful information about near-surface complexity that could be used for designing a geophysical field survey or for seismic processing steps such as statics or imaging.

Using Ambient Noise for Investigating Cultural Heritage Sites and Evaluating Seismic Site Response

NASA Astrophysics Data System (ADS)

D'Amico, S.; Farrugia, D.; Galea, P. M.; Ruben, B. P., Sr.

2016-12-01

Recordings of ambient noise as well as use of the HVSR technique represent a common tool for evaluating seismic site response. In this study we applied such techniques to several cultural heritage sites located on the Maltese archipelago (Central Mediterranean). In particular, two of the Maltese watchtowers, built by the Knights of St. John between 1637 and 1659, were investigated together with the megalithic temple site of Mnajdra. Array data were acquired using the Micromed SoilSpy Rosina™ equipped with 4.5 Hz vertical geophones, setting the array in an L-shaped configuration. The Extended Spatial Autocorrelation (ESAC) technique was used to extract Rayleigh-wave dispersion curves. Moreover, single-station data close to the array was collected using a Tromino 3-component seismograph (www.tromino.eu), and the H/V curves were extracted. The dispersion curves and the H/V curves were jointly inverted using the Genetic Algorithm (GA) to obtain the shear-wave velocity profile. A fixed number of layers was used in the inversion and ranges for the layer thickness, P-wave and S-wave velocity, and density were specified. The obtained velocity profiles were used to compute the amplification function for the site based on the square root of the effective seismic impedance, also known as the quarter-wavelength approximation. This was used in the simulation of ground motion parameters at the site for various earthquakes using the stochastic one-dimensional site response analysis algorithm, Extended Source Simulation (EXSIM). In addition, the fundamental period and the damping ratio of the watchtowers was obtained by recording ambient vibrations. In the megalithic temples we were also able to evaluate the coverage of the soil deposits within the structure, comparing our results with previous study that used different geophysical techniques. In conclusion, this study enables us to map the seismic amplification hazard and provides primary data on the seismic risk assessment of each cultural heritage site.

Evaluation of high frequency ghost cavitation emissions for two different seismic air-gun arrays using numerical modelling

NASA Astrophysics Data System (ADS)

Khodabandeloo, Babak; Landrø, Martin

2017-04-01

Sound is deployed by marine mammals for variety of vital purposes such as finding food, communication, echolocation, etc. On the other hand human activities generate underwater noise. One major type of acoustic source is marine seismic acquisition which is carried out to image layers beneath the seabed exploiting reflected acoustic and elastic waves. Air-gun arrays are the most common and efficient marine seismic sources. Field measurements using broad band hydrophones have revealed that acoustic energies emitted by air-gun arrays contains frequencies from a few Hz up to tens of kHz. Frequencies below 200 Hz benefit seismic imaging and the rest is normally considered as wasted energy. On the other hand, the high frequency range (above 200 Hz) overlaps with hearing curves of many marine mammals and especially toothed whales and may have an impact on their behavior. A phenomenon called ghost cavitation is recently recognized to be responsible for a major part of these high frequencies (> 5 kHz). Acoustic pressure waves of individual air guns reflected from sea surface can cause the hydrostatic pressure to drop towards zero close to the source array. In these regions there is a high probability for water vapor cavity growth and subsequent collapse. We have simulated ghost cavitation cloud using numerical modelling and the results are validated by comparing with field measurements. The model is used to compare the amount of high frequency noise due to ghost cavitation for two different air gun arrays. Both of the arrays have three subarrays but the array distance for the one with 2730 in3 air volume is 6 meters and for the slightly bigger array (3250 in3 in air volume) the subarrays are separated by 8 meters. Simulation results indicate that the second array, despite larger subarray distance, generates stronger ghost cavitation signal.

Near- Source, Seismo-Acoustic Signals Accompanying a NASCAR Race at the Texas Motor Speedway

NASA Astrophysics Data System (ADS)

Stump, B. W.; Hayward, C.; Underwood, R.; Howard, J. E.; MacPhail, M. D.; Golden, P.; Endress, A.

2014-12-01

Near-source, seismo-acoustic observations provide a unique opportunity to characterize urban sources, remotely sense human activities including vehicular traffic and monitor large engineering structures. Energy separately coupled into the solid earth and atmosphere provides constraints on not only the location of these sources but also the physics of the generating process. Conditions and distances at which these observations can be made are dependent upon not only local geological conditions but also atmospheric conditions at the time of the observations. In order to address this range of topics, an empirical, seismo-acoustic study was undertaken in and around the Texas Motor Speedway in the Dallas-Ft. Worth area during the first week of April 2014 at which time a range of activities associated with a series of NASCAR races occurred. Nine, seismic sensors were deployed around the 1.5-mile track for purposes of documenting the direct-coupled seismic energy from the passage of the cars and other vehicles on the track. Six infrasound sensors were deployed on a rooftop in a rectangular array configuration designed to provide high frequency beam forming for acoustic signals. Finally, a five-element infrasound array was deployed outside the track in order to characterize how the signals propagate away from the sources in the near-source region. Signals recovered from within the track were able to track and characterize the motion of a variety of vehicles during the race weekend including individual racecars. Seismic data sampled at 1000 sps documented strong Doppler effects as the cars approached and moved away from individual sensors. There were faint seismic signals that arrived at seismic velocity but local acoustic to seismic coupling as supported by the acoustic observations generated the majority of seismic signals. Actual seismic ground motions were small as demonstrated by the dominance of regional seismic signals from a magnitude 4.0 earthquake that arrived at the local seismometers as the race began. The infrasound arrays recorded a variety of atmosphere only processes including substantial helicopter traffic although the array outside the track did not capture the details of the race as a result of the rapid attenuation of high frequency signals.

On the potential of seismic rotational motion measurements for extraterrestrial seismology

NASA Astrophysics Data System (ADS)

Schmelzbach, Cedric; Sollberger, David; Khan, Amir; Greenhalgh, Stewart; Van Renterghem, Cederic; Robertsson, Johan

2017-04-01

Classically, seismological recordings consist of measurements of translational ground motion only. However, in addition to three vector components of translation there are three components of rotation to consider, leading to six degrees of freedom. Of particular interest is thereby the fact that measuring rotational motion means isolating shear (S) waves. Recording the rotational motion requires dedicated rotational sensors. Alternatively, since the rotational motion is given by the curl of the vectorial displacements, the rotational motion around the two horizontal axes can be computed from the horizontal spatial gradients of vertical translational recordings if standard translational seismometers are placed in an areal array at the free surface. This follows from the zero stress free surface condition. Combining rotational and translational motion measurements opens up new ways of analyzing seismic data, such as facilitating much improved arrival identification and wavefield separation (e.g., P-/S-wave separation), and local slowness (arrival direction and velocity) determination. Such combined measurements maximize the seismic information content that a single six-component station or a small station array can provide, and are of particular interest for sparse or single-station measurements such as in extraterrestrial seismology. We demonstrate the value of the analysis of combined translational and rotational recordings by re-evaluating data from the Apollo 17 lunar seismic profiling experiment (LSPE). The LSPE setup consisted of four vertical-component geophones arranged in a star-like geometry. This areal receiver layout enables computing the horizontal spatial gradients by spatial finite differencing of the vertical-component data for two perpendicular directions and, hence, the estimation of rotational motion around two horizontal axes. Specifically, the recorded seismic waveform data originated from eight explosive packages as well as from continuously listening to the natural lunar seismic activity of moonquakes. As an example, the combined analysis of translational and rotational motion from the active-source LSPE data provides, for the first time, the possibility to extract S-wave information from the enigmatic and reverbatory lunar seismic waveform data, which hithertofore had masked later arriving S-waves. The identification of S-waves enables to characterize the shallow lunar crust in a full elastic sense. The resultant Poisson's ratio profile allows discriminating shallow basalt layers of different degree of fracturing. Our successful analysis of the Apollo 17 data highlights the anticipated significant value of rotational measurements for future extraterrestrial seismology missions.

Applications of seismic spatial wavefield gradient and rotation data in exploration seismology

NASA Astrophysics Data System (ADS)

Schmelzbach, C.; Van Renterghem, C.; Sollberger, D.; Häusler, M.; Robertsson, J. O. A.

2017-12-01

Seismic spatial wavefield gradient and rotation data have the potential to open up new ways to address long-standing problems in land-seismic exploration such as identifying and separating P-, S-, and surface waves. Gradient-based acquisition and processing techniques could enable replacing large arrays of densely spaced receivers by sparse spatially-compact receiver layouts or even one single multicomponent station with dedicated instruments (e.g., rotational seismometers). Such approaches to maximize the information content of single-station recordings are also of significant interest for seismic measurements at sites with limited access such as boreholes, the sea bottom, and extraterrestrial seismology. Arrays of conventional three-component (3C) geophones enable measuring not only the particle velocity in three dimensions but also estimating their spatial gradients. Because the free-surface condition allows to express vertical derivatives in terms of horizontal derivatives, the full gradient tensor and, hence, curl and divergence of the wavefield can be computed. In total, three particle velocity components, three rotational components, and divergence, result seven-component (7C) seismic data. Combined particle velocity and gradient data can be used to isolate the incident P- or S-waves at the land surface or the sea bottom using filtering techniques based on the elastodynamic representation theorem. Alternatively, as only S-waves exhibit rotational motion, rotational measurements can directly be used to identify S-waves. We discuss the derivations of the gradient-based filters as well as their application to synthetic and field data, demonstrating that rotational data can be of particular interest to S-wave reflection and P-to-S-wave conversion imaging. The concept of array-derived gradient estimation can be extended to source arrays as well. Therefore, source arrays allow us to emulate rotational (curl) and dilatational (divergence) sources. Combined with 7C recordings, a total of 49 components of the seismic wavefield can be excited and recorded. Such data potentially allow to further improve wavefield separation and may find application in directional imaging and coherent noise suppression.

Application of Seismic Array Processing to Tsunami Early Warning

NASA Astrophysics Data System (ADS)

An, C.; Meng, L.

2015-12-01

Tsunami wave predictions of the current tsunami warning systems rely on accurate earthquake source inversions of wave height data. They are of limited effectiveness for the near-field areas since the tsunami waves arrive before data are collected. Recent seismic and tsunami disasters have revealed the need for early warning to protect near-source coastal populations. In this work we developed the basis for a tsunami warning system based on rapid earthquake source characterisation through regional seismic array back-projections. We explored rapid earthquake source imaging using onshore dense seismic arrays located at regional distances on the order of 1000 km, which provides faster source images than conventional teleseismic back-projections. We implement this method in a simulated real-time environment, and analysed the 2011 Tohoku earthquake rupture with two clusters of Hi-net stations in Kyushu and Northern Hokkaido, and the 2014 Iquique event with the Earthscope USArray Transportable Array. The results yield reasonable estimates of rupture area, which is approximated by an ellipse and leads to the construction of simple slip models based on empirical scaling of the rupture area, seismic moment and average slip. The slip model is then used as the input of the tsunami simulation package COMCOT to predict the tsunami waves. In the example of the Tohoku event, the earthquake source model can be acquired within 6 minutes from the start of rupture and the simulation of tsunami waves takes less than 2 min, which could facilitate a timely tsunami warning. The predicted arrival time and wave amplitude reasonably fit observations. Based on this method, we propose to develop an automatic warning mechanism that provides rapid near-field warning for areas of high tsunami risk. The initial focus will be Japan, Pacific Northwest and Alaska, where dense seismic networks with the capability of real-time data telemetry and open data accessibility, such as the Japanese HiNet (>800 instruments) and the Earthscope USArray Transportable Array (~400 instruments), are established.

Crustal structure of the Izu Collision zone, central Japan, revealed by dense seismic array observations

NASA Astrophysics Data System (ADS)

Kurashimo, E.; Sato, H.; Abe, S.; Kato, N.; Ishikawa, M.; Obara, K.

2009-12-01

In central Japan, the Philippine Sea Plate (PSP) subducts beneath the Tokyo Metropolitan area, the Kanto region. In western Kanto region, the Izu-Bonin arc (IBA) within the PSP has been colliding from the south with the Honshu arc, forming a complex structure called the Izu-Collision zone (ICZ). Several active faults were formed in and around the ICZ. The geometry of the subducting PSP and the overlying crustal structure of the ICZ are important to constrain the process of earthquake occurrence and the crustal evolution process associated with arc-arc collision. Recent seismic experiments reveal the geometry of the subducting PSP beneath the Kanto region (Sato et al., 2005). The Japanese islands, including the ICZ, are covered with dense arrays of permanent seismic stations, which provide good constraints on velocity structures by a tomographic method. Such studies reveal a general picture of the lithospheric structure such as a descending plate configuration (e.g. Matsubara et al., 2008). However, since an average spacing of the permanent station is typically 20 km, a detailed structure in the upper crust, which is imperative for an understanding of the active tectonics, cannot be well constrained by permanent array alone. Two dense seismic array observations were conducted to obtain a structural image beneath the ICZ. One is a 40-km-long line (EW-line) located in the northern part of the ICZ and the other is a 55-km-long line (NS-line) located in the central part of the ICZ. Seventy-five 3-component portable seismographs were deployed on EW-line with 500 to 700 m interval and waveforms were recorded during a four-month period from October, 2008. Forty 3-component portable seismographs were deployed on NS-line with about 1 km spacing and waveforms were recorded during the three month period from January, 2006. In order to obtain a high-resolution velocity model, a well-controlled hypocenter is essential. Due to this, we combined the seismic array data with permanent seismic station data. P- and S-wave arrival time data were obtained from 247 events and 16,144 P- and 13,723 S-wave arrival times were used for the inversion analysis. Arrival times of local earthquakes were used in a joint inversion for earthquake locations and 3-D Vp and Vp/Vs structures, using the iterative damped least-squares algorithm, simul2000 (Thurber and Eberhart-Phillips, 1999). The P-wave velocity structure shows that low velocity zones exist along the estimated deeper extension of the active faults and high velocity zones exist beneath the Tanzawa Mountains and Misaka Mountains. The Tanzawa Mountains and the Misaka Mountains are considered as fragments of the IBA (e.g. Niitsuma, 1989). We obtained a seismic velocity model revealing good correlations with the surface geology along the profile. Acknowledgments: This study was supported by the Earthquake Research Institute cooperative research program.

Scanning Seismic Intrusion Detector

NASA Technical Reports Server (NTRS)

Lee, R. D.

1982-01-01

Scanning seismic intrusion detector employs array of automatically or manually scanned sensors to determine approximate location of intruder. Automatic-scanning feature enables one operator to tend system of many sensors. Typical sensors used with new system are moving-coil seismic pickups. Detector finds uses in industrial security systems.

Back-Projection Imaging of extended, diffuse seismic sources in volcanic and hydrothermal systems

NASA Astrophysics Data System (ADS)

Kelly, C. L.; Lawrence, J. F.; Beroza, G. C.

2017-12-01

Volcanic and hydrothermal systems exhibit a wide range of seismicity that is directly linked to fluid and volatile activity in the subsurface and that can be indicative of imminent hazardous activity. Seismograms recorded near volcanic and hydrothermal systems typically contain "noisy" records, but in fact, these complex signals are generated by many overlapping low-magnitude displacements and pressure changes at depth. Unfortunately, excluding times of high-magnitude eruptive activity that typically occur infrequently relative to the length of a system's entire eruption cycle, these signals often have very low signal-to-noise ratios and are difficult to identify and study using established seismic analysis techniques (i.e. phase-picking, template matching). Arrays of short-period and broadband seismic sensors are proven tools for monitoring short- and long-term changes in volcanic and hydrothermal systems. Time-reversal techniques (i.e. back-projection) that are improved by additional seismic observations have been successfully applied to locating volcano-seismic sources recorded by dense sensor arrays. We present results from a new computationally efficient back-projection method that allows us to image the evolution of extended, diffuse sources of volcanic and hydrothermal seismicity. We correlate short time-window seismograms from receiver-pairs to find coherent signals and propagate them back in time to potential source locations in a 3D subsurface model. The strength of coherent seismic signal associated with any potential source-receiver-receiver geometry is equal to the correlation of the short time-windows of seismic records at appropriate time lags as determined by the velocity structure and ray paths. We stack (sum) all short time-window correlations from all receiver-pairs to determine the cumulative coherence of signals at each potential source location. Through stacking, coherent signals from extended and/or repeating sources of short-period energy radiation interfere constructively while background noise signals interfere destructively, such that the most likely source locations of the observed seismicity are illuminated. We compile results to analyze changes in the distribution and prevalence of these sources throughout a systems entire eruptive cycle.

A Volcano Monitoring Seismo-Acoustic Network in the CNMI

NASA Astrophysics Data System (ADS)

Howard, J. E.; Crippen, S. E.; Hayward, C.; Quick, J. E.

2011-12-01

In late spring and early summer of 2011, a seismo-acoustic network was installed in the Commonwealth of the Northern Mariana Islands (CNMI) for volcano monitoring. The network consists of a seismo-acoustic array on Saipan, an acoustic array on Sarigan with one seismometer, and a seismic network on Anatahan. On Saipan the array consists of a central site and 3 embedded triangular arrays with apertures of 100 m, 300 m and 1000 m. Four 50-foot porous hoses in a clover-leaf arrangement are used for spatial filtering at each acoustic site. Broadband seismometers were installed at the central site and the 1000 m sites. The Sarigan Array consists of a central acoustic site with 5 surrounding sites evenly spaced at 50 m radius, and one broadband seismic station. Two hoses were used for each site on Sarigan. Four broadband seismic stations were also installed on Anatahan which last erupted in 2005. Data from each array is sent by radio telemetry to the Emergency Management Office on Saipan, where it is routed to the USGS and SMU. Data will be used for volcano monitoring which will allow the CNMI to resume economic activity in the uninhabited northern islands. Initial data streams show high seismic noise levels as expected for an island installation. The Sarigan acoustic sites are also noisy as a result of being more exposed to wind than the Saipan sites. Many small events have already been observed in the infrasound data. This network was installed through the collaborative efforts of CNMI, USGS and SMU.

An ocean bottom seismometer study of shallow seismicity near the Mid- America Trench offshore Guatemala ( Pacific).

USGS Publications Warehouse

Ambos, E.L.; Hussong, D.M.; Holman, C.E.

1985-01-01

Five ocean bottom seismometers recorded seismicity near the Mid-America Trench offshore Guatemala for 27 days in 1979. The array was emplaced in the lower slope region, just above the topographic trench. Approximately 170 events were recorded by 3 or more seismometers, and almost half were located with statistical hypocentral errors of <10 km. Most epicenters were located immediately landward of the trench axis, and many were further confined to a zone NW of the array. In terms of depth, most events were located within the subducting Cocos plate rather than in the overlying plate or at the plate-plate boundary. Most magnitudes ranged between 3.0 and 4.0 mb, and the threshold magnitude of locatable events was about 2.8 mb. Two distinct composite focal mechanisms were determined. One appears to indicate high- angle reverse faulting in the subducting plate, in a plane parallel to trench axis strike. The other, constructed for some earthquakes in the zone NW of the array, seems to show normal faulting along possible fault planes oriented quasi-perpendicular to the trench axis. Projection of our seismicity sample and of well-located WWSSN events from 1954 to 1980 onto a plane perpendicular to the trench axis shows a distinct gap between the shallow seismicity located by our array, and the deeper Wadati-Benioff zone seismicity located by the WWSSN. We tentatively ascribe this gap to inadequate sampling.-from Authors

On the composition of earth's short-period seismic noise field

USGS Publications Warehouse

Koper, K.D.; Seats, K.; Benz, H.

2010-01-01

In the classic microseismic band of 5-20 sec, seismic noise consists mainly of fundamental mode Rayleigh and Love waves; however, at shorter periods seismic noise also contains a significant amount of body-wave energy and higher mode surface waves. In this study we perform a global survey of Earth's short-period seismic noise field with the goal of quantifying the relative contributions of these propagation modes. We examined a year's worth of vertical component data from 18 seismic arrays of the International Monitoring System that were sited in a variety of geologic environments. The apertures of the arrays varied from 2 to 28 km, constraining the periods we analyzed to 0.25-2.5 sec. Using frequency-wavenumber analysis we identified the apparent velocity for each sample of noise and classified its mode of propagation. The dominant component was found to be Lg, occurring in about 50% of the noise windows. Because Lg does not propagate across ocean-continent boundaries, this energy is most likely created in shallow water areas near coastlines. The next most common component was P-wave energy, which accounted for about 28% of the noise windows. These were split between regional P waves (Pn=Pg at 6%), mantle bottoming P waves (14%), and core-sensitive waves (PKP at 8%). This energy is mostly generated in deep water away from coastlines, with a region of the North Pacific centered at 165?? W and 40?? N being especially prolific. The remainder of the energy arriving in the noise consisted of Rg waves (28%), a large fraction of which may have a cultural origin. Hence, in contrast to the classic micro-seismic band of 5-20 sec, at shorter periods fundamental mode Rayleigh waves are the least significant component.

ActiveSeismoPick3D - automatic first arrival determination for large active seismic arrays

NASA Astrophysics Data System (ADS)

Paffrath, Marcel; Küperkoch, Ludger; Wehling-Benatelli, Sebastian; Friederich, Wolfgang

2016-04-01

We developed a tool for automatic determination of first arrivals in active seismic data based on an approach, that utilises higher order statistics (HOS) and the Akaike information criterion (AIC), commonly used in seismology, but not in active seismics. Automatic picking is highly desirable in active seismics as the number of data provided by large seismic arrays rapidly exceeds of what an analyst can evaluate in a reasonable amount of time. To bring the functionality of automatic phase picking into the context of active data, the software package ActiveSeismoPick3D was developed in Python. It uses a modified algorithm for the determination of first arrivals which searches for the HOS maximum in unfiltered data. Additionally, it offers tools for manual quality control and postprocessing, e.g. various visualisation and repicking functionalities. For flexibility, the tool also includes methods for the preparation of geometry information of large seismic arrays and improved interfaces to the Fast Marching Tomography Package (FMTOMO), which can be used for the prediction of travel times and inversion for subsurface properties. Output files are generated in the VTK format, allowing the 3D visualization of e.g. the inversion results. As a test case, a data set consisting of 9216 traces from 64 shots was gathered, recorded at 144 receivers deployed in a regular 2D array of a size of 100 x 100 m. ActiveSeismoPick3D automatically checks the determined first arrivals by a dynamic signal to noise ratio threshold. From the data a 3D model of the subsurface was generated using the export functionality of the package and FMTOMO.

Amplification Factors for Spectral Acceleration Using Borehole Seismic Array in Taiwan

NASA Astrophysics Data System (ADS)

Lai, T. S.; Yih-Min, W.; Chao, W. A.; Chang, C. H.

2017-12-01

In order to reduce the noise from surface to get the high-quality seismic recordings, there are 54 borehole seismic arrays have been installed in Taiwan deployed by Central Weather Bureau (CWB) until the end of 2016. Each array includes two force balance accelerometers, one at the surface and other inside the borehole, as well as one broadband seismometer inside the borehole. The downhole instruments are placed at a depth between 120 and 400 m. The background noise level are lower at the borehole stations, but the amplitudes recorded by borehole stations are smaller than surface stations for the same earthquake due to the different geology conditions. Therefore, the earthquake magnitude estimated by borehole station is smaller than surface station. So far, CWB only use the surface stations in the magnitude determination due to this situation. In this study, we investigate the site effects between surface and downhole for borehole seismic arrays. Using the spectral ratio derived by the two-station spectral method as the transfer function, simulated the waveform recorded by borehole stations to the surface stations. In the future, through the transfer function, the borehole stations will be included in the estimation of earthquake magnitude and the results of amplification factors can provide the information of near-surface site effects for the ground motion simulation applications.

Multi-Phenomenological Analysis of the 12 August 2015 Tianjin, China Chemical Explosion

NASA Astrophysics Data System (ADS)

Pasyanos, M.; Kim, K.; Park, J.; Stump, B. W.; Hayward, C.; Che, I. Y.; Zhao, L.; Myers, S. C.

2016-12-01

We perform a multi-phenomenological analysis of the massive near-surface chemical explosions that occurred in Tianjin, China on 12 August 2015. A recent assessment of these events was performed by Zhao et al. (2016) using local (< 100 km) seismic data. This study considers a regional assessment of the same sequence in the absence of having any local data. We provide additional insight by combining regional seismic analysis with the use of infrasound signals and an assessment of the event crater. Event locations using infrasound signals recorded at Korean and IMS arrays are estimated based on the Bayesian Infrasonic Source Location (BISL) method (Modrak et al., 2010), and improved with azimuthal corrections using a raytracing (Blom and Waxler, 2012) and the Ground-to-Space (G2S) atmospheric models (Drob et al., 2003). The location information provided from the infrasound signals is then merged with the regional seismic arrivals to produce a joint event location. The yields of the events are estimated from seismic and infrasonic observations. Seismic waveform envelope method (Pasyanos et al., 2012) including the free surface effect (Pasyanos and Ford, 2015) is applied to regional seismic signals. Waveform inversion method (Kim and Rodgers, 2016) is used for infrasound signals. A combination of the seismic and acoustic signals can provide insights on the energy partitioning and break the tradeoffs between the yield and the depth/height of explosions, resulting in a more robust estimation of event yield. The yield information from the different phenomenologies are combined through the use of likelihood functions.

Short-Period Seismic Noise in Vorkuta (Russia)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kishkina, S B; Spivak, A A; Sweeney, J J

Cultural development of new subpolar areas of Russia is associated with a need for detailed seismic research, including both mapping of regional seismicity and seismic monitoring of specific mining enterprises. Of special interest are the northern territories of European Russia, including shelves of the Kara and Barents Seas, Yamal Peninsula, and the Timan-Pechora region. Continuous seismic studies of these territories are important now because there is insufficient seismological knowledge of the area and an absence of systematic data on the seismicity of the region. Another task of current interest is the necessity to consider the seismic environment in the design,more » construction, and operation of natural gas extracting enterprises such as the construction of the North European Gas Pipeline. Issues of scientific importance for seismic studies in the region are the complex geodynamical setting, the presence of permafrost, and the complex tectonic structure. In particular, the Uralian Orogene (Fig. 1) strongly affects the propagation of seismic waves. The existing subpolar seismic stations [APA (67,57{sup o}N; 33,40{sup o}E), LVZ (67,90{sup o}N; 34,65{sup o}E), and NRIL (69,50{sup o}N; 88,40{sup o}E)] do not cover the extensive area between the Pechora and Ob Rivers (Fig. 1). Thus seismic observations in the Vorkuta area, which lies within the area of concern, represent a special interest. Continuous recording at a seismic station near the city of Vorkuta (67,50{sup o}N; 64,11{sup o}E) [1] has been conducted since 2005 for the purpose of regional seismic monitoring and, more specifically, detection of seismic signals caused by local mining enterprises. Current surveys of local seismic noise [7,8,9,11], are particularly aimed at a technical survey for the suitability of the site for installation of a small-aperture seismic array, which would include 10-12 recording instruments, with the Vorkuta seismic station as the central element. When constructed, this seismic array will considerably improve the recording capacity of regional and local seismic events. It will allow detection of signatures of seismic waves propagating in submeridional and sublatitudinal directions. The latter is of special interest not only to access the influence of the Urals on propagation patterns of seismic waves, but also to address other questions, such as the structure and dynamic characteristics of the internal dynamo of the Earth [9,13]. Recording seismic waves at low angular distances from seismically active subpolar zones will allow us to collect data on vortical and convective movements in subpolar lithosphere blocks and at the boundary of the inner core of the Earth, possibly giving essential clues to the modeling of the Earth's electromagnetic field [3,13]. The present study considers basic features of seismic noise at the Vorkuta station obtained through the analysis of seismic records from March, 2006 till December, 2007.« less

Application of the H/V and SPAC Method to Estimate a 3D Shear Wave Velocity Model, in the City of Coatzacoalcos, Veracruz.

NASA Astrophysics Data System (ADS)

Morales, L. E. A. P.; Aguirre, J.; Vazquez Rosas, R.; Suarez, G.; Contreras Ruiz-Esparza, M. G.; Farraz, I.

2014-12-01

Methods that use seismic noise or microtremors have become very useful tools worldwide due to its low costs, the relative simplicity in collecting data, the fact that these are non-invasive methods hence there is no need to alter or even perforate the study site, and also these methods require a relatively simple analysis procedure. Nevertheless the geological structures estimated by this methods are assumed to be parallel, isotropic and homogeneous layers. Consequently precision of the estimated structure is lower than that from conventional seismic methods. In the light of these facts this study aimed towards searching a new way to interpret the results obtained from seismic noise methods. In this study, seven triangular SPAC (Aki, 1957) arrays were performed in the city of Coatzacoalcos, Veracruz, varying in sizes from 10 to 100 meters. From the autocorrelation between the stations of each array, a Rayleigh wave phase velocity dispersion curve was calculated. Such dispersion curve was used to obtain a S wave parallel layers velocity (VS) structure for the study site. Subsequently the horizontal to vertical ratio of the spectrum of microtremors H/V (Nogoshi and Igarashi, 1971; Nakamura, 1989, 2000) was calculated for each vertex of the SPAC triangular arrays, and from the H/V spectrum the fundamental frequency was estimated for each vertex. By using the H/V spectral ratio curves interpreted as a proxy to the Rayleigh wave ellipticity curve, a series of VS structures were inverted for each vertex of the SPAC array. Lastly each VS structure was employed to calculate a 3D velocity model, in which the exploration depth was approximately 100 meters, and had a velocity range in between 206 (m/s) to 920 (m/s). The 3D model revealed a thinning of the low velocity layers. This proved to be in good agreement with the variation of the fundamental frequencies observed at each vertex. With the previous kind of analysis a preliminary model can be obtained as a first approximation, so that more careful studies can be conducted to assess a detailed geological characterization of a specific site. The continuous development of the methods that use microtremors, create many areas of interest in the seismic engineering study field. This and other reasons are why these methods have acquired more presence all over the globe.

Seismic fiber optic multiplexed sensors for exploration and reservoir management

NASA Astrophysics Data System (ADS)

Houston, Mark H.

2000-12-01

Reliable downhole communications, control and sensor networks will dramatically improve oil reservoir management practices and will enable the construction of intelligent or smart-well completions. Fiber optic technology will play a key role in the implementation of these communication, control and sensing systems because of inherent advantages of power, weight and reliability over more conventional electronic-based systems. Field test data, acquired using an array of fiber optic seismic hydrophones within a steam-flood, heavy oil- production filed, showed a significant improvement (10X in this specific case) in subsurface resolution as compared to conventional surface seismic acquisition. These results demonstrate the viability of using multiplexed fiber optic sensors for exploration and reservoir management in 3D vertical seismic profiling (VSP) surveys and in permanent sensor arrays for 4D surveys.

Mapping Shear-wave Velocity Structures of the "African Anomaly" Along a Northwest to Southeast Arc From New Zealand to the Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Frodsham, A. E.; Wen, L.

2006-12-01

A previous study [Wang and Wen, 2006] investigated the geometry and shear velocity structure of the "African Anomaly" along a great circle arc from the East Pacific Rise to the Japan Sea, and concluded the anomaly extends 1300 km above the core-mantle boundary, that the sides of the anomaly slope towards the apex and has velocity deviations of -5% in the base and -2% to -3% in the mid-lower mantle. Wang and Wen [2004] also reported on the very low velocity province that forms the base of the "African Anomaly" and its lateral extent, but the northern edge of the anomaly was poorly constrained because of the nature of the seismic data. In this presentation we focus on the nature of the anomaly in a cross-section of the mantle along a great arc, from New Zealand, to the Mid-Atlantic Ridge off the coast of Newfoundland, centered over the anomaly. In particular, we focus on the northern edge of the "African Anomaly" where a paucity of large, deep focus earthquakes makes seismic arrivals from the northwest difficult to analyze. We map the lateral extent, thickness, and shear velocity structures of the "African Anomaly" on the basis of forward travel time and waveform modeling of direct S, ScS, and SKS waves. Seismic data used in this study were collected from PASSCAL arrays: KAAPVAAL seismic array (operating years 1997-1999), Tanzania seismic array (1994- 1995), Ethiopia/Kenya seismic array (2000-2002), and the Global Seismographic Network (1994-2002). We minimize uncertainty from earthquake mislocation by relocation of the earthquakes using a global tomographic shear wave velocity model and also correct for heterogeneities outside the anomaly. We explore various methods of data processing, such as frequency filtration, low fold stacking, and cross correlation, to best interpret the arrival times of the various seismic phases and constrain the nature of the "African Anomaly" along a northwest to southeast cross-section.

Spatial and temporal distribution of the seismicity along two mid-oceanic ridges with contrasted spreading rates in the Indian Ocean

NASA Astrophysics Data System (ADS)

Tsang-Hin-Sun, E.; Perrot, J.; Royer, J. Y.

2015-12-01

The seismicity of the ultra-slow spreading Southwest (14 mm/y) and intermediate spreading Southeast (60 mm/y) Indian ridges was monitored from February 2012 to March 2013 by the OHASISBIO array of 7 autonomous hydrophones. A total of 1471 events were located with 4 instruments or more, inside the array, with a median location uncertainty < 5 km and a completeness magnitude of mb = 3. Both ridges display similar average rates of seismicity, suggesting that there is no systematic relationship between seismicity and spreading rates. Accretion modes do differ, however, by the along-axis distribution of the seismic events. Along the ultra-slow Southwest Indian Ridge, events are sparse but regularly spaced and scattered up to 50 km off-axis. Along the fast Southeast Indian Ridge, events are irregularly distributed, focusing in narrow regions near the ridge axis at segment ends and along transform faults, whereas ridge-segment centers generally appear as seismic gaps (at the level of completeness of the array). Only two clusters, 6 months apart, are identified in a segment-center at 29°S. From the temporal distribution of the clustered events and comparisons with observations in similar mid-oceanic ridge setting, both clusters seem to have a volcanic origin and to be related to a dike emplacement or a possible eruption on the seafloor. Their onset time and migration rate are comparable to volcanic swarms recorded along the Juan de Fuca Ridge. Overall, the rate of seismicity along the two Indian spreading ridges correlates with the large-scale variations in the bathymetry and shear-wave velocity anomaly in the upper mantle, suggesting that the distribution of the low-magnitude seismicity is mainly controlled by along-axis variations in the lithosphere rheology and temperature.

Back-Projection Imaging of extended, high-frequency pre-, co-, and post-eruptive seismicity at El Jefe Geyser, El Tatio Geyser Field, Chile

NASA Astrophysics Data System (ADS)

Kelly, C. L.; Lawrence, J. F.; Beroza, G. C.

2017-12-01

El Tatio Geyser Field in northern Chile is the third largest geyser field in the world. It is comprised of 3 basins that span 10 km x 10 km at an average elevation of 4250 m and contains at least 80 active geysers. Heavy tourist traffic and previous geothermal exploration make the field relatively non-pristine and ideal for performing minimally invasive geophysical experiments. We deployed a dense array of 51 L-28 3-component geophones (1-10 m spacing, corner frequency 4.5 Hz, 1000 Hz sample rate), and 6 Trillium 120 broadband seismometers (2-20 m spacing, long period corner 120 s, 500 Hz sample rate) in a 50 m x 50 m grid in the central Upper Geyser Basin (the largest basin in area at 5 km x 5 km) during October 2012 as part of a collaborative study of hydrothermal systems between Stanford University; U.C. Berkeley; U. of Chile, Santiago; U. of Tokyo; and the USGS. The seismic array was designed to target at El Jefe Geyser (EJG), a columnar geyser (eruption height 1-1.5 m) with a consistent periodic eruption cycle of 132 +/- 3 s. Seismicity at EJG was recorded continuously for 9 days during which 6000 total eruptions occurred. Excluding periods of high anthropogenic noise (i.e. tourist visits, field work), the array recorded 2000 eruptions that we use to create 4D time-lapse images of the evolution of seismic source locations before, during and after EJG eruptions. We use a new back-projection processing technique to locate geyser signals, which tend to be harmonic and diffuse in nature, during characteristic phases of the EJG eruption cycle. We obtain Vp and Vs from ambient-field tomography and estimates of P and S propagation from a hammer source recorded by the array. We use these velocities to back-project and correlate seismic signals from all available receiver-pairs to all potential source locations in a subsurface model assuming straight-line raypaths. We analyze results for individual and concurrent geyser sources throughout an entire EJG eruption cycle and over multiple eruption cycles. We target specific seismic observations by restricting the frequency band of analysis (i.e., high or low frequency bands), and use our results to evaluate changes in source distributions before, during and after eruptions and compare them to synchronous surface observations (downhole pressure/temperature, discharge rate, thermal video).

The Analysis of North Korea's Nuclear Tests by Turkish National Data Center

NASA Astrophysics Data System (ADS)

Semin, K.; Meral Ozel, N.; Destici, T. C.; Necmioglu, O.; Kocak, S.

2013-12-01

The Democratic People's Republic of Korea (DPRK) announced the conduct of a third underground nuclear test on 12 February 2013 in the northeastern part of the country as the previous tests that were conducted in 2009 and 2006. The latest nuclear test is the best detected nuclear event by the global seismic networks. The magnitude estimates show that each new test increased in size when compared with the previous one. As Turkish NDC (National Data Center), we have analyzed the 2013 and 2009 nuclear tests using seismic data from International Monitoring System (IMS) stations through the International Data Center (IDC) located in Vienna. Discrimination analysis was performed based on mb:Ms magnitude ratio and spectral analysis. We have also applied array based waveform cross-correlation to show the similarity of the nuclear tests and precise arrival time measurements for relative location estimates and basic infrasound analysis using two IMS infrasound stations for the 2013 event. Seismic analysis were performed using softwares such as Geotool, EP (Event processor from Norsar) and Seismic Analysis Code (SAC) and the infrasound data were analyzed by using PMCC from CEA-France. The IMS network is operating under the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO). The CTBTO verification system is under continuous development, also making use of the state of the art technologies and methodologies.

Site Effects estimation in the Po Plain area (Northern Italy): correlation between passive geophysical surveys and stratigraphic evidence

NASA Astrophysics Data System (ADS)

Mascandola, Claudia; Massa, Marco; Barani, Simone; Argnani, Andrea; Poggi, Valerio; Martelli, Luca; Albarello, Dario; Pergalani, Floriana; Compagnoni, Massimo; Lovati, Sara

2017-04-01

The recent case of the 2012, Mw 6.1, Emilia seismic sequence (Northern Italy) highlighted the importance of the site effects estimation in the Po Plain, the larger and deeper Italian sedimentary basin. This study, applied on extensive collection of geophysical and geological data in the entire area, allows a macrozonation of the site effects estimation, useful for scientific and applied purpose. In particular, site-response analysis can be performed in defined macrozones, where the geological-geotecnical and geophysical characteristics are homogeneous at macroscale. The collection of the available stratigraphic discontinuities and passive geophysical surveys (single station and array measurements) allowed defining a general macrozonation in terms of amplified frequencies and shear waves velocity (Vs) gradients. The correlation between the obtained geophysical evidence and the known geological information can then be crucial in order to define the most important stratigraphic discontinuities responsible for the local seismic amplification. In particular, ambient vibration data, recorded by all permanent and temporary seismic stations installed in the target region, were collected and then analyzed with the Nakamura technique, to determine the H/V spectral ratio. Moreover, all the available ambient vibration arrays where collected and analyzes to assess the local Vs profile, considering the Rayleigh waves fundamental mode. The Po Plain stratigraphy is defined by regional unconformities (aquifer limits) that have been extensively mapped throughout the basin and by regional geological and structural maps. In general, the H/V results show two ranges of amplified frequencies, both lower than 1 Hz: the former at frequencies lower than about 0.25 Hz and the latter between 0.4 and 1 Hz. The higher frequency range moves from about 0.4 Hz, in the eastern-Adriatic part of the plain, to about 0.8-1.0 Hz in the central and western part. Based on the available seismic array results, this amplification peak seems related to a velocity discontinuity, located in general between 100 m and 300 m of depth, where the Vs exceed 800 m/s. This interface can be ascribed to the seismic bedrock according to the actual seismic code (NTC 2008, Vs> 800 m/s, class A) and may be related to different stratigraphic discontinuities moving from East to West. In order to verify the supposed correspondence between geophysical and geological data, also the H/V ratio where inverted, considering the Sanchez-Sesma method and the nearest array velocity profile as indicative for the target inversion. Finally, an empirical relation between amplified frequencies and depths was calculated, allowing to preliminary map, at regional scale, the most important geological discontinuities for the site effects evaluation. An example of site-specific hazard analysis was performed in correspondence of the INGV seismic station CTL8 in terms of displacement response spectra for periods up to 10 s. The results show that neglecting the effects of the deep discontinuities implies underestimation in hazard evaluation of up to about 49% for MRP of 475 years and about 57% for MRP of 2,475 years, with possible consequences on the design of very tall buildings and large bridges.

Seismic Source Scaling and Discrimination in Diverse Tectonic Environments

DTIC Science & Technology

2009-09-30

3349-3352. Imanishi, K., W. L. Ellsworth, and S. G. Prejean (2004). Earthquake source parameters determined by the SAFOD Pilot Hole seismic array ... seismic discrimination by performing a thorough investigation of* earthquake source scaling using diverse, high-quality datascts from varied tectonic...these corrections has a direct impact on our ability to identify clandestine explosions in the broad regional areas characterized by low seismicity

Dynamic strain and rotation ground motions of the 2011 Tohoku earthquake from dense high-rate GPS observations in Taiwan

NASA Astrophysics Data System (ADS)

Huang, B. S.; Rau, R. J.; Lin, C. J.; Kuo, L. C.

2017-12-01

Seismic waves generated by the 2011 Mw 9.0 Tohoku, Japan earthquake were well recorded by continuous GPS in Taiwan. Those GPS were operated in one hertz sampling rate and densely distributed in Taiwan Island. Those continuous GPS observations and the precise point positioning technique provide an opportunity to estimate spatial derivatives from absolute ground motions of this giant teleseismic event. In this study, we process and investigate more than one and half hundred high-rate GPS displacements and its spatial derivatives, thus strain and rotations, to compare to broadband seismic and rotational sensor observations. It is shown that continuous GPS observations are highly consistent with broadband seismic observations during its surface waves across Taiwan Island. Several standard Geodesy and seismic array analysis techniques for spatial gradients have been applied to those continuous GPS time series to determine its dynamic strain and rotation time histories. Results show that those derivate GPS vertical axis ground rotations are consistent to seismic array determined rotations. However, vertical rotation-rate observations from the R1 rotational sensors have low resolutions and could not compared with GPS observations for this special event. For its dese spatial distribution of GPS stations in Taiwan Island, not only wavefield gradient time histories at individual site was obtained but also 2-D spatial ground motion fields were determined in this study also. In this study, we will report the analyzed results of those spatial gradient wavefields of the 2011 Tohoku earthquake across Taiwan Island and discuss its geological implications.

Phase Velocity and Full-Waveform Analysis of Co-located Distributed Acoustic Sensing (DAS) Channels and Geophone Sensor

NASA Astrophysics Data System (ADS)

Parker, L.; Mellors, R. J.; Thurber, C. H.; Wang, H. F.; Zeng, X.

2015-12-01

A 762-meter Distributed Acoustic Sensing (DAS) array with a channel spacing of one meter was deployed at the Garner Valley Downhole Array in Southern California. The array was approximately rectangular with dimensions of 180 meters by 80 meters. The array also included two subdiagonals within the rectangle along which three-component geophones were co-located. Several active sources were deployed, including a 45-kN, swept-frequency, shear-mass shaker, which produced strong Rayleigh waves across the array. Both DAS and geophone traces were filtered in 2-Hz steps between 4 and 20 Hz to obtain phase velocities as a function of frequency from fitting the moveout of travel times over distances of 35 meters or longer. As an alternative to this traditional means of finding phase velocity, it is theoretically possible to find the Rayleigh-wave phase velocity at each point of co-location as the ratio of DAS and geophone responses, because DAS is sensitive to ground strain and geophones are sensitive to ground velocity, after suitable corrections for instrument response (Mikumo & Aki, 1964). The concept was tested in WPP, a seismic wave propagation program, by first validating and then using a 3D synthetic, full-waveform seismic model to simulate the effect of increased levels of noise and uncertainty as data go from ideal to more realistic. The results obtained from this study provide a better understanding of the DAS response and its potential for being combined with traditional seismometers for obtaining phase velocity at a single location. This analysis is part of the PoroTomo project (Poroelastic Tomography by Adjoint Inverse Modeling of Data from Seismology, Geodesy, and Hydrology, http://geoscience.wisc.edu/feigl/porotomo).

Results From a Borehole Seismometer Array I: Microseismicity at a Productive Geothermal Field, Kilauea Lower East Rift Zone, Puna, Hawaii

NASA Astrophysics Data System (ADS)

Kenedi, C. L.; Shalev, E.; Malin, P.; Kaleikini, M.; Dahl, G.

2008-12-01

Borehole seismometer arrays have proven successful in both the exploration and monitoring of geothermal fields. Because the seismometers are located at depth, they are isolated from human noise and record microearthquakes with clearly identifiable seismic phases that can be used for event location. Further analysis of these events can be used to resolve earthquake clouds into identifiable faults. The local fault and dike structures in Puna, in southeastern Hawaii, are of interest both in terms of electricity production and volcanic hazard monitoring. The geothermal power plant at Puna has a 30MW capacity and is built on a section of the Kilauea Lower East Rift Zone where lava flows erupted as recently as 1955. In order to improve seismic monitoring in this area, we installed eight 3-component borehole seismometers. The instrument depths range from 24 to 210 m (80 to 690 ft); the shallower instruments have 2 Hz geophones and the deepest have 4.5 Hz geophones. The seismometers are located at the vertices of two rhombs, 2 km wide x 4 km long and 4 km wide x 8 km long, both centered at the power plant. Since June 2006, we have located >4500 earthquakes; P- and S-wave arrivals were hand picked and events located using Hypoinverse-2000. Most of the earthquakes occurred at depths between 2.5 and 3 km. The large majority of events were M-0.5 to M0.5; the Gutenberg-Richter b-value is 1.4, which is consistent with microearthquake swarms. Frequency analysis indicates a 7-day periodicity; a Schuster diagram confirms increased seismicity on a weekly cycle. The location, depth, and period of the microearthquakes suggest that power plant activity affects local seismicity. Southwest of the geothermal facility, up-rift towards the Kilauea summit, earthquakes were progressively deeper at greater distances. Depths also increased towards the south, which is consistent with the eastern extension of the south-dipping, east-striking Hilina fault system. To the northeast, down-rift of the array, there is a sudden cessation of seismicity not accounted for by known geologic structures. This borehole seismometer network is providing essential data for the detailed characterization of the Kilauea Lower East Rift Zone and the Puna geothermal field.

Detection of seismic anisotropy using ocean bottom seismometers: a case study from the northern headwall of the Storegga Slide

NASA Astrophysics Data System (ADS)

Exley, R. J. K.; Westbrook, G. K.; Haacke, R. R.; Peacock, S.

2010-10-01

Azimuthal seismic anisotropy has been identified from the analysis of S-waves generated by P to S mode conversion in the Pleistocene sediments that form the northern headwall of the Storegga Slide, which were investigated with a seismic experiment employing a seabed array of ocean-bottom seismometers and a grid of airgun shots. The principal technique used to detect the anisotropy was azimuthal stacking of the radial and transverse horizontal geophone components, after the application of moveout, to show the variations in amplitude, phase and cumulative traveltime effects of S-waves, ultimately providing information that identified the `fast' and `slow' S-wave polarization orientations. Particle-motion analysis was used to corroborate the results and provide further information on the magnitudes of cumulative S-wave splitting. A 2-D ray-traced inversion of the traveltimes of pre-critical P and PS arrivals provided a velocity model from which the variation with depth of Vp, Vs and anisotropy could be compared with lithological and stratigraphic data from a borehole at the centre of the OBS array. Increased anisotropic response was observed to be coincident with high velocity units, which have high mica but low water content and are interpreted to be of glacial origin. The analysis of azimuthal seismic anisotropy shows clear evidence for horizontal transverse isotropy or an orthorhombic symmetry. The distribution in orientations of the fast plane of symmetry is broadly bimodal (E-W and NE-SW) across the OBS array. The E-W group showed correlation with the headwalls of old, buried slides and other faults visible within coherency attributes calculated from an accompanying 3-D seismic data set and with the strike of some of the headwalls of slides shown in multibeam bathymetry. However, the pattern of headwall fractures shown in the bathymetry is complicated and reticulate, and the NE-SW orientation is also well represented. We infer that the cause of the anisotropy is the presence of vertical to sub-vertical, fluid-filled fractures and micro-cracks, partially held open by high pore-fluid pressure. The fracture orientations are controlled primarily by the present-day gravitationally induced down-slope stress, which is mediated by the heterogeneous nature of sub-surface, causing local changes in the orientation of the principal stresses at the margins of incipient or failed slides. The fractures, if connected, are likely to increase vertical permeability within the sediment column significantly, and influence the distribution of gas hydrate within the strata.

Determination of Rayleigh wave ellipticity using single-station and array-based processing of ambient seismic noise

NASA Astrophysics Data System (ADS)

Workman, Eli Joseph

We present a single-station method for the determination of Rayleigh wave ellipticity, or Rayleigh wave horizontal to vertical amplitude ratio (H/V) using Frequency Dependent Polarization Analysis (FDPA). This procedure uses singular value decomposition of 3-by-3 spectral covariance matrices over 1-hr time windows to determine properties of the ambient seismic noise field such as particle motion and dominant wave-type. In FPDA, if the noise is mostly dominated by a primary singular value and the phase difference is roughly 90° between the major horizontal axis and the vertical axis of the corresponding singular vector, we infer that Rayleigh waves are dominant and measure an H/V ratio for that hour and frequency bin. We perform this analysis for all available data from the Earthscope Transportable Array between 2004 and 2014. We compare the observed Rayleigh wave H/V ratios with those previously measured by multicomponent, multistation noise cross-correlation (NCC), as well as classical noise spectrum H/V ratio analysis (NSHV). At 8 sec the results from all three methods agree, suggesting that the ambient seismic noise field is Rayleigh wave dominated. Between 10 and 30 sec, while the general pattern agrees well, the results from FDPA and NSHV are persistently slightly higher ( 2%) and significantly higher (>20%), respectively, than results from the array-based NCC. This is likely caused by contamination from other wave types (i.e., Love waves, body waves, and tilt noise) in the single station methods, but it could also reflect a small, persistent error in NCC. Additionally, we find that the single station method has difficulty retrieving robust Rayleigh wave H/V ratios within major sedimentary basins, such as the Williston Basin and Mississippi Embayment, where the noise field is likely dominated by reverberating Love waves.

Integrated modeling and field study of potential mechanisms forinduced seismicity at The Geysers Goethermal Field, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rutqvist, Jonny; Majer, Ernie; Oldenburg, Curt

2006-06-07

In this paper, we present progress made in a study aimed atincreasing the understanding of the relative contributions of differentmechanisms that may be causing the seismicity occurring at The Geysersgeothermal field, California. The approach we take is to integrate: (1)coupled reservoir geomechanical numerical modeling, (2) data fromrecently upgraded and expanded NCPA/Calpine/LBNL seismic arrays, and (3)tens of years of archival InSAR data from monthly satellite passes. Wehave conducted a coupled reservoir geomechanical analysis to studypotential mechanisms induced by steam production. Our simulation resultscorroborate co-locations of hypocenter field observations of inducedseismicity and their correlation with steam production as reported in theliterature. Seismicmore » and InSAR data are being collected and processed foruse in constraining the coupled reservoir geomechanicalmodel.« less

ANZA Seismic Network- From Monitoring to Science

NASA Astrophysics Data System (ADS)

Vernon, F.; Eakin, J.; Martynov, V.; Newman, R.; Offield, G.; Hindley, A.; Astiz, L.

2007-05-01

The ANZA Seismic Network (http:eqinfo.ucsd.edu) utilizes broadband and strong motion sensors with 24-bit dataloggers combined with real-time telemetry to monitor local and regional seismicity in southernmost California. The ANZA network provides real-time data to the IRIS DMC, California Integrated Seismic Network (CISN), other regional networks, and the Advanced National Seismic System (ANSS), in addition to providing near real-time information and monitoring to the greater San Diego community. Twelve high dynamic range broadband and strong motion sensors adjacent to the San Jacinto Fault zone contribute data for earthquake source studies and continue the monitoring of the seismic activity of the San Jacinto fault initiated 24 years ago. Five additional stations are located in the San Diego region with one more station on San Clemente Island. The ANZA network uses the advance wireless networking capabilities of the NSF High Performance Wireless Research and Education Network (http:hpwren.ucsd.edu) to provide the communication infrastructure for the real-time telemetry of Anza seismic stations. The ANZA network uses the Antelope data acquisition software. The combination of high quality hardware, communications, and software allow for an annual network uptime in excess of 99.5% with a median annual station real-time data return rate of 99.3%. Approximately 90,000 events, dominantly local sources but including regional and teleseismic events, comprise the ANZA network waveform database. All waveform data and event data are managed using the Datascope relational database. The ANZA network data has been used in a variety of scientific research including detailed structure of the San Jacinto Fault Zone, earthquake source physics, spatial and temporal studies of aftershocks, array studies of teleseismic body waves, and array studies on the source of microseisms. To augment the location, detection, and high frequency observations of the seismic source spectrum from local earthquakes, the ANZA network is receiving real-time data from borehole arrays located at the UCSD Thornton Hospital, and from UCSB's Borrego Valley and Garner Valley Downhole Arrays. Finally the ANZA network is acquiring data from seven PBO sites each with 300 meter deep MEMs accelerometers, passive seismometers, and a borehole strainmeter.

Preliminary earthquake locations in the Kenai Peninsula recorded by the MOOS Array and their relationship to structure in the 1964 great earthquake zone

NASA Astrophysics Data System (ADS)

Li, J.; Abers, G. A.; Christensen, D. H.; Kim, Y.; Calkins, J. A.

2011-12-01

Earthquakes in subduction zones are mostly generated at the interface between the subducting and overlying plates. In 2006-2009, the MOOS (Multidisciplinary Observations Of Subduction) seismic array was deployed around the Kenai Peninsula, Alaska, consisting of 34 broadband seismometers recording for 1-3 years. This region spans the eastern end of the Aleutian megathrust that ruptured in the 1964 Mw 9.2 great earthquake, the second largest recorded earthquake, and ongoing seismicity is abundant. Here, we report an initial analysis of seismicity recorded by MOOS, in the context of preliminary imaging. There were 16,462 events detected in one year from initial STA/LTA signal detections and subsequent event associations from the MOOS Array. We manually reviewed them to eliminate distant earthquakes and noise, leaving 11,879 local earthquakes. To refine this catalog, an adaptive auto-regressive onset estimation algorithm was applied, doubling the original dataset and producing 20,659 P picks and 22,999 S picks for one month (September 2007). Inspection shows that this approach lead to almost negligible false alarms and many more events than hand picking. Within the well-sampled part of the array, roughly 200 km by 300 km, we locate 250% more earthquakes for one month than the permanent network catalog, or 10 earthquakes per day on this patch of the megathrust. Although the preliminary locations of earthquakes still show some scatter, we can see a concentration of events in a ~20-km-wide belt, part of which can be interpreted as seismogenic thrust zone. In conjunction with the seismicity study, we are imaging the plate interface with receiver functions. The main seismicity zone corresponds to the top of a low-velocity layer imaged in receiver functions, nominally attributed to the top of the downgoing plate. As we refine velocity models and apply relative relocation algorithms, we expect to improve the precision of the locations substantially. When combined with image of velocity structure from scattered wave migration, we can test whether the thrust zone is above the Yakutat terrane or between the Yakutat terrane and the subducting Pacific plate. Our refined relocations will also improve our understanding of other active faults (e.g., splay faults) and their relationship to the plate boundary.

Crustal and upper mantle structure of the Hangay Dome, central Mongolia

NASA Astrophysics Data System (ADS)

Stachnik, J. C.; Meltzer, A.; Tsaagan, B.; Munkhuu, U.; Russo, R.; Souza, S.; Martin, P.

2013-12-01

The origin and support of high topography within continental interiors away from active tectonic margins remains a fundamental question in the dynamics and deformation of continents. The Hangay Dome in central Mongolia is one such region that is a broad regional uplift with average elevation of about 2 km, sitting between two large strike-slip faults, the Bulnay Fault to the north and the Gobi-Altay Fault to the south. Both of these faults are seismically active and have experienced M8+ earthquakes as recently as 1957. This portion of the Mongolian Plateau is approximately 300 km south of the Baikal Rift and located at the northern margin of the diffuse-deformation field in Central Asia, adjacent to the Siberian Craton. From previous research, the dynamic support of the Hangay Dome has been attributed to both crustal thickening and low density upper mantle material. However, seismic data leading to these interpretations have been limited to global tomographic models and sparse regional sampling of the wave field leaving the question unresolved. To address this major question in plate tectonic theory, in June 2012 a temporary IRIS/PASSCAL/University of Florida array of 72 seismic stations was deployed around the Hangay Dome to determine lithospheric structure in the region. Preliminary results from the first of two years of data are shown from receiver function analysis, ambient noise surface wave tomography, and teleseismic travel time residual analysis. Using teleseismic waveform records from over 300 earthquakes above M5.5 between 30 and 90 degrees epicentral distance, crustal thickness measurements from H-k stacking of receiver functions range from 42 km to 57 km across the array, with thicker crust beneath the highest topography. At each station the bulk crustal Vp/Vs ratio is also determined with median value for the array of 1.77, perhaps indicating a more mafic composition crust in the region.Teleseismic P-wave travel time residuals generally diminish from south to north across the array consistent with thinning crust, however the depth resolution and magnitude of seismic wavespeed anomalies will be further explored with three-dimensional finite-frequency tomography. Constraints on crustal shear wave velocity from ambient noise surface wave tomography complement both the receiver function analysis and teleseismic tomography. Initial inversions of phase velocity dispersion curves in the central Hangay indicate an average crustal Vs of 3.6 km/s within the Hangay Dome, which translates to an average Vp of 6.4 km/s using Vp/Vs of 1.77. Further refinement of current analysis and an additional year of recording will reveal the first high resolution lithospheric scale model in the region.

The Detection of Very Low Frequency Earthquake using Broadband Seismic Array Data in South-Western Japan

NASA Astrophysics Data System (ADS)

Ishihara, Y.; Yamanaka, Y.; Kikuchi, M.

2002-12-01

The existences of variety of low-frequency seismic sources are obvious by the dense and equalized equipment_fs seismic network. Kikuchi(2000) and Kumagai et.al. (2001) analyzed about 50sec period ground motion excited by the volcanic activities Miyake-jima, Izu Islands. JMA is listing the low frequency earthquakes routinely in their hypocenter determination. Obara (2002) detected the low frequency, 2-4 Hz, tremor that occurred along subducting Philippine Sea plate by envelope analysis of high dense and short period seismic network (Hi-net). The monitoring of continuos long period waveform show us the existence of many unknown sources. Recently, the broadband seismic network of Japan (F-net, previous name is FREESIA) is developed and extends to linear array about 3,000 km. We reviewed the long period seismic data and earthquake catalogues. Many candidates, which are excited by unknown sources, are picked up manually. The candidates are reconfirmed in detail by the original seismograms and their rough frequency characteristics are evaluated. Most events have the very low frequency seismograms that is dominated period of 20 _E30 sec and smaller amplitude than ground noise level in shorter period range. We developed the hypocenter determination technique applied the grid search method. Moreover for the major events moment tensor inversion was performed. The most source locates at subducting plate and their depth is greater than 30km. However the location don_ft overlap the low frequency tremor source region. Major event_fs moment magnitude is 4 or greater and estimated source time is around 20 sec. We concluded that low frequency seismic event series exist in wide period range in subduction area. The very low frequency earthquakes occurred along Nankai and Ryukyu trough at southwestern Japan. We are planing to survey the very low frequency event systematically in wider western Pacific region.

Comprehensive Studies on the Seismic Gap between the Wenchuan and Lushan Earthquakes

NASA Astrophysics Data System (ADS)

Liang, C.

2016-12-01

An array of 20 short-period and 15 broadband seismometers were deployed to monitor the seismic gap between the 2008 Ms8.0 Wenchuan earthquake and the 2013 Ms7.0 Lushan earthquake. The Wenchuan earthquake ruptured from epicenter at (31.01°N, 103.42°E) largely northeastward while the Lushan earthquake ruptured from epicenter at (30.3°N, 103.0°E) largely southwestward. The region between the two earthquakes has recorded very few aftershocks and cataloged seismicity before and after the two big earthquakes compared to neighboring segments. As one small segment of the 500KM long Longmen Shan fault system, its absence of seismicity draws hot debate on whether a big one is still in brewing or steady creeping is in control of the strain energy release. The dense array is deployed primarily aimed to detect events that are much smaller than cataloged events and to determine if the segment is experiencing constantly creeping. The preliminary findings include: (1) source mechanisms show that the seismic gap appears to be a transitional zone between north and south segment. The events to the south are primarily thrust while events to north have more or less striking-slip components. This is also the case for both Lushan and Wenchuan earthquake; (2) The receiver function analysis shows that the Moho beneath the seismic Gap is less defined than its adjacent region with relatively weaker Ps conversion phases; (3) Both receiver function and ambient noise tomography show that the velocities in the upper crust is relatively lower in the Gap region than surrounding regions; (4) significant number of small earthquakes are located near surface in the gap region. Further examinations should be conducted before we can make a sounding conclusion on what mechanism is in control of the seismicity in this region.

Seismo-acoustic analysis of thunderstorms at Plostina (Romania) site

NASA Astrophysics Data System (ADS)

Grecu, Bogdan; Ghica, Daniela; Moldovan, Iren; Ionescu, Constantin

2013-04-01

The National Institute for Earth Physics (Romania) operates one of the largest seismic networks in the Eastern Europe. The network includes 97 stations with velocity sensors of which 52 are broadband and 45 are short period, 102 strong motion stations and 8 seismic observatories. Located in the most active seismic region of Romania, i.e. Vrancea area, the Plostina Observatory included initially two seismic stations, one at surface with both broadband and accelerometer sensors and one at 30 m depth with only short period velocity sensor. Starting with 2007, the facilities at Plostina have been upgraded so that at present, the observatory also includes one seismic array (PLOR) of seven elements (PLOR1, PLOR2, PLOR3, PLOR4, PLOR5, PLOR6, PLOR7) with an aperture of 2.5 km, seven infrasound elements (IPL2, IPL3, IPL4, IPH4, IPH5, IPH6, IPH7), two three-component fluxgate sensors, one Boltek EFM-100 electrometer and one La Crosse weather station. The element PLOR4 is co-located with the accelerometer and borehole sensor, two infrasonic elements (IPL4 and IPH4), one fluxgate sensor, the Boltek electrometer and the weather station. All the date are continuously recorded and real-time transmitted to the Romanian National Data Centre (RONDC) in Magurele. The recent developments at Plostina site made possible the improvement of the local miscroseismic activity monitoring as well as conducting of other geophysical studies such as acoustic measurements, observations of the variation of the magnetic field in correlation with solar activity, observations of the variation of radioactive alpha gases concentration, observations of the telluric currents. In this work, we investigate the signals emitted due to the process of lightning and thunder during thunderstorms activity at Plostina site. These signals are well recorded by both seismic and infrasound networks and they are used to perform spectral and specific array analyses. We also perform multiple correlations between the atmospheric parameters recorded by the weather station and seismic and infrasound signals.

Local Seismicity Recorded by ChilePEPPER: Implications for Dynamic Accretionary Prism Response and Long-term Prism Evolution

NASA Astrophysics Data System (ADS)

de Moor, A.; Trehu, A. M.; Tryon, M. D.

2015-12-01

To investigate the dynamic response of the outer accretionary wedge updip from the patch of greatest slip during the Mw8.8 2010 Maule earthquake, 10 Ocean Bottom Seismometers (OBS) were deployed from May 2012 to March 2013 in a small array with an inter-instrument spacing of ~12 km . Nine instruments were recovered, with 4 recording data on 3 intermediate-band 3-component seismometers and a differential pressure gauge and 5 recording data from absolute pressure gauges. [note: All instruments were also equipped with a fluid flow meter sensitive to flow rates as low as 0.0001 cm/yr in or out of the sediments. However, no flow signal was detected.] Here we present hypocenters for 569 local events that have S-P times less than 17 seconds (i.e. within ~125 km of the array) using hand-picked arrival times and a 1D velocity model derived from a 2D seismic refraction profile through the region (Moscoso et al 2011, EPSL). We analyze the distribution of seismicity in the context of published slip models, ChilePEPPER high-resolution seismic reflection data, critical taper analysis done by Cubas et al 2013 (EPSL), and offshore gravity data. The data show distinct segmentation within the outer prism. The northern section of the study area is characterized by a lack of seismicity, accretion of nearly all incoming sediment and a prism at critical taper. In contrast, abundant seismicity, significant sediment underthrusting at the deformation front and a prism below critical taper angle characterize the southern part of the study area. Both coseismic slip and post-rupture local seismicity can be related to density anomalies within the upper plate as revealed by free air gravity data corrected for the effects of bathymetry and the subducting plate. [ChilePEPPER - Project Evaluating Prism Post-Earthquake Response

Seismic &Infrasound Integrated Array "Apatity". Techniques, data processing, first results of observations.

NASA Astrophysics Data System (ADS)

Vinogradov, Y.; Baryshnikov, A.

2003-04-01

Since September 2001 3 infrasound membrane type sensors "K-304 AM" have been installed on the territory seismic array "Apatity" near the lake Imandra. A seismic array comprising 11 short-period sensors (type "Geotech S-500"), disposed on small and large circle (0.4 and 1 km diameter). Infrasound sensors located on small circle near the seismograths. All data are digitized at the array site and transmitted in real time to a processing center in Apatity to the Kola Regional Seismological Centre (KRSC). Common complex we are called - Seismic &Infrasound Integrated Array (SISIA) "Apatity". To support temporary storage the transmitting data in a disk loop and access to the data "NEWNORAC" program was created. This program replaced "NORAC" system developed by Norwegian Institute NORSAR, which was in use in KRSC before. A program package EL (event locator) for display and processing of the data has been modified. Now it includes the following : - quick access to the data stored in the disk loop (last two weeks); - data convertation from disk loop format to CSS 3.0 format; - data filtering using bandpass, highpass, lowpass, adaptive or rejector filters; - calculation of spectra and sonograms (spectral diagrams); - seismic events location with plotting on a map; - calculation of backazimuth and apparent velocity of acoustic wave by similar parts of wave recordings; - loading and processing CSS 3.0 seismic and acoustic data from KRSC archive. To store the acoustic data permanently the program BARCSS was made. It rewrites the data from the disk loop to KRSC archive in CSS 3.0 format. For comparison of acoustic noise level with wind we use data from meteorological station in Kandalaksha city, sampling rate is 3 hours. During the period from October 2001 to October 2002 more than 745 seismic events, which basically connected with mine technical activity of the large mining enterprises at the Kola Peninsula, were registered. The most part of events, caused by ground explosions, was registered by infrasound part of SISIA "Apatity". Their sources were at distances from 38 to 220 km. The result of observations during the first 1 year enabled us to estimate frequency range and main directions of arrivals of acoustic waves and noise level in the place of observations. In accordance with the results and relief a 4-rays wind-noise-reducing pipe array would be install at all 3 sensors at May 2003, for improvement the delectability during windy conditions. A schemes of the SISIA "Apatity", data transmitting and processing and samples of detected signals are shown in the presentation.

Unraveling earthquake stresses: Insights from dynamically triggered and induced earthquakes

NASA Astrophysics Data System (ADS)

Velasco, A. A.; Alfaro-Diaz, R. A.

2017-12-01

Induced seismicity, earthquakes caused by anthropogenic activity, has more than doubled in the last several years resulting from practices related to oil and gas production. Furthermore, large earthquakes have been shown to promote the triggering of other events within two fault lengths (static triggering), due to static stresses caused by physical movement along the fault, and also remotely from the passage of seismic waves (dynamic triggering). Thus, in order to understand the mechanisms for earthquake failure, we investigate regions where natural, induced, and dynamically triggered events occur, and specifically target Oklahoma. We first analyze data from EarthScope's USArray Transportable Array (TA) and local seismic networks implementing an optimized (STA/LTA) detector in order to develop local detection and earthquake catalogs. After we identify triggered events through statistical analysis, and perform a stress analysis to gain insight on the stress-states leading to triggered earthquake failure. We use our observations to determine the role of different transient stresses in contributing to natural and induced seismicity by comparing these stresses to regional stress orientation. We also delineate critically stressed regions of triggered seismicity that may indicate areas susceptible to earthquake hazards associated with sustained fluid injection in provinces of induced seismicity. Anthropogenic injection and extraction activity can alter the stress state and fluid flow within production basins. By analyzing the stress release of these ancient faults caused by dynamic stresses, we may be able to determine if fluids are solely responsible for increased seismic activity in induced regions.

What was that?

USGS Publications Warehouse

Anglin, F. M.; Haddon, R. A. W.

1988-01-01

At 4:20 local time on September 19, 1986, Mrs. Laurie Harder saw a meteor passing across the sky above her home in Yellowknife, N.W.T. She reported her observation to Yellowknife Seismic Station staff who examined the records of the Yellowknife seismic array to see if the associated meteoroid had hit Earth and generated observalbe seismic signals. 

The AlpArray Seismic Network: current status and next steps

NASA Astrophysics Data System (ADS)

Hetényi, György; Molinari, Irene; Clinton, John; Kissling, Edi

2016-04-01

The AlpArray initiative (http://www.alparray.ethz.ch) is a large-scale European collaboration to study the entire Alpine orogen at high resolution and in 3D with a large variety of geoscientific methods. The core element of the initiative is an extensive and dense broadband seismological network, the AlpArray Seismic Network (AASN), which complements the permanent seismological stations to ensure homogeneous coverage of the greater Alpine area. The some 260 temporary stations of the AlpArray Seismic Network are operated as a joint effort by a number of institutions from Austria, Bosnia-Herzegovina, Croatia, Czech Republic, France, Germany, Hungary, Italy, Slovakia and Switzerland. The first stations were installed in Spring 2015 and the full AASN is planned to be operational by early Summer 2016. In this poster we present the actual status of the deployment, the effort undertaken by the contributing groups, station performance, typical noise levels, best practices in installation as well as in data management, often encountered challenges, and planned next steps including the deployment of ocean bottom seismometers in the Ligurian Sea.

Source characterization of a small earthquake cluster at Edmond, Oklahoma using a very dense array

NASA Astrophysics Data System (ADS)

Ng, R.; Nakata, N.

2017-12-01

Recent seismicity in Oklahoma has caught the attention of the public in the last few years since seismicity is commonly related to loss in urban areas. To account for the increase in public interest, improve the understanding of damaging ground motions produced in earthquakes and develop better seismic hazard assessment, we must characterize the seismicity in Oklahoma and its associated structure and source parameters. Regional changes in subsurface stresses have increased seismic activities due to reactivation of faults in places such as central Oklahoma. It is imperative for seismic investigation and modeling to characterize subsurface structural features that may influence the damaging effects of ground motion. We analyze the full-waveform data collected from a temporary dense array of 72 portable seismometers with a 110 meter spacing that were active for a one-month period from May to June 2017, deployed at Edmond, Oklahoma. The data from this one-month duration array captured over 10,000 events and enabled us to make measurements of small-scale lateral variations of earthquake wavefields. We examine the waveform for events using advanced methods of detection, location and determine the source mechanism. We compare our results with selected events listed in the Oklahoma Geological Survey (OGS) and United States Geological Survey (USGS) catalogue. Based on the detection and located small events, we will discuss the causative fault structure at the area and present the results of the investigation.

Thunder-induced ground motions: 1. Observations

NASA Astrophysics Data System (ADS)

Lin, Ting-L.; Langston, Charles A.

2009-04-01

Acoustic pressure from thunder and its induced ground motions were investigated using a small array consisting of five three-component short-period surface seismometers, a three-component borehole seismometer, and five infrasound microphones. We used the array to constrain wave parameters of the incident acoustic and seismic waves. The incident slowness differences between acoustic pressure and ground motions suggest that ground reverberations were first initiated somewhat away from the array. Using slowness inferred from ground motions is preferable to obtain the seismic source parameters. We propose a source equalization procedure for acoustic/seismic deconvolution to generate the time domain transfer function, a procedure similar to that of obtaining teleseismic earthquake receiver functions. The time domain transfer function removes the incident pressure time history from the seismogram. An additional vertical-to-radial ground motion transfer function was used to identify the Rayleigh wave propagation mode of induced seismic waves complementing that found using the particle motions and amplitude variations in the borehole. The initial motions obtained by the time domain transfer functions suggest a low Poisson's ratio for the near-surface layer. The acoustic-to-seismic transfer functions show a consistent reverberation series at frequencies near 5 Hz. This gives an empirical measure of site resonance that depends on the ratio of the layer velocity to layer thickness for earthquake P and S waves. The time domain transfer function approach by transferring a spectral division into the time domain provides an alternative method for studying acoustic-to-seismic coupling.

Using a large-n nodal array to search for remote dynamic triggering in a region of induced seismicity in northern Oklahoma.

NASA Astrophysics Data System (ADS)

Peña-Castro, A. F.; Dougherty, S. L.; Harrington, R. M.; Cochran, E. S.

2017-12-01

Oklahoma has recently experienced a large increase in seismicity that has been linked to injection of large volumes of wastewater into deep disposal wells, a by-product of oil and gas production. Recent studies have shown that areas with active fluid injection and induced seismicity, such as Oklahoma, may be susceptible to dynamic triggering during passage of seismic waves from large, remote earthquakes. In spring 2016, the 1833-station LArge-n Seismic Survey in Oklahoma (LASSO) array was deployed for 30 days to examine an area of active seismicity in Gran County, located in northern Oklahoma. Here we use the LASSO array to look for dynamic triggering caused by teleseismic earthquakes with magnitudes between Mw 6-8 that produce Peak-Ground-Velocities (PGVs) exceeding 10 μm/s at the LASSO array, consistent with PGV values seen to have triggered seismicity at other locations. We focus on examining seismicity around the shallow Mw7.8 event in Ecuador on 04/16/2016 which generated the largest PGV at LASSO (250 µm/s). To establish if earthquake rates change during or following the passage of the teleseismic surface waves, we develop a catalog of earthquakes around the time of each teleseismic event. We first create a preliminary catalogue using a Short-Term Average/Long-Term Average (STA/LTA) detection algorithm window spanning +/- 24 hours around each teleseism,requiring detection at a minimum of 110 LASSO stations to identify an event. Next, we enhance the STA/LTA catalog with manual detections for a period of +/- 1.5 hours around the time of the teleseismic P-wave arrival to explore if triggering occurs that is not detected by the automated procedure. All detected events are then located using standard location techniques. Any observed seismicity rate changes following the teleseismic arrivals will be examined compared to the short-term background rates to determine whether they are statistically significant. If triggering is observed, focal mechanisms will be determined to estimate fault plane orientations and resolve triggering stresses on receiver fault planes. Our preliminary results for the Mw 7.8 Ecuador event suggest there may be delayed triggering that starts roughly 4 hours after the teleseismic phase arrivals, with event rates increasing from 0-5 to 15-25 events per hour.

Geophysical character of the intraplate Wabash Fault System from the Wabash EarthScope FlexArray

NASA Astrophysics Data System (ADS)

Conder, J. A.; Zhu, L.; Wood, J. D.

2017-12-01

The Wabash Seismic Array was an EarthScope funded FlexArray deployment across the Wabash Fault System. The Wabash system is long known for oil and gas production. The fault system is often characterized as an intraplate seismic zone as it has produced several earthquakes above M4 in the last 50 years and potentially several above M7 in the Holocene. While earthquakes are far less numerous in the Wabash system than in the nearby New Madrid seismic zone, the seismic moment is nearly twice that of New Madrid over the past 50 years. The array consisted of 45 broadband instruments deployed across the axis to study the larger structure and 3 smaller phased arrays of 9 short-period instruments each to get a better sense of the local seismic output of smaller events. First results from the northern phased array indicate that seismicity in the Wabash behaves markedly differently than in New Madrid, with a low b-value around 0.7. Receiver functions show a 50 km thick crust beneath the system, thickening somewhat to the west. A variable-depth, positive-amplitude conversion in the deep crust gives evidence for a rift pillow at the base of the system within a dense lowermost crustal layer. Low Vs and a moderate negative amplitude conversion in the mid crust suggest a possible weak zone that could localize deformation. Shear wave splitting shows fast directions consistent with absolute plate motion across the system. Split times drop in magnitude to 0.5-0.7 seconds within the valley while in the 1-1.5 second range outside the valley. This magnitude decrease suggests a change in mantle signature beneath the fault system, possibly resulting from a small degree of local flow in the asthenosphere either along axis (as may occur with a thinned lithosphere) or by vertical flow (e.g., from delamination or dripping). We are building a 2D tomographic model across the region, relying primarily on teleseismic body waves. The tomography will undoubtedly show variations in crustal structure that will give additional context to the receiver function results. Possibly more importantly, the lithospheric structure will discriminate between hypotheses of mantle flow required to give the observed shear wave splitting signature.

Seismic reflection response from cross-correlations of ambient vibrations on non-conventional hidrocarbon reservoir

NASA Astrophysics Data System (ADS)

Huerta, F. V.; Granados, I.; Aguirre, J.; Carrera, R. Á.

2017-12-01

Nowadays, in hydrocarbon industry, there is a need to optimize and reduce exploration costs in the different types of reservoirs, motivating the community specialized in the search and development of alternative exploration geophysical methods. This study show the reflection response obtained from a shale gas / oil deposit through the method of seismic interferometry of ambient vibrations in combination with Wavelet analysis and conventional seismic reflection techniques (CMP & NMO). The method is to generate seismic responses from virtual sources through the process of cross-correlation of records of Ambient Seismic Vibrations (ASV), collected in different receivers. The seismic response obtained is interpreted as the response that would be measured in one of the receivers considering a virtual source in the other. The acquisition of ASV records was performed in northern of Mexico through semi-rectangular arrays of multi-component geophones with instrumental response of 10 Hz. The in-line distance between geophones was 40 m while in cross-line was 280 m, the sampling used during the data collection was 2 ms and the total duration of the records was 6 hours. The results show the reflection response of two lines in the in-line direction and two in the cross-line direction for which the continuity of coherent events have been identified and interpreted as reflectors. There is certainty that the events identified correspond to reflections because the time-frequency analysis performed with the Wavelet Transform has allowed to identify the frequency band in which there are body waves. On the other hand, the CMP and NMO techniques have allowed to emphasize and correct the reflection response obtained during the correlation processes in the frequency band of interest. The results of the processing and analysis of ASV records through the seismic interferometry method have allowed us to see interesting results in light of the cross-correlation process in combination with the Wavelet analysis and conventional seismic reflection techniques. Therefore it was possible to recover the seismic response on each analyzed source-receiver pair, allowing us to obtain the reflection response of each analyzed seismic line.

Explosion source strong ground motions in the Mississippi embayment

USGS Publications Warehouse

Langston, C.A.; Bodin, P.; Powell, C.; Withers, M.; Horton, S.; Mooney, W.

2006-01-01

Two strong-motion arrays were deployed for the October 2002 Embayment Seismic Excitation Experiment to study the spatial variation of strong ground motions in the deep, unconsolidated sediments of the Mississippi embayment because there are no comparable strong-motion data from natural earthquakes in the area. Each linear array consisted of eight three-component K2 accelerographs spaced 15 m apart situated 1.2 and 2.5 kin from 2268-kg and 1134-kg borehole explosion sources, respectively. The array data show distinct body-wave and surface-wave arrivals that propagate within the thick, unconsolidated sedimentary column, the high-velocity basement rocks, and small-scale structure near the surface. Time-domain coherence of body-wave and surface-wave arrivals is computed for acceleration, velocity, and displacement time windows. Coherence is high for relatively low-frequency verticalcomponent Rayleigh waves and high-frequency P waves propagating across the array. Prominent high-frequency PS conversions seen on radial components, a proxy for the direct S wave from earthquake sources, lose coherence quickly over the 105-m length of the array. Transverse component signals are least coherent for any ground motion and appear to be highly scattered. Horizontal phase velocity is computed by using the ratio of particle velocity to estimates of the strain based on a plane-wave-propagation model. The resulting time-dependent phase-velocity map is a useful way to infer the propagation mechanisms of individual seismic phases and time windows of three-component waveforms. Displacement gradient analysis is a complementary technique for processing general spatial-array data to obtain horizontal slowness information.

Integrating Low-Cost Mems Accelerometer Mini-Arrays (mama) in Earthquake Early Warning Systems

NASA Astrophysics Data System (ADS)

Nof, R. N.; Chung, A. I.; Rademacher, H.; Allen, R. M.

2016-12-01

Current operational Earthquake Early Warning Systems (EEWS) acquire data with networks of single seismic stations, and compute source parameters assuming earthquakes to be point sources. For large events, the point-source assumption leads to an underestimation of magnitude, and the use of single stations leads to large uncertainties in the locations of events outside the network. We propose the use of mini-arrays to improve EEWS. Mini-arrays have the potential to: (a) estimate reliable hypocentral locations by beam forming (FK-analysis) techniques; (b) characterize the rupture dimensions and account for finite-source effects, leading to more reliable estimates for large magnitudes. Previously, the high price of multiple seismometers has made creating arrays cost-prohibitive. However, we propose setting up mini-arrays of a new seismometer based on low-cost (<$150), high-performance MEMS accelerometer around conventional seismic stations. The expected benefits of such an approach include decreasing alert-times, improving real-time shaking predictions and mitigating false alarms. We use low-resolution 14-bit Quake Catcher Network (QCN) data collected during Rapid Aftershock Mobilization Program (RAMP) in Christchurch, NZ following the M7.1 Darfield earthquake in September 2010. As the QCN network was so dense, we were able to use small sub-array of up to ten sensors spread along a maximum area of 1.7x2.2 km2 to demonstrate our approach and to solve for the BAZ of two events (Mw4.7 and Mw5.1) with less than ±10° error. We will also present the new 24-bit device details, benchmarks, and real-time measurements.

Multi-Array Back-Projections of The 2015 Gorkha Earthquake With Physics-Based Aftershock Calibrations

NASA Astrophysics Data System (ADS)

Meng, L.; Zhang, A.; Yagi, Y.

2015-12-01

The 2015 Mw 7.8 Nepal-Gorkha earthquake with casualties of over 9,000 people is the most devastating disaster to strike Nepal since the 1934 Nepal-Bihar earthquake. Its rupture process is well imaged by the teleseismic MUSIC back-projections (BP). Here, we perform independent back-projections of high-frequency recordings (0.5-2 Hz) from the Australian seismic network (AU), the North America network (NA) and the European seismic network (EU), located in complementary orientations. Our results of all three arrays show unilateral linear rupture path to the east of the hypocenter. But the propagating directions and the inferred rupture speeds differ significantly among different arrays. To understand the spatial uncertainties of the BP analysis, we image four moderate-size (M5~6) aftershocks based on the timing correction derived from the alignment of the initial P-wave of the mainshock. We find that the apparent source locations inferred from BP are systematically biased along the source-array orientation, which can be explained by the uncertainty of the 3D velocity structure deviated from the 1D reference model (e.g. IASP91). We introduced a slowness error term in travel time as a first-order calibration that successfully mitigates the source location discrepancies of different arrays. The calibrated BP results of three arrays are mutually consistent and reveal a unilateral rupture propagating eastward at a speed of 2.7 km/s along the down-dip edge of the locked Himalaya thrust zone over ~ 150 km, in agreement with a narrow slip distribution inferred from finite source inversions.

Continuous catchment-scale monitoring of geomorphic processes with a 2-D seismological array

NASA Astrophysics Data System (ADS)

Burtin, A.; Hovius, N.; Milodowski, D.; Chen, Y.-G.; Wu, Y.-M.; Lin, C.-W.; Chen, H.

2012-04-01

The monitoring of geomorphic processes during extreme climatic events is of a primary interest to estimate their impact on the landscape dynamics. However, available techniques to survey the surface activity do not provide a relevant time and/or space resolution. Furthermore, these methods hardly investigate the dynamics of the events since their detection are made a posteriori. To increase our knowledge of the landscape evolution and the influence of extreme climatic events on a catchment dynamics, we need to develop new tools and procedures. In many past works, it has been shown that seismic signals are relevant to detect and locate surface processes (landslides, debris flows). During the 2010 typhoon season, we deployed a network of 12 seismometers dedicated to monitor the surface processes of the Chenyoulan catchment in Taiwan. We test the ability of a two dimensional array and small inter-stations distances (~ 11 km) to map in continuous and at a catchment-scale the geomorphic activity. The spectral analysis of continuous records shows a high-frequency (> 1 Hz) seismic energy that is coherent with the occurrence of hillslope and river processes. Using a basic detection algorithm and a location approach running on the analysis of seismic amplitudes, we manage to locate the catchment activity. We mainly observe short-time events (> 300 occurrences) associated with debris falls and bank collapses during daily convective storms, where 69% of occurrences are coherent with the time distribution of precipitations. We also identify a couple of debris flows during a large tropical storm. In contrast, the FORMOSAT imagery does not detect any activity, which somehow reflects the lack of extreme climatic conditions during the experiment. However, high resolution pictures confirm the existence of links between most of geomorphic events and existing structures (landslide scars, gullies...). We thus conclude to an activity that is dominated by reactivation processes. It highlights the major interest of a seismic monitoring since it allows a detailed spatial and temporal survey of events that classic approaches are not able to observe. In the future, dense two dimensional seismological arrays will assess in real-time the landscape dynamics of an entire catchment, tracking sediments from slopes to rivers.

Inversion of ground-motion data from a seismometer array for rotation using a modification of Jaeger's method

USGS Publications Warehouse

Chi, Wu-Cheng; Lee, W.H.K.; Aston, J.A.D.; Lin, C.J.; Liu, C.-C.

2011-01-01

We develop a new way to invert 2D translational waveforms using Jaeger's (1969) formula to derive rotational ground motions about one axis and estimate the errors in them using techniques from statistical multivariate analysis. This procedure can be used to derive rotational ground motions and strains using arrayed translational data, thus providing an efficient way to calibrate the performance of rotational sensors. This approach does not require a priori information about the noise level of the translational data and elastic properties of the media. This new procedure also provides estimates of the standard deviations of the derived rotations and strains. In this study, we validated this code using synthetic translational waveforms from a seismic array. The results after the inversion of the synthetics for rotations were almost identical with the results derived using a well-tested inversion procedure by Spudich and Fletcher (2009). This new 2D procedure can be applied three times to obtain the full, three-component rotations. Additional modifications can be implemented to the code in the future to study different features of the rotational ground motions and strains induced by the passage of seismic waves.

Seismicity of the rocky mountains and Rio Grande Rift from the EarthScope Transportable Array and CREST temporary seismic networks, 2008-2010

NASA Astrophysics Data System (ADS)

Nakai, J. S.; Sheehan, A. F.; Bilek, S. L.

2017-03-01

We developed a catalog of small magnitude (ML -0.1 to 4.7) seismicity across Colorado and New Mexico from the EarthScope USArray Transportable Array and CREST (Colorado Rocky Mountains Experiment and Seismic Transects) seismic networks from 2008 to 2010 to characterize active deformation in the Rio Grande Rift. We recorded over 900 earthquakes in the Rio Grande Rift region, not including induced earthquakes and mine blasts, and find that the rift is actively deforming both broadly and in distinct regions. Seismic events that are likely induced, mostly in the Raton Basin, make up 66% of the catalog (1837 earthquakes). Neogene faults in the northern rift in north central Colorado are seismically active in the North Park Basin and northwestern Colorado. The central rift from the San Luis Basin (southern Colorado) to south of the Socorro Magma Body is the most seismically active rift region, and seismicity delineates the deformation in the Colorado Plateau transition zone, which is spatially correlated with volcanic vents, dikes, and faults within the western Jemez Lineament. The eastern Jemez Lineament is nearly aseismic and surrounded by a halo of seismicity culminating in boundaries defined by recent moderate (Mw 3.9 and Mw 3.3) earthquakes. The southern rift is characterized by diffuse seismicity in Texas and Mexico. This study provides an updated seismic catalog built with uniformity in seismometer coverage and low epicentral uncertainties ( 2 km) that allows for regional evaluation of seismicity. During this time period, clusters of seismicity and moderate magnitude earthquakes characterize deformation in a low-strain rate extensional environment.

Improved microseismic event locations through large-N arrays and wave-equation imaging and inversion

NASA Astrophysics Data System (ADS)

Witten, B.; Shragge, J. C.

2016-12-01

The recent increased focus on small-scale seismicity, Mw < 4 has come about primarily for two reasons. First, there is an increase in induced seismicity related to injection operations primarily for wastewater disposal and hydraulic fracturing for oil and gas recovery and for geothermal energy production. While the seismicity associated with injection is sometimes felt, it is more often weak. Some weak events are detected on current sparse arrays; however, accurate location of the events often requires a larger number of (multi-component) sensors. This leads to the second reason for an increased focus on small magnitude seismicity: a greater number of seismometers are being deployed in large N-arrays. The greater number of sensors decreases the detection threshold and therefore significantly increases the number of weak events found. Overall, these two factors bring new challenges and opportunities. Many standard seismological location and inversion techniques are geared toward large, easily identifiable events recorded on a sparse number of stations. However, with large-N arrays we can detect small events by utilizing multi-trace processing techniques, and increased processing power equips us with tools that employ more complete physics for simultaneously locating events and inverting for P- and S-wave velocity structure. We present a method that uses large-N arrays and wave-equation-based imaging and inversion to jointly locate earthquakes and estimate the elastic velocities of the earth. The technique requires no picking and is thus suitable for weak events. We validate the methodology through synthetic and field data examples.

Proceedings of the 11th Annual DARPA/AFGL Seismic Research symposium

NASA Astrophysics Data System (ADS)

Lewkowicz, James F.; McPhetres, Jeanne M.

1990-11-01

The following subjects are covered: near source observations of quarry explosions; small explosion discrimination and yield estimation; Rg as a depth discriminant for earthquakes and explosions: a case study in New England; a comparative study of high frequency seismic noise at selected sites in the USSR and USA; chemical explosions and the discrimination problem; application of simulated annealing to joint hypocenter determination; frequency dependence of Q(sub Lg) and Q in the continental crust; statistical approaches to testing for compliance with a threshold test ban treaty; broad-band studies of seismic sources at regional and teleseismic distances using advanced time series analysis methods; effects of depth of burial and tectonic release on regional and teleseismic explosion waveforms; finite difference simulations of seismic wave excitation at Soviet test sites with deterministic structures; stochastic geologic effects on near-field ground motions; the damage mechanics of porous rock; nonlinear attenuation mechanism in salt at moderate strain; compressional- and shear-wave polarizations at the Anza seismic array; and a generalized beamforming approach to real time network detection and phase association.

Seismic Imaging of UXO-Contaminated Underwater Sites (Interim Report)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gritto, Roland; Korneev, Valeri; Nihei, Kurt

2004-11-30

Finite difference modeling with 2-dimensional models were conducted to evaluate the performance of source-receiver arrays to locate UXO in littoral environments. The model parameters were taken from measurements in coastal areas with typical bay mud and from examples in the literature. Seismic arrays are well suited to focus energy by steering the elements of the array to any point in the medium that acts as an energy source. This principle also applies to seismic waves that are backscattered by buried UXO. The power of the array is particularly evident in strong noise conditions when the signal-to-noise ratio is too lowmore » to observe the scattered signal on the seismograms. Using a seismic array, it was possible to detect and locate the UXO with a reliability similar to noise free situations. When the UXO was positioned within 3-6 wavelengths of the incident signal from the source array, the resolution was good enough to determine the dimensions of the UXO from the scattered waves. Beyond this distance this distinction decreased gradually while the location and the center of the UXO were still determined reliably. The location and the dimensions of two adjacent UXO were resolved down to a separation of 1/3 of the dominant wavelength of the incident wave, at which time interference effects began to appear. In the investigated cases, the ability to locate a UXO was independent on the use of a model with a rippled or a flat seafloor, as long as the array was located above the UXO. Nevertheless, the correct parameters of the seafloor interface were obtained in these cases. An investigation to find the correct migration velocity in the sediments to locate the UXO revealed that a range of velocity gradients centered around the correct velocity model produced comparable results, which needs to be further investigated with physical modeling.« less

Shear wave velocities in the upper mantle of the Western Alps: new constraints using array analysis of seismic surface waves

NASA Astrophysics Data System (ADS)

Lyu, Chao; Pedersen, Helle A.; Paul, Anne; Zhao, Liang; Solarino, Stefano

2017-07-01

It remains challenging to obtain absolute shear wave velocities of heterogeneities of small lateral extension in the uppermost mantle. This study presents a cross-section of Vs across the strongly heterogeneous 3-D structure of the western European Alps, based on array analysis of data from 92 broad-band seismic stations from the CIFALPS experiment and from permanent networks in France and Italy. Half of the stations were located along a dense sublinear array. Using a combination of these stations and off-profile stations, fundamental-mode Rayleigh wave dispersion curves were calculated using a combined frequency-time beamforming approach. We calculated dispersion curves for seven arrays of approximately 100 km aperture and 14 arrays of approximately 50 km aperture, the latter with the aim of obtaining a 2-D vertical cross-section of Vs beneath the western Alps. The dispersion curves were inverted for Vs(z), with crustal interfaces imposed from a previous receiver function study. The array approach proved feasible, as Vs(z) from independent arrays vary smoothly across the profile length. Results from the seven large arrays show that the shear velocity of the upper mantle beneath the European plate is overall low compared to AK135 with the lowest velocities in the internal part of the western Alps, and higher velocities east of the Alps beneath the Po plain. The 2-D Vs model is coherent with (i) a ∼100 km thick eastward-dipping European lithosphere west of the Alps, (ii) very high velocities beneath the Po plain, coherent with the presence of the Alpine (European) slab and (iii) a narrow low-velocity anomaly beneath the core of the western Alps (from the Briançonnais to the Dora Maira massif), and approximately colocated with a similar anomaly observed in a recent teleseismic P-wave tomography. This intriguing anomaly is also supported by traveltime variations of subvertically propagating body waves from two teleseismic events that are approximately located on the profile great circle.

Digital interactive image analysis by array processing

NASA Technical Reports Server (NTRS)

Sabels, B. E.; Jennings, J. D.

1973-01-01

An attempt is made to draw a parallel between the existing geophysical data processing service industries and the emerging earth resources data support requirements. The relationship of seismic data analysis to ERTS data analysis is natural because in either case data is digitally recorded in the same format, resulting from remotely sensed energy which has been reflected, attenuated, shifted and degraded on its path from the source to the receiver. In the seismic case the energy is acoustic, ranging in frequencies from 10 to 75 cps, for which the lithosphere appears semi-transparent. In earth survey remote sensing through the atmosphere, visible and infrared frequency bands are being used. Yet the hardware and software required to process the magnetically recorded data from the two realms of inquiry are identical and similar, respectively. The resulting data products are similar.

Systematic detection of seismic events at Mount St. Helens with an ultra-dense array

NASA Astrophysics Data System (ADS)

Meng, X.; Hartog, J. R.; Schmandt, B.; Hotovec-Ellis, A. J.; Hansen, S. M.; Vidale, J. E.; Vanderplas, J.

2016-12-01

During the summer of 2014, an ultra-dense array of 900 geophones was deployed around the crater of Mount St. Helens and continuously operated for 15 days. This dataset provides us an unprecedented opportunity to systematically detect seismic events around an active volcano and study their underlying mechanisms. We use a waveform-based matched filter technique to detect seismic events from this dataset. Due to the large volume of continuous data ( 1 TB), we performed the detection on the GPU cluster Stampede (https://www.tacc.utexas.edu/systems/stampede). We build a suite of template events from three catalogs: 1) the standard Pacific Northwest Seismic Network (PNSN) catalog (45 events); 2) the catalog from Hansen&Schmandt (2015) obtained with a reverse-time imaging method (212 events); and 3) the catalog identified with a matched filter technique using the PNSN permanent stations (190 events). By searching for template matches in the ultra-dense array, we find 2237 events. We then calibrate precise relative magnitudes for template and detected events, using a principal component fit to measure waveform amplitude ratios. The magnitude of completeness and b-value of the detected catalog is -0.5 and 1.1, respectively. Our detected catalog shows several intensive swarms, which are likely driven by fluid pressure transients in conduits or slip transients on faults underneath the volcano. We are currently relocating the detected catalog with HypoDD and measuring the seismic velocity changes at Mount St. Helens using the coda wave interferometry of detected repeating earthquakes. The accurate temporal-spatial migration pattern of seismicity and seismic property changes should shed light on the physical processes beneath Mount St. Helens.

Small-scale seismic inversion using surface waves extracted from noise cross correlation.

PubMed

Gouédard, Pierre; Roux, Philippe; Campillo, Michel

2008-03-01

Green's functions can be retrieved between receivers from the correlation of ambient seismic noise or with an appropriate set of randomly distributed sources. This principle is demonstrated in small-scale geophysics using noise sources generated by human steps during a 10-min walk in the alignment of a 14-m-long accelerometer line array. The time-domain correlation of the records yields two surface wave modes extracted from the Green's function between each pair of accelerometers. A frequency-wave-number Fourier analysis yields each mode contribution and their dispersion curve. These dispersion curves are then inverted to provide the one-dimensional shear velocity of the near surface.

Study of Rayleigh-Love coupling from Spatial Gradient Observation

NASA Astrophysics Data System (ADS)

Lin, C. J.; Hosseini, K.; Donner, S.; Vernon, F.; Wassermann, J. M.; Igel, H.

2017-12-01

We present a new method to study Rayleigh-Love coupling. Instead of using seismograms solely, where ground motion is recorded as function of time, we incorporate with rotation and strain, also called spatial gradient where ground is represented as function of distance. Seismic rotation and strain are intrinsic different observable wavefield so are helpful to indentify wave type and wave propagation. A Mw 7.5 earthquake on 29 March 2015 occurred in Kokopo, Papua New Guinea recorded by a dense seismic array at PFO, California are used to obtaint seismic spatial gradient. We firstly estimate time series of azimuthal direction and phase velocity of SH wave and Rayleigh wave by analyzing collocated seismograms and rotations. This result also compares with frequency wavenumber methods using a nearby ANZA seismic array. We find the direction of Rayleigh wave fits well with great-circle back azimuth during wave propagation, while the direction of Love wave deviates from that, especially when main energy of Rayleigh wave arrives. From the analysis of cross-correlation between areal strain and vertical rotation, it reveals that high coherence, either positive or negative, happens at the same time when Love wave deparate from great-circle path. We also find the observed azimuth of Love wave and polarized particle motion of Rayleigh wave fits well with the fast direction of Rayleigh wave, for the period of 50 secs. We conclude the cause of deviated azimuth of Love wave is due to Rayleigh-Love coupling, as surface wave propagates through the area with anisotropic structure.

Seismic Wave Velocity in the Subducted Oceanic Crust from Autocorrelation of Tectonic Tremor Signals

NASA Astrophysics Data System (ADS)

Ducellier, A.; Creager, K.

2017-12-01

Hydration and dehydration of minerals in subduction zones play a key role in the geodynamic processes that generate seismicity and that allow tectonic plates to subduct. Detecting the presence of water in the subducted plate is thus crucial to better understand the seismogenesis and the consequent seismic hazard. A landward dipping, low velocity layer has been detected in most subduction zones. In Cascadia, this low velocity zone is characterized by a low S-wave velocity and a very high Poisson's ratio, which has been interpreted as high pore-fluid pressure in the upper half part of the subducted oceanic crust. Most previous studies were based on seismic reflection imaging, receiver function analysis, or body wave tomography, with seismic sources located far from the low velocity zone. In contrast, the sources of the tectonic tremors generated during Episodic Tremor and Slip (ETS) events are located on the plate boundary. As the sources of the tremors are much closer to the low velocity zone, seismic waves recorded during ETS events should illuminate the area with greater precision. Most methods to detect and locate tectonic tremors and low-frequency earthquakes are based on the cross correlation of seismic signals; either signals at the same station for different events, or the same event at different stations. We use the autocorrelation of the seismic signal recorded by eight arrays of stations, located in the Olympic Peninsula, Washington. Each tremor, assumed to be on the plate boundary, generates a direct wave and reflected and converted waves from both the strong shear-wave velocity contrast in the mid-oceanic crust, and from the Moho of the subducted oceanic crust. The time lag between the arrivals of these different waves at a seismic station corresponds to a peak of amplitude on the autocorrelation signals. Using the time lags observed for different locations of the tremor source, we intend to invert for the seismic wave velocity of the subducted oceanic crust under the arrays. Identifying zones with lower S-wave velocity and a high Poisson's ratio will then help detecting the presence of water in the subducted oceanic crust. Our ultimate goal is contributing to a better understanding of the mechanism of ETS and subduction zone processes.

Seismic Activity offshore Martinique and Dominique islands (Lesser Antilles subduction zone)

NASA Astrophysics Data System (ADS)

Ruiz Fernandez, Mario; Galve, Audrey; Monfret, Tony; Charvis, Philippe; Laigle, Mireille; Flueh, Ernst; Gallart, Josep; Hello, Yann

2010-05-01

In the framework of the European project Thales was Right, two seismic surveys (Sismantilles II and Obsantilles) were carried out to better constrain the lithospheric structure of the Lesser Antilles subduction zone, its seismic activity and to evaluate the associated seismic hazards. Sismantilles II experiment was conducted in January, 2007 onboard R/V Atalante (IFREMER). A total of 90 OBS belonging to Géoazur, INSU-CNRS and IFM-Geomar were deployed on a regular grid, offshore Antigua, Guadeloupe, Dominique and Martinique islands. During the active part of the survey, more than 2500 km of multichannel seismic profiles were shot along the grid lines. Then the OBS remained on the seafloor continuously recording for the seismic activity for approximately 4 months. On April 2007 Obsantilles experiment, carried out onboard R/V Antea (IRD), was focused on the recovery of those OBS and the redeployment of 28 instruments (Géoazur OBS) off Martinique and Dominica Islands for 4 additional months of continuous recording of the seismicity. This work focuses on the analysis of the seismological data recorded in the southern sector of the study area, offshore Martinique and Dominique. During the two recording periods, extending from January to the end of August 2007, more than 3300 seismic events were detected in this area. Approximately 1100 earthquakes had enough quality to be correctly located. Station corrections, obtained from multichannel seismic profiles, were introduced to each OBS to take in to account the sedimentary cover and better constrain the hypocentral determinations. Results show events located at shallower depths in the northern sector of the array, close to the Tiburon Ridge, where the seismic activity is mainly located between 20 to 40 km depth. In the southern sector, offshore Martinique, hypocenters become deeper, ranging to 60 km depth and dipping to the west. Focal solutions have also been obtained using the P wave polarities of the best azimuthally constrained earthquakes (Gap smaller than 90°). Focal mechanisms also reveal some differences between the northern and southern sector of the array. Whereas in the southern sector most of the analysed events show purely reverse fault solutions, in the northern area events present strike slip and normal fault solutions and could be related to intraplate deformation.

Detecting Micro-seismicity and Long-duration Tremor-like Events from the Oklahoma Wavefield Experiment

NASA Astrophysics Data System (ADS)

Li, C.; Li, Z.; Peng, Z.; Zhang, C.; Nakata, N.

2017-12-01

Oklahoma has experienced abrupt increase of induced seismicity in the last decade. An important way to fully understand seismic activities in Oklahoma is to obtain more complete earthquake catalogs and detect different types of seismic events. The IRIS Community Wavefield Demonstration Experiment was deployed near Enid, Oklahoma in Summer of 2016. The dataset from this ultra-dense array provides an excellent opportunity for detecting microseismicity in that region with wavefield approaches. Here we examine continuous waveforms recorded by 3 seismic lines using local coherence for ultra-dense arrays (Li et al., 2017), which is a measure of cross-correlation of waveform at each station with its nearby stations. So far we have detected more than 5,000 events from 06/22/2016 to 07/20/2016, and majority of them are not listed on the regional catalog of Oklahoma or global catalogs, indicating that they are local events. We also identify 15-20 long-period long-duration events, some of them lasting for more than 500 s. Such events have been found at major plate-boundary faults (also known as deep tectonic tremor), as well as during hydraulic fracturing, slow-moving landslides and glaciers. Our next step is to locate these possible tremor-like events with their relative arrival times across the array and compare their occurrence times with solid-earth tides and injection histories to better understand their driving mechanisms.

Microseismic monitoring of CO2 injection at the Penn West Enhanced Oil Recovery pilot project, Canada: implications for detection of wellbore leakage.

PubMed

Martínez-Garzón, Patricia; Bohnhoff, Marco; Kwiatek, Grzegorz; Zambrano-Narváez, Gonzalo; Chalaturnyk, Rick

2013-09-02

A passive seismic monitoring campaign was carried out in the frame of a CO2-Enhanced Oil Recovery (EOR) pilot project in Alberta, Canada. Our analysis focuses on a two-week period during which prominent downhole pressure fluctuations in the reservoir were accompanied by a leakage of CO2 and CH4 along the monitoring well equipped with an array of short-period borehole geophones. We applied state of the art seismological processing schemes to the continuous seismic waveform recordings. During the analyzed time period we did not find evidence of induced micro-seismicity associated with CO2 injection. Instead, we identified signals related to the leakage of CO2 and CH4, in that seven out of the eight geophones show a clearly elevated noise level framing the onset time of leakage along the monitoring well. Our results confirm that micro-seismic monitoring of reservoir treatment can contribute towards improved reservoir monitoring and leakage detection.

Microseismic Monitoring of CO2 Injection at the Penn West Enhanced Oil Recovery Pilot Project, Canada: Implications for Detection of Wellbore Leakage

PubMed Central

Martínez-Garzón, Patricia; Bohnhoff, Marco; Kwiatek, Grzegorz; Zambrano-Narváez, Gonzalo; Chalaturnyk, Rick

2013-01-01

A passive seismic monitoring campaign was carried out in the frame of a CO2-Enhanced Oil Recovery (EOR) pilot project in Alberta, Canada. Our analysis focuses on a two-week period during which prominent downhole pressure fluctuations in the reservoir were accompanied by a leakage of CO2 and CH4 along the monitoring well equipped with an array of short-period borehole geophones. We applied state of the art seismological processing schemes to the continuous seismic waveform recordings. During the analyzed time period we did not find evidence of induced micro-seismicity associated with CO2 injection. Instead, we identified signals related to the leakage of CO2 and CH4, in that seven out of the eight geophones show a clearly elevated noise level framing the onset time of leakage along the monitoring well. Our results confirm that micro-seismic monitoring of reservoir treatment can contribute towards improved reservoir monitoring and leakage detection. PMID:24002229

DOE Office of Scientific and Technical Information (OSTI.GOV)

Froemyr, E.; Berteussen, K.A.; Jahren, L.

Small scale seismic surveys have the potential of providing low-cost high resolution subsurface images of limited targets. Crucial to the success of this method is to understand the character and level of ambient noise. Based on this understanding appropriate source strength and receiver fold can be determined in order to obtain the necessary signal to noise ratio at target depth. Saga Petroleum a.s. and Read Well Services A/S performed a test off-shore Norway using geophones on the seabed. The receivers consisted of two small geophone arrays separated by 1 km. A 3 km line was host symmetrically above the receivermore » arrays. The line was shot in a non-continuous fashion by moving from one position to the next with 5 repetitive shots fired at each shot position. A small airgun array was used. A large proportion of the noise exhibits clear spatial coherence. The most significant noise sources are the receiver vessel and the shooting boat. Spectral and spatial analysis reveals that additional sources of noise are present including subsurface sources. The target reflector was top reservoir at approximately 2.1 sec. two-way time. With 4 geophones in each array and repetitive shooting, top reservoir is visible but weak. The area is in general complex but the authors may infer that reduce vessel noise coupled with increased source strength can provide a high resolution subsurface image revealing details not seen on the standard marine seismic section.« less

Residual topography and gravity anomalies reveal structural controls on co-seismic slip in the 2011 Mw 9.0 Tohoku-oki earthquake

NASA Astrophysics Data System (ADS)

Bassett, D.; Watts, A. B.; Sandwell, D. T.; Fialko, Y. A.

2016-12-01

We performed shear wave splitting analysis on 203 permanent (French RLPB, CEA and Catalonian networks) and temporary (PYROPE and IberArray experiments) broad-band stations around the Pyrenees. These measurements considerably enhance the spatial resolution and coverage of seismic anisotropy in that region. In particular, we characterize with different shear wave splitting analysis methods the small-scale variations of splitting parameters φ and δt along three dense transects crossing the western and central Pyrenees with an interstation spacing of about 7 km. While we find a relatively coherent seismic anisotropy pattern in the Pyrenean domain, we observe abrupt changes of splitting parameters in the Aquitaine Basin and delay times along the Pyrenees. We moreover observe coherent fast directions despite complex lithospheric structures in Iberia and the Massif Central. This suggests that two main sources of anisotropy are required to interpret seismic anisotropy in this region: (i) lithospheric fabrics in the Aquitaine Basin (probably frozen-in Hercynian anisotropy) and in the Pyrenees (early and late Pyrenean dynamics); (ii) asthenospheric mantle flow beneath the entire region (imprint of the western Mediterranean dynamics since the Oligocene).

Seismicity and Fault Zone Structure Near the Xinfengjiang Water Reservoir, Guangdong, China

NASA Astrophysics Data System (ADS)

Yang, H.; Sun, X.; He, L.; Wang, S.

2015-12-01

Xingfengjiang Water Reservoir (XWR) was built in 1958 and the first impoundment was conducted in 1959. Immediately following the reservoir impoundment, a series of earthquakes occurred in the vicinity of the XWR, including the 1962 M6.1 earthquake that occurred ~1 km next to the dam. Numerous small earthquakes take place in this region presently, making it one of the most active seismic zones in Guangdong. To investigate the present seismicity and associated fault zone structure, we deployed a temporary seismic network, including a dense linear array across the Ren-Zi-Shi fault southwest to the reservoir. The temporary network is consisted of 42 stations that are operated in the field for more than one month. Because of the mountainous terrain, it is impossible to deploy broadband sensors. Here we use DDV-5 seismometer with a central frequency of 120Hz-5s that is independent on external GPS and battery. During our deployment, numerous earthquakes were recorded. Preliminary results of travel time analysis have shown the characteristic of low velocity fault zone. More detailed analysis, including relocation of earthquakes, ambient noise cross correlation, and modeling body waves, will be presented.

Decay of Hurricanes Tracked by Dense Seismic Array

NASA Astrophysics Data System (ADS)

Lamontagne, A.; Tanimoto, T.

2014-12-01

Tropical cyclones (hurricanes and typhoons) are mostly atmospheric phenomena but they also generate significant ground motions in the solid earth when they become strong. If a dense seismological array existed along the path of a hurricane, we could learn about some processes near the hurricane eye and the change of its intensity through seismic data. We found a few cases of tropical cyclones that passed through the Transportable Array of Earthscope (TA) in the last four years. They provide some interesting time-evolving characteristics of hurricanes but in most cases seismic signals are too weak to gain any insight into the processes. The only exception we have found so far is Hurricane Isaac in 2012. Hurricane Isaac was mostly a tropical storm during its lifetime but it became a hurricane about 12 hours before the first landfall at the mouth of the Mississippi river at 0000 UTC August 29. The eye then went back over the ocean, but stayed near the coast, and made landfall again at 0800 UTC August 29. After this landfall, it went through the TA. This gave us an opportunity to study the decay of this hurricane based on seismic data. Our basic data are amplitude-distance plots for each 6-hour hurricane location. We confine our analysis to frequencies below 0.02 Hz because in higher frequency bands seismic waves were broader oceans, not necessarily near the hurricane eye. Right after the landfall, we found a sharp peak at about 75 km from the eye. This is most likely the location of the eyewall, where a strong ascending flow is known to exist. Over the next 12 hours, we see this peak deteriorate, which is undoubtedly related to the decay of the hurricane after landfall. The peak remained at the same location for these 12 hours and then in the following 18 hours started to move farther from the eye, to about 250 km. Therefore, we can monitor how the eyewall deteriorated over the 30 hours after landfall. The emphasis of this study will be on Hurricane Isaac but we will also report other cases for comparison and to clarify what we can learn about the processes near the hurricane eye by seismic data.

A Centerless Circular Array Method: Extracting Maximal Information on Phase Velocities of Rayleigh Waves From Microtremor Records From a Simple Seismic Array

NASA Astrophysics Data System (ADS)

Cho, I.; Tada, T.; Shinozaki, Y.

2005-12-01

We have developed a Centerless Circular Array (CCA) method of microtremor exploration, an algorithm that enables to estimate phase velocities of Rayleigh waves by analyzing vertical-component records of microtremors that are obtained with an array of three or five seismic sensors placed around a circumference. Our CCA method shows a remarkably high performance in long-wavelength ranges because, unlike the frequency-wavenumber spectral method, our method does not resolve individual plane-wave components in the process of identifying phase velocities. Theoretical considerations predict that the resolving power of our CCA method in long-wavelength ranges depends upon the SN ratio, or the ratio of power of the propagating components to that of the non-propagating components (incoherent noise) contained in the records from the seismic array. The applicability of our CCA method to small-sized arrays on the order of several meters in radius has already been confirmed in our earlier work (Cho et al., 2004). We have deployed circular seismic arrays of different sizes at test sites in Japan where the underground structure is well documented through geophysical exploration, and have applied our CCA method to microtremor records to estimate phase velocities of Rayleigh waves. The estimates were then checked against "model" phase velocities that are derived from theoretical calculations. For arrays of 5, 25, 300 and 600 meters in radii, the estimated and model phase velocities demonstrated fine agreement within a broad wavelength range extending from a little larger than 3r (r: the array radius) up to at least 40r, 14r, 42r and 9r, respectively. This demonstrates the applicability of our CCA method to arrays on the order of several to several hundreds of meters in radii, and also illustrates, in a typical way, the markedly high performance of our CCA method in long-wavelength ranges. We have also invented a mathematical model that enables to evaluate the SN ratio in a given microtremor field, and have applied it to real data. Theory predicts that our CCA method underestimates the phase velocities when noise is present. Using the evaluated SN ratio and the phase velocity dispersion curve model, we have calculated the apparent values of phase velocities which theory expects should be obtained by our CCA method in long-wavelength ranges, and have confirmed that the outcome agreed very well with the phase velocities estimated from real data. This demonstrates that the mathematical assumptions, on which our CCA method relies, remains valid over a wide range of wavelengths which we are examining, and also implies that, even in the absence of a priori knowledge of the phase velocity dispersion curve, the SN ratio evaluated with our mathematical model could be used to identify the resolution limit of our CCA method in long-wavelength ranges. We have thus been able to demonstrate, on the basis of theoretical considerations and real data analysis, both the capabilities and limitations of our CCA method.

Monitoring daily and sub-daily variations in crustal strain with seismic arrays

NASA Astrophysics Data System (ADS)

Mao, S.; Campillo, M.; van der Hilst, R. D.; Brenguier, F.; Hillers, G.

2017-12-01

We demonstrate that we can monitor deformation of the shallow crust (with hourly temporal resolution) directly with seismic waves, by measuring relative seismic wave speed changes (dv/v) due to relatively known periodical forcing (tides and changes in atmospheric temperature) at Piton de la Fournaise Volcano (PdF), La Réunion. We use ambient seismic noise recorded (for one month) at VolcArray, an experiment with three arrays of 49 vertical-component geophones deployed on a 7x7 grid of approximately 80 m spacing. Through noise-based coda wave interferometry we infer for each array the average relative changes in propagation speed of seismic waves (dv/v) as a function of time, which relate to temporal changes in medium properties within 100m depth. The variations in dv/v ( 0.05%) on time-scales longer than a day are best explained by effects of precipitation on pore pressure. In contrast, the (weaker) daily and sub-daily fluctuations of dv/v ( 0.01%) are likely to be caused by tidal and thermal effects. We verify that the inferred variations of dv/v are unrelated to spatiotemporal changes of noise wavefields. We further compare the power spectrum of dv/v with spectra of simulated tide-induced volumetric strain, temperature records, very broadband (VBB) seismograms, and borehole tilt records. In all five types of data, dominant peaks are found at around diurnal, semi-diurnal, and ter-diurnal frequencies. A comparison of phase and spectra of the data suggests that the tidal and thermal effects on dv/v are of similar magnitude but vary with frequency. Theoretical modeling of tide- and temperature-induced strain in different frequency bands agrees with the relative magnitude of the two effects on dv/v from passive monitoring.

Seismic risk analysis for the Babcock and Wilcox facility, Leechburg, Pennsylvania

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1977-10-21

The results of a detailed seismic risk analysis of the Babcock and Wilcox Plutonium Fuel Fabrication facility at Leechburg, Pennsylvania are presented. This report focuses on earthquakes; the other natural hazards, being addressed in separate reports, are severe weather (strong winds and tornados) and floods. The calculational method used is based on Cornell's work (1968); it has been previously applied to safety evaluations of major projects. The historical seismic record was established after a review of available literature, consultation with operators of local seismic arrays and examination of appropriate seismic data bases. Because of the aseismicity of the region aroundmore » the site, an analysis different from the conventional closest approach in a tectonic province was adapted. Earthquakes as far from the site as 1,000 km were included, as were the possibility of earthquakes at the site. In addition, various uncertainties in the input were explicitly considered in the analysis. The results of the risk analysis, which include a Bayesian estimate of the uncertainties, are presented, expressed as return period accelerations. The best estimate curve indicates that the Babcock and Wilcox facility will experience 0.05 g every 220 years and 0.10 g every 1400 years. The bounding curves roughly represent the one standard deviation confidence limits about the best estimate, reflecting the uncertainty in certain of the input. Detailed examination of the results show that the accelerations are very insensitive to the details of the source region geometries or the historical earthquake statistics in each region and that each of the source regions contributes almost equally to the cumulative risk at the site. If required for structural analysis, acceleration response spectra for the site can be constructed by scaling the mean response spectrum for alluvium in WASH 1255 by these peak accelerations.« less

RAPID DETERMINATION OF FOCAL DEPTH USING A GLOBAL NETWORK OF SMALL-APERTURE SEISMIC ARRAYS

NASA Astrophysics Data System (ADS)

Seats, K.; Koper, K.; Benz, H.

2009-12-01

The National Earthquake Information Center (NEIC) of the United States Geological Survey (USGS) operates 24 hours a day, 365 days a year with the mission of locating and characterizing seismic events around the world. A key component of this task is quickly determining the focal depth of each seismic event, which has a first-order effect on estimates of ground shaking used in the impact assessment applications of emergency response activities. Current methods of depth estimation used at the NEIC include arrival time inversion both with and without depth phases, a Bayesian depth constraint based on historical seismicity (1973-present), and moment tensor inversion primarily using P- and S-wave waveforms. In this study, we explore the possibility of automated modeling of waveforms from vertical-component arrays of the International Monitoring System (IMS) to improve rapid depth estimation at NEIC. Because these arrays are small-aperture, they are effective at increasing signal to noise ratios for frequencies of 1 Hz and higher. Currently, NEIC receives continuous real-time data from 23 IMS arrays. Following work done by previous researchers, we developed a technique that acts as an array of arrays. For a given epicentral location we calculate fourth root beams for each IMS array in the distance range of 30 to 95 degrees at the expected slowness vector of the first arrival. Because the IMS arrays are small-aperture, these beams highlight energy that has slowness similar to the first arrival, such as depth phases. The beams are rectified by taking the envelope and then automatically aligned on the largest peak within 5 seconds of the expected arrival time. The station beams are then combined into network beams assuming a range of depths varying from 10 km to 700 km in increments of 1 km. The network beams are computed assuming both pP and sP propagation, and a measure of beam power is output as a function of depth for both propagation models, as well as their sum. We validated this approach using several hundred seismic events in the magnitude range 4.5-6.5 mb that occurred in 2008 and 2009. In most cases, clear spikes in the network beam power existed at depths around those estimated by the NEIC using traditional location procedures. However, in most cases there was also a bimodality in the network beam power because of the ambiguity between assuming pP or sP propagation for later arriving energy. There were only a handful of cases in which a seismic event generated both sP and pP phases with sizes large enough to resolve the ambiguity. We are currently working to include PKP arrivals into the network beams and experimenting with various tuning parameters to improve the efficiency of the algorithm. This promising approach will allow NEIC to significantly and systematically improve the quality of hypocentral locations reported in the PDE and provide NEIC with additional valuable information on seismic source parameters needed in emergency response applications.

Detection and interpretation of seismoacoustic events at German infrasound stations

NASA Astrophysics Data System (ADS)

Pilger, Christoph; Koch, Karl; Ceranna, Lars

2016-04-01

Three infrasound arrays with collocated or nearby installed seismometers are operated by the Federal Institute for Geosciences and Natural Resources (BGR) as the German National Data Center (NDC) for the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Infrasound generated by seismoacoustic events is routinely detected at these infrasound arrays, but air-to-ground coupled acoustic waves occasionally show up in seismometer recordings as well. Different natural and artificial sources like meteoroids as well as industrial and mining activity generate infrasonic signatures that are simultaneously detected at microbarometers and seismometers. Furthermore, many near-surface sources like earthquakes and explosions generate both seismic and infrasonic waves that can be detected successively with both technologies. The combined interpretation of seismic and acoustic signatures provides additional information about the origin time and location of remote infrasound events or about the characterization of seismic events distinguishing man-made and natural origins. Furthermore, seismoacoustic studies help to improve the modelling of infrasound propagation and ducting in the atmosphere and allow quantifying the portion of energy coupled into ground and into air by seismoacoustic sources. An overview of different seismoacoustic sources and their detection by German infrasound stations as well as some conclusions on the benefit of a combined seismoacoustic analysis are presented within this study.

Seismic imaging along a 600 km transect of the Alaska Subduction zone (Invited)

NASA Astrophysics Data System (ADS)

Calkins, J. A.; Abers, G. A.; Freymueller, J. T.; Rondenay, S.; Christensen, D. H.

2010-12-01

We present earthquake locations, scattered wavefield migration images, and phase velocity maps from preliminary analysis of combined seismic data from the Broadband Experiment Across the Alaska Range (BEAAR) and Multidisciplinary Observations of Onshore Subduction (MOOS) projects. Together, these PASSCAL broadband arrays sampled a 500+ km transect across a portion of the subduction zone characterized by the Yakutat terrane/Pacific plate boundary in the downgoing plate, and the Denali volcanic gap in the overriding plate. These are the first results from the MOOS experiment, a 34-station array that was deployed from 2006-2008 to fill in the gap between the TACT offshore refraction profile (south and east of the coastline of the Kenai Peninsula), and the BEAAR array (spanning the Alaska Range between Talkeetna and Fairbanks). 2-D images of the upper 150 km of the subduction zone were produced by migrating forward- and back-scattered arrivals in the coda of P waves from large teleseismic earthquakes, highlighting S-velocity perturbations from a smoothly-varying background model. The migration images reveal a shallowly north-dipping low velocity zone that is contiguous near 20 km depth on its updip end with previously obtained images of the subducting plate offshore. The low velocity zone steepens further to the north, and terminates near 120 km beneath the Alaska Range. We interpret this low velocity zone to be the crust of the downgoing plate, and the reduced seismic velocities to be indicative of hydrated gabbroic compositions. Earthquakes located using the temporary arrays and nearby stations of the Alaska Regional Seismic Network correlate spatially with the inferred subducting crust. Cross-sections taken along nearly orthogonal strike lines through the MOOS array reveal that both the dip angle and the thickness of the subducting low velocity zone change abruptly across a roughly NNW-SSE striking line drawn through the eastern Kenai Peninsula, coincident with a distinct change in locking at the subduction interface as revealed by previous geodetic studies. On the west end of the Kenai Peninsula, where seismically imaged downgoing crust appears oceanic, the geodetic signal mainly reflects postseismic deformation from the 1964 earthquake as evinced by southeast trending displacement vectors (with respect to fixed North America). While postseismic relaxation continues east of the boundary, NNW-directed elastic deformation due to locking at the plate boundary dominates the geodetic signal, and imaging reveals thickened Yakutat crust is subducting. The collocation of sharp changes in both deep structure and surface deformation suggest that the nature of the plate interface changes drastically across the western edge of the Yakutat block and that variations in downgoing plate structure control the strain field in the overriding plate.

Coda Wave Analysis in Central-Western North America Using Earthscope Transportable Array Data

NASA Astrophysics Data System (ADS)

Escudero, C. R.; Doser, D. I.

2011-12-01

We determined seismic wave attenuation in the western and central United States (e.g. Washington, Oregon, California, Idaho, Nevada, Montana, Wyoming, Colorado, New Mexico, North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, and Texas) using coda waves. We selected approximately twenty moderate earthquakes (magnitude between 5.5 and 6.5) located along the Mexican subduction zone, Gulf of California, southern and northern California, and off the coast of Oregon for the analysis. These events were recorded by the EarthScope transportable array (TA) network from 2008 to 2011. In this study we implemented a method based on the assumption that coda waves are single backscattered waves from randomly distributed heterogeneities to calculate the coda Q. The frequencies studied lie between 1 and 15 Hz. The scattering attenuation is calculated for frequency bands centered at 1.5, 3, 5, 7.5, 10.5, and 13.5 Hz. In this work, we present coda Q resolution maps along with a correlation analysis between coda Q and seismicity, tectonic and geology setting. We observed higher attenuation (low coda Q values) in regions of sedimentary cover, and lower attenuation (high coda Q values) in hard rock regions. Using the 4-6 Hz frequency band, we found the best general correlation between coda Q and central-western North America bedrock geology.

Crustal deformation and seismic measurements in the region of McDonald Observatory, West Texas. [Texas and Northern Chihuahua, Mexico

NASA Technical Reports Server (NTRS)

Dorman, H. J.

1981-01-01

The arrival times of regional and local earthquakes and located earthquakes in the Basin and Range province of Texas and in the adjacent areas of Chihuahua, Mexico from January 1976 to August 1980 at the UT'NASA seismic array are summarized. The August 1931 Texas earthquake is reevaluated and the seismicity and crustal structure of West Texas is examined. A table of seismic stations is included.

Bighorns Arch Seismic Experiment (BASE): Amplitude Response to Different Seismic Charge Configurations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harder, S. H., Killer, K. C., Worthington, L. L., Snelson, C. M.

2010-09-02

Contrary to popular belief, charge weight is not the most important engineering parameter determining the seismic amplitudes generated by a shot. The scientific literature has long claimed that the relationship, A ~R2L1/2, where A is the seismic amplitude generated by a shot, R is the radius of the seismic charge and L is the length of that charge, holds. Assuming the coupling to the formation and the pressure generated by the explosive are constants, this relationship implies that the one should be able to increase the charge radius while decreasing the charge length and obtain more seismic amplitude with lessmore » charge weight. This has significant implications for the economics of lithospheric seismic shots, because shallower holes and small charge sizes decrease cost. During the Bighorns Array Seismic Experiment (BASE) conducted in the summer of 2010, 24 shots with charge sizes ranging from 110 to 900 kg and drill hole diameters of 300 and 450 mm were detonated and recorded by an array of up to 2000 single-channel Texan seismographs. Maximum source-receiver offset of 300 km. Five of these shots were located within a one-acre square in an effort to eliminate coupling effects due to differing geological formations. We present a quantitative comparison of the data from these five shots to experimentally test the equation above.« less

Analysis of the Seismicity Associated to the Subduction of the Rivera Plate using OBS and Onland Stations.

NASA Astrophysics Data System (ADS)

Nuñez-Cornu, F. J.; Barba, D. C., Sr.; Danobeitia, J.; Bandy, W. L.; Zamora-Camacho, A.; Marquez-Ramirez, V. H.; Ambros, M.; Gomez, A.; Sandoval, J. M.; Mortera-Gutierrez, C. A.

2016-12-01

The second stage of TsuJal Project includes the study of passive seismic activity in the region of the plate Rivera and Jalisco block by anchoring OBS and densifying the network of seismic stations on land for at least four months. This stage began in April 2016 with the deployment of 25 Obsidian stations with sensor Le-3D MkIII from the northern part of Nayarit state to the south of Colima state, including the Marias Islands. This temporal seismic network complements the Jalisco Seismic Network (RESAJ) for a total of 50 stations. Offshore, ten OBS type LCHEAPO 2000 with 4 channel (3 seismic short period and 1 pressure) were deployed, in the period from 19 to 30 April 2016 using the BO El Puma from UNAM. The OBS were deployed in an array from the Marias Islands to offcoast of the border of Colima and Michoacan states. On May 4, an earthquake with Ml = 4.2 took place in the contact area of the Rivera Plate, Cocos Plate and the Middle America Trench, subsequently occurred a seismic swarm with over 200 earthquakes until May 16, including an earthquake with Ml = 5.0 on May 7. A second swarm took place between May 28 and Jun 4 including an earthquake with Ml = 4.8 on Jun 1. An analysis of the quality of different location methods is presented: automatic preliminary RESAJ location using Antelope; location with revised RESAJ phases in Antelope; relocation of RESAJ data with hypo and a regional velocity model; relocation of RESAJ data with hypo adding data from the temporal seismic network stations; and finally the relocation adding the data from the OBS network. Moreover, the tectonic implications of these earthquakes are discussed.

Sled-Mounted Geophone Arrays for Near-Surface (0-4m) Seismic Profiling in Highly-attenuating Sedimentary Facies: Atchafalaya Basin Indian Bayou, Louisiana

NASA Astrophysics Data System (ADS)

Lorenzo, J. M.; Saanumi, A. A.; Westbrook, C. C.; Egnew, S. F.; Bentley, S. J.

2004-12-01

Towed land-geophone seismic arrays have the potential to increase markedly the efficiency for collecting near-surface (0-100m) high-resolution seismic data, but viable cases are few and have been limited to a narrow range of near-surface sedimentary facies. During November 2003 through June 2004 we conducted extensive seismic tests with traditional geophones mounted on low-cost Π -shaped sleds. We targeted human habitation surfaces within the upper few meters of a crevasse splay complex in the Atchafalaya Basin study area, Indian Bayou Wildlife Management Area, Louisiana, U.S. For seismic-to-core correlation, sealed, continuous test cores were run through a multi-sensor to test for magnetic susceptibility, bulk sediment density and electrical resistivity. We compared 24-channel seismic data using a variety of seismic source-receiver combinations. Sources comprised a 12-gauge pipe-gun, a 0.22 caliber-powered piston gun, an accelerated weight drop, and a small claw hammer. Commercial blanks, 2g-black-powder, and primer-only shells were fired by the pipe gun. Receivers included 100-Hz vertical-, and 14-Hz-horizontal-component geophones. For comparison, both ground-planted and geophones mounted on wooden and iron sleds 0.3 and 1.2m long respectively. Geophones mounted on steel sleds produced data of adequate quality. Whereas traditional ground-planted geophones showed better data quality, time and cost efficiency make mounted phones more feasible for regional studies as traditional arrays are prohibitively expensive. Because of the high seismic attenuation, only horizontal-component geophones mounted on heavy (9-kg) steel sleds provided useful data, although the shallowest reflection observed in the shear wave data came from a boundary at ~ 19m depth, too far below the target depth of 4-5 m. Instead, we forward-modeled refraction traveltime data to derive the acoustic and SH velocity structure.

Multi-Sensor Data Fusion Project

DTIC Science & Technology

2000-02-28

seismic network by detecting T phases generated by underground events ( generally earthquakes ) and associating these phases to seismic events. The...between underwater explosions (H), underground sources, mostly earthquake - generated (7), and noise detections (N). The phases classified as H are the only...processing for infrasound sensors is most similar to seismic array processing with the exception that the detections are based on a more sophisticated

Crustal and Uppermost Mantle Structure beneath the Western United States from USArray Regional Phase Analysis

NASA Astrophysics Data System (ADS)

Buehler, Janine Sylvia

The aim of this dissertation is to improve our understanding of the crust and uppermost mantle structure in the western United States, profiting from the wealth of regional phase data recorded at USArray stations. USArray, a transportable seismic array of ˜400 seismometers, has greatly increased seismic data coverage across the United States in the past few years, and allows imaging of the lithosphere of the North American continent with better resolution and new methods. The regional phases are often challenging to analyze, especially in a tectonically-active region like the western United States, because of their sensitivities to the heterogeneities of the crust and uppermost mantle. However, knowledge of the seismic structure of the lithosphere is not only essential in order to accurately image the velocity structure at greater depths, but also for constraining geodynamic models that reconstruct the tectonic evolution of the continent, and hence the information that is carried by the regional phases is very valuable. The data set used in this study consists mostly of the regional seismic phases Pn and Sn, which propagate horizontally along the Moho in the mantle lid and constrain the seismic velocity structure at a confined depth. We applied traditional tomographic methods that profit from the improved ray coverage through USArray, but also employed array-based techniques that take advantage of the regular station spacing of the transportable array and don't depend on regularization. In addition, we used stacking methods to image the propagation efficiency of the Sn phase, which is often highly attenuated in tectonically active regions, on a regional scale. The results complement other seismic studies that average over greater depth intervals, such as surface- and body-wave tomographies and anisotropy analysis from shear-wave splitting, to provide information on temperature, composition, and tectonic processes at depth. Comparisons between Pn azimuthal anisotropy and fast polarization direction from shear wave splitting suggest significant vertical changes in anisotropy in several regions of the upper mantle beneath the western United States. Sn can in theory further constrain the nature of anisotropy in the mantle lid. However, we have so far been unable to resolve shear-wave splitting directly in the Sn waveforms as the phase is often attenuated and difficult to detect. Still, we obtained evidence for Sn propagation in several regions of the western United States such as the central Great Basin and the northeastern part of the Colorado Plateau. We found that there are enough quality Sn picks for joint Pn-Sn tomography and identified prominent Vp/Vs anomalies, such as large high Vp/Vs regions --- typically associated with partial melt --- below the Snake River Plain and the Colorado Plateau.

Seismicity and Crustal Anisotropy Beneath the Western Segment of the North Anatolian Fault: Results from a Dense Seismic Array

NASA Astrophysics Data System (ADS)

Turkelli, N.; Teoman, U.; Altuncu Poyraz, S.; Cambaz, D.; Mutlu, A. K.; Kahraman, M.; Houseman, G. A.; Rost, S.; Thompson, D. A.; Cornwell, D. G.; Utkucu, M.; Gülen, L.

2013-12-01

The North Anatolian Fault (NAF) is one of the major strike slip fault systems on Earth comparable to San Andreas Fault in some ways. Devastating earthquakes have occurred along this system causing major damage and casualties. In order to comprehensively investigate the shallow and deep crustal structure beneath the western segment of NAF, a temporary dense seismic network for North Anatolia (DANA) consisting of 73 broadband sensors was deployed in early May 2012 surrounding a rectangular grid of by 70 km and a nominal station spacing of 7 km with the aim of further enhancing the detection capability of this dense seismic array. This joint project involves researchers from University of Leeds, UK, Bogazici University Kandilli Observatory and Earthquake Research Institute (KOERI), and University of Sakarya and primarily focuses on upper crustal studies such as earthquake locations (especially micro-seismic activity), receiver functions, moment tensor inversions, shear wave splitting, and ambient noise correlations. To begin with, we obtained the hypocenter locations of local earthquakes that occured within the DANA network. The dense 2-D grid geometry considerably enhanced the earthquake detection capability which allowed us to precisely locate events with local magnitudes (Ml) less than 1.0. Accurate earthquake locations will eventually lead to high resolution images of the upper crustal structure beneath the northern and southern branches of NAF in Sakarya region. In order to put additional constraints on the active tectonics of the western part of NAF, we also determined fault plane solutions using Regional Moment Tensor Inversion (RMT) and P wave first motion methods. For the analysis of high quality fault plane solutions, data from KOERI and the DANA project were merged. Furthermore, with the aim of providing insights on crustal anisotropy, shear wave splitting parameters such as lag time and fast polarization direction were obtained for local events recorded within the seismic network with magnitudes larger than 2.5.

Imaging Crustal Structure with Waveform and HV Ratio of Body-wave Receiver Function

NASA Astrophysics Data System (ADS)

Chong, J.; Chu, R.; Ni, S.; Meng, Q.; Guo, A.

2017-12-01

It is known that receiver function has less constraint on the absolute velocity, and joint inversion of receiver function and surface wave dispersion has been widely applied to reduce the non-uniqueness of velocity and interface depth. However, some studies indicate that the receiver function itself is capable for determining the absolute shear wave velocity. In this study, we propose to measure the receiver function HV ratio which takes advantage of the amplitude information of the radial and vertical receiver functions to constrain the shear-wave velocity. Numerical analysis indicates that the receiver function HV ratio is sensitive to the average shear wave velocity in the depth range it samples, and can help to reduce the non-uniqueness of receiver function waveform inversion. A joint inversion scheme has been developed, and both synthetic tests and real data application proved the feasibility of the joint inversion. The method has been applied to the dense seismic array of ChinArray program in SE Tibet during the time period from August 2011 to August 2012 in SE Tibet (ChinArray-Himalaya, 2011). The measurements of receiver function HV ratio reveals the lateral variation of the tectonics in of the study region. And main features of the velocity structure imagined by the new joint inversion method are consistent with previous studies. KEYWORDS: receiver function HV ratio, receiver function waveform inversion, crustal structure ReferenceChinArray-Himalaya. 2011. China Seismic Array waveform data of Himalaya Project. Institute of Geophysics, China Earthquake Administration. doi:10.12001/ChinArray.Data. Himalaya. Jiajun Chong, Risheng Chu*, Sidao Ni, Qingjun Meng, Aizhi Guo, 2017. Receiver Function HV Ratio, a New Measurement for Reducing Non-uniqueness of Receiver Function Waveform Inversion. (under revision)

Properties of Repetitive Long-Period Seismicity at Villarrica Volcano, Chile

NASA Astrophysics Data System (ADS)

Richardson, J.; Waite, G. P.; Palma, J.; Johnson, J. B.

2011-12-01

Villarrica Volcano, Chile hosts a persistent lava lake and is characterized by degassing and long-period seismicity. In order to better understand the relationship between outgassing and seismicity, we recorded broadband seismic and acoustic data along with high-rate SO2 emission data. We used both a densely-spaced linear array deployed on the northern flank of Villarrica, during the austral summer of 2011, and a wider aperture array of stations distributed around the volcano that was active in the austral summer of 2010. Both deployments consisted of three-component broadband stations and were augmented with broadband infrasound sensors. Of particular interests are repetitive, ~1 Hz seismic and coincident infrasound signals that occurred approximately every 2 minutes. Because these events are typically very low amplitude, we used a matched filter approach to identify them. We windowed several high-amplitude records of these events from broadband seismic stations near the vent. The record section of each event served as a template to compare with the entire dataset by cross-correlation. This approach identified ~20,000 nearly identical events during the ~7 day deployment of the linear array, which were otherwise difficult to identify in the raw records. Assuming that all of the events that we identified have identical source mechanisms and depths, we stack the large suite of events to produce low-noise records and particle motions at receivers farther than 5 km from the vent. We find that the records from stations near the edifice are dominated by tangential particle motion, suggesting the influence of near-field components. Correlation of these data with broadband acoustic data collected at the summit suggest that these repeatable seismic processes are linked to acoustic emissions, probably due to gas bubbles bursting at the magma free surface, as no eruptive products besides gas were being emitted by the volcano during the instrument deployment. The acoustic signals affiliated with the repetitive seismic signals do not seem directly related to the continuous, well-correlated acoustic tremor observed both at the vent and at roughly 6 km away from small-aperture acoustic arrays (also reported by other groups in 2009, 2010). We also correlate the acoustic and repetitive seismic signals with high time resolution (~1 Hz sampling rate), sulfur dioxide emissions measured with an ultraviolet camera. Because a subset of stations operated during both 2010 and 2011, we could tie events from both deployments to generate a single stacked event at all 17 stations. We will present results of finite-difference modeling of this event stack using a simple homogeneous velocity structure.

Coda-wave and ambient noise interferometry using an offset vertical array at Iwanuma site, northeast Japan

NASA Astrophysics Data System (ADS)

Minami, K.; Yamamoto, M.; Nishimura, T.; Nakahara, H.; Shiomi, K.

2013-12-01

Seismic interferometry using vertical borehole arrays is a powerful tool to estimate the shallow subsurface structure and its time lapse changes. However, the wave fields surrounding borehole arrays are non-isotropic due to the existence of ground surface and non-uniform distribution of sources, and do not meet the requirements of the seismic interferometry in a strict sense. In this study, to examine differences between wave fields of coda waves and ambient noise, and to estimate their effects on the results of seismic interferometry, we conducted a temporal seismic experiment using zero-offset and offset vertical arrays. We installed two 3-components seismometers (hereafter called Surface1 and Surface2) at the ground surface in the vicinity of NIED Iwanuma site (Miyagi Pref., Japan). Surface1 is placed just above the Hi-net downhole seismometer whose depth is 101 m, and Surface2 is placed 70 m away from Surface1. To extract the wave propagation between these 3 seismometers, we compute the cross-correlation functions (CCFs) of coda-wave and ambient noise for each pair of the zero-offset vertical (Hi-net-Surface1), finite-offset vertical (Hi-net-Surface2), and horizontal (Surface1-Surface2) arrays. We use the frequency bands of 4-8, 8-16 Hz in the CCF computation. The characteristics of obtained CCFs are summarized as follows; (1) in all frequency bands, the peak lag times of CCFs from coda waves are almost the same between the vertical and offset-vertical arrays irrespective of different inter-station distance, and those for the horizontal array are around 0 s. (2) the peak lag times of CCFs from ambient noise show slight differences, that is, those obtained from the vertical array are earlier than those from the offset-vertical array, and those from the horizontal array are around 0.05 s. (3) the peak lag times of CCFs for the vertical array obtained from ambient noise analyses are earlier than those from the coda-wave analyses. These results indicate that wave fields of coda-wave are mainly composed of vertically propagating waves, while those of ambient noise are composed of both vertically and horizontally propagating waves. To explain these characteristics of the CCFs obtained from different wave fields, we conducted a numerical simulation of interferometry based on the concept of stationary phase. Here, we assume isotropic upward incidence of SV-wave into a homogeneous half-space, and compute CCFs for the zero-offset and finite-offset vertical arrays by taking into account the reflection and conversion of P-SV waves at the free surface. Due to the effectively non-isotropic wave field, the simulated CCF for the zero-offset vertical array shows slight delay in peak lag time and its amplitudes decrease in the acausal part. On the other hand, the simulated CCF for finite-offset vertical array shows amplitude decrease and no peak lag time shift. These results are consistent with the difference in peak lag times obtained from coda-wave and ambient noise analyses. Our observations and theoretical consideration suggest that the careful consideration of wave fields is important in the application of seismic interferometry to borehole array data.

Observation of Infrasonic/Acoustic/Seismic Waves Induced by Hypersonic Reentry of Hayabusa

NASA Astrophysics Data System (ADS)

Yamamoto, M.-Y.; Ishihara, Y.; Hiramatsu, Y.; Furumoto, M.; Fujita, K.

2012-05-01

Observation of infrasonic/acoustic/seismic waves induced by hypersonic reentry of HAYABUSA was carried out on June 13, 2010. Results by 3-sites arrayed observation will be shown in detail by comparison with multiple-sites optical observation.

Seismic Readings from the Deepest Borehole in the New Madrid Seismic Zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woolery, Edward W; Wang, Zhenming; Sturchio, Neil C

2006-03-01

Since the 1980s, the research associated with the UK network has been primarily strong-motion seismology of engineering interest. Currently the University of Kentucky operates a strong-motion network of nine stations in the New Madrid Seismic Zone. A unique feature of the network is the inclusions of vertical strong-motion arrays, each with one or two downhole accelerometers. The deepest borehole array is 260 m below the surfaces at station VASA in Fulton County, Kentucky. A preliminary surface seismic refraction survey was conducted at the site before drilling the hole at VSAS (Woolery and Wang, 2002). The depth to the Paleozoic bedrockmore » at the site was estimated to be approximately 595 m, and the depth to the first very stiff layer (i.e. Porters Creek Clay) was found to be about 260 m. These depths and stratigraphic interpretation correlated well with a proprietary seismic reflection line and the Ken-Ten Oil Exploration No. 1 Sanger hole (Schwalb, 1969), as well as our experience in the area (Street et al., 1995; Woolery et al., 1999).« less

Earthquake Source Parameter Estimates for the Charlevoix and Western Quebec Seismic Zones in Eastern Canada

NASA Astrophysics Data System (ADS)

Onwuemeka, J.; Liu, Y.; Harrington, R. M.; Peña-Castro, A. F.; Rodriguez Padilla, A. M.; Darbyshire, F. A.

2017-12-01

The Charlevoix Seismic Zone (CSZ), located in eastern Canada, experiences a high rate of intraplate earthquakes, hosting more than six M >6 events since the 17th century. The seismicity rate is similarly high in the Western Quebec seismic zone (WQSZ) where an MN 5.2 event was reported on May 17, 2013. A good understanding of seismicity and its relation to the St-Lawrence paleorift system requires information about event source properties, such as static stress drop and fault orientation (via focal mechanism solutions). In this study, we conduct a systematic estimate of event source parameters using 1) hypoDD to relocate event hypocenters, 2) spectral analysis to derive corner frequency, magnitude, and hence static stress drops, and 3) first arrival polarities to derive focal mechanism solutions of selected events. We use a combined dataset for 817 earthquakes cataloged between June 2012 and May 2017 from the Canadian National Seismograph Network (CNSN), and temporary deployments from the QM-III Earthscope FlexArray and McGill seismic networks. We first relocate 450 events using P and S-wave differential travel-times refined with waveform cross-correlation, and compute focal mechanism solutions for all events with impulsive P-wave arrivals at a minimum of 8 stations using the hybridMT moment tensor inversion algorithm. We then determine corner frequency and seismic moment values by fitting S-wave spectra on transverse components at all stations for all events. We choose the final corner frequency and moment values for each event using the median estimate at all stations. We use the corner frequency and moment estimates to calculate moment magnitudes, static stress-drop values and rupture radii, assuming a circular rupture model. We also investigate scaling relationships between parameters, directivity, and compute apparent source dimensions and source time functions of 15 M 2.4+ events from second-degree moment estimates. To the first-order, source dimension estimates from both methods generally agree. We observe higher corner frequencies and higher stress drops (ranging from 20 to 70 MPa) typical of intraplate seismicity in comparison with interplate seismicity. We follow similar approaches to studying 25 MN 3+ events reported in the WQSZ using data recorded by the CNSN and USArray Transportable Array.

Microearthquake mechanism from wave amplitudes recorded by a close-to-surface seismic array at Ocnele Mari, Romania

NASA Astrophysics Data System (ADS)

Jechumtálová, Z.; Šílený, J.; Trifu, C.-I.

2014-06-01

The resolution of event mechanism is investigated in terms of the unconstrained moment tensor (MT) source model and the shear-tensile crack (STC) source model representing a slip along the fault with an off-plane component. Data are simulated as recorded by the actual seismic array installed at Ocnele Mari (Romania), where sensors are placed in shallow boreholes. Noise is included as superimposed on synthetic data, and the analysis explores how the results are influenced (i) by data recorded by the complete seismic array compared to that provided by the subarray of surface sensors, (ii) by using three- or one-component sensors and (iii) by inverting P- and S-wave amplitudes versus P-wave amplitudes only. The orientation of the pure shear fracture component is resolved almost always well. On the other hand, the noise increase distorts the non-double-couple components (non-DC) of the MT unless a high-quality data set is available. The STC source model yields considerably less spurious non-shear fracture components. Incorporating recordings at deeper sensors in addition to those obtained from the surface ones allows for the processing of noisier data. Performance of the network equipped with three-component sensors is only slightly better than that with uniaxial sensors. Inverting both P- and S-wave amplitudes compared to the inversion of P-wave amplitudes only markedly improves the resolution of the orientation of the source mechanism. Comparison of the inversion results for the two alternative source models permits the assessment of the reliability of non-shear components retrieved. As example, the approach is investigated on three microseismic events occurred at Ocnele Mari, where both large and small non-DC components were found. The analysis confirms a tensile fracturing for two of these events, and a shear slip for the third.

Imaging of Heterogeneous Structure beneath the Metropolitan Tokyo Area

NASA Astrophysics Data System (ADS)

Nakagawa, S.; Sakai, S.; Kurashimo, E.; Kato, A.; Hagiwara, H.; Kasahara, K.; Tanada, T.; Obara, K.; Hirata, N.

2009-12-01

Beneath the metropolitan Tokyo area, the Philippine Sea Plate (PSP) subducts and causes damaged mega-thrust earthquakes. The Dai-Dai-Toku Project revealed the geometry of the upper surface of PSP, and estimated a rupture process and a ground motion of the 1923 Kanto earthquake [Sato et al., 2005]. Hagiwara et al. (2006) estimated the velocity structure of Boso peninsula. However, these results are not sufficient for the assessment of the entire picture of the seismic hazards beneath the metropolitan Tokyo area including those due to an intra-slab M7+ earthquake. So, we have carried out a 5-year project since 2007, the Special Project for Earthquake Disaster Mitigation in the Metropolitan Tokyo area. Proving the more detailed geometry and physical properties (e.g. velocities, densities, attenuation) of PSP is very important to attain this issue. The core item of this project is the dense seismic array observation in metropolitan area, which is called the MeSO-net (Metropolitan Seismic Observation network). In order to obtain the high resolution images of a velocity structure, it is requested to construct a seismic network with a spacing of 2-5 km. The total number of seismic stations of the MeSO-net will be about 400 and will be deployed in 4 years. We deployed the 178 seismic stations, which construct 5 seismic arrays such as Tsukuba-Fujisawa (TF) array etc., by 2008, and we are now deploying the 45 seismic stations in this year. The MeSO-net data are quasi-real-time transferred to the data center at ERI [Kasahara et al., 2007; Nakagawa et al., 2007]. In this study, we applied the tomography to image the heterogeneous structure under the metropolitan Tokyo area. We selected events from the catalogue by Hagiwara et al. (2006) and merged the new event data observed by MeSO-net with these data. Around the Kanto region there are several seismic explorations using active sources were carried out [Sato et al., 2005; Oikawa et al., 2007]. Since these data may improve the velocity structure in shallower part, we added the arrival time data of these explorations into the dataset. Then, we applied the double-difference tomography method [Zhang and Thurber, 2003] to this dataset and estimated the fine-scale velocity structure. The initial velocity structure is the same in Hagiwara et al. (2006), and the VP/VS ratio is set to 1.73 for all grid nodes. The TF array passes directory above Tokyo and is parallel to Boso peninsula. The depth section of P-wave velocity structure along the TF array clearly shows that thin low-velocity layer which overlies high-velocity layer subducts towards northeast. This low-velocity layer corresponds to the oceanic crust of the subducting PSP. The increase of MeSO-net stations and event data may improve images of heterogeneous structure and contribute the purpose of this special project. Acknowledgement: This study was supported by the Earthquake Research Institute cooperative research program.

Relative velocity change measurement based on seismic noise analysis in exploration geophysics

NASA Astrophysics Data System (ADS)

Corciulo, M.; Roux, P.; Campillo, M.; Dubuq, D.

2011-12-01

Passive monitoring techniques based on noise cross-correlation analysis are still debated in exploration geophysics even if recent studies showed impressive performance in seismology at larger scale. Time evolution of complex geological structure using noise data includes localization of noise sources and measurement of relative velocity variations. Monitoring relative velocity variations only requires the measurement of phase shifts of seismic noise cross-correlation functions computed for successive time recordings. The existing algorithms, such as the Stretching and the Doublet, classically need great efforts in terms of computation time, making them not practical when continuous dataset on dense arrays are acquired. We present here an innovative technique for passive monitoring based on the measure of the instantaneous phase of noise-correlated signals. The Instantaneous Phase Variation (IPV) technique aims at cumulating the advantages of the Stretching and Doublet methods while proposing a faster measurement of the relative velocity change. The IPV takes advantage of the Hilbert transform to compute in the time domain the phase difference between two noise correlation functions. The relative velocity variation is measured through the slope of the linear regression of the phase difference curve as a function of correlation time. The large amount of noise correlation functions, classically available at exploration scale on dense arrays, allows for a statistical analysis that further improves the precision of the estimation of the velocity change. In this work, numerical tests first aim at comparing the IPV performance to the Stretching and Doublet techniques in terms of accuracy, robustness and computation time. Then experimental results are presented using a seismic noise dataset with five days of continuous recording on 397 geophones spread on a ~1 km-squared area.

Estimating the location of baleen whale calls using dual streamers to support mitigation procedures in seismic reflection surveys.

PubMed

Abadi, Shima H; Tolstoy, Maya; Wilcock, William S D

2017-01-01

In order to mitigate against possible impacts of seismic surveys on baleen whales it is important to know as much as possible about the presence of whales within the vicinity of seismic operations. This study expands on previous work that analyzes single seismic streamer data to locate nearby calling baleen whales with a grid search method that utilizes the propagation angles and relative arrival times of received signals along the streamer. Three dimensional seismic reflection surveys use multiple towed hydrophone arrays for imaging the structure beneath the seafloor, providing an opportunity to significantly improve the uncertainty associated with streamer-generated call locations. All seismic surveys utilizing airguns conduct visual marine mammal monitoring surveys concurrent with the experiment, with powering-down of seismic source if a marine mammal is observed within the exposure zone. This study utilizes data from power-down periods of a seismic experiment conducted with two 8-km long seismic hydrophone arrays by the R/V Marcus G. Langseth near Alaska in summer 2011. Simulated and experiment data demonstrate that a single streamer can be utilized to resolve left-right ambiguity because the streamer is rarely perfectly straight in a field setting, but dual streamers provides significantly improved locations. Both methods represent a dramatic improvement over the existing Passive Acoustic Monitoring (PAM) system for detecting low frequency baleen whale calls, with ~60 calls detected utilizing the seismic streamers, zero of which were detected using the current R/V Langseth PAM system. Furthermore, this method has the potential to be utilized not only for improving mitigation processes, but also for studying baleen whale behavior within the vicinity of seismic operations.

Estimating the location of baleen whale calls using dual streamers to support mitigation procedures in seismic reflection surveys

PubMed Central

Abadi, Shima H.; Tolstoy, Maya; Wilcock, William S. D.

2017-01-01

In order to mitigate against possible impacts of seismic surveys on baleen whales it is important to know as much as possible about the presence of whales within the vicinity of seismic operations. This study expands on previous work that analyzes single seismic streamer data to locate nearby calling baleen whales with a grid search method that utilizes the propagation angles and relative arrival times of received signals along the streamer. Three dimensional seismic reflection surveys use multiple towed hydrophone arrays for imaging the structure beneath the seafloor, providing an opportunity to significantly improve the uncertainty associated with streamer-generated call locations. All seismic surveys utilizing airguns conduct visual marine mammal monitoring surveys concurrent with the experiment, with powering-down of seismic source if a marine mammal is observed within the exposure zone. This study utilizes data from power-down periods of a seismic experiment conducted with two 8-km long seismic hydrophone arrays by the R/V Marcus G. Langseth near Alaska in summer 2011. Simulated and experiment data demonstrate that a single streamer can be utilized to resolve left-right ambiguity because the streamer is rarely perfectly straight in a field setting, but dual streamers provides significantly improved locations. Both methods represent a dramatic improvement over the existing Passive Acoustic Monitoring (PAM) system for detecting low frequency baleen whale calls, with ~60 calls detected utilizing the seismic streamers, zero of which were detected using the current R/V Langseth PAM system. Furthermore, this method has the potential to be utilized not only for improving mitigation processes, but also for studying baleen whale behavior within the vicinity of seismic operations. PMID:28199400

First seismic shear wave velocity profile of the lunar crust as extracted from the Apollo 17 active seismic data by wavefield gradient analysis

NASA Astrophysics Data System (ADS)

Sollberger, David; Schmelzbach, Cedric; Robertsson, Johan O. A.; Greenhalgh, Stewart A.; Nakamura, Yosio; Khan, Amir

2016-04-01

We present a new seismic velocity model of the shallow lunar crust, including, for the first time, shear wave velocity information. So far, the shear wave velocity structure of the lunar near-surface was effectively unconstrained due to the complexity of lunar seismograms. Intense scattering and low attenuation in the lunar crust lead to characteristic long-duration reverberations on the seismograms. The reverberations obscure later arriving shear waves and mode conversions, rendering them impossible to identify and analyze. Additionally, only vertical component data were recorded during the Apollo active seismic experiments, which further compromises the identification of shear waves. We applied a novel processing and analysis technique to the data of the Apollo 17 lunar seismic profiling experiment (LSPE), which involved recording seismic energy generated by several explosive packages on a small areal array of four vertical component geophones. Our approach is based on the analysis of the spatial gradients of the seismic wavefield and yields key parameters such as apparent phase velocity and rotational ground motion as a function of time (depth), which cannot be obtained through conventional seismic data analysis. These new observables significantly enhance the data for interpretation of the recorded seismic wavefield and allow, for example, for the identification of S wave arrivals based on their lower apparent phase velocities and distinct higher amount of generated rotational motion relative to compressional (P-) waves. Using our methodology, we successfully identified pure-mode and mode-converted refracted shear wave arrivals in the complex LSPE data and derived a P- and S-wave velocity model of the shallow lunar crust at the Apollo 17 landing site. The extracted elastic-parameter model supports the current understanding of the lunar near-surface structure, suggesting a thin layer of low-velocity lunar regolith overlying a heavily fractured crust of basaltic material showing high (>0.4 down to 60 m) Poisson's ratios. Our new model can be used in future studies to better constrain the deep interior of the Moon. Given the rich information derived from the minimalistic recording configuration, our results demonstrate that wavefield gradient analysis should be critically considered for future space missions that aim to explore the interior structure of extraterrestrial objects by seismic methods. Additionally, we anticipate that the proposed shear wave identification methodology can also be applied to the routinely recorded vertical component data from land seismic exploration on Earth.

Earthquakes: Risk, Monitoring, Notification, and Research

DTIC Science & Technology

2007-02-02

Global Seismic Network (GSN). The GSN is a system of broadband digital seismographs arrayed around the globe and designed to collect high-quality...39 states face some risk from earthquakes. Seismic hazards are greatest in the western United States, particularly California, Alaska, Washington...Oregon, and Hawaii. The Rocky Mountain region, a portion of the central United States known as the New Madrid Seismic Zone, and portions of the eastern

Monitoring of Microseismicity with ArrayTechniques in the Peach Tree Valley Region

NASA Astrophysics Data System (ADS)

Garcia-Reyes, J. L.; Clayton, R. W.

2016-12-01

This study is focused on the analysis of microseismicity along the San Andreas Fault in the PeachTree Valley region. This zone is part of the transition zone between the locked portion to the south (Parkfield, CA) and the creeping section to the north (Jovilet, et al., JGR, 2014). The data for the study comes from a 2-week deployment of 116 Zland nodes in a cross-shaped configuration along (8.2 km) and across (9 km) the Fault. We analyze the distribution of microseismicity using a 3D backprojection technique, and we explore the use of Hidden Markov Models to identify different patterns of microseismicity (Hammer et al., GJI, 2013). The goal of the study is to relate the style of seismicity to the mechanical state of the Fault. The results show the evolution of seismic activity as well as at least two different patterns of seismic signals.

Induced seismicity response of hydraulic fracturing: results of a multidisciplinary monitoring at the Wysin site, Poland.

PubMed

López-Comino, J A; Cesca, S; Jarosławski, J; Montcoudiol, N; Heimann, S; Dahm, T; Lasocki, S; Gunning, A; Capuano, P; Ellsworth, W L

2018-06-05

Shale oil and gas exploitation by hydraulic fracturing experienced a strong development worldwide over the last years, accompanied by a substantial increase of related induced seismicity, either consequence of fracturing or wastewater injection. In Europe, unconventional hydrocarbon resources remain underdeveloped and their exploitation controversial. In UK, fracturing operations were stopped after the M w 2.3 Blackpool induced earthquake; in Poland, operations were halted in 2017 due to adverse oil market conditions. One of the last operated well at Wysin, Poland, was monitored independently in the framework of the EU project SHEER, through a multidisciplinary system including seismic, water and air quality monitoring. The hybrid seismic network combines surface mini-arrays, broadband and shallow borehole sensors. This paper summarizes the outcomes of the seismological analysis of these data. Shallow artificial seismic noise sources were detected and located at the wellhead active during the fracturing stages. Local microseismicity was also detected, located and characterised, culminating in two events of M w 1.0 and 0.5, occurring days after the stimulation in the vicinity of the operational well, but at very shallow depths. A sharp methane peak was detected ~19 hours after the M w 0.5 event. No correlation was observed between injected volumes, seismicity and groundwater parameters.

Illuminating sesmic discontinuities with receiver functions from a dense array in Mexico City

NASA Astrophysics Data System (ADS)

Perez-Campos, X.; Rodríguez-Domínguez, M. Á.; González-López, A.; Espindola, V. H.; Quintanar, L.; Ramirez-Guzman, L.

2017-12-01

Mexico City, with close to 10 million inhabitants, has grown over a sedimentary basin, from an old dried lake. This has been a big factor in amplifying the seismic waves from large subduction earthquakes, located > 300 km away on the Pacific coast, which represents a significant hazard. For this reason, it is of great interest to improve the knowledge of the seismic structure of the city and its details on spatial variations to reduce the uncertainty in ground motion modeling. In May 2017, such array started its way in Mexico City. It consists of 18 broadband stations, that record in place for 3-5 days, moving then to a new location. In total, the city will be covered with 343 recording sites. In this work, we present preliminary results of receiver functions obtained in such array and in permanent stations of the Seismic Network of the Valley of Mexico. Despite the few teleseismic events, the small spacing between stations ( 500 m) allows identification of converted Ps phases from the Moho discontinuity, as well as other converted phases, which might be related to subtle changes in the vertical and lateral seismic structure. This Project was funded by the Secretaria de Ciencia, Tecnología e Innovación (SECITI) of Mexico City. Project SECITI/073/2016.

Network capability estimation. Vela network evaluation and automatic processing research. Technical report. [NETWORTH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snell, N.S.

1976-09-24

NETWORTH is a computer program which calculates the detection and location capability of seismic networks. A modified version of NETWORTH has been developed. This program has been used to evaluate the effect of station 'downtime', the signal amplitude variance, and the station detection threshold upon network detection capability. In this version all parameters may be changed separately for individual stations. The capability of using signal amplitude corrections has been added. The function of amplitude corrections is to remove possible bias in the magnitude estimate due to inhomogeneous signal attenuation. These corrections may be applied to individual stations, individual epicenters, ormore » individual station/epicenter combinations. An option has been added to calculate the effect of station 'downtime' upon network capability. This study indicates that, if capability loss due to detection errors can be minimized, then station detection threshold and station reliability will be the fundamental limits to network performance. A baseline network of thirteen stations has been performed. These stations are as follows: Alaskan Long Period Array, (ALPA); Ankara, (ANK); Chiang Mai, (CHG); Korean Seismic Research Station, (KSRS); Large Aperture Seismic Array, (LASA); Mashhad, (MSH); Mundaring, (MUN); Norwegian Seismic Array, (NORSAR); New Delhi, (NWDEL); Red Knife, Ontario, (RK-ON); Shillong, (SHL); Taipei, (TAP); and White Horse, Yukon, (WH-YK).« less

Development of a Single Station 6C-Approach for Array Analysis and Microzonation: Using Vertical Rotation Rate to Estimate Love-Wave Disperion Curves and Direction Finding

NASA Astrophysics Data System (ADS)

Wassermann, J. M.; Wietek, A.; Hadziioannou, C.; Igel, H.

2014-12-01

Microzonation, i.e. the estimation of (shear) wave velocity profiles of the upper few 100m in dense 2D surface grids is one of the key methods to understand the variation in seismic hazard caused by ground shaking events. In this presentation we introduce a novel method for estimating the Love-wave phase velocity dispersion by using ambient noise recordings. We use the vertical component of rotational motions inherently present in ambient noise and the well established relation to simultaneous recordings of transverse acceleration. In this relation the frequency dependent phase velocity of a plane SH (or Love)-type wave acts as a proportionality factor between the anti-correlated amplitudes of both measures. In a first step we used synthetic data sets with increasing complexity to evaluate the proposed technique and the developed algorithm to extract the direction and amplitude of the incoming ambient noise wavefield measured at a single site. Since reliable weak rotational motion sensors are not yet readily available, we apply array derived rotation measurements in order to test our method. We next use the technique to analyze different real data sets of ambient noise measurements as well as seismic recordings at active volcanoes and compare these results with findings of the Spatial AutoCorrelation technique which was applied to the same data set. We demonstrate that the newly developed technique shows comparable results to more classical, strictly array based methods. Furthermore, we show that as soon as portable weak motion rotational motion sensors are available, a single 6C-station approach will be feasible, not only for microzonation but also for general array applications, with performance comparable to more classical techniques. An important advantage, especially in urban environments, is that with this approach, the number of seismic stations needed is drastically reduced.

Infrasound Generation from the HH Seismic Hammer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, Kyle Richard

2014-10-01

The HH Seismic hammer is a large, "weight-drop" source for active source seismic experiments. This system provides a repetitive source that can be stacked for subsurface imaging and exploration studies. Although the seismic hammer was designed for seismological studies it was surmised that it might produce energy in the infrasonic frequency range due to the ground motion generated by the 13 metric ton drop mass. This study demonstrates that the seismic hammer generates a consistent acoustic source that could be used for in-situ sensor characterization, array evaluation and surface-air coupling studies for source characterization.

Precision Seismic Monitoring of Volcanic Eruptions at Axial Seamount

NASA Astrophysics Data System (ADS)

Waldhauser, F.; Wilcock, W. S. D.; Tolstoy, M.; Baillard, C.; Tan, Y. J.; Schaff, D. P.

2017-12-01

Seven permanent ocean bottom seismometers of the Ocean Observatories Initiative's real time cabled observatory at Axial Seamount off the coast of the western United States record seismic activity since 2014. The array captured the April 2015 eruption, shedding light on the detailed structure and dynamics of the volcano and the Juan de Fuca midocean ridge system (Wilcock et al., 2016). After a period of continuously increasing seismic activity primarily associated with the reactivation of caldera ring faults, and the subsequent seismic crisis on April 24, 2015 with 7000 recorded events that day, seismicity rates steadily declined and the array currently records an average of 5 events per day. Here we present results from ongoing efforts to automatically detect and precisely locate seismic events at Axial in real-time, providing the computational framework and fundamental data that will allow rapid characterization and analysis of spatio-temporal changes in seismogenic properties. We combine a kurtosis-based P- and S-phase onset picker and time domain cross-correlation detection and phase delay timing algorithms together with single-event and double-difference location methods to rapidly and precisely (tens of meters) compute the location and magnitudes of new events with respect to a 2-year long, high-resolution background catalog that includes nearly 100,000 events within a 5×5 km region. We extend the real-time double-difference location software DD-RT to efficiently handle the anticipated high-rate and high-density earthquake activity during future eruptions. The modular monitoring framework will allow real-time tracking of other seismic events such as tremors and sea-floor lava explosions that enable the timing and location of lava flows and thus guide response research cruises to the most interesting sites. Finally, rapid detection of eruption precursors and initiation will allow for adaptive sampling by the OOI instruments for optimal recording of future eruptions. With a higher eruption recurrence rate than land-based volcanoes the Axial OOI observatory offers the opportunity to monitor and study volcanic eruptions throughout multiple cycles.

Seismic Prediction While Drilling (SPWD): Seismic exploration ahead of the drill bit using phased array sources

NASA Astrophysics Data System (ADS)

Jaksch, Katrin; Giese, Rüdiger; Kopf, Matthias

2010-05-01

In the case of drilling for deep reservoirs previous exploration is indispensable. In recent years the focus shifted more on geological structures like small layers or hydrothermal fault systems. Beside 2D- or 3D-seismics from the surface and seismic measurements like Vertical Seismic Profile (VSP) or Seismic While Drilling (SWD) within a borehole these methods cannot always resolute this structures. The resolution is worsen the deeper and smaller the sought-after structures are. So, potential horizons like small layers in oil exploration or fault zones usable for geothermal energy production could be failed or not identified while drilling. The application of a device to explore the geology with a high resolution ahead of the drill bit in direction of drilling would be of high importance. Such a device would allow adjusting the drilling path according to the real geology and would minimize the risk of discovery and hence the costs for drilling. Within the project SPWD a device for seismic exploration ahead of the drill bit will be developed. This device should allow the seismic exploration to predict areas about 50 to 100 meters ahead of the drill bit with a resolution of one meter. At the GFZ a first prototype consisting of different units for seismic sources, receivers and data loggers has been designed and manufactured. As seismic sources four standard magnetostrictive actuators and as receivers four 3-component-geophones are used. Every unit, actuator or geophone, can be rotated in steps of 15° around the longitudinal axis of the prototype to test different measurement configurations. The SPWD prototype emits signal frequencies of about 500 up to 5000 Hz which are significant higher than in VSP and SWD. An increased radiation of seismic wave energy in the direction of the borehole axis allows the view in areas to be drilled. Therefore, every actuator must be controlled independently of each other regarding to amplitude and phase of the source signal to maximize the energy of the seismic source in order to reach a sufficient exploration range. The next step for focusing is to use the method of phased array. Dependent of the seismic wave velocities of the surrounding rock, the distance of the actuators to each other and the used frequencies the signal phases for each actuator can be determined. Since one year several measurements with the prototype have been realized under defined conditions at a test site in a mine. The test site consists of a rock block surrounded from three galleries with a dimension of about 100 by 200 meters. For testing the prototype two horizontal boreholes were drilled. They are directed to one of the gallery to get a strong reflector. The quality of the data of the borehole seismics in amplitude and frequency spectra show overall a good signal-to-noise ratio and correlate strongly with the fracture density along the borehole and are associated with a lower signal-to-noise ratio. Additionally, the geophones of the prototype show reflections from ahead and rearward in the seismic data. In particular, the reflections from the gallery ahead are used for the calibration of focusing. The direct seismic wave field indicates distinct compression and shear waves. The analysis of several seismic measurements with a focus on the direct seismic waves shows that the phased array technology explicit can influence the directional characteristics of the radiated seimic waves. The amplitudes of the seismic waves can be enhanced up to three times more in the desired direction and simultaneously be attenuated in the reverse direction. A major step for the directional investigation in boreholes has accomplished. But the focusing of the seismic waves has to be improved to maximize the energy in the desired direction in more measurements by calibrating the initiating seismic signals of the sources. A next step this year is the development of a wireline prototype for application in vertical boreholes with depths not more than 2000 meters are planned. The prototype must be modified and adapted to the conditions in deep boreholes with respect to pressure and temperature. This project is funded by the German Federal Environment Ministry.

The AlpArray-CASE project: temporary broadband seismic network deployment and characterization

NASA Astrophysics Data System (ADS)

Dasović, Iva; Molinari, Irene; Stipčević, Josip; Šipka, Vesna; Salimbeni, Simone; Jarić, Dejan; Prevolnik, Snježan; Kissling, Eduard; Clinton, John; Giardini, Domenico

2017-04-01

While the northern part of the Adriatic microplate will be accurately imaged within the AlpArray project, its central and southern parts deserve detailed studies to obtain a complete picture of its structure and evolution. The Adriatic microplate forms the upper plate in the Western and Central Alps whereas it forms the lower plate in the Apennines and the Dinarides. However, the tectonics of Adriatic microplate is not well constrained and remains controversial, especially with regard to its contact with the Dinarides. The primary goal of the Central Adriatic Seismic Experiment (CASE) is to provide high quality seismological data and to shed light on seismicity and 3D lithospheric structure of the central Adriatic microplate and its boundaries. The CASE project is an international AlpArray Complementary Experiment carried out by four institutions: Department of Earth Sciences and Swiss Seismological Service of ETH Zürich (CH), Department of Geophysics and Croatian Seismological Service of Faculty of Science at University of Zagreb (HR), Republic Hydrometeorological Service of Republic of Srpska (BIH) and Istituto Nazionale di Geofisica e Vulcanologia (I). It establishes a temporary seismic network, expected to be operational at least for one year, composed by existing permanent and temporary seismic stations operated by the institutions involved and newly deployed temporary seismic stations, installed in November and December 2016, provided by ETH Zürich and INGV: five in Croatia, four in Bosnia and Herzegovina and two in Italy. In this work, we present stations sites and settings and discuss their characteristics in terms of site-effects and noise level of each station. In particular, we analyse the power spectral density estimates in order to investigate major sources of noise and background noise.

Passive (Micro-) Seismic Event Detection by Identifying Embedded "Event" Anomalies Within Statistically Describable Background Noise

NASA Astrophysics Data System (ADS)

Baziw, Erick; Verbeek, Gerald

2012-12-01

Among engineers there is considerable interest in the real-time identification of "events" within time series data with a low signal to noise ratio. This is especially true for acoustic emission analysis, which is utilized to assess the integrity and safety of many structures and is also applied in the field of passive seismic monitoring (PSM). Here an array of seismic receivers are used to acquire acoustic signals to monitor locations where seismic activity is expected: underground excavations, deep open pits and quarries, reservoirs into which fluids are injected or from which fluids are produced, permeable subsurface formations, or sites of large underground explosions. The most important element of PSM is event detection: the monitoring of seismic acoustic emissions is a continuous, real-time process which typically runs 24 h a day, 7 days a week, and therefore a PSM system with poor event detection can easily acquire terabytes of useless data as it does not identify crucial acoustic events. This paper outlines a new algorithm developed for this application, the so-called SEED™ (Signal Enhancement and Event Detection) algorithm. The SEED™ algorithm uses real-time Bayesian recursive estimation digital filtering techniques for PSM signal enhancement and event detection.

Seismologically determined bedload flux during the typhoon season.

PubMed

Chao, Wei-An; Wu, Yih-Min; Zhao, Li; Tsai, Victor C; Chen, Chi-Hsuan

2015-02-05

Continuous seismic records near river channels can be used to quantify the energy induced by river sediment transport. During the 2011 typhoon season, we deployed a seismic array along the Chishan River in the mountain area of southern Taiwan, where there is strong variability in water discharge and high sedimentation rates. We observe hysteresis in the high-frequency (5-15 Hz) seismic noise level relative to the associated hydrological parameters. In addition, our seismic noise analysis reveals an asymmetry and a high coherence in noise cross-correlation functions for several station pairs during the typhoon passage, which corresponds to sediment particles and turbulent flows impacting along the riverbed where the river bends sharply. Based on spectral characteristics of the seismic records, we also detected 20 landslide/debris flow events, which we use to estimate the sediment supply. Comparison of sediment flux between seismologically determined bedload and derived suspended load indicates temporal changes in the sediment flux ratio, which imply a complex transition process from the bedload regime to the suspension regime between typhoon passage and off-typhoon periods. Our study demonstrates the possibility of seismologically monitoring river bedload transport, thus providing valuable additional information for studying fluvial bedrock erosion and mountain landscape evolution.

Seismologically determined bedload flux during the typhoon season

PubMed Central

Chao, Wei-An; Wu, Yih-Min; Zhao, Li; Tsai, Victor C.; Chen, Chi-Hsuan

2015-01-01

Continuous seismic records near river channels can be used to quantify the energy induced by river sediment transport. During the 2011 typhoon season, we deployed a seismic array along the Chishan River in the mountain area of southern Taiwan, where there is strong variability in water discharge and high sedimentation rates. We observe hysteresis in the high-frequency (5–15 Hz) seismic noise level relative to the associated hydrological parameters. In addition, our seismic noise analysis reveals an asymmetry and a high coherence in noise cross-correlation functions for several station pairs during the typhoon passage, which corresponds to sediment particles and turbulent flows impacting along the riverbed where the river bends sharply. Based on spectral characteristics of the seismic records, we also detected 20 landslide/debris flow events, which we use to estimate the sediment supply. Comparison of sediment flux between seismologically determined bedload and derived suspended load indicates temporal changes in the sediment flux ratio, which imply a complex transition process from the bedload regime to the suspension regime between typhoon passage and off-typhoon periods. Our study demonstrates the possibility of seismologically monitoring river bedload transport, thus providing valuable additional information for studying fluvial bedrock erosion and mountain landscape evolution. PMID:25652082

Seismic aftershock monitoring for on-site inspection purposes. Experience from Integrated Field Exercise 2008.

NASA Astrophysics Data System (ADS)

Labak, P.; Arndt, R.; Villagran, M.

2009-04-01

One of the sub-goals of the Integrated Field Experiment in 2008 (IFE08) in Kazakhstan was testing the prototype elements of the Seismic aftershock monitoring system (SAMS) for on-site inspection purposes. The task of the SAMS is to collect the facts, which should help to clarify nature of the triggering event. Therefore the SAMS has to be capable to detect and identify events as small as magnitude -2 in the inspection area size up to 1000 km2. Equipment for 30 mini-arrays and 10 3-component stations represented the field equipment of the SAMS. Each mini-array consisted of a central 3-component seismometer and 3 vertical seismometers at the distance about 100 m from the central seismometer. The mini-arrays covered approximately 80% of surrogate inspection area (IA) on the territory of former Semipalatinsk test site. Most of the stations were installed during the first four days of field operations by the seismic sub-team, which consisted of 10 seismologists. SAMS data center comprised 2 IBM Blade centers and 8 working places for data archiving, detection list production and event analysis. A prototype of SAMS software was tested. Average daily amount of collected raw data was 15-30 GB and increased according to the amount of stations entering operation. Routine manual data screening and data analyses were performed by 2-6 subteam members. Automatic screening was used for selected time intervals. Screening was performed using the Sonoview program in frequency domain and using the Geotool and Hypolines programs for screening in time domain. The screening results were merged into the master event list. The master event list served as a basis of detailed analysis of unclear events and events identified to be potentially in the IA. Detailed analysis of events to be potentially in the IA was performed by the Hypoline and Geotool programs. In addition, the Hyposimplex and Hypocenter programs were also used for localization of events. The results of analysis were integrated in the visual form using the Seistrain/geosearch program. Data were fully screened for the period 5.-13.9.2008. 360 teleseismic, regional and local events were identified. Results of the detection and analysis will be presented and consequences for further SAMS development will be discussed.

New Insights on the Structure of the Cascadia Subduction Zone from Amphibious Seismic Data

NASA Astrophysics Data System (ADS)

Janiszewski, Helen Anne

A new onshore-offshore seismic dataset from the Cascadia subduction zone was used to characterize mantle lithosphere structure from the ridge to the volcanic arc, and plate interface structure offshore within the seismogenic zone. The Cascadia Initiative (CI) covered the Juan de Fuca plate offshore the northwest coast of the United States with an ocean bottom seismometer (OBS) array for four years; this was complemented by a simultaneous onshore seismic array. Teleseismic data recorded by this array allows the unprecedented imaging of an entire tectonic plate from its creation at the ridge through subduction initiation and back beyond the volcanic arc along the entire strike of the Cascadia subduction zone. Higher frequency active source seismic data also provides constraints on the crustal structure along the plate interface offshore. Two seismic datasets were used to image the plate interface structure along a line extending 100 km offshore central Washington. These are wide-angle reflections from ship-to-shore seismic data from the Ridge-To-Trench seismic cruise and receiver functions calculated from a densely spaced CI OBS focus array in a similar region. Active source seismic observations are consistent with reflections from the plate interface offshore indicating the presence of a P-wave velocity discontinuity. Until recently, there has been limited success in using the receiver function technique on OBS data. I avoid these traditional challenges by using OBS constructed with shielding deployed in shallow water on the continental shelf. These data have quieter horizontals and avoid water- and sediment-multiple contamination at the examined frequencies. The receiver functions are consistently modeled with a velocity structure that has a low velocity zone (LVZ) with elevated P to S-wave velocity ratios at the plate interface. A similar LVZ structure has been observed onshore and interpreted as a combination of elevated pore-fluid pressures or metasediments. This new offshore result indicates that the structure may persist updip indicating the plate interface may be weak. To focus more broadly on the entire subduction system, I calculate phase velocities from teleseismic Rayleigh waves from 20-100 s period across the entire onshore-offshore array. The shear-wave velocity model calculated from these data can provide constrains on the thermal structure of the lithosphere both prior to and during subduction of the Juan de Fuca plate. Using OBS data in this period band requires removal of tilt and compliance noise, two types of water-induced noise that affect long period data. To facilitate these corrections on large seismic arrays such as the CI, an automated quality control routine was developed for selecting noise windows for the calculation of the required transfer functions. These corrections typically involve either averaging out transient signals, which requires the assumption of stationarity of the noise over the long periods of time, or laborious hand selection of noise segments. This new method calculates transfer functions based on daily time series that exclude transient signals, but allows for the investigation of long-term variation over the course of an instrument's deployment. I interpret these new shoreline-crossing phase velocity maps in terms of the tectonics associated with the Cascadia subduction system. Major findings include that oceanic plate cooling models do not explain the velocities observed beneath the Juan de Fuca plate, that slow velocities in the forearc appear to be more prevalent in areas modeled to have experienced high slip in past Cascadia megathrust earthquakes, and along strike variations in phase velocity reflect variations in arc structure and backarc tectonics.

Seismic Tomography and the Development of a State Velocity Profile

NASA Astrophysics Data System (ADS)

Marsh, S. J.; Nakata, N.

2017-12-01

Earthquakes have been a growing concern in the State of Oklahoma in the last few years and as a result, accurate earthquake location is of utmost importance. This means using a high resolution velocity model with both lateral and vertical variations. Velocity data is determined using ambient noise seismic interferometry and tomography. Passive seismic data was acquired from multiple IRIS networks over the span of eight years (2009-2016) and filtered for earthquake removal to obtain the background ambient noise profile for the state. Seismic Interferometry is applied to simulate ray paths between stations, this is done with each possible station pair for highest resolution. Finally the method of seismic tomography is used to extract the velocity data and develop the state velocity map. The final velocity profile will be a compilation of different network analyses due to changing station availability from year to year. North-Central Oklahoma has a dense seismic network and has been operating for the past few years. The seismic stations are located here because this is the most seismically active region. Other parts of the state have not had consistent coverage from year to year, and as such a reliable and high resolution velocity profile cannot be determined from this network. However, the Transportable Array (TA) passed through Oklahoma in 2014 and provided a much wider and evenly spaced coverage. The goal of this study is to ultimately combine these two arrays over time, and provide a high quality velocity profile for the State of Oklahoma.

Seismic Noise Characterization in the Northern Mississippi Embayment

NASA Astrophysics Data System (ADS)

Wiley, S.; Deshon, H. R.; Boyd, O. S.

2009-12-01

We present a study of seismic noise sources present within the northern Mississippi embayment near the New Madrid Seismic Zone (NMSZ). The northern embayment contains up to 1 km of unconsolidated coastal plain sediments overlying bedrock, making it an inherently noisy environment for seismic stations. The area is known to display high levels of cultural noise caused by agricultural activity, passing cars, trains, etc. We characterize continuous broadband seismic noise data recorded for the months of March through June 2009 at six stations operated by the Cooperative New Madrid Seismic Network. We looked at a single horizontal component of data during nighttime hours, defined as 6:15PM to 5:45AM Central Standard Time, which we determined to be the lowest amplitude period of noise for the region. Hourly median amplitudes were compared to daily average wind speeds downloaded from the National Oceanic and Atmospheric Administration. We find a correlation between time periods of increased noise and days with high wind speeds, suggesting that wind is likely a prevalent source of seismic noise in the area. The effects of wind on seismic recordings may result from wind induced tree root movement which causes ground motion to be recorded at the vaults located ~3m below ground. Automated studies utilizing the local network or the EarthScope Transportable Array, scheduled to arrive in the area in 2010-11, should expect to encounter wind induced noise fluctuations and must account for this in their analysis.

Data quality control and tools in passive seismic experiments exemplified on the Czech broadband seismic pool MOBNET in the AlpArray collaborative project

NASA Astrophysics Data System (ADS)

Vecsey, Luděk; Plomerová, Jaroslava; Jedlička, Petr; Munzarová, Helena; Babuška, Vladislav; AlpArray Working Group

2017-12-01

This paper focuses on major issues related to the data reliability and network performance of 20 broadband (BB) stations of the Czech (CZ) MOBNET (MOBile NETwork) seismic pool within the AlpArray seismic experiments. Currently used high-resolution seismological applications require high-quality data recorded for a sufficiently long time interval at seismological observatories and during the entire time of operation of the temporary stations. In this paper we present new hardware and software tools we have been developing during the last two decades while analysing data from several international passive experiments. The new tools help to assure the high-quality standard of broadband seismic data and eliminate potential errors before supplying data to seismological centres. Special attention is paid to crucial issues like the detection of sensor misorientation, timing problems, interchange of record components and/or their polarity reversal, sensor mass centring, or anomalous channel amplitudes due to, for example, imperfect gain. Thorough data quality control should represent an integral constituent of seismic data recording, preprocessing, and archiving, especially for data from temporary stations in passive seismic experiments. Large international seismic experiments require enormous efforts from scientists from different countries and institutions to gather hundreds of stations to be deployed in the field during a limited time period. In this paper, we demonstrate the beneficial effects of the procedures we have developed for acquiring a reliable large set of high-quality data from each group participating in field experiments. The presented tools can be applied manually or automatically on data from any seismic network.

The Caucasus Seismic Network (CNET): Seismic Structure of the Greater and Lesser Caucasus

NASA Astrophysics Data System (ADS)

Sandvol, E. A.; Mackey, K. G.; Nabelek, J.; Yetermishli, G.; Godoladze, T.; Babayan, H.; Malovichko, A.

2017-12-01

The Greater Caucasus are a portion of the Alpine-Himalayan mountain belt that has undergone rapid uplift in the past 5 million years, thus serving as a unique natural laboratory to study the early stages of orogenesis. Relatively lower resolution seismic velocity models of this region show contradictory lateral variability. Furthermore, recent waveform modeling of seismograms has clearly demonstrated the presence of deep earthquakes (with a maximum hypocentral depth of 175 km) below the Greater Caucasus. The region has been largely unexplored in terms of the detailed uppermost mantle and crustal seismic structure due in part to the disparate data sets that have not yet been merged as well as key portions being sparsely instrumented. We have established collaborative agreements across the region. Building on these agreements we recently deployed a major multi-national seismic array across the Greater Caucasus to address fundamental questions about the nature of continental deformation in this poorly understood region. Our seismic array has two components: (1) a grid of stations spanning the entire Caucasus and (2) two seismic transects consisting of stations spaced at distances of less than 10 km that cross the Greater Caucasus. In addition to the temporary stations, we are working to integrate data from the national networks to produce high resolution images of the seismic structure. Using data from over 106 new seismic stations in Azerbaijan, Armenia, Russia, and Georgia, we hope to gain a better understanding of the recent uplift ( 5 Ma) of the Greater Caucasus and the nature of seismogenic deformation in the region.

Broadband calibration of the R/V Marcus G. Langseth four-string seismic sources

NASA Astrophysics Data System (ADS)

Tolstoy, M.; Diebold, J.; Doermann, L.; Nooner, S.; Webb, S. C.; Bohnenstiehl, D. R.; Crone, T. J.; Holmes, R. C.

2009-08-01

The R/V Marcus G. Langseth is the first 3-D seismic vessel operated by the U.S. academic community. With up to a four-string, 36-element source and four 6-km-long solid state hydrophone arrays, this vessel promises significant new insights into Earth science processes. The potential impact of anthropogenic sound sources on marine life is an important topic to the marine seismic community. To ensure that operations fully comply with existing and future marine mammal permitting requirements, a calibration experiment was conducted in the Gulf of Mexico in 2007-2008. Results are presented from deep (˜1.6 km) and shallow (˜50 m) water sites, obtained using the full 36-element (6600 cubic inches) seismic source. This array configuration will require the largest safety radii, and the deep and shallow sites provide two contrasting operational environments. Results show that safety radii and the offset between root-mean-square and sound exposure level measurements were highly dependent on water depth.

Multimodal approach to seismic pavement testing

USGS Publications Warehouse

Ryden, N.; Park, C.B.; Ulriksen, P.; Miller, R.D.

2004-01-01

A multimodal approach to nondestructive seismic pavement testing is described. The presented approach is based on multichannel analysis of all types of seismic waves propagating along the surface of the pavement. The multichannel data acquisition method is replaced by multichannel simulation with one receiver. This method uses only one accelerometer-receiver and a light hammer-source, to generate a synthetic receiver array. This data acquisition technique is made possible through careful triggering of the source and results in such simplification of the technique that it is made generally available. Multiple dispersion curves are automatically and objectively extracted using the multichannel analysis of surface waves processing scheme, which is described. Resulting dispersion curves in the high frequency range match with theoretical Lamb waves in a free plate. At lower frequencies there are several branches of dispersion curves corresponding to the lower layers of different stiffness in the pavement system. The observed behavior of multimodal dispersion curves is in agreement with theory, which has been validated through both numerical modeling and the transfer matrix method, by solving for complex wave numbers. ?? ASCE / JUNE 2004.

Teleseismic Array Studies of Earth's Core-Mantle Boundary

NASA Astrophysics Data System (ADS)

Alexandrakis, Catherine

2011-12-01

The core mantle boundary (CMB) is an inaccessible and complex region, knowledge of which is vital to our understanding of many Earth processes. Above it is the heterogeneous lower-mantle. Below the boundary is the outer-core, composed of liquid iron, and/or nickel and some lighter elements. Elucidation of how these two distinct layers interact may enable researchers to better understand the geodynamo, global tectonics, and overall Earth history. One parameter that can be used to study structure and limit potential chemical compositions is seismic-wave velocity. Current global-velocity models have significant uncertainties in the 200 km above and below the CMB. In this thesis, these regions are studied using three methods. The upper outer core is studied using two seismic array methods. First, a modified vespa, or slant-stack method is applied to seismic observations at broadband seismic arrays, and at large, dense groups of broadband seismic stations dubbed 'virtual' arrays. Observations of core-refracted teleseismic waves, such as SmKS, are used to extract relative arrivaltimes. As with previous studies, lower -mantle heterogeneities influence the extracted arrivaltimes, giving significant scatter. To remove raypath effects, a new method was developed, called Empirical Transfer Functions (ETFs). When applied to SmKS waves, this method effectively isolates arrivaltime perturbations caused by outer core velocities. By removing raypath effects, the signals can be stacked further reducing scatter. The results of this work were published as a new 1D outer-core model, called AE09. This model describes a well-mixed outer core. Two array methods are used to detect lower mantle heterogeneities, in particular Ultra-Low Velocity Zones (ULVZs). The ETF method and beam forming are used to isolate a weak P-wave that diffracts along the CMB. While neither the ETF method nor beam forming could adequately image the low-amplitude phase, beam forms of two events indicate precursors to the SKS and SKKS phase, which may be ULVZ indicators. Finally, cross-correlated observed and modelled beams indicate a tendency towards a ULVZ-like lower mantle in the study region.

High-Resolution Fault Zone Monitoring and Imaging Using Long Borehole Arrays

NASA Astrophysics Data System (ADS)

Paulsson, B. N.; Karrenbach, M.; Goertz, A. V.; Milligan, P.

2004-12-01

Long borehole seismic receiver arrays are increasingly used in the petroleum industry as a tool for high--resolution seismic reservoir characterization. Placing receivers in a borehole avoids the distortion of reflected seismic waves by the near-surface weathering layer which leads to greatly improved vector fidelity and a much higher frequency content of 3-component recordings. In addition, a borehole offers a favorable geometry to image near-vertically dipping or overturned structure such as, e.g., salt flanks or faults. When used for passive seismic monitoring, long borehole receiver arrays help reducing depth uncertainties of event locations. We investigate the use of long borehole seismic arrays for high-resolution fault zone characterization in the vicinity of the San Andreas Fault Observatory at Depth (SAFOD). We present modeling scenarios to show how an image of the vertically dipping fault zone down to the penetration point of the SAFOD well can be obtained by recording surface sources in a long array within the deviated main hole. We assess the ability to invert fault zone reflections for rock physical parameters by means of amplitude versus offset or angle (AVO/AVA) analyzes. The quality of AVO/AVA studies depends on the ability to illuminate the fault zone over a wide range of incidence angles. We show how the length of the receiver array and the receiver spacing within the borehole influence the size of the volume over which reliable AVO/AVA information could be obtained. By means of AVO/AVA studies one can deduce hydraulic properties of the fault zone such as the type of fluids that might be present, the porosity, and the fluid saturation. Images of the fault zone obtained from a favorable geometry with a sufficient illumination will enable us to map fault zone properties in the surrounding of the main hole penetration point. One of the targets of SAFOD is to drill into an active rupture patch of an earthquake cluster. The question of whether or not this goal has indeed been achieved at the time the fault zone is penetrated can only be answered if the rock properties found at the penetration point can be compared to the surrounding volume. This task will require mapping of rock properties inverted from AVO/AVA analyzes of fault zone reflections. We will also show real data examples of a test deployment of a 4000 ft, 80-level clamped 3-component receiver array in the SAFOD main hole in 2004.

Combination of different seismic methods and geotechnical sounding for a rapid characterization of the near-surface ground

NASA Astrophysics Data System (ADS)

Dietrich, P.; Kretschmer, F.; Vienken, T.; Popp, S.

2009-04-01

For economical and feasible seismic exploration of the near-surface ground, an approach has been developed for the joint application of reflection and refraction seismics as well as multi-channel analysis of surface waves (MASW). The measuring concept was tested within the research project COMEXTECH, dealing with the exploration of construction ground. Besides the overall characterization of the subsurface by refraction and reflection seismics, the MASW can be used for the derivation of relevant soil parameters such as soil stiffness. The centre of the measuring concept represents a land streamer, pulled by a vehicle equipped with the seismic source. The 24-channel land streamer may be tipped with different geophones, according to the focus of investigation. We used three fully equipped land streamers with 72 channels at all at the test site Nauen close to Berlin, Germany. The first 24 positions of the land streamer nearby the seismic source were filled with 4.5 Hz geophones. The next two land streamers were tipped with 14 Hz geophones, respectively. The idea behind this arrangement is that the positions close to the shot point, which are not utilisable for reflection seismics, can be used for the interpretation of surface waves. The signal was given with an accelerated weight drop mounted on a cross-country vehicle. Shots were arranged every meter, and four shots per shot point were executed for an increased signal/noise ratio. Three registration units (GeodeTM by Geometrics) were connected in series for signal recording. At the site, a profile of 164 m length was investigated in bidirectional manner in combination with geotechnical exploration technique. The purpose of bidirectional recording is to check the reliability and sensitivity of the seismic array and to increase the resolution of the image of the subsurface. By using the same shot points forth and back, a multiple overlap rate for certain common depth points (CDP) can be achieved, which is thought to result in an increased data quality. Geotechnical investigations comprise the use of Cone Penetrating Tests (CPT) for characterization of properties of the subsurface. Thereby the lithology may be derived by means of the friction ratio, which represents the ratio of the in-situ determined parameters of sleeve friction and cone resistance during CPT soundings. First results of data processing are available for the interpolated shear wave velocities (Vs) of the analysis of the Rayleigh-type surface waves on a multichannel record (MASW) by using the program SURFSEIS. The velocities are more or less laterally layered with zones of lower velocities (<180 m/s) in the upper subsurface and in about 5 m depth at the southern part of the profile. The strong increase of shear-wave velocities in 10 m depth and below (>250 m/s) is supposed to correspondent to a glacial moraine underlying the sandy sediments. The characterization of the near-surface ground by MASW corresponds well with the results of the nearby CPT soundings. By comparing the MASW results of the forward and backward recording of the profile, however, it turns out that the methodical approach of bidirectional seismic measurements still needs some tests. The produced 2-D Vs profiles show some marginal differences in the Vs-distribution in detail. Processing of seismic refraction and reflection data are in progress yet. In summery, the land streamer has the real advantage of fast data recording with a variable geophone array for different applications. The slight loss in quality of seismic data does not limit the use of the land streamer even on arable land. If carefully performed, geophones fitted on the land streamer still record data in an adequate quality for a feasible characterization of the subsurface, as shown in our study. Especially along long profiles the employment of a land streamer outplays stuck geophones by the fast progress in data recording due to the pulled array of geophones in a fixed geometry.

Seismic surveys test on Innerhytta Pingo, Adventdalen, Svalbard Islands

NASA Astrophysics Data System (ADS)

Boaga, Jacopo; Rossi, Giuliana; Petronio, Lorenzo; Accaino, Flavio; Romeo, Roberto; Wheeler, Walter

2015-04-01

We present the preliminary results of an experimental full-wave seismic survey test conducted on the Innnerhytta a Pingo, located in the Adventdalen, Svalbard Islands, Norway. Several seismic surveys were adopted in order to study a Pingo inner structure, from classical reflection/refraction arrays to seismic tomography and surface waves analysis. The aim of the project IMPERVIA, funded by Italian PNRA, was the evaluation of the permafrost characteristics beneath this open-system Pingo by the use of seismic investigation, evaluating the best practice in terms of logistic deployment. The survey was done in April-May 2014: we collected 3 seismic lines with different spacing between receivers (from 2.5m to 5m), for a total length of more than 1 km. We collected data with different vertical geophones (with natural frequency of 4.5 Hz and 14 Hz) as well as with a seismic snow-streamer. We tested different seismic sources (hammer, seismic gun, fire crackers and heavy weight drop), and we verified accurately geophone coupling in order to evaluate the different responses. In such peculiar conditions we noted as fire-crackers allow the best signal to noise ratio for refraction/reflection surveys. To ensure the best geophones coupling with the frozen soil, we dug snow pits, to remove the snow-cover effect. On the other hand, for the surface wave methods, the very high velocity of the permafrost strongly limits the generation of long wavelengths both with these explosive sources as with the common sledgehammer. The only source capable of generating low frequencies was a heavy drop weight system, which allows to analyze surface wave dispersion below 10 Hz. Preliminary data analysis results evidence marked velocity inversions and strong velocity contrasts in depth. The combined use of surface and body waves highlights the presence of a heterogeneous soil deposit level beneath a thick layer of permafrost. This is the level that hosts the water circulation from depth controlling the Pingo structure evolution.

Field test investigation of high sensitivity fiber optic seismic geophone

NASA Astrophysics Data System (ADS)

Wang, Meng; Min, Li; Zhang, Xiaolei; Zhang, Faxiang; Sun, Zhihui; Li, Shujuan; Wang, Chang; Zhao, Zhong; Hao, Guanghu

2017-10-01

Seismic reflection, whose measured signal is the artificial seismic waves ,is the most effective method and widely used in the geophysical prospecting. And this method can be used for exploration of oil, gas and coal. When a seismic wave travelling through the Earth encounters an interface between two materials with different acoustic impedances, some of the wave energy will reflect off the interface and some will refract through the interface. At its most basic, the seismic reflection technique consists of generating seismic waves and measuring the time taken for the waves to travel from the source, reflect off an interface and be detected by an array of geophones at the surface. Compared to traditional geophones such as electric, magnetic, mechanical and gas geophone, optical fiber geophones have many advantages. Optical fiber geophones can achieve sensing and signal transmission simultaneously. With the development of fiber grating sensor technology, fiber bragg grating (FBG) is being applied in seismic exploration and draws more and more attention to its advantage of anti-electromagnetic interference, high sensitivity and insensitivity to meteorological conditions. In this paper, we designed a high sensitivity geophone and tested its sensitivity, based on the theory of FBG sensing. The frequency response range is from 10 Hz to 100 Hz and the acceleration of the fiber optic seismic geophone is over 1000pm/g. sixteen-element fiber optic seismic geophone array system is presented and the field test is performed in Shengli oilfield of China. The field test shows that: (1) the fiber optic seismic geophone has a higher sensitivity than the traditional geophone between 1-100 Hz;(2) The low frequency reflection wave continuity of fiber Bragg grating geophone is better.

Magnetotelluric Investigation of Melt Storage Beneath Okmok Caldera, Alaska

NASA Astrophysics Data System (ADS)

Bennington, N. L.; Bedrosian, P.; Key, K.; Zelenak, G.

2015-12-01

Alaska accounts for nearly 99% of the seismic moment release within the US. Much of this is associated with the Aleutian volcanic arc, the most tectonically active region in North America, and an ideal location for studying arc magmatism. Okmok is an active volcano located in the central Aleutian arc, defined by a pair of nested, 10 km diameter calderas. The subdued topography of Okmok, relative to other Aleutian volcanoes, improves access and permits dense sampling within the caldera closer to the underlying magmatic system. Okmok volcano was selected as the site of study for this project due to frequent volcanic activity and the presence of a crustal magma reservoir as inferred from previous coarse resolution seismic studies. In June-July 2015, we carried out an amphibious geophysical field deployment at Okmok. Onshore work in and around the volcano included collection of an array of magnetotelluric (MT) stations and installation of a temporary, year-long seismic array. A ring of 3D offshore MT deployments made around the island augments the onshore array. An additional 2D tectonic-scale profile spans the trench, volcanic arc, and backarc. This new geophysical data will be used to gain a greater understanding of Aleutian arc melt generation, migration, and storage beneath an active caldera. We present results from the analysis of the newly collected amphibious 3D MT data. This data will be used to model the distribution and migration of melt within Okmok's crustal magma reservoir. Initial processing of the data shows strong MT signal levels, in particular from a geomagnetic storm that occurred from June 21-23, 2015. A companion abstract discussing the 2D tectonic scale MT profile, which constrains the mantle and deep crust beneath Okmok volcano, is discussed by Zelenak et al.

Blind Source Separation of Seismic Events with Independent Component Analysis: CTBT related exercise

NASA Astrophysics Data System (ADS)

Rozhkov, Mikhail; Kitov, Ivan

2015-04-01

Blind Source Separation (BSS) methods used in signal recovery applications are attractive for they use minimal a priori information about the signals they are dealing with. Homomorphic deconvolution and cepstrum estimation are probably the only methods used in certain extent in CTBT applications that can be attributed to the given branch of technology. However Expert Technical Analysis (ETA) conducted in CTBTO to improve the estimated values for the standard signal and event parameters according to the Protocol to the CTBT may face problems which cannot be resolved with certified CTBTO applications and may demand specific techniques not presently used. The problem to be considered within the ETA framework is the unambiguous separation of signals with close arrival times. Here, we examine two scenarios of interest: (1) separation of two almost co-located explosions conducted within fractions of seconds, and (2) extraction of explosion signals merged with wavetrains from strong earthquake. The importance of resolving the problem related to case 1 is connected with the correct explosion yield estimation. Case 2 is a well-known scenario of conducting clandestine nuclear tests. While the first case can be approached somehow with the means of cepstral methods, the second case can hardly be resolved with the conventional methods implemented at the International Data Centre, especially if the signals have close slowness and azimuth. Independent Component Analysis (in its FastICA implementation) implying non-Gaussianity of the underlying processes signal's mixture is a blind source separation method that we apply to resolve the mentioned above problems. We have tested this technique with synthetic waveforms, seismic data from DPRK explosions and mining blasts conducted within East-European platform as well as with signals from strong teleseismic events (Sumatra, April 2012 Mw=8.6, and Tohoku, March 2011 Mw=9.0 earthquakes). The data was recorded by seismic arrays of the International Monitoring System of CTBTO and by small-aperture seismic array Mikhnevo (MHVAR) operated by the Institute of Geosphere Dynamics, Russian Academy of Sciences. Our approach demonstrated a good ability of separation of seismic sources with very close origin times and locations (hundreds of meters), and/or having close arrival times (fractions of seconds), and recovering their waveforms from the mixture. Perspectives and limitations of the method are discussed.

Crustal structure of the Kaapvaal craton and its significance for early crustal evolution

NASA Astrophysics Data System (ADS)

James, David E.; Niu, Fenglin; Rokosky, Juliana

2003-12-01

High-quality seismic data obtained from a dense broadband array near Kimberley, South Africa, exhibit crustal reverberations of remarkable clarity that provide well-resolved constraints on the structure of the lowermost crust and Moho. Receiver function analysis of Moho conversions and crustal multiples beneath the Kimberley array shows that the crust is 35 km thick with an average Poisson's ratio of 0.25. The density contrast across the Moho is ˜15%, indicating a crustal density about 2.86 gm/cc just above the Moho, appropriate for felsic to intermediate rock compositions. Analysis of waveform broadening of the crustal reverberation phases suggests that the Moho transition can be no more than 0.5 km thick and the total variation in crustal thickness over the 2400 km 2 footprint of the array no more than 1 km. Waveform and travel time analysis of a large earthquake triggered by deep gold mining operations (the Welkom mine event) some 200 km away from the array yield an average crustal thickness of 35 km along the propagation path between the Kimberley array and the event. P- and S-wave velocities for the lowermost crust are modeled to be 6.75 and 3.90 km/s, respectively, with uppermost mantle velocities of 8.2 and 4.79 km/s, respectively. Seismograms from the Welkom event exhibit theoretically predicted but rarely observed crustal reverberation phases that involve reflection or conversion at the Moho. Correlation between observed and synthetic waveforms and phase amplitudes of the Moho reverberations suggests that the crust along the propagation path between source and receiver is highly uniform in both thickness and average seismic velocity and that the Moho transition zone is everywhere less than about 2 km thick. While the extremely flat Moho, sharp transition zone and low crustal densities beneath the region of study may date from the time of crustal formation, a more geologically plausible interpretation involves extensive crustal melting and ductile flow during the major craton-wide Ventersdorp tectonomagmatic event near the end of Archean time.

Geographic boundary of the “Pacific Anomaly” near the Earth’s core-mantle boundary

NASA Astrophysics Data System (ADS)

He, Y.; Wen, L.

2009-12-01

Seismic tomography have revealed a broad, seismically low velocity anomaly in the Earth’s lower mantle beneath the Pacific (we term it the “Pacific Anomaly”), surrounded by the circum-Pacific high velocity zone. Here, we determine geographical boundary and average shear velocity structure of the Pacific Anomaly near the core-mantle boundary based on travel time analysis of ScSH-SH and ScS2-SS phases. We further constrain the detailed structure of the transition from the base of the Pacific Anomaly to the northern high velocity zone along two perpendicular cross sections on the basis of forward waveform modeling of the seismic data. Two cross-sections include one great arc across the Anomaly from New Zealand to Alaska and another from Solomon Islands to North America. Our seismic data are collected from those recorded in the China National Digital Seismographic Network, and many permanent and temporal arrays from the Incorporated Research Institutions for Seismology. The observed ScS-SH and ScS2-SS differential travel time residuals allow the entire geographic boundary of the anomaly to be clearly defined. The seismic data suggest that the average shear velocity reduction inside the anomaly reaches -5% in the lowermost 300 km of the mantle. Waveform analysis of the seismic data sampling the edge of the anomaly further validates the model of the boundary previously deduced by differential-travel-time-residual data, and suggests that the northern boundary is characterized by a shear velocity model with the low-velocity region accompanied by a high velocity structure.

Seismic Strong Motion Array Project (SSMAP) to Record Future Large Earthquakes in the Nicoya Peninsula area, Costa Rica

NASA Astrophysics Data System (ADS)

Simila, G.; McNally, K.; Quintero, R.; Segura, J.

2006-12-01

The seismic strong motion array project (SSMAP) for the Nicoya Peninsula in northwestern Costa Rica is composed of 10 13 sites including Geotech A900/A800 accelerographs (three-component), Ref-Teks (three- component velocity), and Kinemetric Episensors. The main objectives of the array are to: 1) record and locate strong subduction zone mainshocks [and foreshocks, "early aftershocks", and preshocks] in Nicoya Peninsula, at the entrance of the Nicoya Gulf, and in the Papagayo Gulf regions of Costa Rica, and 2) record and locate any moderate to strong upper plate earthquakes triggered by a large subduction zone earthquake in the above regions. Our digital accelerograph array has been deployed as part of our ongoing research on large earthquakes in conjunction with the Earthquake and Volcano Observatory (OVSICORI) at the Universidad Nacional in Costa Rica. The country wide seismographic network has been operating continuously since the 1980's, with the first earthquake bulletin published more than 20 years ago, in 1984. The recording of seismicity and strong motion data for large earthquakes along the Middle America Trench (MAT) has been a major research project priority over these years, and this network spans nearly half the time of a "repeat cycle" (50 years) for large (Ms 7.5- 7.7) earthquakes beneath the Nicoya Peninsula, with the last event in 1950. Our long time co-collaborators include the seismology group OVSICORI, with coordination for this project by Dr. Ronnie Quintero and Mr. Juan Segura. Numerous international investigators are also studying this region with GPS and seismic stations (US, Japan, Germany, Switzerland, etc.). Also, there are various strong motion instruments operated by local engineers, for building purposes and mainly concentrated in the population centers of the Central Valley. The major goal of our project is to contribute unique scientific information pertaining to a large subduction zone earthquake and its related seismic activity when the next large earthquake occurs in Nicoya. A centralized data base will be created within the main seismic network files at OVSICORI, with various local personnel working in teams that will be responsible to collect data within 3 days following a large mainshock.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ford, Sean R.; Walter, William R.

Seismic waveform correlation offers the prospect of greatly reducing event detection thresholds when compared with more conventional processing methods. Correlation is applicable for seismic events that in some sense repeat, that is they have very similar waveforms. A number of recent studies have shown that correlated seismic signals may form a significant fraction of seismicity at regional distances. For the particular case of multiple nuclear explosions at the same test site, regional distance correlation also allows very precise relative location measurements and could offer the potential to lower thresholds when multiple events exist. Using the Comprehensive Nuclear-Test-Ban Treaty (CTBT) Internationalmore » Monitoring System (IMS) seismic array at Matsushiro, Japan (MJAR), Gibbons and Ringdal (2012) were able to create a multichannel correlation detector with a very low false alarm rate and a threshold below magnitude 3.0. They did this using the 2006 or 2009 Democratic People’s Republic of Korea (DPRK) nuclear explosion as a template to search through a data stream from the same station to find a match via waveform correlation. In this paper, we extend the work of Gibbons and Ringdal (2012) and measure the correlation detection threshold at several other IMS arrays. We use this to address three main points. First, we show the IMS array station at Mina, Nevada (NVAR), which is closest to the Nevada National Security Site (NNSS), is able to detect a chemical explosion that is well under 1 ton with the right template. Second, we examine the two IMS arrays closest to the North Korean (DPRK) test site (at Ussuriysk, Russian Federation [USRK] and Wonju, Republic of Korea [KSRS]) to show that similarly low thresholds are possible when the right templates exist. We also extend the work of Schaff et al. (2012) and measure the correlation detection threshold at the nearest Global Seismic Network (GSN) three-component station (MDJ) at Mudanjiang, Heilongjiang Province, China, from the New China Digital Seismograph Network (IC). To conclude, we use these results to explore the recent claim by Zhang and Wen (2015) that the DPRK conducted “…a low-yield nuclear test…” on 12 May 2010.« less

2015 Volcanic Tsunami Earthquake near Torishima Island: Array analysis of ocean bottom pressure gauge records

NASA Astrophysics Data System (ADS)

Fukao, Y.; Sugioka, H.; Ito, A.; Shiobara, H.; Sandanbata, O.; Watada, S.; Satake, K.

2016-12-01

An array of ocean bottom pressure gauges was deployed off east of Aogashima island of the Izu-Bonin arc from May 2014 to May 2015. The array consists of 10 ocean bottom pressure gauges using ParoScientific quartz resonators which can measure absolute water pressure at 7000m depth with nano-resolution. The array configures equilateral triangles with minimum and maximum lengths of 10 and 30km. This array recorded seismic and tsunami waves from the CLVD-type earthquake (M5.7) of May 02, 2015, that occurred near Torishima Island 100 km distant from the array. Comparison with records of ordinary thrust earthquakes with similar magnitudes at similar distances indicates that this event generated anomalously large tsunamis relative to seismic waves. We made an array analysis for the phase speed, propagating azimuth and travel time of tsunami wave in a frequency range 1-10 mHz, where the dispersion effect is significant. The results show excellent agreements with the frequency-dependent ray-tracing calculations. The tsunami trace apparently starts with positive onset (pressure increase) and reaches a maximum amplitude of about 200Pa (≈2cm in tsunami height). A closer inspection, however, shows a preceding negative small pulse (Fig. 1), suggesting that the seafloor deformation at the tsunami source consists of a central large uplift and a peripheral small depression. This mode of deformation is qualitatively consistent with a finite CLVD source uniformly shortened laterally and uniformly stretched vertically without volume change. The detection of weak initial motions is indebted to the array deployment of sensitive pressure gauges far away from coastal regions. The bandpass-filtered waveform is drastically different between the lower and higher frequency ranges. The waveform is single-peaked in the lower frequency range (<5 mHz) but is ringing in the higher frequency range (>5 mHz), corresponding to the tsunami spectrum that consists of the broad primary peak around 3.5 mHz and the sharp double peaks at around 6.5 and 9 mHz. We interpret the broad primary peak as due to the tsunami source associated with seafloor deformation and the sharp double peaks as due to wave resonance (seiche) inside the Smith Caldera.

Characteristic Analysis of Air-gun Source Wavelet based on the Vertical Cable Data

NASA Astrophysics Data System (ADS)

Xing, L.

2016-12-01

Air guns are important sources for marine seismic exploration. Far-field wavelets of air gun arrays, as a necessary parameter for pre-stack processing and source models, plays an important role during marine seismic data processing and interpretation. When an air gun fires, it generates a series of air bubbles. Similar to onshore seismic exploration, the water forms a plastic fluid near the bubble; the farther the air gun is located from the measurement, the more steady and more accurately represented the wavelet will be. In practice, hydrophones should be placed more than 100 m from the air gun; however, traditional seismic cables cannot meet this requirement. On the other hand, vertical cables provide a viable solution to this problem. This study uses a vertical cable to receive wavelets from 38 air guns and data are collected offshore Southeast Qiong, where the water depth is over 1000 m. In this study, the wavelets measured using this technique coincide very well with the simulated wavelets and can therefore represent the real shape of the wavelets. This experiment fills a technology gap in China.

Ambient Seismic Noise Monitoring of Time-lapse Velocity Changes During CO2 Injection at Otway, South Australia

NASA Astrophysics Data System (ADS)

Saygin, E.; Lumley, D. E.

2017-12-01

We use continuous seismic data recorded with an array of 909 buried geophones at Otway, South Australia, to investigate the potential of using ambient seismic noise for time-lapse monitoring of the subsurface. The array was installed prior to a 15,000 ton CO2 injection in 2016-17, in order to detect and monitor the evolution of the injected CO2 plume, and any associated microseismic activity. Continuously recorded data from the vertical components of the geophone array were cross-correlated to retrieve the inter-station Green's functions. The dense collection of Green's functions contains diving body waves and surface Rayleigh waves. Green's Functions were then compared with each other at different time frames including the pre-injection period to track subtle changes in the travel times due to the CO2 injection. Our results show a clear change in the velocities of Green's functions at the start of injection for both body waves and surface waves for wave paths traversing the injection area, whereas the observed changes are much smaller for areas which are far from the injection well.

A New Moonquake Catalog from Apollo 17 Seismic Data II: Lunar Surface Gravimeter: Implications of Expanding the Passive Seismic Array

NASA Astrophysics Data System (ADS)

Phillips, D.; Dimech, J. L.; Weber, R. C.

2017-12-01

Apollo 17's Lunar Surface Gravimeter (LSG) was deployed on the Moon in 1972, and was originally intended to detect gravitational waves as a confirmation of Einstein's general theory of relativity. Due to a design problem, the instrument did not function as intended. However, remotely-issued reconfiguration commands permitted the instrument to act effectively as a passive seismometer. LSG recorded continuously until Sept. 1977, when all surface data recording was terminated. Because the instrument did not meet its primary science objective, little effort was made to archive the data. Most of it was eventually lost, with the exception of data spanning the period March 1976 until Sept. 1977, and a recent investigation demonstrated that LSG data do contain moonquake signals (Kawamura et al., 2015). The addition of useable seismic data at the Apollo 17 site has important implications for event location schemes, which improve with increasing data coverage. All previous seismic event location attempts were limited to the four stations deployed at the Apollo 12, 14, 15, and 16 sites. Apollo 17 extends the functional aperture of the seismic array significantly to the east, permitting more accurate moonquake locations and improved probing of the lunar interior. Using the standard location technique of linearized arrival time inversion through a known velocity model, Kawamura et al. (2015) used moonquake signals detected in the LSG data to refine location estimates for 49 deep moonquake clusters, and constrained new locations for five previously un-located clusters. Recent efforts of the Apollo Lunar Surface Experiments Package Data Recovery Focus Group have recovered some of the previously lost LSG data, spanning the time period April 2, 1975 to June 30, 1975. In this study, we expand Kawamura's analysis to the newly recovered data, which contain over 200 known seismic signals, including deep moonquakes, shallow moonquakes, and meteorite impacts. We have completed initial data processing and verified the presence of deep moonquake signals in the recovered data. This positions us well for the application of automated event-detection techniques that have been successfully applied to the Apollo 16 Passive Seismic Experiment data as well as the Apollo 17 Lunar Seismic Profiling Experiment data.

The multi-parameter borehole system and high resolution seismic studies in the western part of the main Marmara Fault in the frame of MARSITE Project.

NASA Astrophysics Data System (ADS)

Ozel, Oguz; Guralp, Cansun; Tunc, Suleyman; Yalcinkaya, Esref

2016-04-01

The main objective of this study is to install a multi-parameter borehole system and surface array as close to the main Marmara Fault (MMF) in the western Marmara Sea as possible, and measure continuously the evolution of the state of the fault zone surrounding the MMF and to detect any anomaly or change, which may occur before earthquakes by making use of the data from the arrays already running in the eastern part of the Marmara Sea. The multi-parameter borehole system is composed of very wide dynamic range and stable borehole (VBB) broad band seismic sensor, and incorporate strain meter, tilt meter, and temperature and local hydrostatic pressure measuring devices. The borehole seismic station uses the latest update technologies and design ideas to record "Earth tides" signals to the smallest magnitude -3 events. Additionally, a surface microearthquake observation array, consisting of 8-10 seismometers around the borehole is established to obtain continuous high resolution locations of micro-seismicity and to better understand the existing seismically active structures and their roles in local tectonic settings.Bringing face to face the seismograms of microearthquakes recorded by borehole and surface instruments portrays quite different contents. The shorter recording duration and nearly flat frequency spectrum up to the Nyquist frequencies of borehole records are faced with longer recording duration and rapid decay of spectral amplitudes at higher frequencies of a surface seismogram. The main causative of the observed differences are near surface geology effects that mask most of the source related information the seismograms include, and that give rise to scattering, generating longer duration seismograms. In view of these circumstances, studies on microearthquakes employing surface seismograms may bring on misleading results. Particularly, the works on earthquake physics and nucleation process of earthquakes requires elaborate analysis of tiny events. It is obvious from the studies on the nucleation process of the 1999 earthquake that tens of minutes before the major rupture initiate noteworthy microearthquake activity happened. The starting point of the 1999 rupture was a site of swarm activity noticed a few decades prior the main shock. Nowadays, analogous case is probable in western Marmara Sea region, prone to a major event in near future where the seismic activity is prevailing along the impending rupture zone. Deploying a borehole system eastern end of the Ganos fault zone may yield invaluable data to closely inspect and monitor the last stages of the preparation stage of major rupture.

Downhole Microseismic Monitoring at a Carbon Capture, Utilization, and Storage Site, Farnsworth Unit, Ochiltree County, Texas

NASA Astrophysics Data System (ADS)

Ziegler, A.; Balch, R. S.; van Wijk, J.

2015-12-01

Farnsworth Oil Field in North Texas hosts an ongoing carbon capture, utilization, and storage project. This study is focused on passive seismic monitoring at the carbon injection site to measure, locate, and catalog any induced seismic events. A Geometrics Geode system is being utilized for continuous recording of the passive seismic downhole bore array in a monitoring well. The array consists of 3-component dual Geospace OMNI-2400 15Hz geophones with a vertical spacing of 30.5m. Downhole temperature and pressure are also monitored. Seismic data is recorded continuously and is produced at a rate of over 900GB per month, which must be archived and reviewed. A Short Term Average/Long Term Average (STA/LTA) algorithm was evaluated for its ability to search for events, including identification and quantification of any false positive events. It was determined that the algorithm was not appropriate for event detection with the background level of noise at the field site and for the recording equipment as configured. Alternatives are being investigated. The final intended outcome of the passive seismic monitoring is to mine the continuous database and develop a catalog of microseismic events/locations and to determine if there is any relationship to CO2 injection in the field. Identifying the location of any microseismic events will allow for correlation with carbon injection locations and previously characterized geological and structural features such as faults and paleoslopes. Additionally, the borehole array has recorded over 1200 active sources with three sweeps at each source location that were acquired during a nearby 3D VSP. These data were evaluated for their usability and location within an effective radius of the array and were stacked to improve signal-noise ratio and are used to calibrate a full field velocity model to enhance event location accuracy. Funding for this project is provided by the U.S. Department of Energy under Award No. DE-FC26-05NT42591.

Heterogeneous Structure and Seismicity beneath the Tokyo Metropolitan Area

NASA Astrophysics Data System (ADS)

Nakagawa, S.; Kato, A.; Sakai, S.; Nanjo, K.; Panayotopoulos, Y.; Kurashimo, E.; Obara, K.; Kasahara, K.; Aketagawa, T.; Kimura, H.; Hirata, N.

2010-12-01

Beneath the Tokyo metropolitan area, the Philippine Sea Plate (PSP) subducts and causes damaged mega-thrust earthquakes. Sato et al. (2005) revealed the geometry of upper surface of PSP, and Hagiwara et al. (2006) estimated the velocity structure beneath Boso peninsula. However, these results are not sufficient for the assessment of the entire picture of the seismic hazards beneath the Tokyo metropolitan area including those due to an intra-slab M7+ earthquake. So, we launched the Special Project for Earthquake Disaster Mitigation in the Tokyo Metropolitan area (Hirata et al., 2009). Proving the more detailed geometry and physical properties (e.g. velocities, densities, attenuation) and stress field within PSP is very important to attain this issue. The core item of this project is a dense seismic array called Metropolitan Seismic Observation network (MeSO-net) for making observations in the metropolitan area (Sakai and Hirata, 2009; Kasahara et al., 2009). We deployed the 249 seismic stations with a spacing of 5 km. Some parts of stations construct 5 linear arrays at interval of 2 km such as Tsukuba-Fujisawa (TF) array, etc. The TF array runs from northeast to southwest through the center of Tokyo. In this study, we applied the tomography method to image the heterogeneous structure under the Tokyo metropolitan area. We selected events from the Japan Meteorological Agency (JMA) unified earthquake list. All data of MeSO-net were edited into event data by the selected JMA unified earthquake list. We picked the P and S wave arrival times. The total number of stations and events are 421 and 1,256, respectively. Then, we applied the double-difference tomography method (Zhang and Thurber, 2003) to this dataset and estimated the fine-scale velocity structure. The grid nodes locate 10 km interval in parallel with the array, 20 km interval in perpendicular to the array; and on depth direction, 5 km interval to a depth of less than 50 km and 10 km interval at a depth of more. We used 158,930 (P wave) and 149,308 (S wave) absolute arrival times, and 374,072 (P wave) and 354,912 (S wave) differential travel times. The initial velocity structure is the JMA2001 (Ueno et al., 2001), and the Vp/Vs ratio is set to 1.73 for all grid nodes. We imaged the subducting PSP and Pacific Plate clearly. The depth section of P-wave velocity structure along the TF array clearly shows that thin low-velocity layer which overlies high-velocity layer subducts towards northeast. This low-velocity layer corresponds to the oceanic crust of the subducting PSP. The obtained tomograms combined with seismicity and focal mechanisms indicate that the interior of the subducting PSP is characterized by heterogeneous structures, which could exert a profound influence on the genesis of intra-slab earthquakes. Acknowledgement: This study was supported by the Earthquake Research Institute cooperative research program.

Development and Test of a 1,000 Level 3C Fiber Optic Borehole Seismic Receiver Array Applied to Carbon Sequestration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paulsson, Bjorn N.P.

2015-02-28

To address the critical site characterization and monitoring needs for CCS programs, US Department of Energy (DOE) awarded Paulsson, Inc. in 2010 a contract to design, build and test a fiber optic based ultra-large bandwidth clamped borehole seismic vector array capable of deploying up to one thousand 3C sensor pods suitable for deployment into high temperature and high pressure boreholes. Paulsson, Inc. has completed a design or a unique borehole seismic system consisting of a novel drill pipe based deployment system that includes a hydraulic clamping mechanism for the sensor pods, a new sensor pod design and most important –more » a unique fiber optic seismic vector sensor with technical specifications and capabilities that far exceed the state of the art seismic sensor technologies. These novel technologies were all applied to the new borehole seismic system. In combination these technologies will allow for the deployment of up to 1,000 3C sensor pods in vertical, deviated or horizontal wells. Laboratory tests of the fiber optic seismic vector sensors developed during this project have shown that the new borehole seismic sensor technology is capable of generating outstanding high vector fidelity data with extremely large bandwidth: 0.01 – 6,000 Hz. Field tests have shown that the system can record events at magnitudes much smaller than M-2.3 at frequencies up to 2,000 Hz. The sensors have also proved to be about 100 times more sensitive than the regular coil geophones that are used in borehole seismic systems today. The fiber optic seismic sensors have furthermore been qualified to operate at temperatures over 300°C (572°F). The fibers used for the seismic sensors in the system are used to record Distributed Temperature Sensor (DTS) data allowing additional value added data to be recorded simultaneously with the seismic vector sensor data.« less

Data report for onshore-offshore wide-angle seismic recordings in the Bering-Chukchi Sea, Western Alaska and eastern Siberia

USGS Publications Warehouse

Brocher, Thomas M.; Allen, Richard M.; Stone, David B.; Wolf, Lorraine W.; Galloway, Brian K.

1995-01-01

This report presents fourteen deep-crustal wide-angle seismic reflection and refraction profiles recorded onland in western Alaska and eastern Siberia from marine air gun sources in the Bering-Chukchi Seas. During a 20-day period in August, 1994, the R/V Ewing acquired two long (a total of 3754 km) deep-crustal seismic-reflection profiles on the continental shelf of the Bering and Chukchi Seas, in a collaborative project between Stanford University and the United States Geological Survey (USGS). The Ewing's 137.7 liter (8355 cu. in.) air gun array was the source for both the multichannel reflection and the wide-angle seismic data. The Ewing, operated by the Lamont-Doherty Earth Observatory, steamed northward from Nunivak Island to Barrow, and returned, firing the air gun array at intervals of either 50 m or 75 m. About 37,700 air gun shots were fired along the northward directed Lines 1 and 2, and more than 40,000 air gun shots were fired along the southward directed Line 3. The USGS and the University of Alaska, Fairbanks (UAF), deployed an array of twelve 3-component REFTEK and PDAS recorders in western Alaska and eastern Siberia which continuously recorded the air gun signals fired during the northward bound Lines 1 and 2. Seven of these recorders also continuously recorded the southward bound Line 3. These wide-angle seismic data were acquired to: (1) image reflectors in the upper to lower crust, (2) determine crustal and upper mantle refraction velocities, and (3) provide important constraints on the geometry of the Moho along the seismic lines. In this report, we describe the land recording of wide-angle data conducted by the USGS and the UAF, describe in detail how the wide-angle REFTEK and PDAS data were reduced to common receiver gather seismic sections, and illustrate the wide-angle seismic data obtained by the REFTEKs and PDAS's. Air gun signals were observed to ranges in excess of 400 km, and crustal and upper /mantle refractions indicate substantial variation in the crustal thickness along the transect.

Seismic Reflection Imaging of Detachment Faulting at 13°N on the Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Falder, M.; Reston, T. J.; Peirce, C.; Simão, N.; MacLeod, C. J.; Searle, R. C.

2016-12-01

The observation of domal corrugated surfaces at slow spreading ridges less than two decades ago, has dramatically challenged our understanding of seafloor spreading. These `oceanic core complexes' are believed to be caused by large-scale detachment faults which accommodate plate separation during periods when melt supply is low or absent entirely. Despite increasing recognition of their importance, the mechanics of, and interactions between, detachment faults at OCCs is not well understood. In Jan-Feb 2016, seismic reflection and refraction data were acquired across the 13N OCCs. The twelve-airgun array seismic source was recorded by a 3000m-long streamer, with shots fired with the full array at either 20 s intervals, or with half the array in a "flip flop" fashion every 10 s. A shorter firing rate results in significantly less spatial aliasing and enhances the performance of the F-K domain filtering. Here we present preliminary seismic reflection images of the 13N region. The currently active 13° 20'N detachment fault is imaged continuing downwards from the smooth fault plane exposed at the seabed. Away from the fault, and between the two OCCs in the area, fewer subsurface structures are observed, which may either represent an actual lack of sharp acoustic contrasts or be as a result of the challenging imaging conditions. Acoustic energy scattered by rough bathymetry both within and out of plane of section is the main challenge of seismic reflection imaging in this area and various strategies are being investigated for its attenuation, including prediction based on high-resolution bathymetry acquired.

Regional Seismic Arrays and Nuclear Test Ban Verification

DTIC Science & Technology

1990-12-01

estimation has been difficult to automate, at least for regional and teleseismic signals. A neural network approach might be applicable here. The data must...use of trained neural networks . Of the 95 events examined, 66 were selected for the classification study based on high signal-to-noise ratio and...the International Joint Conference on Neural Networks , Washington, D.C., June, 1989. Menke, W. Geophysical Data Analysis : Discrete Inverse Theory

Design and implementation of a low-cost multichannel seismic noise recorder for array measurements

NASA Astrophysics Data System (ADS)

Soler-Llorens, Juan Luis; Juan Giner-Caturla, Jose; Molina-Palacios, Sergio; Galiana-Merino, Juan Jose; Rosa-Herranz, Julio; Agea-Medina, Noelia

2017-04-01

Soil characterization is the starting point for seismic hazard studies. Currently, the methods based on ambient noise measurements are very used because they are non-invasive methods and relatively easy to implement in urban areas. Among these methods, the analysis of array measurements provides the dispersion curve and subsequently the shear-wave velocity profile associated to the site under study. In this case, we need several sensors recording simultaneously and a data acquisition system with one channel by sensor, what can become the complete equipment unaffordable for small research groups. In this work, we have designed and implemented a low-cost multichannel ambient noise recorder for array measurements. The complete system is based on Arduino, an open source electronic development platform, which allows recording 12 differential input channels simultaneously. Besides, it is complemented with a conditioning circuit that includes an anti-aliasing filter and a selectable gain between 0 and 40dB. The data acquisition is set up through a user-friendly graphical user interface. It is important to note that the electronic scheme as well as the programming code are open hardware and software, respectively, so it allows other researchers to suite the system to their particular requirements. The developed equipment has been tested at several sites around the province of Alicante (southeast of Spain), where the soil characteristics are well-known from previous studies. Array measurements have been taken and after that, the recorded data have been analysed using the frequency-wavenumber (f-k) and the extended spatial autocorrelation (ESAC) methods. The comparison of the obtained dispersion curves with the ones obtained in previous studies shows the suitability of the implemented low-cost system for array measurements.

Pacific Array of, by and for Global Deep Earth Research

NASA Astrophysics Data System (ADS)

Kawakatsu, H.

2016-12-01

Recent advances in ocean bottom geophysical observations, together with advances in the analysis methodology, have now enabled us to resolve the regional 1-D structure of the entire lithosphere- asthenosphere system (LAS), from the surface to a depth of ˜200km, including seismic anisotropy (azimuthal), with deployments of ˜10-15 BBOBSs & OBEMs each for a year or so (Takeo et al, 2013, 2016; Baba et al., 2013; Lin et al. 2016). Thus the in-situ characterization of the physical properties of the entire oceanic LAS without a priori assumption for the shallow-most structure, the assumption often made for global studies, has become possible. We are now entering a new stage that a large scale array experiment in the ocean (e.g., Pacific Array: http://gachon.eri.u-tokyo.ac.jp/ hitosi/PArray/) has become approachable: having 10-15 BBOBSs as an array unit for a 1-2-year deployment, and repeating such deployments in a leap-frog way or concurrently (an array of arrays) for a decade or so would enable us to cover a large portion of the Pacific basin. Such array observations not only by giving regional constraints on the 1-D structure (including seismic anisotropy), but also by sharing waveform data for global scale waveform tomography (e.g., Fichtner et al. 2010; French et al. 2013; Zhu & Tromp 2013), would drastically increase our knowledge of how plate tectonics works beneath oceanic basins, as well as of the large scale picture of the interior of the Earth. For such an array of arrays to be realized, international collaboration seems essential. If three or four countries collaborate together, it may be achieved within a 10-year time frame that makes this concept attractive. It is also essential that global seismology, geodynamics, and deep earth (GSGD) communities work closely with the ocean science community for Pacific Array to be realized, as they would get most benefit from it. While unit array deployments may have their own scientific goals, it is important that they are planned to fit within a larger international Pacific Array structure. The GSGD community should take a lead in providing such an umbrella, as well as stimulating collaborations between different disciplines .

DOE Office of Scientific and Technical Information (OSTI.GOV)

Myers, S; Larsen, S; Wagoner, J

Seismic imaging and tracking methods have intelligence and monitoring applications. Current systems, however, do not adequately calibrate or model the unknown geological heterogeneity. Current systems are also not designed for rapid data acquisition and analysis in the field. This project seeks to build the core technological capabilities coupled with innovative deployment, processing, and analysis methodologies to allow seismic methods to be effectively utilized in the applications of seismic imaging and vehicle tracking where rapid (minutes to hours) and real-time analysis is required. The goal of this project is to build capabilities in acquisition system design, utilization of full three-dimensional (3D)more » finite difference modeling, as well as statistical characterization of geological heterogeneity. Such capabilities coupled with a rapid field analysis methodology based on matched field processing are applied to problems associated with surveillance, battlefield management, finding hard and deeply buried targets, and portal monitoring. This project, in support of LLNL's national-security mission, benefits the U.S. military and intelligence community. Fiscal year (FY) 2003 was the final year of this project. In the 2.5 years this project has been active, numerous and varied developments and milestones have been accomplished. A wireless communication module for seismic data was developed to facilitate rapid seismic data acquisition and analysis. The E3D code was enhanced to include topographic effects. Codes were developed to implement the Karhunen-Loeve (K-L) statistical methodology for generating geological heterogeneity that can be utilized in E3D modeling. The matched field processing methodology applied to vehicle tracking and based on a field calibration to characterize geological heterogeneity was tested and successfully demonstrated in a tank tracking experiment at the Nevada Test Site. A three-seismic-array vehicle tracking testbed was installed on site at LLNL for testing real-time seismic tracking methods. A field experiment was conducted over a tunnel at the Nevada Site that quantified the tunnel reflection signal and, coupled with modeling, identified key needs and requirements in experimental layout of sensors. A large field experiment was conducted at the Lake Lynn Laboratory, a mine safety research facility in Pennsylvania, over a tunnel complex in realistic, difficult conditions. This experiment gathered the necessary data for a full 3D attempt to apply the methodology. The experiment also collected data to analyze the capabilities to detect and locate in-tunnel explosions for mine safety and other applications. In FY03 specifically, a large and complex simulation experiment was conducted that tested the full modeling-based approach to geological characterization using E2D, the K-L statistical methodology, and matched field processing applied to tunnel detection with surface seismic sensors. The simulation validated the full methodology and the need for geological heterogeneity to be accounted for in the overall approach. The Lake Lynn site area was geologically modeled using the code Earthvision to produce a 32 million node 3D model grid for E3D. Model linking issues were resolved and a number of full 3D model runs were accomplished using shot locations that matched the data. E3D-generated wavefield movies showed the reflection signal would be too small to be observed in the data due to trapped and attenuated energy in the weathered layer. An analysis of the few sensors coupled to bedrock did not improve the reflection signal strength sufficiently because the shots, though buried, were within the surface layer and hence attenuated. Ability to model a complex 3D geological structure and calculate synthetic seismograms that are in good agreement with actual data (especially for surface waves and below the complex weathered layer) was demonstrated. We conclude that E3D is a powerful tool for assessing the conditions under which a tunnel could be detected in a specific geological setting. Finally, the Lake Lynn tunnel explosion data were analyzed using standard array processing techniques. The results showed that single detonations could be detected and located but simultaneous detonations would require a strategic placement of arrays.« less

Seismoelectric imaging of shallow targets

USGS Publications Warehouse

Haines, S.S.; Pride, S.R.; Klemperer, S.L.; Biondi, B.

2007-01-01

We have undertaken a series of controlled field experiments to develop seismoelectric experimental methods for near-surface applications and to improve our understanding of seismoelectric phenomena. In a set of off-line geometry surveys (source separated from the receiver line), we place seismic sources and electrode array receivers on opposite sides of a man-made target (two sand-filled trenches) to record separately two previously documented seismoelectric modes: (1) the electromagnetic interface response signal created at the target and (2) the coseismic electric fields located within a compressional seismic wave. With the seismic source point in the center of a linear electrode array, we identify the previously undocumented seismoelectric direct field, and the Lorentz field of the metal hammer plate moving in the earth's magnetic field. We place the seismic source in the center of a circular array of electrodes (radial and circumferential orientations) to analyze the source-related direct and Lorentz fields and to establish that these fields can be understood in terms of simple analytical models. Using an off-line geometry, we create a multifold, 2D image of our trenches as dipping layers, and we also produce a complementary synthetic image through numerical modeling. These images demonstrate that off-line geometry (e.g., crosswell) surveys offer a particularly promising application of the seismoelectric method because they effectively separate the interface response signal from the (generally much stronger) coseismic and source-related fields. ?? 2007 Society of Exploration Geophysicists.

EarthScope's Transportable Array: Advancing Eastward

NASA Astrophysics Data System (ADS)

Busby, R. W.; Vernon, F.; Newman, R. L.; Astiz, L.

2006-12-01

EarthScope's Transportable Array has installed more than 200 high-quality broadband seismic stations over the last 3 years in the western US. These stations have a nominal spacing of 70 km and are part of an eventual 400 station array that migrates from west to east at a rate of 18 stations per month. The full 400 stations will be operating by September 2007. Stations have a residence time of about 2 years before being relocated to the next site. Throughout the continental US, 1623 sites are expected to be occupied. Standardized procedures and protocols have been developed to streamline all aspects of Transportable Array operations, from siting to site construction and installation to equipment purchasing and data archiving. Earned Value Management tools keep facility installation and operation on budget and schedule. A diverse, yet efficient, infrastructure installs and maintains the Transportable Array. Sensors, dataloggers, and other equipment are received and tested by the IRIS PASSCAL Instrument Center and shipped to regional storage facilities. To engage future geoscientists in the project, students are trained to conduct field and analytical reconnaissance to identify suitable seismic station sites. Contract personnel are used for site verification; vault construction; and installation of sensors, power, and communications systems. IRIS staff manages permitting, landowner communications, and station operations and maintenance. Seismic signal quality and metadata are quality-checked at the Array Network Facility at the University of California-San Diego and simultaneously archived at the IRIS Data Management Center in Seattle. Station equipment has been specifically designed for low power, remote, unattended operation and uses diverse two-way IP communications for real-time transmission. Digital cellular services, VSAT satellite, and commercial DSL, cable or wireless transport services are employed. Automatic monitoring of status, signal quality and earthquake event detection as well as operational alarms for low voltage and water intrusion are performed by a robust data acquisition package. This software is coupled with a host of network management tools and display managers operated by the Array Network Facility to allow managers, field personnel, and network operations staff to visualize array performance in real-time and to access historical information for diagnostics. Current data recording proficiency is 99.1%, with real-time telemetry averaging about 91%. EarthScope, IRIS and the USGS are working with regional seismic network operators, both existing and newly formed, to transition some of the Transportable Array stations into regional network assets. Each region has unique circumstances and interested parties are invited to exchange ideas on how this might be accomplished in their area. Contact busby@iris.edu for more information.

Initial results from seismic monitoring at the Aquistore CO 2 storage site, Saskatchewan, Canada

DOE PAGES

White, D. J.; Roach, L. A.N.; Roberts, B.; ...

2014-12-31

The Aquistore Project, located near Estevan, Saskatchewan, is one of the first integrated commercial-scale CO 2 storage projects in the world that is designed to demonstrate CO 2 storage in a deep saline aquifer. Starting in 2014, CO 2 captured from the nearby Boundary Dam coal-fired power plant will be transported via pipeline to the storage site and to nearby oil fields for enhanced oil recovery. At the Aquistore site, the CO 2 will be injected into a brine-filled sandstone formation at ~3200 m depth using the deepest well in Saskatchewan. The suitability of the geological formations that will hostmore » the injected CO 2 has been predetermined through 3D characterization using high-resolution 3D seismic images and deep well information. These data show that 1) there are no significant faults in the immediate area of the storage site, 2) the regional sealing formation is continuous in the area, and 3) the reservoir is not adversely affected by knolls on the surface of the underlying Precambrian basement. Furthermore, the Aquistore site is located within an intracratonic region characterized by extremely low levels of seismicity. This is in spite of oil-field related water injection in the nearby Weyburn-Midale field where a total of 656 million m 3 of water have been injected since the 1960`s with no demonstrable related induced seismicity. A key element of the Aquistore research program is the further development of methods to monitor the security and subsurface distribution of the injected CO 2. Toward this end, a permanent areal seismic monitoring array was deployed in 2012, comprising 630 vertical-component geophones installed at 20 m depth on a 2.5x2.5 km regular grid. This permanent array is designed to provide improved 3D time-lapse seismic imaging for monitoring subsurface CO 2. Prior to the onset of CO 2 injection, calibration 3D surveys were acquired in May and November of 2013. Comparison of the data from these surveys relative to the baseline 3D survey data from 2012 shows excellent repeatability (NRMS less than 10%) which will provide enhanced monitoring sensitivity to smaller amounts of CO 2. The permanent array also provides continuous passive monitoring for injection-related microseismicity. Passive monitoring has been ongoing since the summer of 2012 in order to establish levels of background seismicity before CO 2 injection starts in 2014. Microseismic monitoring was augmented in 2013 by the installation of 3 broadband seismograph stations surrounding the Aquistore site. These surface installations should provide a detection capability of seismic events with magnitudes as low as ~0. Downhole seismic methods are also being utilized for CO 2 monitoring at the Aquistore site. Baseline crosswell tomographic images depict details (meters-scale) of the reservoir in the 150-m interval between the observation and injection wells. This level of resolution is designed to track the CO 2 migration between the wells during the initial injection period. A baseline 3D vertical seismic profile (VSP) was acquired in the fall of 2013 to provide seismic images with resolution on a scale between that provided by the surface seismic array and the downhole tomography. The 3D VSP was recorded simultaneously using both a conventional array of downhole geophones (60-levels) and an optical fibre system. The latter utilized an optical fiber cable deployed on the outside of the monitor well casing and cemented in place. A direct comparison of these two methodologies will determine the suitability of using the fiber cable for ongoing time-lapse VSP monitoring.« less

Composition and variation of noise recorded at the Yellowknife Seismic Array, 1991-2007

USGS Publications Warehouse

Koper, K.D.; De Foy, B.; Benz, H.

2009-01-01

We analyze seismic noise recorded on the 18 short-period, vertical component seismometers of the Yellowknife Seismic Array (YKA). YKA has an aperture of 23 km and is sited on cratonic lithosphere in an area with low cultural noise. These properties make it ideal for studying natural seismic noise at periods of 1-3 s. We calculated frequency-wave number spectra in this band for over 6,000 time windows that were extracted once per day for 17 years (1991-2007). Slowness analysis reveals a rich variety of seismic phases originating from distinct source regions: Rg waves from the Great Slave Lake; Lg waves from the Atlantic, Pacific, and Arctic Oceans; and teleseismic P waves from the north Pacific and equatorial mid-Atlantic regions. The surface wave energy is generated along coastlines, while the body wave energy is generated at least in part in deep-water, pelagic regions. Surface waves tend to dominate at the longer periods and, just as in earthquake seismograms, Lg is the most prominent arrival. Although the periods we study are slightly shorter than the classic double-frequency microseismic band of 4-10 s, the noise at YKA has clear seasonal behavior that is consistent with the ocean wave climate in the Northern Hemisphere. The temporal variation of most of the noise sources can be well fit using just two Fourier components: yearly and biyearly terms that combine to give a fast rise in microseismic power from mid-June through mid-October, followed by a gradual decline. The exception is the Rg energy from the Great Slave Lake, which shows a sharp drop in noise power over a 2-week period in November as the lake freezes. The L g noise from the east has a small but statistically significant positive slope, perhaps implying increased ocean wave activity in the North Atlantic over the last 17 years. Copyright 2009 by the American Geophysical Union.

Multi-Array Detection, Association and Location of Infrasound and Seismo-Acoustic Events in Utah

DTIC Science & Technology

2008-09-30

techniques for detecting , associating, and locating infrasound signals at single and multiple arrays and then combining the processed results with...was detected and located by both infrasound and seismic instruments (Figure 3). Infrasound signals at all three arrays , from one of the explosions, are...COVERED (From - To) 30-Sep-2008 REPRINT 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER MULTI- ARRAY DETECTION , ASSOCIATION AND LOCATION OF INFRASOUND FA8718

Infrasound's capability to detect and characterise volcanic events, from local to regional scale.

NASA Astrophysics Data System (ADS)

Taisne, Benoit; Perttu, Anna

2017-04-01

Local infrasound and seismic networks have been successfully used for identification and quantification of explosions at single volcanoes. However the February, 2014 eruption of Kelud volcano, Indonesia, destroyed most of the local monitoring network. The use of remote seismic and infrasound sensors proved to be essential in the reconstruction of the eruptive sequence. The first recorded explosive event, with relatively weak seismic and infrasonic signature, was followed by a 2 hour sustained signal detected as far away as 11,000 km by infrasound sensors and up to 2,300 km away by seismometers. The volcanic intensity derived from these observations places the 2014 Kelud eruption between the intensity of the 1980 Mount St. Helens and the 1991 Pinatubo eruptions. The use of remote seismic stations and infrasound arrays in deriving valuable information about the onset, evolution, and intensity of volcanic eruptions is clear from the Kelud example. After this eruption the Singapore Infrasound Array became operational. This array, along with the other regional infrasound arrays which are part of the International Monitoring System, have recorded events from fireballs and regional volcanoes. The detection capability of this network for any specific volcanic event is not only dependent on the amplitude of the source, but also the propagation effects, noise level at each station, and characteristics of the regional persistent noise sources (like the microbarum). Combining the spatial and seasonal characteristics of this noise, within the same frequency band as significant eruptive events, with the probability of such events to occur, gives us a comprehensive understanding of detection capability for any of the 750 active or potentially active volcanoes in Southeast Asia.

Infrasound and Seismic Recordings of Rocket Launches from Kennedy Space Center, 2016-2017

NASA Astrophysics Data System (ADS)

McNutt, S. R.; Thompson, G.; Brown, R. G.; Braunmiller, J.; Farrell, A. K.; Mehta, C.

2017-12-01

We installed a temporary 3-station seismic-infrasound network at Kennedy Space Center (KSC) in February 2016 to test sensor calibrations and train students in field deployment and data acquisitions techniques. Each station featured a single broadband 3-component seismometer and a 3-element infrasound array. In May 2016 the network was scaled back to a single station due to other projects competing for equipment. To date 8 rocket launches have been recorded by the infrasound array, as well as 2 static tests, 1 aborted launch and 1 rocket explosion (see next abstract). Of the rocket launches recorded 4 were SpaceX Falcon-9, 2 were ULA Atlas-5 and 2 were ULA Delta-IV. A question we attempt to answer is whether the rocket engine type and launch trajectory can be estimated with appropriate travel-time, amplitude-ratio and spectral techniques. For example, there is a clear Doppler shift in seismic and infrasound spectrograms from all launches, with lower frequencies occurring later in the recorded signal as the rocket accelerates away from the array. Another question of interest is whether there are relationships between jet noise frequency, thrust and/or nozzle velocity. Infrasound data may help answer these questions. We are now in the process of deploying a permanent seismic and infrasound array at the Astronaut Beach House. 10 more rocket launches are schedule before AGU. NASA is also conducting a series of 33 sonic booms over KSC beginning on Aug 21st. Launches and other events at KSC have provided rich sources of signals that are useful to characterize and gain insight into physical processes and wave generation from man-made sources.

Assessing the monitoring performance using a synthetic microseismic catalogue for hydraulic fracturing

NASA Astrophysics Data System (ADS)

Ángel López Comino, José; Kriegerowski, Marius; Cesca, Simone; Dahm, Torsten; Mirek, Janusz; Lasocki, Stanislaw

2016-04-01

Hydraulic fracturing is considered among the human operations which could induce or trigger seismicity or microseismic activity. The influence of hydraulic fracturing operations is typically expected in terms of weak magnitude events. However, the sensitivity of the rock mass to trigger seismicity varies significantly for different sites and cannot be easily predicted prior to operations. In order to assess the sensitivity of microseismity to hydraulic fracturing operations, we perform a seismic monitoring at a shale gas exploration/exploitation site in the central-western part of the Peribaltic synclise at Pomerania (Poland). The monitoring will be continued before, during and after the termination of hydraulic fracturing operations. The fracking operations are planned in April 2016 at a depth 4000 m. A specific network setup has been installed since summer 2015, including a distributed network of broadband stations and three small-scale arrays. The network covers a region of 60 km2. The aperture of small scale arrays is between 450 and 950 m. So far no fracturing operations have been performed, but seismic data can already be used to assess the seismic noise and background microseismicity, and to investigate and assess the detection performance of our monitoring setup. Here we adopt a recently developed tool to generate a synthetic catalogue and waveform dataset, which realistically account for the expected microseismicity. Synthetic waveforms are generated for a local crustal model, considering a realistic distribution of hypocenters, magnitudes, moment tensors, and source durations. Noise free synthetic seismograms are superposed to real noise traces, to reproduce true monitoring conditions at the different station locations. We estimate the detection probability for different magnitudes, source-receiver distances, and noise conditions. This information is used to estimate the magnitude of completeness at the depth of the hydraulic fracturing horizontal wells. Our technique is useful to evaluate the efficiency of the seismic network and validate detection and location algorithms, taking into account the signal to noise ratio. The same dataset may be used at a later time, to assess the performance of other seismological analysis, such as hypocentral location, magnitude estimation and source parameters inversion. This work is funded by the EU H2020 SHEER project.

Infrasonic induced ground motions

NASA Astrophysics Data System (ADS)

Lin, Ting-Li

On January 28, 2004, the CERI seismic network recorded seismic signals generated by an unknown source. Our conclusion is that the acoustic waves were initiated by an explosive source near the ground surface. The meteorological temperature and effective sound speed profiles suggested existence of an efficient near-surface waveguide that allowed the acoustic disturbance to propagate to large distances. An explosion occurring in an area of forest and farms would have limited the number of eyewitnesses. Resolution of the source might be possible by experiment or by detailed analysis of the ground motion data. A seismo-acoustic array was built to investigate thunder-induced ground motions. Two thunder events with similar N-wave waveforms but different horizontal slownesses are chosen to evaluate the credibility of using thunder as a seismic source. These impulsive acoustic waves excited P and S reverberations in the near surface that depend on both the incident wave horizontal slowness and the velocity structure in the upper 30 meters. Nineteen thunder events were chosen to further investigate the seismo-acoustic coupling. The consistent incident slowness differences between acoustic pressure and ground motions suggest that ground reverberations were first initiated somewhat away from the array. Acoustic and seismic signals were used to generate the time-domain transfer function through the deconvolution technique. Possible non-linear interaction for acoustic propagation into the soil at the surface was observed. The reverse radial initial motions suggest a low Poisson's ratio for the near-surface layer. The acoustic-to-seismic transfer functions show a consistent reverberation series of the Rayleigh wave type, which has a systematic dispersion relation to incident slownesses inferred from the seismic ground velocity. Air-coupled Rayleigh wave dispersion was used to quantitatively constrain the near-surface site structure with constraints afforded by near-surface body wave refraction and Rayleigh wave dispersion data. Theoretical standard high-frequency and air-coupled Rayleigh wave dispersion calculated by the inferred site structure match the observed dispersion curves. Our study suggests that natural or controlled air-borne pressure sources can be used to investigate the near-surface site structures for earthquake shaking hazard studies.

Infrasound and seismic analysis of the SpaceX Falcon9 explosion sequence of 1-September-2016

NASA Astrophysics Data System (ADS)

Thompson, G.; McNutt, S. R.; Brown, R. G.; Braunmiller, J.; Mehta, C.

2017-12-01

During a static launch test on 1-Sep-2016 at Kennedy Space Center, a SpaceX Falcon 9 rocket exploded causing loss of the rocket and the payload, and extensively damaging the launch complex. The sequence was captured by a 3-element infrasound array and a broadband 3-component seismometer at the Astronaut Beach House, just 0.87 miles (1.4 km) from the launch pad. Manual picking identified 153 impulsive airwave signals over a 26-minute interval and these were compared to video recordings of the sequence. The explosion onset consisted of a moderate signal on both seismic and infrasound (52 Pa) instruments. This corresponds to the rupture of the second-stage fuel tank. We found no signals before this, so we do not believe that there was an external cause. The primary fuel tank ruptured 4 seconds later and was the strongest event by far, producing an infrasound signal that exceeded 1400 Pa ( 2000 Pa in reduced pressure). The seismic signal consists mainly of air-coupled Rayleigh waves with frequencies of 5-23 Hz. The infrasound events occurred in four clusters. The first cluster included the onset and main events and 46 smaller events. This was followed by several minutes without infrasound signals during which a 3.5 minute continuous seismic vibration occurred. Cluster 2 consisted of 4 events ranging from 117-256 Pa. Cluster 3 comprised 96 events of 7-78 Pa. Cluster 4 consisted of 5 events with overpressures of 23-63 Pa. Gaps of several minutes without infrasound and seismic signals occurred between clusters 2 and 3, and 3 and 4. In terms of energy, the main event dominated; in terms of numbers, cluster 3 had the most infrasound events. The seismic and infrasound data are complementary to video recordings of the explosion, and provide additional characterization that may be useful to interpret the sequence of events. Because of the proximity of our array to this rocket explosion, our dataset may be unique.

Upper-Mantel Earthquakes in the Australia-Pacific Plate Boundary Zone and the Roots of the Alpine Fault

NASA Astrophysics Data System (ADS)

Boese, C. M.; Warren-Smith, E.; Townend, J.; Stern, T. A.; Lamb, S. H.

2016-12-01

Seismicity in the upper mantle in continental collision zones is relatively rare, but observed around the world. Temporary seismometer deployments have repeatedly detected mantle earthquakes at depths of 40-100 km within the Australia-Pacific plate boundary zone beneath the South Island of New Zealand. Here, the transpressive Alpine Fault constitutes the primary plate boundary structure linking subduction zones of opposite polarity farther north and south. The Southern Alps Microearthquake Borehole Array (SAMBA) has been operating continuously since November 2008 along a 50 km-long section of the central Alpine Fault, where the rate of uplift of the Southern Alps is highest. To date it has detected more than 40 small to moderate-sized mantle events (1≤ML≤3.9). The Central Otago Seismic Array (COSA) has been in operation since late 2012 and detected 15 upper mantle events along the sub-vertical southern Alpine Fault. Various mechanisms have been proposed to explain the occurrence of upper mantle seismicity in the South Island, including intra-continental subduction (Reyners 1987, Geology); high shear-strain gradients due to depressed geotherms and viscous deformation of mantle lithosphere (Kohler and Eberhart-Phillips 2003, BSSA); high strain rates resulting from plate bending (Boese et al. 2013, EPSL), and underthrusting of the Australian plate (Lamb et al. 2015, G3). Focal mechanism analysis reveals a variety of mechanisms for the upper mantle events but predominantly strike-slip and reverse faulting. In this study, we apply spectral analysis to better constrain source parameters for these mantle events. These results are interpreted in conjunction with new information about crustal structure and low-frequency earthquakes near the Moho and in light of existing velocity, attenuation and resistivity models.

Thermally Induced Vibrations of the Hubble Space Telescope's Solar Array 3 in a Test Simulated Space Environment

NASA Technical Reports Server (NTRS)

Early, Derrick A.; Haile, William B.; Turczyn, Mark T.; Griffin, Thomas J. (Technical Monitor)

2001-01-01

NASA Goddard Space Flight Center and the European Space Agency (ESA) conducted a disturbance verification test on a flight Solar Array 3 (SA3) for the Hubble Space Telescope using the ESA Large Space Simulator (LSS) in Noordwijk, the Netherlands. The LSS cyclically illuminated the SA3 to simulate orbital temperature changes in a vacuum environment. Data acquisition systems measured signals from force transducers and accelerometers resulting from thermally induced vibrations of the SAI The LSS with its seismic mass boundary provided an excellent background environment for this test. This paper discusses the analysis performed on the measured transient SA3 responses and provides a summary of the results.

Apollo lunar surface experiments package. Apollo 17 ALSEP (array E) familiarization course handout

NASA Technical Reports Server (NTRS)

1972-01-01

The familiarization course for the Apollo 17 ALSEP (ARRAY E) is presented. The subjects discussed are: (1) power and data subsystems, (2) lunar surface gravimeter, (3) lunar mass spectrometer, (4) lunar seismic profiling experiment, and (5) heat flow experiment.

Seismic Migration Imaging of the Crust and Upper Mantle Discontinuity Structure beneath Southern Taiwan

NASA Astrophysics Data System (ADS)

Liu, Y.-S.; Kuo, B.-Y.

2009-04-01

Taiwan is located in the convergent plate boundary zone where the Philippine Sea plate has obliquely collided on the Asian continental margin, initiating the arc-continent collision and subsequent mountain-building in Taiwan. Receiver function has been a powerful tool to image seismic velocity discontinuity structure in the crust and upper mantle which can help illuminate the deep dynamic process of active Taiwan orogeny. In this study, we adopt backprojection migration processing of teleseismic receiver functions to investigate the crust and upper mantle discontinuities beneath southern Taiwan, using the data from Southern Taiwan Transect Seismic Array (STTA), broadband stations of Central Weather Bureau (CWB), Broadband Array in Taiwan for Seismology (BATS), and Taiwan Integrated Geodynamics Research (TAIGER). This composite east-west trending linear array has the aperture of about 150 km with the station spacing of ~5-10 km. Superior to the common midpoint (CMP) stack approach, the migration can properly image the dipping, curved, or laterally-varying topography of discontinuous interfaces which very likely exist under the complicated tectonic setting of Taiwan. We first conduct synthetic experiments to test the depth and lateral resolution of migration images based on the WKBJ synthetic waveforms calculated from available source and receiver distributions. We will next construct the 2-D migration image under the array to reveal the topographic variation of the Moho and lithosphere discontinuities beneath southern Taiwan.

Structure and tectonics of the Main Himalayan Thrust and associated faults from recent earthquake and seismic imaging studies using the NAMASTE array

NASA Astrophysics Data System (ADS)

Karplus, M. S.; Pant, M.; Velasco, A. A.; Nabelek, J.; Kuna, V. M.; Sapkota, S. N.; Ghosh, A.; Mendoza, M.; Adhikari, L. B.; Klemperer, S. L.

2017-12-01

The India-Eurasia collision zone presents a significant earthquake hazard, as demonstrated by the recent, devastating April 25, 2015 M=7.8 Gorkha earthquake and the following May 12, 2015 M=7.3 earthquake. Important questions remain, including distinguishing possible geometries of the Main Himalayan Thrust (MHT), the role of other regional faults, the crustal composition and role of fluids in faulting, and the details of the rupture process, including structural causes and locations of rupture segmentation both along-strike and down-dip. These recent earthquakes and their aftershocks provide a unique opportunity to learn more about this collision zone. In June 2015, funded by NSF, we deployed the Nepal Array Measuring Aftershock Seismicity Trailing Earthquake (NAMASTE) array of 46 seismic stations distributed across eastern and central Nepal, spanning the region with most of the aftershocks. This array remained in place for 11 months from June 2015 to May 2016. We combine new results from this aftershock network in Nepal with previous geophysical and geological studies across the Himalaya to derive a new understanding of the tectonics of the Himalaya and southern Tibet in Nepal and surrounding countries. We focus on structure and composition of the Main Himalayan Thrust and compare this continent-continent subduction megathrust with megathrusts in other subduction zones.

Infrasound from thunder: A natural seismic source

NASA Astrophysics Data System (ADS)

Lin, Ting-L.; Langston, Charles A.

2007-07-01

A small array consisting of five three-component short-period surface seismometers, a three-component borehole seismometer, and five infrasound microphones was built to investigate thunder-induced ground motions. Data from two thunder events with similar N-wave waveforms but different horizontal slownesses are chosen as examples of data collected by the array. These impulsive acoustic waves excited P and S reverberations in the near surface that depend on both the incident wave horizontal slowness and the velocity structure in the upper 30 meters at the site. Although the depth of the borehole is relatively shallow compared to a seismic wave wavelength, velocity amplitude in the radial component decays as much as 63 percent with depth but vertical component amplitudes are unaffected consistent with air-coupled Rayleigh wave excitation. Naturally occurring thunder appears to be a useful seismic source to empirically determine site resonance characteristics for hazards assessments.

High-resolution probing of inner core structure with seismic interferometry

NASA Astrophysics Data System (ADS)

Huang, Hsin-Hua; Lin, Fan-Chi; Tsai, Victor C.; Koper, Keith D.

2015-12-01

Increasing complexity of Earth's inner core has been revealed in recent decades as the global distribution of seismic stations has improved. The uneven distribution of earthquakes, however, still causes a biased geographical sampling of the inner core. Recent developments in seismic interferometry, which allow for the retrieval of core-sensitive body waves propagating between two receivers, can significantly improve ray path coverage of the inner core. In this study, we apply such earthquake coda interferometry to 1846 USArray stations deployed across the U.S. from 2004 through 2013. Clear inner core phases PKIKP2 and PKIIKP2 are observed across the entire array. Spatial analysis of the differential travel time residuals between the two phases reveals significant short-wavelength variation and implies the existence of strong structural variability in the deep Earth. A linear N-S trending anomaly across the middle of the U.S. may reflect an asymmetric quasi-hemispherical structure deep within the inner core with boundaries of 99°W and 88°E.

Geophysical examination of coal deposits

NASA Astrophysics Data System (ADS)

Jackson, L. J.

1981-04-01

Geophysical techniques for the solution of mining problems and as an aid to mine planning are reviewed. Techniques of geophysical borehole logging are discussed. The responses of the coal seams to logging tools are easily recognized on the logging records. Cores for laboratory analysis are cut from selected sections of the borehole. In addition, information about the density and chemical composition of the coal may be obtained. Surface seismic reflection surveys using two dimensional arrays of seismic sources and detectors detect faults with throws as small as 3 m depths of 800 m. In geologically disturbed areas, good results have been obtained from three dimensional surveys. Smaller faults as far as 500 m in advance of the working face may be detected using in seam seismic surveying conducted from a roadway or working face. Small disturbances are detected by pulse radar and continuous wave electromagnetic methods either from within boreholes or from underground. Other geophysical techniques which explicit the electrical, magnetic, gravitational, and geothermal properties of rocks are described.

Spatiotemporal distribution of the seismicity along the Mid-Atlantic Ridge north of the Azores from hydroacoustic data: Insights into seismogenic processes in a ridge-hot spot context

NASA Astrophysics Data System (ADS)

Goslin, J.; Perrot, J.; Royer, J.-Y.; Martin, C.; LourençO, N.; Luis, J.; Dziak, R. P.; Matsumoto, H.; Haxel, J.; Fowler, M. J.; Fox, C. G.; Lau, A. T.-K.; Bazin, S.

2012-02-01

The seismicity of the North Atlantic was monitored from May 2002 to September 2003 by the `SIRENA array' of autonomous hydrophones. The hydroacoustic signals provide a unique data set documenting numerous low-magnitude earthquakes along the section of the Mid-Atlantic Ridge (MAR) located in a ridge-hot spot interaction context. During the experiment, 1696 events were detected along the MAR axis between 40°N and 51°N, with a magnitude of completeness level ofmb≈ 2.4. Inside the array, location errors are in the order of 2 km, and errors in the origin time are less than 1 s. From this catalog, 15 clusters were detected. The distribution of source level (SL) versus time within each cluster is used to discriminate clusters occurring in a tectonic context from those attributed to non-tectonic (i.e. volcanic or hydrothermal) processes. The location of tectonic and non-tectonic sequences correlates well with regions with positive and negative Mantle Bouguer Anomalies (MBAs), indicating the presence of thinner/colder and thicker/warmer crust respectively. At the scale of the entire array, both the complete and declustered catalogs derived from the hydroacoustic signals show an increase of the seismicity rate from the Azores up to 43°30'N suggesting a diminishing influence of the Azores hot spot on the ridge-axis temperature, and well correlated with a similar increase in the along-axis MBAs. The comparison of the MAR seismicity with the Residual MBA (RMBA) at different scales leads us to think that the low-magnitude seismicity rates are directly related to along-axis variations in lithosphere rheology and temperatures.

Monitoring the West Bohemian earthquake swarm in 2008/2009 by a temporary small-aperture seismic array

NASA Astrophysics Data System (ADS)

Hiemer, Stefan; Roessler, Dirk; Scherbaum, Frank

2012-04-01

The most recent intense earthquake swarm in West Bohemia lasted from 6 October 2008 to January 2009. Starting 12 days after the onset, the University of Potsdam monitored the swarm by a temporary small-aperture seismic array at 10 km epicentral distance. The purpose of the installation was a complete monitoring of the swarm including micro-earthquakes ( M L < 0). We identify earthquakes using a conventional short-term average/long-term average trigger combined with sliding-window frequency-wavenumber and polarisation analyses. The resulting earthquake catalogue consists of 14,530 earthquakes between 19 October 2008 and 18 March 2009 with magnitudes in the range of - 1.2 ≤ M L ≤ 2.7. The small-aperture seismic array substantially lowers the detection threshold to about M c = - 0.4, when compared to the regional networks operating in West Bohemia ( M c > 0.0). In the course of this work, the main temporal features (frequency-magnitude distribution, propagation of back azimuth and horizontal slowness, occurrence rate of aftershock sequences and interevent-time distribution) of the recent 2008/2009 earthquake swarm are presented and discussed. Temporal changes of the coefficient of variation (based on interevent times) suggest that the swarm earthquake activity of the 2008/2009 swarm terminates by 12 January 2009. During the main phase in our studied swarm period after 19 October, the b value of the Gutenberg-Richter relation decreases from 1.2 to 0.8. This trend is also reflected in the power-law behavior of the seismic moment release. The corresponding total seismic moment release of 1.02×1017 Nm is equivalent to M L,max = 5.4.

Theoretical and practical considerations for the design of the iMUSH active-source seismic experiment

NASA Astrophysics Data System (ADS)

Kiser, E.; Levander, A.; Harder, S. H.; Abers, G. A.; Creager, K. C.; Vidale, J. E.; Moran, S. C.; Malone, S. D.

2013-12-01

The multi-disciplinary imaging of Magma Under St. Helens (iMUSH) experiment seeks to understand the details of the magmatic system that feeds Mount St. Helens using active- and passive-source seismic, magnetotelluric, and petrologic data. The active-source seismic component of this experiment will take place in the summer of 2014 utilizing all of the 2600 PASSCAL 'Texan' Reftek instruments which will record twenty-four 1000-2000 lb shots distributed around the Mount St. Helens region. The instruments will be deployed as two consecutive refraction profiles centered on the volcano, and a series of areal arrays. The actual number of areal arrays, as well as their locations, will depend strongly on the length of the experiment (3-4 weeks), the number of instrument deployers (50-60), and the time it will take per deployment given the available road network. The current work shows how we are balancing these practical considerations against theoretical experiment designs in order to achieve the proposed scientific goals with the available resources. One of the main goals of the active-source seismic experiment is to image the magmatic system down to the Moho (35-40 km). Calculating sensitivity kernels for multiple shot/receiver offsets shows that direct P waves should be sensitive to Moho depths at offsets of 150 km, and therefore this will likely be the length of the refraction profiles. Another primary objective of the experiment is to estimate the locations and volumes of different magma accumulation zones beneath the volcano using the areal arrays. With this in mind, the optimal locations of these arrays, as well as their associated shots, are estimated using an eigenvalue analysis of the approximate Hessian for each possible experiment design. This analysis seeks to minimize the number of small eigenvalues of the approximate Hessian that would amplify the propagation of data noise into regions of interest in the model space, such as the likely locations of magma reservoirs. In addition, this analysis provides insight into the tradeoff between the number of areal array deployments and the information that will be gained from the experiment. An additional factor incorporated into this study is the expected data quality in different regions around Mount St. Helens. Expected data quality is determined using the signal-to-noise ratios of data from existing seismometers in the region, and from forward modeling the wavefields from different experiment designs using SPECFEM3D software. In particular, we are interested in evaluating how topography near the volcano and low velocity volcaniclastic layers affect data quality. This information is especially important within 5 km of the volcano where only hiking trails are available for instrument deployment, and in a large area north of the volcano where road maintenance has lagged since the 1980 eruption. Instrument deployment will be slow in these regions, and therefore it is essential to understand if deployment of instruments here is a reasonable use of resources. A final step of this study will be validating different experiment designs based upon the above criteria by inverting synthetic data from velocity models that contain a generalized representation of the magma system to confirm that the main features of the models can be recovered.

The NSF Earthscope USArray Instrumentation Network

NASA Astrophysics Data System (ADS)

Davis, G. A.; Vernon, F.

2012-12-01

Since 2004, the Transportable Array component of the USArray Instrumentation Network has collected high resolution seismic data in near real-time from over 400 geographically distributed seismic stations. The deployed footprint of the array has steadily migrated across the continental United States, starting on the west coast and gradually moving eastward. As the network footprint shifts, stations from various regional seismic networks have been incorporated into the dataset. In 2009, an infrasound and barometric sensor component was added to existing core stations and to all new deployments. The ongoing success of the project can be attributed to a number of factors, including reliable communications to each site, on-site data buffering, largely homogenous data logging hardware, and a common phase-locked time reference between all stations. Continuous data quality is ensured by thorough human and automated review of data from the primary sensors and over 24 state-of-health parameters from each station. The staff at the Array Network Facility have developed a number of tools to visualize data and troubleshoot problematic stations remotely. In the event of an emergency or maintenance on the server hardware, data acquisition can be shifted to alternate data centers through the use of virtualization technologies.

Seismic and Biological Sources of Ambient Ocean Sound

NASA Astrophysics Data System (ADS)

Freeman, Simon Eric

Sound is the most efficient radiation in the ocean. Sounds of seismic and biological origin contain information regarding the underlying processes that created them. A single hydrophone records summary time-frequency information from the volume within acoustic range. Beamforming using a hydrophone array additionally produces azimuthal estimates of sound sources. A two-dimensional array and acoustic focusing produce an unambiguous two-dimensional `image' of sources. This dissertation describes the application of these techniques in three cases. The first utilizes hydrophone arrays to investigate T-phases (water-borne seismic waves) in the Philippine Sea. Ninety T-phases were recorded over a 12-day period, implying a greater number of seismic events occur than are detected by terrestrial seismic monitoring in the region. Observation of an azimuthally migrating T-phase suggests that reverberation of such sounds from bathymetric features can occur over megameter scales. In the second case, single hydrophone recordings from coral reefs in the Line Islands archipelago reveal that local ambient reef sound is spectrally similar to sounds produced by small, hard-shelled benthic invertebrates in captivity. Time-lapse photography of the reef reveals an increase in benthic invertebrate activity at sundown, consistent with an increase in sound level. The dominant acoustic phenomenon on these reefs may thus originate from the interaction between a large number of small invertebrates and the substrate. Such sounds could be used to take census of hard-shelled benthic invertebrates that are otherwise extremely difficult to survey. A two-dimensional `map' of sound production over a coral reef in the Hawaiian Islands was obtained using two-dimensional hydrophone array in the third case. Heterogeneously distributed bio-acoustic sources were generally co-located with rocky reef areas. Acoustically dominant snapping shrimp were largely restricted to one location within the area surveyed. This distribution of sources could reveal small-scale spatial ecological limitations, such as the availability of food and shelter. While array-based passive acoustic sensing is well established in seismoacoustics, the technique is little utilized in the study of ambient biological sound. With the continuance of Moore's law and advances in battery and memory technology, inferring biological processes from ambient sound may become a more accessible tool in underwater ecological evaluation and monitoring.

Global Seismic Monitoring: Past, Present, and Future

NASA Astrophysics Data System (ADS)

Zoback, M.; Benz, H.; Oppenheimer, D.

2007-12-01

Global seismological observations began in April 1889 when an earthquake in Tokyo, Japan was accurately recorded in Germany on two different horizontal pendulum instruments. However, modern global observational seismology really began 46 years ago when the 120-station World Wide Standard Seismograph Network was installed by the US to monitor underground nuclear tests and earthquakes using well-calibrated short- and long- period stations. At the same time rapid advances in computing technology enabled researchers to begin sophisticated analysis of the increasing amount of seismic data, which led to better understanding of earthquake source properties and their use in establishing plate tectonics. Today, global seismic networks are operated by German (Geophon), France (Geoscope), the United States (Global Seismograph Network) and the International Monitoring System. Presently, the Federation of Digital Seismograph Networks registers more than 1,000 broadband stations world-wide, a small percentage of the total number of digital seismic stations around the world. Following the devastating Kobe, Japan and Northridge, California earthquakes, Japan and the US have led the world in the integration of existing seismic sensor systems (weak and strong motion) into development of near-real-time, post-earthquake response products like ShakeMap, detailing the spatial distribution of strong shaking. Future challenges include expanding real-time integration of both seismic and geodetic sensor systems to produce early warning of strong shaking, rapid source determination, as well as near-realtime post- earthquake damage assessment. Seismic network data, hydro-acoustic arrays, deep water tide gauges, and satellite imagery of wave propagation should be integrated in real-time to provide input for hydrodynamic modeling yielding the distribution, timing and size of tsunamis runup--which would then be available instantly on the web, e.g. in a Google Earth format. Dense arrays of strong motion sensors together with deployment of MEMS-type accelerometers in buildings and equipment routinely connected to the Web could potentially provide thousands of measurements of damaging strong ground motion. This technology could ultimately become part of smart building design enabling critical facilities to change their structural response to imminent strong shaking. Looking further forward, it is likely that a continuously observing spaceborne system could image the occurrence of "silent" or "slow" earthquakes as well as the propagation of ground displacement by surface waves at scales of continents.

Seismic Interferometry of Gulf of Mexico Basin Opening (GUMBO) Data: Extraction of Body and Surface Waves with a Mixed-Mode Array

NASA Astrophysics Data System (ADS)

Thangraj, J. S.; Quiros, D.; Pulliam, J.

2017-12-01

The Gulf of Mexico (GoM) is a relative small oceanic basin that formed by rifting between the continental blocks of North America and Yucatan in the Middle to Late Jurassic. Following the breakup, seafloor spreading continued until the Early Cretaceous. Since then, subsidence and sedimentation have shaped the GoM margin that we see today. To better understand the opening of the GoM, a long-offset (307 km) seismic refraction line was acquired in 2010. The transect was located on the northwest GoM margin, and consisted of several types of instruments. This mixed-mode array combined 31 ocean bottom seismographs (OBS), 412 high-frequency instruments (4.5 Hz geophones with RefTek 125A "Texan" digitizers) and 12 broadband stations. The R/V Iron Cat provided the airgun source used in the refraction experiment. The airgun generated 2028 shots in a period of 2.5 days which were recorded by the entire array. The airgun-generated seismic energy was clearly visible on the OBS recordings, however its amplitude was too low to be discerned on most of the onshore stations. In fact, this energy was only visible on Texan stations 1-50 (station 1 is located at the coast), extending 18 km inland, limiting the extend of the velocity model that can be obtained. Here, we apply seismic interferometry techniques to the 2.5 days of continuous data recorded by the Texan array with the goal of extending the spatial range for which the airgun-generated seismic energy can be observed. Preliminary results show that by treating the 2.5 days of continuously recorded airgun data as ambient noise, and applying time-domain cross-correlation, we can observe energy propagating 50 to 70 km inland with apparent velocities of 1800 - 2200 ms-1. These velocities agree with the compressional seismic velocity for the top 5 km of sediments under the GoM obtained from the OBS records, suggesting that we are observing compressional energy in the virtual source gathers (VSG). We also observe arrivals in the VSG that exhibit dispersive behavior, which we interpret to be Rayleigh waves. Current efforts are focused on extending the spatial range of the airgun-generated seismic energy further inland (> 70 km) by creating more VSG, to obtain a body wave velocity model along the transect. Similarly, we are inverting the Rayleigh waves in the VSG to obtain a shear wave velocity model.

Preliminary results of receiver function analysis of seismic data recorded from a broadband deployment across the Gulf Coast Plain

NASA Astrophysics Data System (ADS)

Gurrola, H.; Pratt, K. W.; Pulliam, J.; Dunbar, J. A.

2011-12-01

In summer of 2010, 21 broadband seismographs were installed at 16-18 km spacing along a transect running from Johnson City, TX, (on the Edwards Plateau), to Matagorda Island to study the current structure of this rifted passive margin. The large magnetic anomaly that parallels the coast throughout the Gulf region moves on-shore beneath our transect such that we will be able to investigate the source of this anomaly. A second important target that will be imaged in this Balcones fault which is associated with the Ouachita front. This project is funded by a grant from the Norman Hackerman Advanced Research Program (NHARP), a biannual competition among Texas Universities to support research, and makes use of Texas Tech, Baylor, and UT Austin equipment. As a result, the deployment includes a less uniform array of seismic equipment, (10 Trillium compact seismometers and 10 Guralps; including 40Ts, 3Ts and 3ESPs), than projects supported by the IRIS PASSCAL center. Our vault construction was similar to Flexible array vaults, but Gulf Coast provides a more challenging environment for deployment than most encountered in the western US. The shallow water table and loose sediment can become almost fluid when storms deluge the area with rain. In dry periods, mud cracks near the vaults cause the vaults to tilt. As a result, even high quality, shallow seismic vaults can "float" or shift sufficiently to cause one or two components of the seismic stations to drift against their stops in days or weeks. As a result, the only data consistently available from all our stations, are vertical components. Horizontal component data from the summer of 2010 can be hit and miss due to the tilting of the vaults. These issues have been reduced in the summer of 2011 due to the drought. To address the data's shortcomings, we will average the vertical components from our stations and nearby EarthScope TA stations, (up 300 km away), to isolate the cleanest representation of the incoming P-wave, (with local PPp reverberations averaged out). This is essentially beam forming for the optimal teleseismic ray path. The clean P-wave will then be deconvolved from the vertical components at each station to produce a vertical component receiver function that will enable us to model and stack local P-wave reverberations to produce a 2-D image of lithospheric structure. To produce traditional receiver functions from time periods where one component is lost from several stations, we will treat neighboring stations as arrays and recover an "array averaged three-component seismogram" for each loacation. These "beamed" seismograms will allow imaging of the crust, lithospheric mantle, and transition zone beneath the broadband array using traditional receiver function stacking or migration.

Seismic and Infrasound Energy Generation and Propagation at Local and Regional Distances Phase 1 - Divine Strake Experiment

DTIC Science & Technology

2007-10-11

large mine collapse (M=3.9) and shallow earthquake (M=3.9) indicates that there were no signals generated by these events. A new type of infrasound ...provide data to document the propagation of the acoustic signals between the infrasound array sites and allow us to estimate group velocities since...in near-source acoustic and seismic signals . 10 Near-source acoustic and seismic signals recorded at UTTR3 Explosion generated infrasound signals

Upper-mantle deformation beneath the Pyrenean domain inferred from SKS splitting in northern Spain and southern France

NASA Astrophysics Data System (ADS)

Bonnin, Mickaël; Chevrot, Sébastien; Gaudot, Ianis; Haugmard, Méric

2017-08-01

We performed shear wave splitting analysis on 203 permanent (French RLPB, CEA and Catalonian networks) and temporary (PyrOPE and IberArray experiments) broad-band stations around the Pyrenees. These measurements considerably enhance the spatial resolution and coverage of seismic anisotropy in that region. In particular, we characterize with different shear wave splitting analysis methods the small-scale variations of splitting parameters ϕ and δt along three dense transects crossing the western and central Pyrenees with an interstation spacing of about 7 km. While we find a relatively coherent seismic anisotropy pattern in the Pyrenean domain, we observe abrupt changes of splitting parameters in the Aquitaine Basin and delay times along the Pyrenees. We moreover observe coherent fast directions despite complex lithospheric structures in Iberia and the Massif Central. This suggests that two main sources of anisotropy are required to interpret seismic anisotropy in this region: (i) lithospheric fabrics in the Aquitaine Basin (probably frozen-in Hercynian anisotropy) and in the Pyrenees (early and late Pyrenean dynamics); (ii) asthenospheric mantle flow beneath the entire region (imprint of the western Mediterranean dynamics since the Oligocene).

Upper-Mantle Deformation Beneath the Pyrenean Domain Inferred from SKS Splitting in Northern Spain and Southern France

NASA Astrophysics Data System (ADS)

Bonnin, M. J. A.; Chevrot, S.; Gaudot, I.; Haugmard, M.

2017-12-01

We performed shear wave splitting analysis on 203 permanent (French RLPB, CEA and Catalonian networks) and temporary (PYROPE and IberArray experiments) broad-band stations around the Pyrenees. These measurements considerably enhance the spatial resolution and coverage of seismic anisotropy in that region. In particular, we characterize with different shear wave splitting analysis methods the small-scale variations of splitting parameters φ and δt along three dense transects crossing the western and central Pyrenees with an interstation spacing of about 7 km. While we find a relatively coherent seismic anisotropy pattern in the Pyrenean domain, we observe abrupt changes of splitting parameters in the Aquitaine Basin and delay times along the Pyrenees. We moreover observe coherent fast directions despite complex lithospheric structures in Iberia and the Massif Central. This suggests that two main sources of anisotropy are required to interpret seismic anisotropy in this region: (i) lithospheric fabrics in the Aquitaine Basin (probably frozen-in Hercynian anisotropy) and in the Pyrenees (early and late Pyrenean dynamics); (ii) asthenospheric mantle flow beneath the entire region (imprint of the western Mediterranean dynamics since the Oligocene).

Seismic velocity change and slip rate during the 2006 Guerrero (Mexico) slow slip event

NASA Astrophysics Data System (ADS)

Rivet, Diane; Radiguet, Mathilde; Campillo, Michel; Cotton, Fabrice; Shapiro, Nikolai; Krishna Singh, Shri; Kostoglodov, Vladimir

2010-05-01

We measure temporal change of the seismic velocity in the crust below the Guerrero region during the 2006 slow sleep event (SSE). We use repeated cross-correlations of ambient seismic noise recorded at 26 broad-band stations of the MesoAmerica Seismic Experiment (MASE). The cross-correlations are computed over 90 days with a moving window of 10 days from January 2005 to July 2007. To insure measurements independent of noise source variations, we only take into account the travel time change within the coda. For period of 8 to 20s, we observe a decrease in velocity starting in April 2006 with a maximum change of -0.3% of the initial velocity in June 2006. At these periods, the Rayleigh waves are sensitive to velocity changes down to the lower crust. In the other hand, we compute the deformation rate below the MASE array from a slip propagation model of the SSE observed by means of the displacement time-series of 15 continuous GPS stations. Slip initiates in the western part of the Guerrero Gap and propagates southeastward. The propagation velocity is of the order of 1 km/day. We then compare the seismic velocity change measured from continuous seismological data with the deformation rate inferred from geodetic measurements below the MASE array. We obtain a good agreement between the time of maximal seismic velocity change (July 2006) and the time of maximum deformation associated with the SSE (July to August 2006). This result shows that the long-term velocity change associated with the SSE can be detected using continuous seismic recordings. Since the SSE does not emit seismic waves, which interact with the superficial layers, the result indicates that the velocity change is due to deformation at depth.

BASE Flexible Array Preliminary Lithospheric Structure Analysis

NASA Astrophysics Data System (ADS)

Yeck, W. L.; Sheehan, A. F.; Anderson, M. L.; Siddoway, C. S.; Erslev, E.; Harder, S. H.; Miller, K. C.

2009-12-01

The Bighorns Arch Seismic Experiment (BASE) is a Flexible Array experiment integrated with EarthScope. The goal of BASE is to develop a better understanding of how basement-involved foreland arches form and what their link is to plate tectonic processes. To achieve this goal, the crustal structure under the Bighorn Mountain range, Bighorn Basin, and Powder River Basin of northern Wyoming and southern Montana are investigated through the deployment of 35 broadband seismometers, 200 short period seismometers, 1600 “Texan” instruments using active sources and 800 “Texan” instruments monitoring passive sources, together with field structural analysis of brittle structures. The novel combination of these approaches and anticipated simultaneous data inversion will give a detailed structural crustal image of the Bighorn region at all levels of the crust. Four models have been proposed for the formation of the Bighorn foreland arch: subhorizontal detachment within the crust, lithospheric buckling, pure shear lithospheric thickening, and fault blocks defined by lithosphere-penetrating thrust faults. During the summer of 2009, we deployed 35 broadband instruments, which have already recorded several magnitude 7+ teleseismic events. Through P wave receiver function analysis of these 35 stations folded in with many EarthScope Transportable Array stations in the region, we present a preliminary map of the Mohorovicic discontinuity. This crustal map is our first test of how the unique Moho geometries predicted by the four hypothesized models of basement involved arches fit seismic observations for the Bighorn Mountains. In addition, shear-wave splitting analysis for our first few recorded teleseisms helps us determine if strong lithospheric deformation is preserved under the range. These analyses help lead us to our final goal, a complete 4D (3D spatial plus temporal) lithospheric-scale model of arch formation which will advance our understanding of the mechanisms accommodating and driving basement-involved arch formation as well as continental lithospheric rheology.

An automated multi-scale network-based scheme for detection and location of seismic sources

NASA Astrophysics Data System (ADS)

Poiata, N.; Aden-Antoniow, F.; Satriano, C.; Bernard, P.; Vilotte, J. P.; Obara, K.

2017-12-01

We present a recently developed method - BackTrackBB (Poiata et al. 2016) - allowing to image energy radiation from different seismic sources (e.g., earthquakes, LFEs, tremors) in different tectonic environments using continuous seismic records. The method exploits multi-scale frequency-selective coherence in the wave field, recorded by regional seismic networks or local arrays. The detection and location scheme is based on space-time reconstruction of the seismic sources through an imaging function built from the sum of station-pair time-delay likelihood functions, projected onto theoretical 3D time-delay grids. This imaging function is interpreted as the location likelihood of the seismic source. A signal pre-processing step constructs a multi-band statistical representation of the non stationary signal, i.e. time series, by means of higher-order statistics or energy envelope characteristic functions. Such signal-processing is designed to detect in time signal transients - of different scales and a priori unknown predominant frequency - potentially associated with a variety of sources (e.g., earthquakes, LFE, tremors), and to improve the performance and the robustness of the detection-and-location location step. The initial detection-location, based on a single phase analysis with the P- or S-phase only, can then be improved recursively in a station selection scheme. This scheme - exploiting the 3-component records - makes use of P- and S-phase characteristic functions, extracted after a polarization analysis of the event waveforms, and combines the single phase imaging functions with the S-P differential imaging functions. The performance of the method is demonstrated here in different tectonic environments: (1) analysis of the one year long precursory phase of 2014 Iquique earthquake in Chile; (2) detection and location of tectonic tremor sources and low-frequency earthquakes during the multiple episodes of tectonic tremor activity in southwestern Japan.

Three-component borehole wall-locking seismic detector

DOEpatents

Owen, Thomas E.

1994-01-01

A seismic detector for boreholes is described that has an accelerometer sensor block for sensing vibrations in geologic formations of the earth. The density of the seismic detector is approximately matched to the density of the formations in which the detector is utilized. A simple compass is used to orient the seismic detector. A large surface area shoe having a radius approximately equal to the radius of the borehole in which the seismic detector is located may be pushed against the side of the borehole by actuating cylinders contained in the seismic detector. Hydraulic drive of the cylinders is provided external to the detector. By using the large surface area wall-locking shoe, force holding the seismic detector in place is distributed over a larger area of the borehole wall thereby eliminating concentrated stresses. Borehole wall-locking forces up to ten times the weight of the seismic detector can be applied thereby ensuring maximum detection frequency response up to 2,000 hertz using accelerometer sensors in a triaxial array within the seismic detector.

International Monitoring System Correlation Detection at the North Korean Nuclear Test Site at Punggye-ri with Insights from the Source Physics Experiment

DOE PAGES

Ford, Sean R.; Walter, William R.

2015-05-06

Seismic waveform correlation offers the prospect of greatly reducing event detection thresholds when compared with more conventional processing methods. Correlation is applicable for seismic events that in some sense repeat, that is they have very similar waveforms. A number of recent studies have shown that correlated seismic signals may form a significant fraction of seismicity at regional distances. For the particular case of multiple nuclear explosions at the same test site, regional distance correlation also allows very precise relative location measurements and could offer the potential to lower thresholds when multiple events exist. Using the Comprehensive Nuclear-Test-Ban Treaty (CTBT) Internationalmore » Monitoring System (IMS) seismic array at Matsushiro, Japan (MJAR), Gibbons and Ringdal (2012) were able to create a multichannel correlation detector with a very low false alarm rate and a threshold below magnitude 3.0. They did this using the 2006 or 2009 Democratic People’s Republic of Korea (DPRK) nuclear explosion as a template to search through a data stream from the same station to find a match via waveform correlation. In this paper, we extend the work of Gibbons and Ringdal (2012) and measure the correlation detection threshold at several other IMS arrays. We use this to address three main points. First, we show the IMS array station at Mina, Nevada (NVAR), which is closest to the Nevada National Security Site (NNSS), is able to detect a chemical explosion that is well under 1 ton with the right template. Second, we examine the two IMS arrays closest to the North Korean (DPRK) test site (at Ussuriysk, Russian Federation [USRK] and Wonju, Republic of Korea [KSRS]) to show that similarly low thresholds are possible when the right templates exist. We also extend the work of Schaff et al. (2012) and measure the correlation detection threshold at the nearest Global Seismic Network (GSN) three-component station (MDJ) at Mudanjiang, Heilongjiang Province, China, from the New China Digital Seismograph Network (IC). To conclude, we use these results to explore the recent claim by Zhang and Wen (2015) that the DPRK conducted “…a low-yield nuclear test…” on 12 May 2010.« less

The Central and Eastern U.S. Seismic Network: Legacy of USArray

NASA Astrophysics Data System (ADS)

Eakins, J. A.; Astiz, L.; Benz, H.; Busby, R. W.; Hafner, K.; Reyes, J. C.; Sharer, G.; Vernon, F.; Woodward, R.

2014-12-01

As the USArray Transportable Array entered the central and eastern United States, several Federal agencies (National Science Foundation, U.S. Geological Survey, U.S. Nuclear Regulatory Commission, and Department of Energy) recognized the unique opportunity to retain TA stations beyond the original timeline. The mission of the CEUSN is to produce data that enables researchers and Federal agencies alike to better understand the basic geologic questions, background earthquake rates and distribution, seismic hazard potential, and associated societal risks of this region. The selected long-term sub-array from Transportable Array (TA) stations includes nearly 200 sites, complemented by 100 broadband stations from the existing regional seismic networks to form the Central and Eastern United States Network (CEUSN). Multiple criteria for site selection were weighed by an inter-agency TA Station Selection (TASS) Working Group: seismic noise characteristics, data availability in real time, proximity to nuclear power plants, and homogeneous distribution throughout the region. The Array Network Facility (ANF) started collecting data for CEUSN network stations since late 2013, with all stations collected since May 2014. Regional seismic data streams are collected in real-time from the IRIS Data Management Center (DMC). TA stations selected to be part of CEUSN, retain the broadband sensor to which a 100 sps channel is added, the infrasound and environmental channels, and, at some stations, accelerometers are deployed. The upgraded sites become part of the N4 network for which ANF provides metadata and can issue remote commands to the station equipment. Stations still operated by TA, but planned for CEUSN, are included in the virtual network so all stations are currently available now. By the end of 2015, the remaining TA stations will be upgraded. Data quality control procedures developed for TA stations at ANF and at the DMC are currently performed on N4 data. However, teleseismic and regional events are only picked a few times a month to fulfill data quality checks on the data. The assembled CEUSN data sets can be requested from the DMC with the _CEUSN virtual network code. Acknowledgments to Seismic Regional Network Operators: C. Ammon, J. Ebel, D. Doser, R. Hermann, A. Holland, W-Y. Kim, C. Langston, T. Owens, and M. Withers.

Passive monitoring of a sea dike during a tidal cycle using sea waves as a seismic noise source

NASA Astrophysics Data System (ADS)

Joubert, Anaëlle; Feuvre, Mathieu Le; Cote, Philippe

2018-05-01

Over the past decade, ambient seismic noise has been used successfully to monitor various geological objects with high accuracy. Recently, it has been shown that surface seismic waves propagating within a sea dike body can be retrieved from the cross-correlation of ambient seismic noise generated by sea waves. We use sea wave impacts to monitor the response of a sea dike during a tidal cycle using empirical Green's functions. These are obtained either by cross-correlation or deconvolution, from signals recorded by sensors installed linearly on the crest of a dike. Our analysis is based on delay and spectral amplitude measurements performed on reconstructed surface waves propagating along the array. We show that localized variations of velocity and attenuation are correlated with changes in water level as a probable consequence of water infiltration inside the structure. Sea dike monitoring is of critical importance for safety and economic reasons, as internal erosion is generally only detected at late stages by visual observations. The method proposed here may provide a solution for detecting structural weaknesses, monitoring progressive internal erosion, and delineating areas of interest for further geotechnical studies, in view to understanding the erosion mechanisms involved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harben, P E; Harris, D; Myers, S

Seismic imaging and tracking methods have intelligence and monitoring applications. Current systems, however, do not adequately calibrate or model the unknown geological heterogeneity. Current systems are also not designed for rapid data acquisition and analysis in the field. This project seeks to build the core technological capabilities coupled with innovative deployment, processing, and analysis methodologies to allow seismic methods to be effectively utilized in the applications of seismic imaging and vehicle tracking where rapid (minutes to hours) and real-time analysis is required. The goal of this project is to build capabilities in acquisition system design, utilization and in full 3Dmore » finite difference modeling as well as statistical characterization of geological heterogeneity. Such capabilities coupled with a rapid field analysis methodology based on matched field processing are applied to problems associated with surveillance, battlefield management, finding hard and deeply buried targets, and portal monitoring. This project benefits the U.S. military and intelligence community in support of LLNL's national-security mission. FY03 was the final year of this project. In the 2.5 years this project has been active, numerous and varied developments and milestones have been accomplished. A wireless communication module for seismic data was developed to facilitate rapid seismic data acquisition and analysis. The E3D code was enhanced to include topographic effects. Codes were developed to implement the Karhunen-Loeve (K-L) statistical methodology for generating geological heterogeneity that can be utilized in E3D modeling. The matched field processing methodology applied to vehicle tracking and based on a field calibration to characterize geological heterogeneity was tested and successfully demonstrated in a tank tracking experiment at the Nevada Test Site. A 3-seismic-array vehicle tracking testbed was installed on-site at LLNL for testing real-time seismic tracking methods. A field experiment was conducted over a tunnel at the Nevada Site that quantified the tunnel reflection signal and, coupled with modeling, identified key needs and requirements in experimental layout of sensors. A large field experiment was conducted at the Lake Lynn Laboratory, a mine safety research facility in Pennsylvania, over a tunnel complex in realistic, difficult conditions. This experiment gathered the necessary data for a full 3D attempt to apply the methodology. The experiment also collected data to analyze the capabilities to detect and locate in-tunnel explosions for mine safety and other applications.« less

Expanding Coherent Array Processing to Larger Apertures Using Empirical Matched Field Processing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ringdal, F; Harris, D B; Kvaerna, T

2009-07-23

We have adapted matched field processing, a method developed in underwater acoustics to detect and locate targets, to classify transient seismic signals arising from mining explosions. Matched field processing, as we apply it, is an empirical technique, using observations of historic events to calibrate the amplitude and phase structure of wavefields incident upon an array aperture for particular repeating sources. The objective of this project is to determine how broadly applicable the method is and to understand the phenomena that control its performance. We obtained our original results in distinguishing events from ten mines in the Khibiny and Olenegorsk miningmore » districts of the Kola Peninsula, for which we had exceptional ground truth information. In a cross-validation test, some 98.2% of 549 explosions were correctly classified by originating mine using just the Pn observations (2.5-12.5 Hz) on the ARCES array at ranges from 350-410 kilometers. These results were achieved despite the fact that the mines are as closely spaced as 3 kilometers. Such classification performance is significantly better than predicted by the Rayleigh limit. Scattering phenomena account for the increased resolution, as we make clear in an analysis of the information carrying capacity of Pn under two alternative propagation scenarios: free-space propagation and propagation with realistic (actually measured) spatial covariance structure. The increase in information capacity over a wide band is captured by the matched field calibrations and used to separate explosions from very closely-spaced sources. In part, the improvement occurs because the calibrations enable coherent processing at frequencies above those normally considered coherent. We are investigating whether similar results can be expected in different regions, with apertures of increasing scale and for diffuse seismicity. We verified similar performance with the closely-spaced Zapolyarni mines, though discovered that it may be necessary to divide event populations from a single mine into identifiable subpopulations. For this purpose, we perform cluster analysis using matched field statistics calculated on pairs of individual events as a distance metric. In our initial work, calibrations were derived from ensembles of events ranging in number to more than 100. We are considering the performance now of matched field calibrations derived with many fewer events (even, as mentioned, individual events). Since these are high-variance estimates, we are testing the use of cross-channel, multitaper, spectral estimation methods to reduce the variance of calibrations and detection statistics derived from single-event observations. To test the applicability of the technique in a different tectonic region, we have obtained four years of continuous data from 4 Kazakh arrays and are extracting large numbers of event segments. Our initial results using 132 mining explosions recorded by the Makanchi array are similar to those obtained in the European Arctic. Matched field processing clearly separates the explosions from three closely-spaced mines located approximately 400 kilometers from the array, again using waveforms in a band (6-10 Hz) normally considered incoherent for this array. Having reproduced ARCES-type performance with another small aperture array, we have two additional objectives for matched field processing. We will attempt to extend matched field processing to larger apertures: a 200 km aperture (the KNET) and, if data permit, to an aperture comprised of several Kazakh arrays. We also will investigate the potential of developing matched field processing to roughly locate and classify natural seismicity, which is more diffuse than the concentrated sources of mining explosions that we have investigated to date.« less

Recent seismicity and crustal stress field in the Lucanian Apennines and surrounding areas (Southern Italy): Seismotectonic implications

NASA Astrophysics Data System (ADS)

Maggi, C.; Frepoli, A.; Cimini, G. B.; Console, R.; Chiappini, M.

2009-01-01

We analyzed the instrumental seismicity of Southern Italy in the area including the Lucanian Apennines and Bradano foredeep, making use of the most recent seismological data base available so far. P- and S-wave arrival times, recorded by the Italian National Seismic Network (RSNC) operated by the Istituto Nazionale di Geofisica e Vulcanologia (INGV), were re-picked along with those of the SAPTEX temporary array deployed in the region in the period 2001-2004. For some events located in the upper Val d'Agri, we also used data from the Eni-Agip oil company seismic network. We examined the seismicity occurred during the period between 2001 and 2006, considering 514 events with magnitudes M ≥ 2.0. We computed the VP/ VS ratio obtaining a value of 1.83 and we carried out an analysis for the one-dimensional (1D) velocity model that approximates the seismic structure of the study area. Earthquakes were relocated and, for well- recorded events, we also computed 108 fault plane solutions. Finally, using 58 solutions, the most constrained, we computed regional stress field in the study area. Earthquake distribution shows three main seismic regions: the westernmost (Lucanian Apennines) characterized by high background seismicity, mostly with shallow hypocenters, the easternmost below the Bradano foredeep and the Murge with deeper and more scattered seismicity, and finally the more isolated and sparse seismicity localized in the Sila Range and in the offshore area along the northeastern Calabrian coast. Focal mechanisms computed in this work are in large part normal and strike-slip solutions and their tensional axes ( T-axes) have a generalized NE-SW orientation. The denser station coverage allowed us to improve hypocenters determination compared to those obtained by using only RSNC data, for a better characterization of the crustal and subcrustal seismicity in the study area.

Development of a 300°C 3C Fiber Optic Downhole Seismic Receiver Array for Surveying and Monitoring of Geothermal Reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paulsson, Bjorn N.P.

2016-06-29

To address the critical site characterization and monitoring needs for Enhance Geothermal Systems (EGS) programs, US Department of Energy (DOE) awarded Paulsson, Inc. in 2011 a contract to design, build and test a high temperature fiber optic based ultra-large bandwidth clamped borehole seismic vector array capable of deploying a large number of 3C sensor pods suitable for deployment into high temperature and high pressure boreholes. Paulsson, Inc. has completed a design or a unique borehole seismic system consisting of a novel drill pipe based deployment system that includes a hydraulic clamping mechanism for the sensor pods, a new sensor podmore » design and most important – a unique fiber optic seismic vector sensor with technical specifications and capabilities that far exceed the state of the art seismic sensor technologies. These novel technologies were all applied to the new borehole seismic system. In combination these technologies will allow for the deployment of up to 1,000 3C sensor pods in vertical, deviated or horizontal wells. Laboratory tests of the fiber optic seismic vector sensors developed during this project have shown that the new borehole seismic sensor technology is capable of generating outstanding high vector fidelity data with extremely large bandwidth: 0.01 – 6,000 Hz. Field tests have shown that the system can record events at magnitudes much smaller than M-4.0 at frequencies over 2,000 Hz. The sensors have also proved to be about 100 times more sensitive than the regular coil geophones that are used in borehole seismic systems today. The fiber optic seismic sensors have furthermore been qualified to operate at temperatures over 300°C (572°F). The data telemetry fibers used for the seismic vector sensors in the system are also used to simultaneously record Distributed Temperature Sensor (DTS) and Distributed Acoustic Sensor (DAS) data allowing additional value added data to be recorded simultaneously with the seismic vector sensor data.« less

Observations and interpretation of fundamental mode Rayleigh wavefields recorded by the Transportable Array (USArray)

USGS Publications Warehouse

Pollitz, F.F.

2008-01-01

Broadband recordings of the dense Transportable Array (TA) in the western United States provide unparalleled detailed images of long-period seismic surface wavefields. With 400 stations spanning most of the western United States, wavefronts of fundamental mode Rayleigh waves may be visualized coherently across the array at periods ???40 s. In order to constrain the Rayleigh wave phase velocity structure in the western United States, I assemble a data set of vertical component seismograms from 53 teleseismic events recorded by the TA from April 2006 to October 2007. Complex amplitude spectra from these recordings at peni ods 27-100 s are interpreted using the multiplane wave tomographic method of Friederich and Wielandt (1995) and Pollitz (1999). This analysis yields detailed surface wave phase velocity and three-dimensional shear wave velocity patterns across the North American plate boundary zone, elucidating the active processes in the highly heterogeneous western U.S. upper mantle.

Apollo lunar surface experiments package

NASA Technical Reports Server (NTRS)

1972-01-01

Developments in the ALSEP program are reported. A summary of the status for the total ALSEP program is included. Other areas discussed include: (1) status of Apollo 16 (array D) and Apollo 17 (array E), (2) lunar seismic profiling experiment, (3) lunar ejecta and meteorites experiment, and (4) lunar mass spectrometer experiments.

Fiber Optic Geophysics Sensor Array

NASA Astrophysics Data System (ADS)

Grochowski, Lucjan

1989-01-01

The distributed optical sensor arrays are analysed in view of specific needs of 3-D seismic explorations methods. There are compared advantages and disadventages of arrays supported by the sensors which are modulated in intensity and phase. In these systems all-fiber optic structures and their compabilities with digital geophysic formats are discussed. It was shown that the arrays based on TDM systems with the intensity modulated sensors are economically and technically the best matched for geophysic systems supported by a large number of the sensors.

Seismicity detection around the subduting seamount off Ibaraki the Japan Trench using dense OBS array data

NASA Astrophysics Data System (ADS)

Nakatani, Y.; Mochizuki, K.; Shinohara, M.; Yamada, T.; Hino, R.; Ito, Y.; Murai, Y.; Sato, T.

2013-12-01

A subducting seamount which has a height of about 3 km was revealed off Ibaraki in the Japan Trench by a seismic survey (Mochizuki et al., 2008). Mochizuki et al. (2008) also interpreted that interplate coupling was weak over the seamount because seismicity was low and the slip of the recent large earthquake did not propagate over it. To carry out further investigation, we deployed dense ocean bottom seismometers (OBSs) array around the seamount for about a year. During the observation period, seismicity off Ibaraki was activated due to the occurrence of the 2011 Tohoku earthquake. The southern edge of the mainshock rupture area was considered to be located around off Ibaraki by many source analyses. Moreover, Kubo et al. (2013) proposes the seamount played an important role in the rupture termination of the largest aftershock. Therefore, in this study, we try to understand about spatiotemporal variation of seismicity around the seamount before and after the Mw 9.0 event as a first step to elucidate relationship between the subducting seamount and seismogenic behavior. We used velocity waveforms of 1 Hz long-term OBSs which were densely deployed at station intervals of about 6 km. The sampling rate is 200 Hz and the observation period is from October 16, 2010 to September 19, 2011. Because of the ambient noise and effects of thick seafloor sediments, it is difficult to apply methods which have been used to on-land observational data for detecting seismicity to OBS data and to handle continuous waveforms automatically. We therefore apply back-projection method (e.g., Kiser and Ishii, 2012) to OBS waveform data which estimate energy-release source by stacking waveforms. Among many back-projection methods, we adopt a semblance analysis (e.g., Honda et al., 2008) which can detect feeble waves. First of all, we constructed a 3-D velocity structure model off Ibaraki by compiling the results of marine seismic surveys (e.g., Nakahigashi et al., 2012). Then, we divided a target area into small areas and calculated P-wave traveltimes between each station and all small areas by fast marching method (Rawlinson et al., 2006). After constructing theoretical travel-time tables, we applied a proper frequency filter to the observed waveforms and estimated seismic energy release by projecting semblance values. As the result of applying our method, we could successfully detect magnitude 2-3 earthquakes.

Characterizing seismic noise in the 2-20 Hz band at a gravitational wave observatory

NASA Astrophysics Data System (ADS)

Coward, D.; Turner, J.; Blair, D.; Galybin, K.

2005-04-01

We present a study of seismic noise, using an array of seismic sensors, at the Australian International Gravitational Observatory. We show that despite excellent attenuation of 2-20 Hz seismic waves from the soil properties of the site, which is confirmed by a specific experiment, there are important technical issues associated with local sources of vibration originating from within the laboratory buildings. In particular, we identify vibrations from air-filtration equipment propagating throughout the site. We find significant building resonances in the 2-13 Hz band and identify seismic noise originating from regional mine blasts hundreds of kilometers distant. All these noise sources increase the performance requirements on vibration isolation in the 2-20 Hz frequency band.

High-resolution seismic data regularization and wavefield separation

NASA Astrophysics Data System (ADS)

Cao, Aimin; Stump, Brian; DeShon, Heather

2018-04-01

We present a new algorithm, non-equispaced fast antileakage Fourier transform (NFALFT), for irregularly sampled seismic data regularization. Synthetic tests from 1-D to 5-D show that the algorithm may efficiently remove leaked energy in the frequency wavenumber domain, and its corresponding regularization process is accurate and fast. Taking advantage of the NFALFT algorithm, we suggest a new method (wavefield separation) for the detection of the Earth's inner core shear wave with irregularly distributed seismic arrays or networks. All interfering seismic phases that propagate along the minor arc are removed from the time window around the PKJKP arrival. The NFALFT algorithm is developed for seismic data, but may also be used for other irregularly sampled temporal or spatial data processing.

Joint seismic-infrasonic processing of recordings from a repeating source of atmospheric explosions.

PubMed

Gibbons, Steven J; Ringdal, Frode; Kvaerna, Tormod

2007-11-01

A database has been established of seismic and infrasonic recordings from more than 100 well-constrained surface explosions, conducted by the Finnish military to destroy old ammunition. The recorded seismic signals are essentially identical and indicate that the variation in source location and magnitude is negligible. In contrast, the infrasonic arrivals on both seismic and infrasound sensors exhibit significant variation both with regard to the number of detected phases, phase travel times, and phase amplitudes, which would be attributable to atmospheric factors. This data set provides an excellent database for studies in sound propagation, infrasound array detection, and direction estimation.

Propagation of Exploration Seismic Sources in Shallow Water

NASA Astrophysics Data System (ADS)

Diebold, J. B.; Tolstoy, M.; Barton, P. J.; Gulick, S. P.

2006-05-01

The choice of safety radii to mitigation the impact of exploration seismic sources upon marine mammals is typically based on measurement or modeling in deep water. In shallow water environments, rule-of-thumb spreading laws are often used to predict the falloff of amplitude with offset from the source, but actual measurements (or ideally, near-perfect modeling) are still needed to account for the effects of bathymetric changes and subseafloor characteristics. In addition, the question: "how shallow is 'shallow?'" needs an answer. In a cooperative effort by NSF, MMS, NRL, IAGC and L-DEO, a series of seismic source calibration studies was carried out in the Northern Gulf of Mexico during 2003. The sources used were the two-, six-, ten-, twelve-, and twenty-airgun arrays of R/V Ewing, and a 31-element, 3-string "G" gun array, deployed by M/V Kondor, an exploration industry source ship. The results of the Ewing calibrations have been published, documenting results in deep (3200m) and shallow (60m) water. Lengthy analysis of the Kondor results, presented here, suggests an approach to answering the "how shallow is shallow" question. After initially falling off steadily with source-receiver offset, the Kondor levels suddenly increased at a 4km offset. Ray-based modeling with a complex, realistic source, but with a simple homogeneous water column-over-elastic halfspace ocean shows that the observed pattern is chiefly due to geophysical effects, and not focusing within the water column. The same kind of modeling can be used to predict how the amplitudes will change with decreasing water depth, and when deep-water safety radii may need to be increased. Another set of data (see Barton, et al., this session) recorded in 20 meters of water during early 2005, however, shows that simple modeling may be insufficient when the geophysics becomes more complex. In this particular case, the fact that the seafloor was within the near field of the R/V Ewing source array seems to have given rise to seismic phases not normally seen in marine survey data acquired in deeper water. The associated partitioning of energy is likely to have caused the observed uncharacteristically rapid loss of energy with distance. It appears that in this case, the shallow-water marine mammal safety mitigation measures prescribed and followed were far more stringent than they needed to be. A new approach, wherein received levels detected by the towed 6-km multichannel hydrophone array may be used to modify safety radii has recently been proposed, based on these observations.

3D imaging of geological structures by R-VSP utilizing vibrations caused by shaft excavations at the Mizunami Underground Research Laboratory in Japan

NASA Astrophysics Data System (ADS)

Matsuoka, T.; Hodotsuka, Y.; Ishigaki, K.; Lee, C.

2009-12-01

Japan Atomic Energy Agency is now conducting the Mizunami Underground Research Laboratory (MIU) project. The MIU consists of two shafts (main shaft: 6.5m, ventilation shaft: 4.5m diameter) and horizontal research galleries, in sedimentary and granitic rocks at Mizunami City, Central Japan. The MIU project is a broad scientific study of the deep geological environment providing the basis for research and development for geological disposal of high level radioactive waste. One of the main goals is to establish techniques for investigation, analysis and assessment of the deep geological environment in fractured crystalline rock. As a part of the MIU project, we carried out the Reverse-Vertical Seismic Profile (R-VSP) using vibrations from the blasting for the shaft excavations and drilling of boreholes in the horizontal research galleries and examined the applicability of this method to imaging of geological structures around underground facilities, such as the unconformity between the sedimentary rocks and the basal granite, and faults and fracture zones in the granite. R-VSP method is a seismic method utilizing the receiver arrays on surface and seismic sources underground (e.g. in boreholes). This method is advantageous in that planning of 3-dimensional surveys is easy compared with reflection seismic surveying and conventional VSP because seismic source arrays that are major constraint for conducting surveys on surface are unnecessary. The receiver arrays consist of six radial lines on surface with a central focus on the main shaft. Seven blast rounds for the main shaft excavation from GL-52.8m to GL-250m and the borehole drilling in the GL-200m horizontal research gallery were observed. Three types of data processing, conventional VSP data processing (VSP-CDP transform and VSP migration), Reflection data processing utilizing Seismic interferometry method (“Seismic interferometry”) and Reflection mapping utilizing Image Point transform method (“IP transform”), were performed to obtain reflection images from heterogeneous geological structure. As the results, the reflective events that seemed to correspond with sedimentary layers, the unconformity between sedimentary rocks and granite, and fracture zones in granite could be detected by reflection profiles using “conventional VSP data processing” and “Seismic interferometry”. However, it is difficult to identify the faults around the MIU because they are generally at a high-angle. “IP transform” is one type of Radon transform which change common shot gather to IP domain. Image Points are defined through geometries of sources and reflectors. Reflection signals in time domain can be accumulated and enhanced in IP domain by “IP transform” on the condition of the right angle to a fault. So, by a search of the direction that reflection signals are enhanced using “IP transform”, the locations of faults can be inferred. By this method, the distribution of faults that correspond with faults in the current geological model constructed from investigation data in the MIU project could be detected.

Earthquake source parameters determined using the SAFOD Pilot Hole vertical seismic array

NASA Astrophysics Data System (ADS)

Imanishi, K.; Ellsworth, W. L.; Prejean, S. G.

2003-12-01

We determined source parameters of microearthquakes occurring at Parkfield, CA, using the SAFOD Pilot Hole vertical seismic array. The array consists of 32 stations with 3-component 15 Hz geophones at 40 meter spacing (856 to 2096 m depth) The site is about 1.8 km southwest of a segment of the San Andreas fault characterized by a combination of aseismic creep and repeating microearthquakes. We analyzed seismograms recorded at sample rates of 1kHz or 2kHz. Spectra have high signal-to-noise ratios at frequencies up to 300-400 Hz, showing these data include information on source processes of microearthquakes. By comparing spectra and waveforms at different levels of the array, we observe how attenuation and scattering in the shallow crust affect high-frequency waves. We estimated spectral level (Ω 0), corner frequency (fc) and path-averaged attenuation (Q) at each level of the array by fitting an omega squared model to displacement spectra. While the spectral level changes smoothly with depth, there is significant scatter in fc and Q due to the strong trade-off between these parameters. Because we expect source parameters to vary systematically with depth, we impose a smoothness constraint on Q, Ω 0 and fc as a function of depth. For some of the nearby events, take-off angles to the different levels of the array span a significant part of the focal sphere. Therefore corner frequencies should also change with depth. We smooth measurements using a linear first-difference operator that links Q, Ω 0 and fc at one level to the levels above and below, and use Akaike_fs Bayesian Information Criterion (ABIC) to weight the smoothing operators. We applied this approach to events with high signal-to-noise ratios. For the results with the minimum ABIC, fc does not scatter and Q decreases with decreasing depth. Seismic moments were determined by the spectral level and range from 109 and 1012 Nm. Source radii were estimated from the corner frequency using the circular crack model of Sato and Hirasawa (1973). Estimated values of static stress drop were roughly 1 MPa and do not vary with seismic moment. Q values from all earthquakes were averaged at each level of the array. Average Qp and Qs range from 250 to 350 and from 300 to 400 between the top and bottom of the array, respectively. Increasing Q values as a function of depth explain well the observed decrease in high-frequency content as waves propagate toward the surface. Thus, by jointly analyzing the entire vertical array we can both accurately determine source parameters of microearthquakes and make reliable Q estimates while suppressing the trade-off between fc and Q.

Thirty Years Supporting Portable Arrays: The IRIS Passcal Instrument Center

NASA Astrophysics Data System (ADS)

Beaudoin, B. C.; Anderson, K. R.; Bilek, S. L.; Woodward, R.

2014-12-01

Thirty years have passed since establishment of the IRIS Program for the Array Seismic Studies of the Continental Lithosphere (PASSCAL). PASSCAL was part of a coordinated plan proposed to the National Science Foundation (NSF) defining the instrumentation, data collection and management structure to support a wide range of research in seismology. The PASSCAL program has surpassed the early goal of 6000 data acquisition channels with a current inventory of instrumentation capable of imaging from the near surface to the inner core. Here we present the evolution of the PASSCAL program from instrument depot to full service community resource. PASSCAL has supported close to 1100 PI driven seismic experiments since its inception. Instruments from PASSCAL have covered the globe and have contributed over 7400 SEED stations and 242 assembled data sets to the IRIS Data Management Center in Seattle. Since the combination in 1998 of the Stanford and Lamont instrument centers into the single PASSCAL Instrument Center (PIC) at New Mexico Tech, the facility has grown in scope by adding the EarthScope Array Operations Facility in 2005, the incorporation of the EarthScope Flexible Array, and a Polar support group in 2006. The polar support group enhances portable seismic experiments in extremely harsh polar environments and also extends to special projects such as the Greenland Ice Sheet Monitoring Network (GLISN) and the recent development effort for Geophysical Earth Observatory for Ice Covered Environments (GEOICE). Through these support efforts the PIC has established itself as a resource for field practices, engineered solutions for autonomous seismic stations, and a pioneer in successful seismic recording in polar environments. We are on the cusp of a new generation of instrumentation driven in part by the academic community's desire to record unaliased wavefields in multiple frequency bands and industry's interest in utilizing lower frequency data. As part of the recently funded IRIS proposal to NSF for support of Seismological Facilities for the Advancement of Geoscience and EarthScope (SAGE), IRIS is developing plans for this new instrumentation that will ensure that the PASSCAL program continues to provide state-of-the-art observing capabilities into the coming decades.

Seismicity patterns during a period of inflation at Sierra Negra volcano, Galápagos Ocean Island Chain

NASA Astrophysics Data System (ADS)

Davidge, Lindsey; Ebinger, Cynthia; Ruiz, Mario; Tepp, Gabrielle; Amelung, Falk; Geist, Dennis; Coté, Dustin; Anzieta, Juan

2017-03-01

Basaltic shield volcanoes of the western Galápagos islands are among the most rapidly deforming volcanoes worldwide, but little was known of the internal structure and brittle deformation processes accompanying inflation and deflation cycles. A 15-station broadband seismic array was deployed on and surrounding Sierra Negra volcano, Galápagos from July 2009 through June 2011 to characterize seismic strain patterns during an inter-eruption inflation period and to evaluate single and layered magma chamber models for ocean island volcanoes. We compare precise earthquake locations determined from a 3D velocity model and from a double difference cluster method. Using first-motion of P-arrivals, we determine focal mechanisms for 8 of the largest earthquakes (ML ≤ 1.5) located within the array. Most of the 2382 earthquakes detected by the array occurred beneath the broad (∼9 km-wide) Sierra Negra caldera, at depths from surface to about 8 km below sea level. Although outside our array, frequent and larger magnitude (ML ≤ 3.4) earthquakes occurred at Alcedo and Fernandina volcano, and in a spatial cluster beneath the shallow marine platform between Fernandina and Sierra Negra volcanoes. The time-space relations and focal mechanism solutions from a 4-day long period of intense seismicity June 4-9, 2010 along the southeastern flank of Sierra Negra suggests that the upward-migrating earthquake swarm occurred during a small volume intrusion at depths 5-8 km subsurface, but there was no detectable signal in InSAR data to further constrain geometry and volume. Focal mechanisms of earthquakes beneath the steep intra-caldera faults and along the ring fault system are reverse and strike-slip. These new seismicity data integrated with tomographic, geodetic, and petrological models indicate a stratified magmatic plumbing system: a shallow sill beneath the large caldera that is supplied by magma from a large volume deeper feeding system. The large amplitude inter-eruption inflation of the shallow sill beneath the Sierra Negra caldera is accompanied by only very small magnitude earthquakes, although historical records indicate that larger magnitude earthquakes (Mw <6) occur during eruptions, trapdoor faulting episodes without eruptions, and large volume flank intrusions.

Characterizing Micro- and Macro-Scale Seismicity from Bayou Corne, Louisiana

NASA Astrophysics Data System (ADS)

Baig, A. M.; Urbancic, T.; Karimi, S.

2013-12-01

The initiation of felt seismicity in Bayou Corne, Louisiana, coupled with other phenomena detected by residents on the nearby housing development, prompted a call to install a broadband seismic network to monitor subsurface deformation. The initial deployment was in place to characterize the deformation contemporaneous with the formation of a sinkhole located in close proximity to a salt dome. Seismic events generated during this period followed a swarm-like behaviour with moment magnitudes culminating around Mw2.5. However, the seismic data recorded during this sequence suffer from poor signal to noise, onsets that are very difficult to pick, and the presence of a significant amount of energy arriving later in the waveforms. Efforts to understand the complexity in these waveforms are ongoing, and involve invoking the complexities inherent in recording in a highly attenuating swamp overlying a complex three-dimensional structure with the strong material property contrast of the salt dome. In order to understand the event character, as well as to locally lower the completeness threshold of the sequence, a downhole array of 15 Hz sensors was deployed in a newly drilled well around the salt dome. Although the deployment lasted a little over a month in duration, over 1000 events were detected down to moment magnitude -Mw3. Waveform quality tended to be excellent, with very distinct P and S wave arrivals observable across the array for most events. The highest magnitude events were seen as well on the surface network and allowed for the opportunity to observe the complexities introduced by the site effects, while overcoming the saturation effects on the higher-frequency downhole geophones. This hybrid downhole and surface array illustrates how a full picture of subsurface deformation is only made possible by combining the high-frequency downhole instrumentation to see the microseismicity complemented with a broadband array to accurately characterize the source parameters for the larger magnitude events. Our presentation is focused on investigating this deformation, characterizing the scaling behaviour and the other source processes by taking advantage of the wide-band afforded to us through the deployment.

The Effects of Heterogeneities on Seismic Wave Propagation in the Climax Stock

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hagan Webb, C., Snelson, C. M., White, R., Emmitt, R., Barker, D., Abbott, R., Bonal, N.

2011-12-01

The Comprehensive Nuclear Test-Ban Treaty requires the ability to detect low-yield (less than 150kton) nuclear events. This kind of monitoring can only be done seismically on a regional scale (within 2000km). At this level, it is difficult to distinguish between low-yield nuclear events and non-nuclear events of similar magnitude. In order to confidently identify a nuclear event, a more detailed understanding of nuclear seismic sources is needed. In particular, it is important to know the effects of local geology on the seismic signal. This study focuses on P-wave velocity in heterogeneous granitoid. The Source Physics Experiment (SPE) is currently performingmore » low-yield tests with chemical explosives at the Nevada National Security Site (NNSS). The exact test site was chosen to be in the Climax Stock, a cretaceous granodiorite and quartz-monzonite pluton located in Area 15 of the NNSS. It has been used in the past for the Hard Hat and Pile Driver nuclear tests, which provided legacy data that can be used to simulate wave propagation. The Climax Stock was originally chosen as the site of the SPE partly because of its assumed homogeneity. It has since been discovered that the area of the stock where the SPE tests are being performed contains a perched water table. In addition, the stock is known to contain an extensive network of faults, joints, and fractures, but the exact effect of these structural features on seismic wave velocity is not fully understood. The SPE tests are designed to seismically capture the explosion phenomena from the near- to the far-field transition of the seismic waveform. In the first SPE experiment, 100kg of chemical explosives were set off at a depth of 55m. The blast was recorded with an array of sensors and diagnostics, including accelerometers, geophones, rotational sensors, short-period and broadband seismic sensors, Continuous Reflectometry for Radius vs. Time Experiment, Time of Arrival, Velocity of Detonation, and infrasound sensors. The focus of this study is two-fold: (1) the geophone array that was focused over the SPE shot and (2) a high-resolution seismic profile that was recently acquired at the field site. The geophone array was placed radially around the SPE shot in five directions with 100m spacing and out to a distance of 2 km. The high-resolution profile was about 475m in length with station and shot spacing of 5m using a 7000lb mini-vibe as a source. In both data sets, the first arrivals will be used to develop velocity models. For the geophone array, 1-D P-wave velocity models will be developed to determine an average apparent velocity of the Climax Stock. The high-resolution data will be used to develop a 2-D P-wave velocity model along the seismic profile. This is in an effort to elucidate the water table in more detail and provide additional information on the near-surface structure. These results will be used in the overall modeling effort to fully characterize the test bed and develop a physics-based model to simulate seismic energy from the SPE events.« less

Joint the active source and passive source seismic to research the fine crustal structure of the Lushan area

NASA Astrophysics Data System (ADS)

Chen, Q.; Yu, C.

2017-12-01

On April 20, 2013, Ms7.0 strong earthquake (Lushan earthquake) occurred in Lanshan County Ya'an City, Sichuan Province. It is another earthquake that occurred in the Longmenshan fault zone after the Wenchuan earthquake. However, there is still no conclusive conclusion in relationship between the fine structure of the Lushan area and triggering seismic fault . In this study, the crustal structure, the shallow structure and the hidden faults and the focal mechanism of the Lushan earthquake were analyzed by using the deep seismic reflection profile and the broadband seismic array data. Combined with the surface geological information, the structure and fracture cause of the Lishan earthquake were discussed.We have synthetic analyzed the seismic precursors, fine locating, focal mechanism analysis and time-tomographic imaging of the broadband seismic data before and after the earthquake in Lushan earthquake, and obtained the seismic distribution, the focal mechanism and the crustal fine structure in the Lushan area. And we use these results to detailed interpreted the deep reflection seismic section of the Lushan earthquake zone.The results show that the crust of the Lushan area is characterized by a distinct structure of upper crust with thickness about 14.75km. The nature of the faults is inferred to be thrusting in the region due to the pushing of the crustal material of the Tibetan plateau into the southeast part of the rigid Sichuan basin. The shuangshi-Dachuan fault stretches from the surface to the deep crust at a low angle, and is dominated by thrusting in a form of imbricate structure with small-scale faults nearby. Whereas the Guangyuan-Dayi fault is a positive flower structure with a listric shape, consisting of six branches. Its movement is dominated by thrusting with gentle horizontal slip.

Passive seismic monitoring of natural and induced earthquakes: case studies, future directions and socio-economic relevance

USGS Publications Warehouse

Bohnhoff, Marco; Dresen, Georg; Ellsworth, William L.; Ito, Hisao; Cloetingh, Sierd; Negendank, Jörg

2010-01-01

An important discovery in crustal mechanics has been that the Earth’s crust is commonly stressed close to failure, even in tectonically quiet areas. As a result, small natural or man-made perturbations to the local stress field may trigger earthquakes. To understand these processes, Passive Seismic Monitoring (PSM) with seismometer arrays is a widely used technique that has been successfully applied to study seismicity at different magnitude levels ranging from acoustic emissions generated in the laboratory under controlled conditions, to seismicity induced by hydraulic stimulations in geological reservoirs, and up to great earthquakes occurring along plate boundaries. In all these environments the appropriate deployment of seismic sensors, i.e., directly on the rock sample, at the earth’s surface or in boreholes close to the seismic sources allows for the detection and location of brittle failure processes at sufficiently low magnitude-detection threshold and with adequate spatial resolution for further analysis. One principal aim is to develop an improved understanding of the physical processes occurring at the seismic source and their relationship to the host geologic environment. In this paper we review selected case studies and future directions of PSM efforts across a wide range of scales and environments. These include induced failure within small rock samples, hydrocarbon reservoirs, and natural seismicity at convergent and transform plate boundaries. Each example represents a milestone with regard to bridging the gap between laboratory-scale experiments under controlled boundary conditions and large-scale field studies. The common motivation for all studies is to refine the understanding of how earthquakes nucleate, how they proceed and how they interact in space and time. This is of special relevance at the larger end of the magnitude scale, i.e., for large devastating earthquakes due to their severe socio-economic impact.

Assessing Multiple Methods for Determining Active Source Travel Times in a Dense Array

NASA Astrophysics Data System (ADS)

Parker, L.; Zeng, X.; Thurber, C. H.; Team, P.

2016-12-01

238 three-component nodal seismometers were deployed at the Brady Hot Springs geothermal field in Nevada to characterize changes in the subsurface as a result of changes in pumping conditions. The array consisted of a 500 meter by 1600 meter irregular grid with 50 meter spacing centered in an approximately rectangular 1200 meter by 1600 meter grid with 200 meter spacing. A large vibroseis truck (T-Rex) was deployed as an active seismic source at 216 locations. Over the course of 15 days, the truck occupied each location up to four times. At each location a swept-frequency source between 5 and 80 Hz over 20 seconds was produced using three vibration modes: longitudinal S-wave, transverse S-wave, and P-wave. Seismic wave arrivals were identified using three methods: cross-correlation, deconvolution, and Wigner-Ville distribution (WVD) plus the Hough Transform (HT). Surface wave arrivals were clear for all three modes of vibration using all three methods. Preliminary tomographic models will be presented, using the arrivals of the identified phases. This analysis is part of the PoroTomo project: Poroelastic Tomography by Adjoint Inverse Modeling of Data from Seismology, Geodesy, and Hydrology; http://geoscience.wisc.edu/feigl/porotomo.

Determining SAFOD area microearthquake locations solely with the Pilot Hole seismic array data

NASA Astrophysics Data System (ADS)

Oye, Volker; Chavarria, J. Andres; Malin, Peter E.

2004-05-01

In August 2002, an array of 32 three-component geophones was installed in the San Andreas Fault Observatory at Depth (SAFOD) Pilot Hole (PH) at Parkfield, CA. As an independent test of surface-observation-based microearthquake locations, we have located such events using only data recorded on the PH array. We then compared these locations with locations from a combined set of PH and Parkfield High Resolution Seismic Network (HRSN) observations. We determined the uncertainties in the locations as they relate to errors in the travel time picks and the velocity model by the bootstrap method. Based on the PH and combined locations, we find that the ``C2'' cluster to the northeast of the PH has the smallest location uncertainties. Events in this cluster also have the most similar waveforms and largest magnitudes. This confirms earlier suggestions that the C2 cluster is a promising target for the SAFOD Main Hole.

Infrasound and seismic detections associated with the 7 September 2015 Bangkok fireball

DOE PAGES

Caudron, Corentin; Taisne, Benoit; Perttu, Anna; ...

2016-08-22

A bright fireball was reported at 01:43:35 UTC on September 7, 2015 at a height of ~30 km above 14.5°N, 98.9°E near Bangkok, Thailand. It had a TNT yield equivalent of 3.9 kilotons (kt), making it the largest fireball detected in South–East Asia since the ~50 kt 2009 Sumatra bolide. Infrasonic signals were observed at four infrasound arrays that are part of the International Monitoring System (IMS) and one infrasound array located in Singapore. Acoustic bearings and event origin times inferred from array processing are consistent with the eyewitness accounts. A seismic signal associated with this event was also likelymore » recorded at station SRDT, in Thailand. As a result, an acoustic energy equivalent of 1.15 ± 0.24 kt is derived from the Singaporean acoustic data using the period of the peak energy.« less

Infrasound and seismic detections associated with the 7 September 2015 Bangkok fireball

DOE Office of Scientific and Technical Information (OSTI.GOV)

Caudron, Corentin; Taisne, Benoit; Perttu, Anna

A bright fireball was reported at 01:43:35 UTC on September 7, 2015 at a height of ~30 km above 14.5°N, 98.9°E near Bangkok, Thailand. It had a TNT yield equivalent of 3.9 kilotons (kt), making it the largest fireball detected in South–East Asia since the ~50 kt 2009 Sumatra bolide. Infrasonic signals were observed at four infrasound arrays that are part of the International Monitoring System (IMS) and one infrasound array located in Singapore. Acoustic bearings and event origin times inferred from array processing are consistent with the eyewitness accounts. A seismic signal associated with this event was also likelymore » recorded at station SRDT, in Thailand. As a result, an acoustic energy equivalent of 1.15 ± 0.24 kt is derived from the Singaporean acoustic data using the period of the peak energy.« less

Microseismic Properties of Typhoons in the Western Pacific

NASA Astrophysics Data System (ADS)

Xu, Y.; Koper, K. D.; Burlacu, R.

2017-12-01

We analyzed the ambient seismic noise recorded in 2012 by a temporary array of 240 seismometers deployed in Yunnan, China as part of Phase I of the ChinArray project. The stations were installed with a quasi-uniform spacing of about 70 km by the Yunnan Earthquake Administration. Each station consisted of a three-component Guralp-3ESP seismometer and a Reftek 130 data acquisition system with a sampling interval of 0.01 s. To identify the structure and source of the ambient noise, we applied frequency-dependent polarization analysis to the individual stations and f-k analysis for three sub-arrays consisting of 14-25 stations. The most prominent microseismic signals we observed were surface waves generated at periods of 3-7 s by 15 typhoons that occurred in the Western Pacific, mostly during the summer of 2012. The U.S. Navy's Joint Typhoon Warning Center divides a tropical cyclone into four levels, Tropical Depression (TD), Tropical Storm (TS), Typhoon (TY) and Super Typhoon (ST) based on the estimated wind speed. Four of the 15 analyzed typhoons reached ST intensity. The maximum microseism signals tended to last throughout the lifetime of a typhoon. Sometimes, we observed the splitting of a single microseism spectral peak into two parallel peaks. We compared the seismic observations to storm track data for typhoons Guchol, Jelawat, and Son-Tinh, and with oceanic models of wave-wave interaction. We find that microseismic power is correlated with changes in the direction or speed, or both, of the typhoon track. High wind speed or changing wind speed within the typhoon does not have a clear relationship with the microseismic power.

Surface wave tomography of Europe from ambient seismic noise

NASA Astrophysics Data System (ADS)

Lu, Yang; Stehly, Laurent; Paul, Anne

2017-04-01

We present a European scale high-resolution 3-D shear wave velocity model derived from ambient seismic noise tomography. In this study, we collect 4 years of continuous seismic recordings from 1293 stations across much of the European region (10˚W-35˚E, 30˚N-75˚N), which yields more than 0.8 million virtual station pairs. This data set compiles records from 67 seismic networks, both permanent and temporary from the EIDA (European Integrated Data Archive). Rayleigh wave group velocity are measured at each station pair using the multiple-filter analysis technique. Group velocity maps are estimated through a linearized tomographic inversion algorithm at period from 5s to 100s. Adaptive parameterization is used to accommodate heterogeneity in data coverage. We then apply a two-step data-driven inversion method to obtain the shear wave velocity model. The two steps refer to a Monte Carlo inversion to build the starting model, followed by a linearized inversion for further improvement. Finally, Moho depth (and its uncertainty) are determined over most of our study region by identifying and analysing sharp velocity discontinuities (and sharpness). The resulting velocity model shows good agreement with main geological features and previous geophyical studies. Moho depth coincides well with that obtained from active seismic experiments. A focus on the Greater Alpine region (covered by the AlpArray seismic network) displays a clear crustal thinning that follows the arcuate shape of the Alps from the southern French Massif Central to southern Germany.

H-fractal seismic metamaterial with broadband low-frequency bandgaps

NASA Astrophysics Data System (ADS)

Du, Qiujiao; Zeng, Yi; Xu, Yang; Yang, Hongwu; Zeng, Zuoxun

2018-03-01

The application of metamaterial in civil engineering to achieve isolation of a building by controlling the propagation of seismic waves is a substantial challenge because seismic waves, a superposition of longitudinal and shear waves, are more complex than electromagnetic and acoustic waves. In this paper, we design a broadband seismic metamaterial based on H-shaped fractal pillars and report numerical simulation of band structures for seismic surface waves propagating. Comparative study on the band structures of H-fractal seismic metamaterials with different levels shows that a new level of fractal structure creates new band gap, widens the total band gaps and shifts the same band gap towards lower frequencies. Moreover, the vibration modes for H-fractal seismic metamaterials are computed and analyzed to clarify the mechanism of widening band gaps. A numerical investigation of seismic surface waves propagation on a 2D array of fractal unit cells on the surface of semi-infinite substrate is proposed to show the efficiency of earthquake shielding in multiple complete band gaps.

Interferometric imaging of the San Andreas Fault at Parkfield Using a Massive VSP

NASA Astrophysics Data System (ADS)

Chavarria, J.; Goertz, A.; Karrenbach, M.; Paulsson, B.

2006-12-01

The San Andreas Fault Observatory at Depth (SAFOD) has the goal of investigating the physical processes controlling earthquakes in central California at Parkfield. The observatory consists of a deep well, that intersected the San Andreas Fault at seismogenic depths of ~3.2 km, where recurring microearthquake activity takes place. Previous to the drilling of Phase II, that intersected the fault at the end of Summer 2005, a long array of seismometers was deployed in the deeper part of the well to characterize the fault structure and to aid the monitoring activities of the natural seismicity. The Massive VSP array consisted of 80 three component seismometers that were deployed during April and May 2005. During this period of time we recorded active data from 13 explosions used to refine the velocity models that improved the locations of target events. In addition to this, we continuously monitored passive data from the natural earthquake activity in the area that was dominated by the Parkfield 2004 event aftershock sequence. During the recording time of this project we were able to record one of the target earthquakes of the SAFOD project as well as recently discovered non-volcanic tremor. The data recorded by this deep array of seismometers has provided important information to characterize the structure of the fault at scale that is comparable to the scale of the geologic observations. These observations, derived during drilling of the well, consist of cores and cuttings as well as geophysical logs. With the use of the borehole array of seismometers we have been able to directly correlate this lithologic information with seismic phases observed in the VSP data. This has lead to better understanding the nature of the scattering that takes place in this complex fault zone. Seismic reflections in the dataset were analyzed with Kirchhoff imaging methods to determine a partial image of the San Andreas Fault at depth. Due to the low density distribution of sources in the study area the illumination volume is limited but still shows clear signals originating from sub-vertical structures associated to the strands of the San Andreas fault inferred from high resolution earthquake location. The existing Kirchhoff imaging methods have been complemented with the use of interferometric imaging by which we extract the Green's function of the data recorded by the array. This takes place with the use of correlation analysis of both active and passive data resulting in a dataset where each downhole receiver acts as a virtual source. This analysis has provided a refined image of the structure of the San Andreas Fault at seismogenic depths with which a better understanding of the system can be achieved.

Imaging Subduction, Episodic Tremor and Slip in the Pacific Northwest: Cascadia Arrays For Earthscope (CAFE)

NASA Astrophysics Data System (ADS)

Abers, G. A.; Rondenay, S.; Creager, K. C.; Malone, S. D.; Zhang, Z.; Wech, A. G.; Sweet, J. R.; Melbourne, T. I.; Hacker, B. R.

2007-12-01

Subduction delivers fluids into the Earth's mantle by transport of hydrated crust downward in subducting plates. These fluids are released at depth and may be responsible for a wide variety of phenomena including weakened thrust faults, episodic tremor and slip (ETS), intraslab earthquakes, forearc serpentinization, and arc magmatism. Cascadia is the volcanic arc associated with the youngest subducting plate, and hence a primary EarthScope target. In 2006 we launched Cascadia Arrays For Earthscope (CAFE), an EarthScope effort utilizing Flexible Array, Transportable Array, and PBO facilities, and integrating these data with complementary constraints from geodynamics and geochemistry. Seismic imaging, the emphasis of this presentation, is employed to illuminate (i) the descending oceanic plate, from where fluids are expelled by metamorphism, and (ii) the mantle wedge, where fluids migrate to produce hydrous phases such as serpentine or, beneath the volcanic arc, primary magmas, and (iii) the interface between them where ETS may be produced. The experiment traverses a section of the Cascadia system where earthquakes extend to nearly 100 km depth, thus permitting an investigation of the relationship between the release of fluids and the generation of Wadati-Benioff-zone earthquakes, and crosses regions of ETS excitation. The basic experiment has four components: (1) a 47-element broadband imaging array of Flexible Array instruments integrated with Bigfoot; (2) three small-aperture seismic arrays with 15 additional short-period instruments near known sources of ETS; (3) analysis of the PBO and PANGA GPS data sets to define the details of episodic slip events; and (4) integrative modeling. Sixty-two seismographs were deployed in July 2006; here we present a first look at the experiment and the data collected. Initial data recovery has been excellent, with approximately 12 months of continuous data recovered as of this writing, most delivered to the IRIS DMC. This time window includes an ETS episode in Jan. 2007. Given the success of this deployment, we expect to make good progress toward understanding the relationship between subduction, ETS, and fluid cycling.

Borehole Array Observations of Non-Volcanic Tremor at SAFOD

NASA Astrophysics Data System (ADS)

Ellsworth, W. L.; Luetgert, J. H.; Oppenheimer, D. H.

2005-12-01

We report on the observation of non-volcanic tremor made in the San Andreas Fault Observatory at Depth in May, 2005 during the deployment of a multi-level borehole seismic array in the SAFOD main hole. The seismic array consisted of 80 levels of hydraulically-clamped 3-component, 15 Hz omni-directional geophones spaced 15.24 m apart along a 1200 m section of the inclined borehole between 1538 and 2363 m below the ground surface. The array was provided by Paulsson Geophysical Services, Inc. (P/GSI), and recorded at a sample rate of 4000 sps on 24-bit Geode digital recorders provided by Geometrics, Inc. More than 2 TB of continuous data were recorded during the 2-week deployment. Selected local earthquakes and explosions recorded by the array are available at the Northern California Earthquake Data Center, and the entire unedited data set is available as assembled data at the IRIS Data Management Center. Both data sets are currently in the industry standard SEG2 format. Episodes of non-volcanic tremor are common along this reach of the San Andreas Fault according to Nadeau and Dolenc [2004, DOI: 10.1126/science.1107142], with many originating about 30 km southeast of SAFOD beneath the southern end of the Parkfield segment and northern end of the Simmler segment of the fault. We identified tremor episodes using spectrograms routinely produced by the Northern California Seismic Network (http://quake.usgs.gov/cgi-bin/sgrampark.pl) on which they appear as periods of elevated noise relative to the background. A particularly strong tremor episode occurred on May 10, 2005 between 19:39 and 20:00 UTC. In SAFOD, tremor spectral levels exceed the instrumental noise floor to at least 40 Hz. The spatially unaliased recording of the tremor wavefield on the P/GSI array reveal individual phases that can be tracked continuously across the array. The wavefield is composed of both up- and down-going shear waves that form quasi-stationary interference patterns in which areas of constructive interference recur at the same locations along the array. Such a pattern could arise from a spatially stationary source radiating an extended duration time function into a complex medium.

Large-N in Volcano Settings: Volcanosri

NASA Astrophysics Data System (ADS)

Lees, J. M.; Song, W.; Xing, G.; Vick, S.; Phillips, D.

2014-12-01

We seek a paradigm shift in the approach we take on volcano monitoring where the compromise from high fidelity to large numbers of sensors is used to increase coverage and resolution. Accessibility, danger and the risk of equipment loss requires that we develop systems that are independent and inexpensive. Furthermore, rather than simply record data on hard disk for later analysis we desire a system that will work autonomously, capitalizing on wireless technology and in field network analysis. To this end we are currently producing a low cost seismic array which will incorporate, at the very basic level, seismological tools for first cut analysis of a volcano in crises mode. At the advanced end we expect to perform tomographic inversions in the network in near real time. Geophone (4 Hz) sensors connected to a low cost recording system will be installed on an active volcano where triggering earthquake location and velocity analysis will take place independent of human interaction. Stations are designed to be inexpensive and possibly disposable. In one of the first implementations the seismic nodes consist of an Arduino Due processor board with an attached Seismic Shield. The Arduino Due processor board contains an Atmel SAM3X8E ARM Cortex-M3 CPU. This 32 bit 84 MHz processor can filter and perform coarse seismic event detection on a 1600 sample signal in fewer than 200 milliseconds. The Seismic Shield contains a GPS module, 900 MHz high power mesh network radio, SD card, seismic amplifier, and 24 bit ADC. External sensors can be attached to either this 24-bit ADC or to the internal multichannel 12 bit ADC contained on the Arduino Due processor board. This allows the node to support attachment of multiple sensors. By utilizing a high-speed 32 bit processor complex signal processing tasks can be performed simultaneously on multiple sensors. Using a 10 W solar panel, second system being developed can run autonomously and collect data on 3 channels at 100Hz for 6 months with the installed 16Gb SD card. Initial designs and test results will be presented and discussed.

Constraints on Shear Wave Velocity Heterogeneity and Anisotropy in D' from Finite-Frequency Differential Traveltime Residual Analysis

NASA Astrophysics Data System (ADS)

Liao, T.; Hung, S.; Andrad, E. D.; Liu, Q.

2013-12-01

The D'' region which lies in the lowermost ~250 km of the mantle has long been postulated as a major thermo-chemical boundary layer in the earth's dynamic evolution, where the upwelling plumes most likely originate and the downwelling cold slabs terminate. Numerous seismological investigations have found seismically distinct features, revealing the presence of both strong velocity heterogeneity and anisotropy near the core-mantle boundary. In recent years, the rapid growth of broadband seismograph array data and the advent of array processing methods and finite-frequency wave theory hold great promise for improving global coverage of seismic constraints for refinement of the details and complexity of the D' structure. In this study, we collect all recorded and available broadband waveforms from earthquakes with epicentral distances of 40-145o and magnitudes greater than 5.8 during 2002-2012. A cluster analysis (Houser at al. 2008) is then adopted to simultaneously group the seismic phases of interest with similar waveforms together as clusters and measure relative traveltime shifts between them in the same cluster by waveform cross correlation. We construct a dataset of differential traveltime residuals from composite phases, S(Sdiff), SKS, SKKS, ScS and multiply-reflected ScS phases commonly used to constrain both elastic wave speed heterogeneity and anisotropy in the lowermost mantle. While the splitting of Sdiff phases between the vertically (SV) and transversely (SH) polarized components after correcting for upper mantle anisotropy constrained by SKS/SKKS splitting has been identified as evidence for seismic anisotropy in the D' layer, distinct difference in finite-frequency sensitivity for SVdiff and SHdiff waves may lead to apparent splitting in the isotropic heterogeneous earth (Komatitsch et al. 2010). Finite-frequency sensitivity kernels for measured Sdiff traveltime anomalies, constructed with the interactions of forward and adjoint wavefields accurately calculated by a numerical spectral element method, will be utilized to investigate their contribution to the observed splitting times between the SH and SV components and characterize the inherent elastic anisotropy in D'.

SPREE: A Successful Seismic Array by a Failed Rift System; Analysis of Seismic Noise in the Seismically Quiet Mid-continent

NASA Astrophysics Data System (ADS)

Wolin, E.; van der Lee, S.; Bollmann, T. A.; Revenaugh, J.; Aleqabi, G. I.; Darbyshire, F. A.; Frederiksen, A. W.; Wiens, D.; Shore, P.

2014-12-01

The Superior Province Rifting Earthscope Experiment (SPREE) completed its field recording phase last fall with over 96% data return. While 60% of the stations returned data 100% of the time, only 9 performed below 90% and one station had questionable timing. One station was vandalized, another stolen. One station continued recording after its solar panels were pierced by a bullet, while another two stations survived a wildfire and a blow-down, respectively. The blow-down was an extreme wind event that felled hundreds of thousands of trees around the station. SPREE stations recorded many hundreds of earthquakes. Two regional earthquakes and over 400 teleseismic earthquakes had magnitudes over 5.5 and three, smaller local earthquakes had magnitudes over 2.5. We have calculated power spectral estimates between 0.1-1000 s period for the ~2.5-year lifespan of all 82 SPREE stations. Vertical channels performed quite well across the entire frequency range, falling well below the high noise model of Peterson (1993) and usually within 10-15 dB of nearby Transportable Array stations. SPREE stations' horizontal components suffer from long-period (> 30 s) noise. This noise is quietest at night and becomes up to 30 dB noisier during the day in the summer months. We explore possible causes of this variation, including thermal and atmospheric pressure effects. One possibility is that stations are insulated by snow during the winter, reducing temperature variations within the vault. Spring snowmelt creates instability at many of the SPREE stations, evidenced by frequent recenterings and enhanced long-period noise. For all channels, power in the microseismic band (4-16 s) is strongest in the winter, corresponding to storm season in the Northern Hemisphere, and approximately 20 dB weaker during the summer. The power spectrum and temporal variation of microseismic energy is consistent across the entire SPREE array.

Using Distributed Fiber Optic Sensing to Monitor Large Scale Permafrost Transitions: Preliminary Results from a Controlled Thaw Experiment

NASA Astrophysics Data System (ADS)

Ajo Franklin, J. B.; Wagner, A. M.; Lindsey, N.; Dou, S.; Bjella, K.; Daley, T. M.; Freifeld, B. M.; Ulrich, C.; Gelvin, A.; Morales, A.; James, S. R.; Saari, S.; Ekblaw, I.; Wood, T.; Robertson, M.; Martin, E. R.

2016-12-01

In a warming world, permafrost landscapes are being rapidly transformed by thaw, yielding surface subsidence and groundwater flow alteration. The same transformations pose a threat to arctic infrastructure and can induce catastrophic failure of the roads, runways, and pipelines on which human habitation depends. Scalable solutions to monitoring permafrost thaw dynamics are required to both quantitatively understand biogeochemical feedbacks as well as to protect built infrastructure from damage. Unfortunately, permafrost alteration happens over the time scale of climate change, years to decades, a decided challenge for testing new sensing technologies in a limited context. One solution is to engineer systems capable of rapidly thawing large permafrost units to allow short duration experiments targeting next-generation sensing approaches. We present preliminary results from a large-scale controlled permafrost thaw experiment designed to evaluate the utility of different geophysical approaches for tracking the cause, precursors, and early phases of thaw subsidence. We focus on the use of distributed fiber optic sensing for this challenge and deployed distributed temperature (DTS), strain (DSS), and acoustic (DAS) sensing systems in a 2D array to detect thaw signatures. A 10 x 15 x 1 m section of subsurface permafrost was heated using an array of 120 downhole heaters (60 w) at an experimental site near Fairbanks, AK. Ambient noise analysis of DAS datasets collected at the plot, coupled to shear wave inversion, was utilized to evaluate changes in shear wave velocity associated with heating and thaw. These measurements were confirmed by seismic surveys collected using a semi-permanent orbital seismic source activated on a daily basis. Fiber optic measurements were complemented by subsurface thermistor and thermocouple arrays, timelapse total station surveys, LIDAR, secondary seismic measurements (geophone and broadband recordings), timelapse ERT, borehole NMR, soil moisture measurements, hydrologic measurements, and multi-angle photogrammetry. This unusually dense combination of measurement techniques provides an excellent opportunity to characterize the geophysical signatures of permafrost thaw in a controlled environment.

Long period seismic noise modulated by atmospheric tides

NASA Astrophysics Data System (ADS)

Custódio, Susana; Helffrich, George

2016-04-01

The amplitudes of long-period (LP) seismic noise often exhibit a daily modulation, which is particularly visible on data recorded by temporary stations and horizontal components. These daily variations of the LP noise have been associated with temperature fluctuations. Temperature has been suggested to affect the noise recorded by seismometers by means of thermal convection around the sensor or by causing thermally induced tilts. Recently, we observed a semi-diurnal (12.0 hr) modulation of LP seismic noise amplitudes in seismometers in Portugal, SW Europe. This modulation was associated with the variation of atmospheric pressure, the only environmental signal to display a dominant 12-hr periodicity (at some locations). In this presentation we will present an analysis of this semi-diurnal modulation of long-period seismic noise. We show that the modulation: 1) is not instrument dependent, being recorded in a variety of sensors; 2) is observed in stations in mainland Portugal, Madeira island (N Atlantic), Florida (USA) and Mozambique, where it is strongest; 3) is seen only at a minority of sites without a clear geographical association, thus appearing to be strongly site-dependent; 5) is stronger during the Summer than during the Winter; and 6) is more clearly seen on vertical components. We will use data from the Transportable Array (EarthScope, USA) to investigate the admittance between LP seismic noise variations and co-located atmospheric pressure measurements.

Seismic Discrimination

DTIC Science & Technology

1977-03-31

J\\ "’l \\ UBO \\ NUR UINTA * BASIN ARRAY. UTAH \\ NURMIJARVI, FINLAND »X 1964-1971 ^ • A...Gs N 1 i 1 1 , 1. 50 60 STATION mK UBO UINTA BASIN ARRAY, UTAH 1964-1970 s...appropriate to the Basin and Range geologic province. This comparison indicates that the Colorado Plateau structure is significantly different than

Inverting near-surface models from virtual-source gathers (SM Division Outstanding ECS Award Lecture)

NASA Astrophysics Data System (ADS)

Ruigrok, Elmer; Vossen, Caron; Paulssen, Hanneke

2017-04-01

The Groningen gas field is a massive natural gas accumulation in the north-east of the Netherlands. Decades of production have led to significant compaction of the reservoir rock. The (differential) compaction is thought to have reactivated existing faults and to be the main driver of induced seismicity. The potential damage at the surface is largely affected by the state of the near surface. Thin and soft sedimentary layers can lead to large amplifications. By measuring the wavefield at different depth levels, near-surface properties can directly be estimated from the recordings. Seismicity in the Groningen area is monitored primarily with an array of vertical arrays. In the nineties a network of 8 boreholes was deployed. Since 2015, this network has been expanded with 70 new boreholes. Each new borehole consists of an accelerometer at the surface and four downhole geophones with a vertical spacing of 50 m. We apply seismic interferometry to local seismicity, for each borehole individually. Doing so, we obtain the responses as if there were virtual sources at the lowest geophones and receivers at the other depth levels. From the retrieved direct waves and reflections, we invert for P- & S- velocity and Q models. We discuss different implementations of seismic interferometry and the subsequent inversion. The inverted near-surface properties are used to improve both the source location and the hazard assessment.

High resolution P-wave velocity structure beneath Northeastern Tibet from multiscale seismic tomography

NASA Astrophysics Data System (ADS)

Guo, B.; Gao, X.; Chen, J.; Liu, Q.; Li, S.

2016-12-01

The continuing collision of the northward advancing Indian continent with the Eurasia results in the high elevations and thickened Tibetan Plateau. Numerous geologic and geophysical studies engaged in the mechanics of the Tibetan Plateau deformation and uplift. Many seismic experiments were deployed in south and central Tibet, such as INDEPTH and Hi-climb, but very few in northeastern Tibet. Between 2013 and 2015, The China Seismic Array-experiment operated 670 broadband seismic stations with an average station spacing of 35km. This seismic array located in northeastern Tibet and covered the Qilian Mountains, Qaidam Basin, and part of Songpan-Ganzi, Gobi-Alashan, Yangzi, and Ordos. A new multiscale seismic traveltime tomography technique with sparsity constrains were used to map the upper mantle P-wave velocity structure beneath northeastern Tibet. The seismic tomography algorithm employs sparsity constrains on the wavelet representation velocity model via the L1-norm regularization. This algorithm can efficiently deal with the uneven-sampled volume, and give multiscale images of the model. Our preliminary results can be summarized as follows: 1) in the upper mantle down to 200km, significate low-velocity anomalies exist beneath the northeastern Tibet, and slight high-velocity anomalies beneath the Qaidam basin; 2) under Gobi-Alashan, Yangzi, and Ordos, high-velocity anomalies appear to extend to a depth of 250km, this high-velocity may correspond to the lithosphere; 3) there exist relative high-velocity anomalies at depth of 250km-350km underneath north Tibet, which suggests lithospheric delamination; 4) the strong velocity contrast between north Tibet and Yangzi, Gabi-Alashan is visible down to 200km, which implies the north Tibet boundary.

Advances in Mixed Signal Processing for Regional and Teleseismic Arrays

DTIC Science & Technology

2006-08-15

1: Mixture of signals from two earthquakes from south of Africa and the Philippines observed at USAEDS long-period seismic array in Korea. Correct...window where the detector will miss valid signals . 2 Approaches to detecting signals on arrays all focus on the basic model that expresses the observed...possible use in detecting infrasound signals . The approach is based on orthogonal- ity properties of the eigen vectors of the spectral matrix under a

Recordings from the deepest borehole in the New Madrid Seismic Zone

USGS Publications Warehouse

Wang, Z.; Woolery, E.W.

2006-01-01

The recordings at the deepest vertical strong-motion array (VSAS) from three small events, the 21 October 2004 Tiptonville, Tennessee, earthquake; the 10 February 2005 Arkansas earthquake; and the 2 June 2005 Ridgely, Tennessee, earthquake show some interesting wave-propagation phenomena through the soils: the S-wave is attenuated from 260 m to 30 m depth and amplified from 30 m to the surface. The S-wave arrival times from the three events yielded different shear-wave velocity estimates for the soils. These different estimates may be the result of different incident angles of the S-waves due to different epicentral distances. The epicentral distances are about 22 km, 110 km, and 47 km for the Tiptonville, Arkansas, and Ridgely earthquakes, respectively. These recordings show the usefulness of the borehole strong-motion array. The vertical strong-motion arrays operated by the University of Kentucky have started to accumulate recordings that will provide a database for scientists and engineers to study the effects of the near-surface soils on the strong ground motion in the New Madrid Seismic Zone. More information about the Kentucky Seismic and Strong-Motion Network can be found at www.uky.edu/KGS/geologichazards. The digital recordings are available at ftp://kgsweb.uky.edu.

Observed Melt Season Seismicity of Taylor Glacier, Antarctica

NASA Astrophysics Data System (ADS)

Carmichael, J. D.; Pettit, E. C.; Creager, K. C.

2006-12-01

Sufficient evidence exists to suggest that interaction of crevasses and meltwater accelerates ice cliff disintegration of tidewater glaciers. It is not clear what role meltwater plays in calving characteristics from dry- based polar glaciers. We have obtained seismic data from a six-sensor seismic array deployed in October of 2004 near the terminus cliffs of Taylor Glacier, West Antarctica, to analyze near-cliff seismicity throughout a melt season. Discharge data from the adjacent Lawson stream suggests that dramatic increases in meltwater volume temporally correlate with changes in seismic character near ice cliffs. We calculated source-locations for ice-quake during hours of melting and re-freezing and found most large energy events to be located near the ice cliffs. The associated spectra and waveform characteristics are indicative of literature descriptions of crevassing events.

Noise reduction in long‐period seismograms by way of array summing

USGS Publications Warehouse

Ringler, Adam; Wilson, David; Storm, Tyler; Marshall, Benjamin T.; Hutt, Charles R.; Holland, Austin

2016-01-01

Long‐period (>100  s period) seismic data can often be dominated by instrumental noise as well as local site noise. When multiple collocated sensors are installed at a single site, it is possible to improve the overall station noise levels by applying stacking methods to their traces. We look at the noise reduction in long‐period seismic data by applying the time–frequency phase‐weighted stacking method of Schimmel and Gallart (2007) as well as the phase‐weighted stacking (PWS) method of Schimmel and Paulssen (1997) to four collocated broadband sensors installed in the quiet Albuquerque Seismological Laboratory underground vault. We show that such stacking methods can improve vertical noise levels by as much as 10 dB over the mean background noise levels at 400 s period, suggesting that greater improvements could be achieved with an array involving multiple sensors. We also apply this method to reduce local incoherent noise on horizontal seismic records of the 2 March 2016 Mw 7.8 Sumatra earthquake, where the incoherent noise levels at very long periods are similar in amplitude to the earthquake signal. To maximize the coherency, we apply the PWS method to horizontal data where relative azimuths between collocated sensors are estimated and compared with a simpler linear stack with no azimuthal rotation. Such methods could help reduce noise levels at various seismic stations where multiple high‐quality sensors have been deployed. Such small arrays may also provide a solution to improving long‐period noise levels at Global Seismographic Network stations.

EarthScope Transportable Array Siting Outreach Activities in Alaska and Western Canada

NASA Astrophysics Data System (ADS)

Gardine, L.; Dorr, P. M.; Tape, C.; McQuillan, P.; Taber, J.; West, M. E.; Busby, R. W.

2014-12-01

The EarthScopeTransportable Array is working to locate over 260 stations in Alaska and western Canada. In this region, new tactics and partnerships are needed to increase outreach exposure. IRIS and EarthScope are partnering with the Alaska Earthquake Center, part of University of Alaska Geophysical Institute, to spread awareness of Alaska earthquakes and the benefits of the Transportable Array for Alaskans. Nearly all parts of Alaska are tectonically active. The tectonic and seismic variability of Alaska requires focused attention at the regional level, and the remoteness and inaccessibility of most Alaska villages and towns often makes frequent visits difficult. For this reason, Alaska outreach most often occurs at community events. When a community is accessible, every opportunity to engage the residents is made. Booths at state fairs and large cultural gatherings, such as the annual convention of the Alaska Federation of Natives, are excellent venues to distribute earthquake information and to demonstrate a wide variety of educational products and web-based applications related to seismology and the Transportable Array that residents can use in their own communities. Region-specific publications have been developed to tie in a sense of place for residents of Alaska. The Alaska content for IRIS's Active Earth Monitor will emphasize the widespread tectonic and seismic features and offer not just Alaska residents, but anyone interested in Alaska, a glimpse into what is going on beneath their feet. The concerted efforts of the outreach team will have lasting effects on Alaskan understanding of the seismic hazard and tectonics of the region. Efforts to publicize the presence of the Transportable Array in Alaska, western Canada, and the Lower 48 also continue. There have been recent articles published in university, local and regional newspapers; stories appearing in national and international print and broadcast media; and documentaries produced by some of the world's most respected scientific and educational production companies that have included a segment about EarthScope and the Transportable Array.

Seismic and Infrasound Recordings from Kilauea Volcano: Volcanic Tremor, Lava Outbreaks, and Fissure Eruptions

NASA Astrophysics Data System (ADS)

Fee, D.; Garces, M.; Orr, T.

2007-12-01

The continuous effusion from the Pu'u 'O'o crater complex, the active vent of Kilauea Volcano, Hawaii, produced nearly continuous tremor for years. Recently this tremor was recorded by two infrasound arrays, one at 12.5 km and one at 2.5 km, as well as a broadband seismometer at the closer array. These recordings exhibit significant temporal changes. A sharp, complex spectral peak of ~0.6 Hz is present in nearly the entire dataset, and tends to bifurcate and shift frequency over time. Although the seismic wavefield at Kilauea is complex and path effects appear to play a significant role, this spectral peak is also weakly manifested in the seismic recordings. Array processing of the infrasonic data reveals an abundance of broadband signal as well. Most of the signal appears to originate from the main crater region. However, the 2.5 km array detected the presence of a skylight with growing hornitos ~400 m south of Pu'u 'O'o on the active lava tube system. On June 19th, 2007, the magmatic system at Pu'u 'O'o changed. An intrusion of magma reached the surface 6 km west of the crater complex. The timing and location of the lava outbreak were determined acoustically using array processing. Two distinct acoustic pulses were recorded from the correct azimuth, both exhibiting harmonics. The 7/21 fissure eruption also produced clear infrasound signals. The onset of the fissure eruption east of P'u' 'O'o was apparent beginning around midnight on 7/21 and was focused between ~1.5-5 Hz. Although the fissure eruption continued to produce infrasound, the character of the recorded signal changes over time. A third infrasound array was placed closer to P'u' 'O'o and the fissure to help further constrain the eruption. More detailed results on acoustic signals from the Father's Day Intrusion and Fissure eruption will be presented.

The Pollino Seismic Sequence: Activated Graben Structures in a Seismic Gap

NASA Astrophysics Data System (ADS)

Rößler, Dirk; Passarelli, Luigi; Govoni, Aladino; Bindi, Dino; Cesca, Simone; Hainzl, Sebatian; Maccaferri, Francesco; Rivalta, Eleonora; Woith, Heiko; Dahm, Torsten

2015-04-01

The Mercure Basin (MB) and the Castrovillari Fault (CF) in the Pollino range (Southern Apennines, Italy) represent one of the most prominent seismic gaps in the Italian seismic catalogue, with no M>5.5 earthquakes during the last centuries. In historical times several swarm-like seismic sequences occurred in the area including two intense swarms within the past two decades. The most energetic one started in 2010 and has been still active in 2014. The seismicity culminated in autumn 2012 with a M=5 event on 25 October. The range hosts a number of opposing normal faults forming a graben-like structure. Their rheology and their interactions are unclear. Current debates include the potential of the MB and the CF to host large earthquakes and the style of deformation. Understanding the seismicity and the behaviour of the faults is necessary to assess the tectonics and the seismic hazard. The GFZ German Research Centre for Geosciences and INGV, Italy, have jointly monitored the ongoing seismicity using a small-aperture seismic array, integrated in a temporary seismic network. Based on this installation, we located more than 16,000 local earthquakes that occurred between November 2012 and September 2014. Here we investigate quantitatively all the phases of the seismic sequence starting from January 2010. Event locations along with moment tensor inversion constrain spatially the structures activated by the swarm and the migration pattern of the seismicity. The seismicity forms clusters concentrated within the southern part of the MB and along the Pollino Fault linking MB and CF. Most earthquakes are confined to the upper 10 km of the crust in an area of ~15x15 km2. However, sparse seismicity at depths between 15 and 20 km and moderate seismicity further north with deepening hypocenters also exist. In contrast, the CF appears aseismic; only the northern part has experienced micro-seismicity. The spatial distribution is however more complex than the major tectonic structures mapped for the area. Consistent with mapped faults, the seismicity interested both eastwards and westwards dipping normal faults that define the geometry of seismically active graben-like structures. At least one cluster shows an additional spatio-temporal migration with spreading hypocentres similar to other swarm areas with fluid-triggering mechanisms. The static Coulomb stress change transferred by the largest shock onto the swarm area and on the CF cannot explain the observed high seismicity rate. We study the evolution of the frequency-size distribution of the events and the seismicity rate changes. We find that the majority of the earthquakes cannot be justified as aftershocks (directly related to the tectonics or to earthquake-earthquake interaction) and are best explained by an additional forcing active over the entire sequence. Our findings are consistent with the action of fluids (e.g. pore-pressure diffusion) triggering seismicity on pre-loaded faults. Additional aseismic release of tectonic strain by transient, slow slip is also consistent with our analysis. Analysis of deformation time series may clarify this point in future studies.

The seismic traffic footprint: Tracking trains, aircraft, and cars seismically

NASA Astrophysics Data System (ADS)

Riahi, Nima; Gerstoft, Peter

2015-04-01

Although naturally occurring vibrations have proven useful to probe the subsurface, the vibrations caused by traffic have not been explored much. Such data, however, are less sensitive to weather and low visibility compared to some common out-of-road traffic sensing systems. We study traffic-generated seismic noise measured by an array of 5200 geophones that covered a 7 × 10 km area in Long Beach (California, USA) with a receiver spacing of 100 m. This allows us to look into urban vibrations below the resolution of a typical city block. The spatiotemporal structure of the anthropogenic seismic noise intensity reveals the Blue Line Metro train activity, departing and landing aircraft in Long Beach Airport and their acceleration, and gives clues about traffic movement along the I-405 highway at night. As low-cost, stand-alone seismic sensors are becoming more common, these findings indicate that seismic data may be useful for traffic monitoring.

Seismic anisotropy in the upper mantle beneath the MAGIC array, mid-Atlantic Appalachians: Constraints from SKS splitting and quasi-Love wave propagation

NASA Astrophysics Data System (ADS)

Aragon, J. C.; Long, M. D.; Benoit, M. H.; Servali, A.

2016-12-01

North America's eastern passive continental margin has been modified by several cycles of supercontinent assembly. Its complex surface geology and distinct topography provide evidence of these events, while also raising questions about the extent of deformation in the continental crust, lithosphere, and mantle during past episodes of rifting and mountain building. The Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) is an EarthScope and GeoPRISMS-funded project that involves a collaborative effort among seismologists, geodynamicists, and geomorphologists. One component of the project is a broadband seismic array consisting of 28 instruments in a linear path from coastal Virginia to western Ohio, which operated between October 2013 and October 2016. A key science question addressed by the MAGIC project is the geometry of past lithospheric deformation and present-day mantle flow beneath the Appalachians, which can be probed using observations of seismic anisotropy Here we present observations of SKS splitting and quasi-Love wave arrivals from stations of the MAGIC array, which together constrain seismic anisotropy in the upper mantle. SKS splitting along the array reveals distinct regions of upper mantle anisotropy, with stations in and to the west of the range exhibiting fast directions parallel to the strike of the mountains. In contrast, weak splitting and null SKS arrivals dominate eastern stations in the coastal plain. Documented Love-to-Rayleigh wave scattering for surface waves originating the magnitude 8.3 Illapel, Chile earthquakes in September 2015 provides complementary constraints on anisotropy. These quasi-Love wave arrivals suggest a pronounced change in upper mantle anisotropy at the eastern edge of present-day Appalachian topography. Together, these observations increase our understanding of the extent of lithospheric deformation beneath North America associated with Appalachian orogenesis, as well as the pattern of present-day mantle flow beneath the passive margin.

Detection and location of earthquakes along the west coast of Chile: Examining seismicity in the 2010 M 8.8 Maule and 2014 M 8.1 Iquique earthquake rupture zones.

NASA Astrophysics Data System (ADS)

Diniakos, R. S.; Bilek, S. L.; Rowe, C. A.; Draganov, D.

2015-12-01

The subduction of the Nazca Plate beneath the South American Plate along Chile has led to some of the largest earthquakes recorded on modern seismic instrumentation. These include the 1960 M 9.5 Valdivia, 2010 M 8.8 Maule, and 2014 M 8.1 Iquique earthquakes. Slip heterogeneity for both the 2010 and 2014 earthquakes has been noted in various studies. In order to explore both spatial variations in the continued aftershocks of the 2010 event, and also seismicity to the north along Iquique prior to the 2014 earthquake relative to the high slip regions, we are expanding the catalog of small earthquakes using template matching algorithms to find other small earthquakes in the region. We start with an earthquake catalog developed from regional and local array data; these events provide the templates used to search through waveform data from a temporary seismic array in Malargue, Argentina, located ~300 km west of the Maule region, which operated in 2012. Our template events are first identified on the array stations, and we use a 10-s window around the P-wave arrival as the template. We then use a waveform cross-correlation algorithm to compare the template with day-long seismograms from Malargue stations. The newly detected events are then located using the HYPOINVERSE2000 program. Initial results for 103 templates on 19 of the array stations show that we find 275 new events ,with an average of three new events for each template correlated. For these preliminary results, events from the Maule region appear to provide the most new detections, with an average of ten new events. We will present our locations for the detected events and we will compare them to patterns of high slip along the 2010 rupture zone of the M 8.8 Maule earthquake and the 2014 M 8.1 Iquique event.

Digital seismo-acoustic signal processing aboard a wireless sensor platform

NASA Astrophysics Data System (ADS)

Marcillo, O.; Johnson, J. B.; Lorincz, K.; Werner-Allen, G.; Welsh, M.

2006-12-01

We are developing a low power, low-cost wireless sensor array to conduct real-time signal processing of earthquakes at active volcanoes. The sensor array, which integrates data from both seismic and acoustic sensors, is based on Moteiv TMote Sky wireless sensor nodes (www.moteiv.com). The nodes feature a Texas Instruments MSP430 microcontroller, 48 Kbytes of program memory, 10 Kbytes of static RAM, 1 Mbyte of external flash memory, and a 2.4-GHz Chipcon CC2420 IEEE 802.15.4 radio. The TMote Sky is programmed in TinyOS. Basic signal processing occurs on an array of three peripheral sensor nodes. These nodes are tied into a dedicated GPS receiver node, which is focused on time synchronization, and a central communications node, which handles data integration and additional processing. The sensor nodes incorporate dual 12-bit digitizers sampling a seismic sensor and a pressure transducer at 100 samples per second. The wireless capabilities of the system allow flexible array geometry, with a maximum aperture of 200m. We have already developed the digital signal processing routines on board the Moteiv Tmote sensor nodes. The developed routines accomplish Real-time Seismic-Amplitude Measurement (RSAM), Seismic Spectral- Amplitude Measurement (SSAM), and a user-configured Short Term Averaging / Long Term Averaging (STA LTA ratio), which is used to calculate first arrivals. The processed data from individual nodes are transmitted back to a central node, where additional processing may be performed. Such processing will include back azimuth determination and other wave field analyses. Future on-board signal processing will focus on event characterization utilizing pattern recognition and spectral characterization. The processed data is intended as low bandwidth information which can be transmitted periodically and at low cost through satellite telemetry to a web server. The processing is limited by the computational capabilities (RAM, ROM) of the nodes. Nevertheless, we envision this product to be a useful tool for assessing the state of unrest at remote volcanoes.

Dynamic characterization of the Chamousset rock column before its fall

NASA Astrophysics Data System (ADS)

Levy, C.; Baillet, L.; Jongmans, D.

2009-04-01

The rockfall of Chamousset (volume of 21000m3 ) occurred on November 10, 2007, affecting the 300 m high Urgonian cliff of the southern Vercors massif, French Alps. This event took place when the Vercors plateau was covered by snow. The unstable column was previously detected by observations on the development of a 30 m long fracture back on the plateau. Two aerial Lidar scans of the cliff were acquired before and after the failure, allowing the geometry of the column and of the broken plane to be determined. A temporary seismic array along with two extensometers was installed from July to November 2007. The seismic array consisted of 7 short period seismometers (1 three-components and 6 vertical-component). One vertical seismometer was installed on the column while the other 6 were deployed on the plateau with an array aperture of about 70 m. During the last two months of record, short period seismometers were replaced by 4.5 Hz geophones. The monitoring system recorded in a continuous mode (1000 Hz of frequency sampling) but it stopped to work two weeks before the fall, after the solar panels were covered by snow. During the running period, the seismic array recorded hundreds of local seismic events, from short (less than 0.5 s) impulsive signals to events with a long duration (a few tens of seconds). Our study was first focused on the dynamic response of the column and on the seismic noise frequency content. Fourier spectra of the seismic noise signals recorded on the column and the corresponding spectral ratios showed the presence of several resonance frequencies of the column. The first resonance frequency was measured at 3.6 Hz in July 2007 and it decreases regularly with time to reach 2.6 Hz two weeks before the fall. In parallel, extensometer measurements show that the fracture aperture increased with time during the same period. The dynamic response of a block which separates from a rock mass was 2D numerically modelled. Finite element computations showed that the progressive block decoupling, resulting from a crack propagation inside the mass, generates a decrease of the natural frequency, as it was measured on the site. These results highlight the interest to study the dynamic response of an unstable column for hazard assessment purposes. In a second phase, we studied the recorded impulsive signals in which we were able to identify P and S waves. Seismic experiments were performed in September 2008 on the plateau in order to constrain the ground velocity structure. Preliminary event location shows that the signal sources were located along the broken plane and probably result from micro-cracks along rock bridges.

Modeling the Excitation of Seismic Waves by the Joplin Tornado

NASA Astrophysics Data System (ADS)

Valovcin, Anne; Tanimoto, Toshiro

2017-10-01

Tornadoes generate seismic signals when they contact the ground. Here we examine the signals excited by the Joplin tornado, which passed within 2 km of a station in the Earthscope Transportable Array. We model the tornado-generated vertical seismic signal at low frequencies (0.01-0.03 Hz) and solve for the strength of the seismic source. The resulting source amplitude is largest when the tornado was reported to be strongest (EF 4-5), and the amplitude is smallest when the tornado was weak (EF 0-2). A further understanding of the relationship between source amplitude and tornado intensity could open up new ways to study tornadoes from the ground.

ENAM: A community seismic experiment targeting rifting processes and post-rift evolution of the Mid Atlantic US margin

NASA Astrophysics Data System (ADS)

Van Avendonk, H. J.; Magnani, M. B.; Shillington, D. J.; Gaherty, J. B.; Hornbach, M. J.; Dugan, B.; Long, M. D.; Lizarralde, D.; Becel, A.; Benoit, M. H.; Harder, S. H.; Wagner, L. S.; Christeson, G. L.

2014-12-01

The continental margins of the eastern United States formed in the Early Jurassic after the breakup of supercontinent Pangea. The relationship between the timing of this rift episode and the occurrence of offshore magmatism, which is expressed in the East Coast Magnetic Anomaly, is still unknown. The possible influence of magmatism and existing lithospheric structure on the rifting processes along margin of the eastern U.S. was one of the motivations to conduct a large-scale community seismic experiment in the Eastern North America (ENAM) GeoPRISMS focus site. In addition, there is also a clear need for better high-resolution seismic data with shallow penetration on this margin to better understand the geological setting of submarine landslides. The ENAM community seismic experiment is a project in which a team of scientists will gather both active-source and earthquake seismic data in the vicinity of Cape Hatteras on a 500 km wide section of the margin offshore North Carolina and Virginia. The timing of data acquisition in 2014 and 2015 facilitates leveraging of other geophysical data acquisition programs such as Earthscope's Transportable Array and the USGS marine seismic investigation of the continental shelf. In April of 2014, 30 broadband ocean-bottom seismometers were deployed on the shelf, slope and abyssal plain of the study site. These instruments will record earthquakes for one year, which will help future seismic imaging of the deeper lithosphere beneath the margin. In September and October of 2014, regional marine seismic reflection and refraction data will be gathered with the seismic vessel R/V Marcus Langseth, and airgun shots will also be recorded on land to provide data coverage across the shoreline. Last, in the summer of 2015, a land explosion seismic refraction study will provide constraints on the crustal structure in the adjacent coastal plain of North Carolina and Virginia. All seismic data will be distributed to the community through IRIS/DMC and the LDEO/UTIG Seismic data center. Two workshops are planned for 2015, where new users get an opportunity to engage in basic processing and analysis of the new data set.

Observation and prediction of dynamic ground strains, tilts, and torsions caused by the Mw 6.0 2004 Parkfield, California, earthquake and aftershocks, derived from UPSAR array observations

USGS Publications Warehouse

Spudich, P.; Fletcher, Joe B.

2008-01-01

The 28 September 2004 Parkfield, California, earthquake (Mw 6.0) and four aftershocks (Mw 4.7-5.1) were recorded on 12 accelerograph stations of the U.S. Geological Survey Parkfield seismic array (UPSAR), an array of three-component accelerographs occupying an area of about 1 km2 located 8.8 km from the San Andreas fault. Peak horizontal acceleration and velocity at UPSAR during the mainshock were 0.45g and 27 cm/sec, respectively. We determined both time-varying and peak values of ground dilatations, shear strains, torsions, tilts, torsion rates, and tilt rates by applying a time-dependent geodetic analysis to the observed array displacement time series. Array-derived dilatations agree fairly well with point measurements made on high sample rate recordings of the Parkfield-area dilatometers (Johnston et al., 2006). Torsion Fourier amplitude spectra agree well with ground velocity spectra, as expected for propagating plane waves. A simple predictive relation, using the predicted peak velocity from the Boore-Atkinson ground-motion prediction relation (Boore and Atkinson, 2007) scaled by a phase velocity of 1 km/sec, predicts observed peak Parkfield and Chi-Chi rotations (Huang, 2003) well. However, rotation rates measured during Mw 5 Ito, Japan, events observed on a gyro sensor (Takeo, 1998) are factors of 5-60 greater than those predicted by our predictive relation. This discrepancy might be caused by a scale dependence in rotation, with rotations measured over a short baseline exceeding those measured over long baselines. An alternative hypothesis is that events having significant non-double-couple mechanisms, like the Ito events, radiate much stronger rotations than double-couple events. If this is true, then rotational observations might provide an important source of new information for monitoring seismicity in volcanic areas.

Quality of Green's Functions Improved by Automatic Detection and Removal of Coherent Anthropogenic Noise

NASA Astrophysics Data System (ADS)

Williams, E. F.; Martin, E. R.; Biondi, B. C.; Lindsey, N.; Ajo Franklin, J. B.; Wagner, A. M.; Bjella, K.; Daley, T. M.; Dou, S.; Freifeld, B. M.; Robertson, M.; Ulrich, C.

2016-12-01

We analyze the impact of identifying and removing coherent anthropogenic noise on synthetic Green's functions extracted from ambient noise recorded on a dense linear distributed acoustic sensing (DAS) array. Low-cost, low-impact urban seismic surveys are possible with DAS, which uses dynamic strain sensing to record seismic waves incident to a buried fiber optic cable. However, interferometry and tomography of ambient noise data recorded in urban areas include coherent noise from near-field infrastructure such as cars and trains passing the array, in some cases causing artifacts in estimated Green's functions and potentially incorrect surface wave velocities. Based on our comparison of several methods, we propose an automated, real-time data processing workflow to detect and reduce the impact of these events on data from a dense array in an urban environment. We utilize a recursive STA/LTA (short-term average/long-term average) algorithm on each channel to identify sharp amplitude changes typically associated with an event arrival. In order to distinguish between optical noise and physical events, an event is cataloged only if STA/LTA is triggered on enough channels across the array in a short time window. For each event in the catalog, a conventional semblance analysis is performed across a straight segment of the array to determine whether the event has a coherent velocity signature. Events that demonstrate a semblance peak at low apparent velocities (5-50 m/s) are assumed to represent coherent transportation-related noise and are down-weighted in the time domain before cross-correlation. We show the impact of removing such noise on estimated Green's functions from ambient noise data recorded in Richmond, CA in December 2014. This method has been developed for use on a continuous time-lapse ambient noise survey collected with DAS near Fairbanks, AK, and an upcoming ambient noise survey on the Stanford University campus using DAS with a re-purposed telecommunications fiber optic cable.

Surface-wave and refraction tomography at the FACT Site, Sandia National Laboratories, Albuquerque, New Mexico.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbott, Robert E.; Bartel, Lewis Clark; Pullammanappallil, Satish

2006-08-01

We present a technique that allows for the simultaneous acquisition and interpretation of both shear-wave and compressive-wave 3-D velocities. The technique requires no special seismic sources or array geometries, and is suited to studies with small source-receiver offsets. The method also effectively deals with unwanted seismic arrivals by using the statistical properties of the data itself to discriminate against spurious picks. We demonstrate the technique with a field experiment at the Facility for Analysis, Calibration, and Testing at Sandia National Laboratories, Albuquerque, New Mexico. The resulting 3-D shear-velocity and compressive-velocity distributions are consistent with surface geologic mapping. The averaged velocitiesmore » and V{sub p}/V{sub s} ratio in the upper 30 meters are also consistent with examples found in the scientific literature.« less

Upper Mantle of the Central Part of the Russian Platform by Receiver Function Data.

NASA Astrophysics Data System (ADS)

Goev, Andrey; Kosarev, Grigoriy; Sanina, Irina; Riznichenko, Oksana

2017-04-01

The study of the upper mantle of the Russian Platform (RP) with seismic methods remains limited due to the lack of broadband seismic stations. Existing velocity models have been obtained by using the P-wave travel-times from seismic events interpreted as explosions recorded at the NORSAR array in 1974-75 years. Another source of information is deep seismic sounding data from long-range profiles (exceeding 3000 km) such as QUARTZ, RUBIN-1 and GLOBUS and peaceful nuclear explosions (PNE) as sources. However, the data with the maximum distances larger than 1500 km have been acquired on the RP and only in the northern part. Being useful, these velocity models have low spatial resolution. This study analyzes and integrates all the existing RP upper mantle velocity models with the main focus on the central region. We discuss the completeness of the RP area of the LITHO 1.0 model. Based on results of our analysis, we conclude that it is necessary to get up-to-date velocity models of the upper mantle using broadband stations located at the central part of the RP using Vp/Vs ratio data and anisotropy parameters for robust estimation of the mantle boundaries. By applying the joint inversion of receiver-function (RF) data, travel-time residuals and dispersion curves of surface waves we get new models reaching 300 km depth at the locations of broadband seismic stations at the central part of the RP. We used IRIS stations OBN, ARU along with MHV and mobile array NOV. For each station we attempt to determine thickness of the lithosphere and to locate LVL, LAB, Lehman and Hales boundaries as well as the discontinuities in the transition zones at the depth of 410 and 660 km. Also we investigate the necessity of using short-period and broadband RF separately for more robust estimation of the velocity model of the upper mantle. This publication is based on work supported by the Russian Foundation for Basic Research (RFBR), project 15-05-04938 and by the leading scientific school NS-3345.2014.5

Broadening the Quality and Capabilities of the EarthScope Alaska Transportable Array

NASA Astrophysics Data System (ADS)

Busby, R. W.

2016-12-01

In 2016, the EarthScope Transportable Array (TA) program will have 195 broadband seismic stations operating in Alaska and western Canada. This ambitious project will culminate in a network of 268 new or upgraded real-time seismic stations operating through 2019. The challenging environmental conditions and the remoteness of Alaska have motivated a new method for constructing a high-quality, temporary seismic network. The Alaska TA station design builds on experience of the Lower 48 TA deployment and adds design requirements because most stations are accessible only by helicopter. The stations utilize new high-performance posthole sensors, a specially built hammer/auger drill, and lightweight lithium ion batteries to minimize sling loads. A uniform station design enables a modest crew to build the network on a short timeline and operate them through the difficult conditions of rural Alaska. The Alaska TA deployment has increased the quality of seismic data, with some well-sited 2-3 m posthole stations approaching the performance of permanent Global Seismic Network stations emplaced in 100 m boreholes. The real-time data access, power budget, protective enclosure and remote logistics of these TA stations has attracted collaborations with NASA, NOAA, USGS, AVO and other organizations to add auxiliary sensors to the suite of instruments at many TA stations. Strong motion sensors have been added to (18) stations near the subduction trench to complement SM stations operated by AEC, ANSS and GSN. All TA and most upgraded stations have pressure and infrasound sensors, and 150 TA stations are receiving a Vaisala weather sensor, supplied by the National Weather Service Alaska Region and NASA, capable of measuring temperature, pressure, relative humidity, wind speed/direction, and precipitation intensity. We are also installing about (40) autonomous soil temperature profile kits adjacent to northern stations. While the priority continues to be collecting seismic data, these additional strong motion, atmospheric, and soil temperature sensors may motivate the desire extend the operation of certain stations in cooperation with these organizations. The TA has always been amenable to partnerships in the research and education communities that extend the capabilities and reach of the EarthScope Transportable Array.

Location of the Green Canyon (Offshore Southern Louisiana) Seismic Event of February 10, 2006

USGS Publications Warehouse

Dewey, James W.; Dellinger, Joseph A.

2008-01-01

We calculated an epicenter for the Offshore Southern Louisiana seismic event of February 10, 2006 (the 'Green Canyon event') that was adopted as the preferred epicenter for the event by the USGS/NEIC. The event is held at a focal depth of 5 km; the focal depth could not be reliably calculated but was most likely between 1 km and 15 km beneath sea level. The epicenter was calculated with a radially symmetric global Earth model similar to that routinely used at the USGS/NEIC for all earthquakes worldwide. The location was calculated using P-waves recorded by seismographic stations from which the USGS/NEIC routinely obtains seismological data, plus data from two seismic exploration arrays, the Atlantis ocean-bottom node array, operated by BP in partnership with BHP Billiton Limited, and the CGG Green Canyon phase VIII multi-client towed-streamer survey. The preferred epicenter is approximately 26 km north of an epicenter earlier published by the USGS/NEIC, which was obtained without benefit of the seismic exploration arrays. We estimate that the preferred epicenter is accurate to within 15 km. We selected the preferred epicenter from a suite of trial calculations that attempted to fit arrival times of seismic energy associated with the Green Canyon event and that explored the effect of errors in the velocity model used to calculate the preferred epicenter. The various trials were helpful in confirming the approximate correctness of the preferred epicenter and in assessing the accuracy of the preferred epicenter, but none of the trial calculations, including that of the preferred epicenter, was able to reconcile arrival-time observations and assumed velocity model as well as is typical for the vast majority of earthquakes in and near the continental United States. We believe that remaining misfits between the preferred solution and the observations reflect errors in interpreted arrival times of emergent seismic phases that are due partly to a temporally extended source-time function and partly to failure of our travel-time model to account for the extremely complicated velocity structure of the sedimentary section in which the event occurred.

A wireless sensor network for monitoring volcano-seismic signals

NASA Astrophysics Data System (ADS)

Lopes Pereira, R.; Trindade, J.; Gonçalves, F.; Suresh, L.; Barbosa, D.; Vazão, T.

2014-12-01

Monitoring of volcanic activity is important for learning about the properties of each volcano and for providing early warning systems to the population. Monitoring equipment can be expensive, and thus the degree of monitoring varies from volcano to volcano and from country to country, with many volcanoes not being monitored at all. This paper describes the development of a wireless sensor network (WSN) capable of collecting geophysical measurements on remote active volcanoes. Our main goals were to create a flexible, easy-to-deploy and easy-to-maintain, adaptable, low-cost WSN for temporary or permanent monitoring of seismic tremor. The WSN enables the easy installation of a sensor array in an area of tens of thousands of m2, allowing the location of the magma movements causing the seismic tremor to be calculated. This WSN can be used by recording data locally for later analysis or by continuously transmitting it in real time to a remote laboratory for real-time analyses. We present a set of tests that validate different aspects of our WSN, including a deployment on a suspended bridge for measuring its vibration.

Adaptive Sensor Tuning for Seismic Event Detection in Environment with Electromagnetic Noise

NASA Astrophysics Data System (ADS)

Ziegler, Abra E.

The goal of this research is to detect possible microseismic events at a carbon sequestration site. Data recorded on a continuous downhole microseismic array in the Farnsworth Field, an oil field in Northern Texas that hosts an ongoing carbon capture, utilization, and storage project, were evaluated using machine learning and reinforcement learning techniques to determine their effectiveness at seismic event detection on a dataset with electromagnetic noise. The data were recorded from a passive vertical monitoring array consisting of 16 levels of 3-component 15 Hz geophones installed in the field and continuously recording since January 2014. Electromagnetic and other noise recorded on the array has significantly impacted the utility of the data and it was necessary to characterize and filter the noise in order to attempt event detection. Traditional detection methods using short-term average/long-term average (STA/LTA) algorithms were evaluated and determined to be ineffective because of changing noise levels. To improve the performance of event detection and automatically and dynamically detect seismic events using effective data processing parameters, an adaptive sensor tuning (AST) algorithm developed by Sandia National Laboratories was utilized. AST exploits neuro-dynamic programming (reinforcement learning) trained with historic event data to automatically self-tune and determine optimal detection parameter settings. The key metric that guides the AST algorithm is consistency of each sensor with its nearest neighbors: parameters are automatically adjusted on a per station basis to be more or less sensitive to produce consistent agreement of detections in its neighborhood. The effects that changes in neighborhood configuration have on signal detection were explored, as it was determined that neighborhood-based detections significantly reduce the number of both missed and false detections in ground-truthed data. The performance of the AST algorithm was quantitatively evaluated during a variety of noise conditions and seismic detections were identified using AST and compared to ancillary injection data. During a period of CO2 injection in a nearby well to the monitoring array, 82% of seismic events were accurately detected, 13% of events were missed, and 5% of detections were determined to be false. Additionally, seismic risk was evaluated from the stress field and faulting regime at FWU to determine the likelihood of pressure perturbations to trigger slip on previously mapped faults. Faults oriented NW-SE were identified as requiring the smallest pore pressure changes to trigger slip and faults oriented N-S will also potentially be reactivated although this is less likely.

Ambient seismic noise interferometry in Hawai'i reveals long-range observability of volcanic tremor

USGS Publications Warehouse

Ballmer, Silke; Wolfe, Cecily; Okubo, Paul G.; Haney, Matt; Thurber, Clifford H.

2013-01-01

The use of seismic noise interferometry to retrieve Green's functions and the analysis of volcanic tremor are both useful in studying volcano dynamics. Whereas seismic noise interferometry allows long-range extraction of interpretable signals from a relatively weak noise wavefield, the characterization of volcanic tremor often requires a dense seismic array close to the source. We here show that standard processing of seismic noise interferometry yields volcanic tremor signals observable over large distances exceeding 50 km. Our study comprises 2.5 yr of data from the U.S. Geological Survey Hawaiian Volcano Observatory short period seismic network. Examining more than 700 station pairs, we find anomalous and temporally coherent signals that obscure the Green's functions. The time windows and frequency bands of these anomalous signals correspond well with the characteristics of previously studied volcanic tremor sources at Pu'u 'Ō'ō and Halema'uma'u craters. We use the derived noise cross-correlation functions to perform a grid-search for source location, confirming that these signals are surface waves originating from the known tremor sources. A grid-search with only distant stations verifies that useful tremor signals can indeed be recovered far from the source. Our results suggest that the specific data processing in seismic noise interferometry—typically used for Green's function retrieval—can aid in the study of both the wavefield and source location of volcanic tremor over large distances. In view of using the derived Green's functions to image heterogeneity and study temporal velocity changes at volcanic regions, however, our results illustrate how care should be taken when contamination by tremor may be present.

The IberArray BB seismic network of Topo-Iberia: new constraints revealing the deep structure of the Iberian Peninsula and North Morocco

NASA Astrophysics Data System (ADS)

Gallart, J.; Diaz Cusi, J.; Villasenor, A.; Mancilla, F. D. L.; Bonatto, L.; Schimmel, M.; El moudnib, L.

2014-12-01

Topo-Iberia has been a large-scale Spanish project running from 2007 to 2013 that integrated more than 150 researchers on Earth Sciences. One of its key assets was the management of an observatory platform, named IberArray, aimed to provide new geophysical datasets (seismic, GPS, MT) to constrain the structure of Iberia with unprecedented resolution. The IberArray seismic pool was composed by 70+ BB stations, covering the study area in 3 deployments with a site-density of 60km x 60km. The data base holds ~300 sites, including the permanent networks in the area. Hence it forms a unique seismic database in Europe that allow for multiple analyses to constrain the complex geodinamics of the Western Mediterranean. A summary of new results coming from different techniques is presented here. The SKS splitting analysis has provided a spectacular image of the rotation of the fast velocity direction along the Gibraltar Arc. In central and northern Iberia, the fast polarization directions are close to EW, consistently with global mantle flow models considering contributions of surface plate motion, density variations and net lithosphere rotation. Those results suggest an asthenospheric origin of the observed anisotropy related to present-day mantle flow. Receiver functions have revealed the crustal thickness variations beneath the Rif and southern Iberia, including a crustal root beneath the Rif. The Variscan Iberian massif shows a flat Moho discontinuity, while the areas reworked in the Alpine orogeny show a slightly thicker crust. Beneath N Iberia, the imbrication of the Iberian and Eurasian crusts results in complex receiver functions. Depths exceeding 45 km are observed along the Pyrenean range, while the crust thins to values of 26-28 km close to the Atlantic coasts. The geometry of the 410-km and 660-km discontinuities has been investigated using novel cross-correlation/stacking techniques. Ambient noise tomography allows to identify the main sedimentary basins and to discriminate between the Variscan and the Alpine reworked areas. Local body-wave tomography in North Morocco has improved the location of the small magnitude events on the area and the details of the crustal structure. Teleseismic tomography has confirmed, using an independent data set, the presence of a high-velocity slab beneath the Gibraltar Arc.

Evaluation of a dense seismic array for acquisition of high quality data in the ACROSS observation

NASA Astrophysics Data System (ADS)

Tsuruga, K.; Kunitomo, T.; Hasada, Y.; Kumazawa, M.; Shigeta, N.; Kasahara, J.

2004-12-01

ACROSS is an active monitoring methodology to detect any subtle temporal change of physical properties in the Earth's interior. We demonstrate the potentiality of the ACROSS observation with a dense sensor array. We have conducted a dense seismic array observation at the distance of 1 km from the ACROSS source since 2003. The array is composed of 36 three-component velocity seismometers buried at 1.8 m deep in an area 25 m square. All the data are recorded accurately referring to a GPS clock. We derived and analyzed a transfer function (TF) from the source to a receiver by the following steps: (1) evaluating a force vector as source characteristics, (2) converting the observed data to the displacement vectors by incorporating all the corrections of the instruments, (3) stacking the observed data for an enough time to suppress the temporal noise, (4) extracting ACROSS signal and evaluating noise level, (5) representing TF in a tensor form with the estimated errors, (6) slant-stacking with variable ray parameters, (7) estimating the travel times and amplitudes of the wave arrivals by Sompi Event Analysis (Hasada et al., 2001) and representing the result by a pulse sequence, and (8) deriving the polarization vector for each arrival to identify all the wave modes. We analyzed TF of SH-wave component from 16 to 20 Hz as an example. We obtained good quality TF with S/N ratio up to 104 by stacking for 12 days at the step (3). The spatial noise originated from the local heterogeneity around the array was eliminated by the step (6). Several arrivals were recognized within the time windows from 0.6 to 1.8 s. The maximum amplitude of event traces was detected at the travel time of 1.064 s with a ray parameter of 7.9x10-4 s/m. We also found the scattered waves probably generated by the heterogeneities around the array. The ACROSS dense array observation would provide a lot of information on the underground heterogeneities. Consequently, we have the important and challenging subjects: (1) optimum designing of ACROSS array to acquire the better data and (2) development of new theoretical method to deal with the variable types of the wave.

Shallow Water Propagation

DTIC Science & Technology

2010-02-26

bottom waveguide. The lower contour plot demonstrates that this method, unlike other parabolic equations, can treat seismic sources. 20100308162...solitons. One illustration in Figure 8 shows depth-averaged data at the Naval Research Laboratory vertical line array (VLA) [dashed blue curves...vertical line array about 15 km from the source. The right panel [blue curves] compares corresponding simulations from a three-dimensional adiabatic mode

Earthquake Source Parameters Inferred from T-Wave Observations

NASA Astrophysics Data System (ADS)

Perrot, J.; Dziak, R.; Lau, T. A.; Matsumoto, H.; Goslin, J.

2004-12-01

The seismicity of the North Atlantic Ocean has been recorded by two networks of autonomous hydrophones moored within the SOFAR channel on the flanks of the Mid-Atlantic Ridge (MAR). In February 1999, a consortium of U.S. investigators (NSF and NOAA) deployed a 6-element hydrophone array for long-term monitoring of MAR seismicity between 15o-35oN south of the Azores. In May 2002, an international collaboration of French, Portuguese, and U.S. researchers deployed a 6-element hydrophone array north of the Azores Plateau from 40o-50oN. The northern network (referred to as SIRENA) was recovered in September 2003. The low attenuation properties of the SOFAR channel for earthquake T-wave propagation results in a detection threshold reduction from a magnitude completeness level (Mc) of ˜ 4.7 for MAR events recorded by the land-based seismic networks to Mc=3.0 using hydrophone arrays. Detailed focal depth and mechanism information, however, remain elusive due to the complexities of seismo-acoustic propagation paths. Nonetheless, recent analyses (Dziak, 2001; Park and Odom, 2001) indicate fault parameter information is contained within the T-wave signal packet. We investigate this relationship further by comparing an earthquake's T-wave duration and acoustic energy to seismic magnitude (NEIC) and radiation pattern (for events M>5) from the Harvard moment-tensor catalog. First results show earthquake energy is well represented by the acoustic energy of the T-waves, however T-wave codas are significantly influenced by acoustic propagation effects and do not allow a direct determination of the seismic magnitude of the earthquakes. Second, there appears to be a correlation between T-wave acoustic energy, azimuth from earthquake source to the hydrophone, and the radiation pattern of the earthquake's SH waves. These preliminary results indicate there is a relationship between the T-wave observations and earthquake source parameters, allowing for additional insights into T-wave propagation.

Interpretation of Microseismicity Observed From Surface and Borehole Seismic Arrays During Hydraulic Fracturing in Shale - Bedding Plane Slip Model

NASA Astrophysics Data System (ADS)

Stanek, F.; Jechumtalova, Z.; Eisner, L.

2017-12-01

We present a geomechanical model explaining microseismicity induced by hydraulic fracturing in shales developed from many datasets acquired with two most common types of seismic monitoring arrays, surface and dual-borehole arrays. The geomechanical model explains the observed source mechanisms and locations of induced events from two stimulated shale reservoirs. We observe shear dip-slip source mechanisms with nodal planes aligned with location trends. We show that such seismicity can be explained as a shearing along bedding planes caused by aseismic opening of vertical hydraulic fractures. The source mechanism inversion was applied only to selected high-quality events with sufficient signal-to-noise ratio. We inverted P- and P- and S-wave arrival amplitudes to full-moment tensor and decomposed it to shear, volumetric and compensated linear vector dipole components. We also tested an effect of noise presented in the data to evaluate reliability of non-shear components. The observed seismicity from both surface and downhole monitoring of shale stimulations is very similar. The locations of induced microseismic events are limited to narrow depth intervals and propagate along distinct trend(s) showing fracture propagation in direction of maximum horizontal stress from injection well(s). The source mechanisms have a small non-shear component which can be partly explained as an effect of noise in the data, i.e. events represent shearing on faults. We observe predominantly dip-slip events with a strike of the steeper (almost vertical) nodal plane parallel to the fracture propagation. Therefore the other possible nodal plane is almost horizontal. The rake angles of the observed mechanisms divide these dip-slips into two groups with opposite polarities. It means that we observe opposite movements on the nearly identically oriented faults. Realizing a typical structural weakness of shale in horizontal planes, we interpret observed microseismicity as a result of shearing along bedding planes caused by seismically silent (aseismic) vertical fracture opening.

Structure of the North Anatolian Fault Zone from the Autocorrelation of Ambient Seismic Noise

NASA Astrophysics Data System (ADS)

Taylor, George; Rost, Sebastian; Houseman, Gregory

2016-04-01

In recent years the technique of cross-correlating the ambient seismic noise wavefield at two seismometers to reconstruct empirical Green's Functions for the determination of Earth structure has been a powerful tool to study the Earth's interior without earthquakes or man-made sources. However, far less attention has been paid to using auto-correlations of seismic noise to reveal body wave reflections from interfaces in the subsurface. In principle, the Green's functions thus derived should be comparable to the Earth's impulse response to a co-located source and receiver. We use data from a dense seismic array (Dense Array for Northern Anatolia - DANA) deployed across the northern branch of the North Anatolian Fault Zone (NAFZ) in the region of the 1999 magnitude 7.6 Izmit earthquake in western Turkey. The NAFZ is a major strike-slip system that extends ~1200 km across northern Turkey and continues to pose a high level of seismic hazard, in particular to the mega-city of Istanbul. We construct body wave images for the entire crust and the shallow upper mantle over the ~35 km by 70 km footprint of the 70-station DANA array. Using autocorrelations of the vertical component of ground motion, P-wave reflections can be retrieved from the wavefield to constrain crustal structure. We show that clear P-wave reflections from the crust-mantle boundary (Moho) can be retrieved using the autocorrelation technique, indicating topography on the Moho on horizontal scales of less than 10 km. Offsets in crustal structure can be identified that seem to be correlated with the surface expression of the northern branch of the fault zone, indicating that the NAFZ reaches the upper mantle as a narrow structure. The southern branch has a less clear effect on crustal structure. We also see evidence of several discontinuities in the mid-crust in addition to an upper mantle reflector that we interpret to represent the Hales discontinuity.

Studying local earthquakes in the area Baltic-Bothnia Megashear using the data of the POLENET/LAPNET temporary array

NASA Astrophysics Data System (ADS)

Usoltseva, Olga; Kozlovskaya, Elena

2016-07-01

Earthquakes in areas within continental plates are still not completely understood, and progress on understanding intraplate seismicity is slow due to a short history of instrumental seismology and sparse regional seismic networks in seismically non-active areas. However, knowledge about position and depth of seismogenic structures in such areas is necessary in order to estimate seismic hazard for such critical facilities such as nuclear power plants and nuclear waste deposits. In the present paper we address the problem of seismicity in the intraplate area of northern Fennoscandia using the information on local events recorded by the POLENET/LAPNET (Polar Earth Observing Network) temporary seismic array during the International Polar Year 2007-2009. We relocate the seismic events using the program HYPOELLIPS (a computer program for determining local earthquake hypocentral parameters) and grid search method. We use the first arrivals of P waves of local events in order to calculate a 3-D tomographic P wave velocity model of the uppermost crust (down to 20 km) for a selected region inside the study area and show that the velocity heterogeneities in the upper crust correlate well with known tectonic units. We compare the position of the velocity heterogeneities with the seismogenic structures delineated by epicentres of relocated events and demonstrate that these structures generally do not correlate with the crustal units formed as a result of crustal evolution in the Archaean and Palaeoproterozoic. On the contrary, they correlate well with the postglacial faults located in the area of the Baltic-Bothnia Megashear (BBMS). Hypocentres of local events have depths down to 30 km. We also obtain the focal mechanism of a selected event with good data quality. The focal mechanism is of oblique type with strike-slip prevailing. Our results demonstrate that the Baltic-Bothnia Megashear is an important large-scale, reactivated tectonic structure that has to be taken into account when estimating seismic hazard in northern Fennoscandia.

A new moonquake catalog from Apollo 17 seismic data I: Lunar Seismic Profiling Experiment: Thermal moonquakes and implications for surface processes

NASA Astrophysics Data System (ADS)

Weber, R. C.; Dimech, J. L.; Phillips, D.; Molaro, J.; Schmerr, N. C.

2017-12-01

Apollo 17's Lunar Seismic Profiling Experiment's (LSPE) primary objective was to constrain the near-surface velocity structure at the landing site using active sources detected by a 100 m-wide triangular geophone array. The experiment was later operated in "listening mode," and early studies of these data revealed the presence of thermal moonquakes - short-duration seismic events associated with terminator crossings. However, the full data set has never been systematically analyzed for natural seismic signal content. In this study, we analyze 8 months of continuous LSPE data using an automated event detection technique that has previously successfully been applied to the Apollo 16 Passive Seismic Experiment data. We detected 50,000 thermal moonquakes from three distinct event templates, representing impulsive, intermediate, and emergent onset of seismic energy, which we interpret as reflecting their relative distance from the array. Impulsive events occur largely at sunrise, possibly representing the thermal "pinging" of the nearby lunar lander, while emergent events occur at sunset, possibly representing cracking or slumping in more distant surface rocks and regolith. Preliminary application of an iterative event location algorithm to a subset of the impulsive waveforms supports this interpretation. We also perform 3D modeling of the lunar surface to explore the relative contribution of the lander, known rocks and surrounding topography to the thermal state of the regolith in the vicinity of the Apollo 17 landing site over the course of the lunar diurnal cycle. Further development of both this model and the event location algorithm may permit definitive discrimination between different types of local diurnal events e.g. lander noise, thermally-induced rock breakdown, or fault creep on the nearby Lee-Lincoln scarp. These results could place important constraints on both the contribution of seismicity to regolith production, and the age of young lobate scarps.

Seismic reflection and refraction data acquired in Canada Basin, Northwind Ridge and Northwind Basin, Arctic Ocean in 1988, 1992 and 1993

USGS Publications Warehouse

Grantz, Arthur; Hart, Patrick E.; May, Steven D.

2004-01-01

Seismic reflection and refraction data were collected in generally ice-covered waters of the Canada Basin and the eastern part of the Chukchi Continental Borderland of the Amerasia Basin, Arctic Ocean, during the late summers of 1988, 1992, and 1993. The data were acquired from a Polar class icebreaker, the U.S. Coast Guard Cutter Polar Star, using a seismic reflection system designed by the U.S. Geological Survey (USGS). The northernmost data extend to 78? 48' N latitude. In 1988, 155 km of reflection data were acquired with a prototype system consisting of a single 195 cubic inch air gun seismic source and a two-channel hydrophone streamer with a 150-m active section. In 1992 and 1993, 500 and 1,900 km, respectively, of seismic reflection profile data were acquired with an improved six air gun, 674 to 1303 cubic inch tuned seismic source array and the same two-channel streamer. In 1993, a 12-channel streamer with a 150-m active section was used to record five of the reflection lines and one line was acquired using a three air gun, 3,000 cubic inch source. All data were recorded with a DFS-V digital seismic recorder. Processed sections feature high quality vertical incidence images to more than 6 km of sub-bottom penetration in the Canada Basin. Refraction data were acquired with U.S. Navy sonobuoys recorded simultaneously with the seismic reflection profiles. In 1988 eight refraction profiles were recorded with the single air gun, and in 1992 and 1993 a total of 47 refraction profiles were recorded with the six air gun array. The sonobuoy refraction records, with offsets up to 35 km, provide acoustic velocity information to complement the short-offset reflection data. The report includes trackline maps showing the location of the data, as well as both digital data files (SEG-Y) and images of all of the profiles.

Investigation of Earthquake and Geyser Events in the Upper Geyser Basin of Yellowstone National Park from a Nodal Array

NASA Astrophysics Data System (ADS)

Garcia, S.; Karplus, M. S.; Farrell, J.; Lin, F. C.; Smith, R. B.

2017-12-01

A large seismic nodal array incorporating 133 three-component, 5-Hz geophones deployed for two weeks in early November 2015 in the Upper Geyser Basin recorded earthquake and hydrothermal activity. The University of Utah, the University of Texas at El Paso, and Yellowstone National Park collaborated to deploy Fairfield Nodal ZLand 3-C geophones concentrically centered around the Old Faithful Geyser with an average station spacing of 50 m and an aperture of 1 km. The array provided a unique dataset to investigate wave propagation through various fractures and active geysers in a hydrothermal field located over the Yellowstone hotspot. The complicated sub-surface features associated with the hydrothermal field appear to impact earthquake wave propagation in the Upper Geyser Basin and to generate seismic signals. Previous work using ambient noise cross-correlation has found an intricately fractured sub-surface that provides pathways for water beneath parts of the Upper Geyser Basin that likely feed Old Faithful and other nearby geysers and hot springs. For this study, we used the data to create visualizations of local earthquake, teleseismic earthquake, and hydrothermal events as they propagate through the array. These ground motion visualizations allow observation of wave propagation through the geyser field, which may indicate the presence of anomalous structure impacting seismic velocities and attenuation. Three teleseismic events were observed in the data, two 6.9MW earthquakes that occurred off the coast of Coquimbo, Colombia 9,000km from the array and one 6.5MW near the Aleutian Islands 4,500km from the array. All three teleseismic events observed in the data exhibited strong direct P-wave arrivals and several additional phases. One local earthquake event (2.5ML) 100km from the Upper Geyser Basin was also well-recorded by the array. Time-domain spectrograms show the dominant frequencies present in the recordings of these events. The two 6.9MW earthquakes in Chile were one hour apart and offered interesting signals that also included a geyser tremor between the two events.

Crustal seismic structure beneath the southwest Yunnan region from joint inversion of body-wave and surface wave data

NASA Astrophysics Data System (ADS)

Luo, Y.; Thurber, C. H.; Zeng, X.; Zhang, L.

2016-12-01

Data from 71 broadband stations of a dense transportable array deployed in southwest Yunnan makes it possible to improve the resolution of the seismic model in this region. Continuous waveforms from 12 permanent stations of the China National Seismic Network were also used in this study. We utilized one-year continuous vertical component records to compute ambient noise cross-correlation functions (NCF). More than 3,000 NCFs were obtained and used to measure group velocities between 5 and 25 seconds with the frequency-time analysis method. This frequency band is most sensitive to crustal seismic structure, especially the upper and middle crust. The group velocity at short-period shows a clear azimuthal anisotropy with a north-south fast direction. The fast direction is consistent with previous seismic results revealed from shear wave splitting. More than 2,000 group velocity measurements were employed to invert the surface wave dispersion data for group velocity maps. We applied a finite difference forward modeling algorithm with an iterative inversion. A new body-wave and surface wave joint inversion algorithm (Fang et al., 2016) was utilized to improve the resolution of both P and S models. About 60,000 P wave and S wave arrivals from 1,780 local earthquakes, which occurred from May 2011 to December 2013 with magnitudes larger than 2.0, were manually picked. The new high-resolution seismic structure shows good consistency with local geological features, e.g. Tengchong Volcano. The earthquake locations also were refined with our new velocity model.

Sensor Emplacement Techniques and Seismic Noise Analysis for USArray Transportable Array Seismic Stations

NASA Astrophysics Data System (ADS)

Frassetto, A.; Busby, R. W.; Hafner, K.; Woodward, R.; Sauter, A.

2013-12-01

In preparation for the upcoming deployment of EarthScope's USArray Transportable Array (TA) in Alaska, the National Science Foundation (NSF) has supported exploratory work on seismic station design, sensor emplacement, and communication concepts appropriate for this challenging high-latitude environment. IRIS has installed several experimental stations to evaluate different sensor emplacement schemes both in Alaska and in the lower-48 of the U.S. The goal of these tests is to maintain or enhance a station's noise performance while minimizing its footprint and the weight of the equipment, materials, and overall expense required for its construction. Motivating this approach are recent developments in posthole broadband seismometer design and the unique conditions for operating in Alaska, where there are few roads, cellular communications are scarce, most areas are only accessible by small plane or helicopter, and permafrost underlies much of the state. We will review the methods used for directly emplacing broadband seismometers in comparison to the current methods used for the lower-48 TA. These new methods primarily focus on using a portable drill to make a bored hole three to five meters, beneath the active layer of the permafrost, or by coring 1-2 meters deep into surface bedrock. Both methods are logistically effective in preliminary trials. Subsequent station performance has been assessed quantitatively using probability density functions summed from power spectral density estimates. These are calculated for the continuous time series of seismic data recorded for each channel of the seismometer. There are five test stations currently operating in Alaska. One was deployed in August 2011 and the remaining four in October 2012. Our results show that the performance of seismometers in Alaska with auger-hole or core-hole installations can sometimes exceed that of the quietest TA stations in the lower-48, particularly horizontal components at long periods. A comparison of the performance of the various installations is discussed.

Examining the Effect of Temperature, Pressure, Seismicity and Diffuse Fluid Flow on Floc Events at Axial Seamount

NASA Astrophysics Data System (ADS)

Rahman, M.; Crone, T. J.; Knuth, F.; Garcia, C.; Soule, D. C.; Fatland, R.

2017-12-01

Flocculation (floc) events are characterized by the ejection of bacterial material, possibly associated with thermophiles originating from warmer sub-seafloor habitats, into the water column. These events are anecdotally linked to magmatic and tectonic processes common in mid-ocean ridge seafloor environments. However, little is known about the relationship between flocculation events and other potentially triggering processes. The Cabled Array at Axial Seamount provides a suite of interdisciplinary real-time datasets to examine system-level processes governing the volcanic marine environment. The eruption at Axial Seamount in 2015 creates an opportunity to study this volcanic system as it evolves post eruption and identify the relationships between the temperature, pressure, seismicity and the biological response. The Diffuse Vent Fluid 3-D Temperature Array (TMPSF), located within the ASHES hydrothermal vent field at Axial Seamount, uses 24 separate sensors to provide a 3-dimensional distribution of diffuse flow temperatures near the Mushroom hydrothermal vent. Preliminary analysis suggests that the temperature signal is strongly influenced by tides observed using the ocean bottom pressure sensors, which may be related to either gradual shifts in tidal currents above the seafloor, or related to subsurface flux. CamHD, also located within the ASHES field, produces high definition video data, which we analyze to identify changes in water column floc concentration. These data streams allow us to examine the controls on the temperature signal and the associated correlations with microbial seafloor processes. We are currently examining the flocculation event identified in Crone (2016) to determine its relationship to changes in seawater temperatures near the seafloor, seismic activity and seafloor pressure. We will use this proxy to examine other CamHD data and determine if subsequent flocculation events have occurred and if they have a similar relationship to local thermal and seismic activity.

Discovery of non-volcanic tremor and contribution to earth science by NIED Hi-net

NASA Astrophysics Data System (ADS)

Obara, K.

2015-12-01

Progress of seismic observation network brings breakthroughs in the earth science at each era. High sensitivity seismograph network (Hi-net) was constructed by National Research Institute for Earth Science and Disaster Prevention (NIED) as a national project in order to improve the detection capability of microearthquake after disastrous 1995 Kobe earthquake. Hi-net has been contributing to not only monitoring of seismicity but also producing many research results like as discoveries of non-volcanic tremor and other slow earthquakes. More important thing is that we have continued to make efforts to monitor all of data visually and effectively. The discovery of tremor in southwest Japan stimulated PGC researchers to search similar seismic signature in Cascadia because of a couple of common features in the tremor in Japan and slow slip event (SSE) they already discovered in Cascadia. At last, episodic tremor and slip (ETS) was discovered, then the SSE associated with tremor was also detected in Japan by using the tilting data measured by high-sensitivity accelerometer attached with the Hi-net. This coupling phenomena strengthened the connection between seismology and geodesy. Widely separated spectrum of tremor and SSE motivated us to search intervened phenomena, then we found very low frequency earthquake during ETS episode. These slow earthquakes obey a scaling law different from ordinary earthquake. This difference is very important to resolve the earthquake physics. Hi-net is quite useful for not only three-dimensional imaging of underground structure beneath the Japan Islands, but also resolving deep Earth interior by using teleseismic events or ambient noises and source rupture process of large earthquakes by using back-projection analysis as a remote array. Hi-net will continue to supply unexpected new discoveries. I expect that multiple installation of similar dense seismic array in the world will give us great opportunity to discover more important and explore a new regime in the earth science.

Pockets, conduits, channels, and plumes: links to volcanism and orogeny in the rollback dominated western Mediterranean

NASA Astrophysics Data System (ADS)

Miller, Meghan S.; Sun, Daoyuan; O'Driscoll, Leland; Becker, Thorsten W.; Holt, Adam; Diaz, Jordi; Thomas, Christine

2015-04-01

Detailed mantle and lithospheric structure from the Canary Islands to Iberia have been imaged with data from recent temporary deployments and select permanent stations from over 300 broadband seismometers. The stations extended across Morocco and Spain as part of the PICASSO, IberArray, and Morocco-Münster experiments. We present results from S receiver functions (SRF), shear wave splitting, waveform modeling, and geodynamic models that help constrain the tectonic evolution of the westernmost Mediterranean, including orogenesis of the Atlas Mountains and occurrence of localized alkaline volcanism. Our receiver function images, in agreement with previous geophysical modeling, show that the lithosphere is thin (~65 km) beneath the Atlas, but thickens (~100 km) over a very short length scale at the flanks of the mountains. We find that these dramatic changes in lithospheric thickness also correspond to dramatic decreases in delay times inferred from S and SKS splitting observations of seismic anisotropy. Pockets and conduits of low seismic velocity material below the lithosphere extend along much of the Atlas to Southern Spain and correlate with the locations of Pliocene-Quaternary magmatism. Waveform analysis from the USC linear seismic array across the Atlas Mountains constrains the position, shape, and physical characteristics of one localized, low velocity conduit that extends from the uppermost mantle (~200 km depth) up to the volcanoes in the Middle Atlas. The shape, position and temperature of these seismically imaged low velocity anomalies, topography of the base of the lithosphere, morphology of the subducted slab beneath the Alboran Sea, position of the West African Craton and correlation with mantle flow inferred from shear wave splitting suggest that the unusually high topography of the Atlas Mountains and isolated recent volcanics are due to active mantle support that may be from material channeled from the Canary Island plume.

Seismic velocities and geologic logs from boreholes at three downhole arrays in San Francisco, California

USGS Publications Warehouse

Gibbs, James F.; Fumal, Thomas E.; Borcherdt, Roger D.; Warrick, Richard E.; Liu, Hsi-Ping; Westerlund, Robert E.

1994-01-01

The Loma Prieta earthquake of October 17, 1989 (1704 PST), has reinforced observations made by Wood and others (1908) after the 1906 San Francisco earthquake, that poor ground conditions (soft soil) increase the likelihood of shaking damage to structures. Since 1908 many studies (for example Borcherdt, 1970, Borcherdt and Gibbs, 1976, Borcherdt and Glassmoyer, 1992) have shown that soft soils amplify seismic waves at frequencies that can be damaging to structures. Damage in the City of San Francisco from the Loma Prieta earthquake was concentrated in the Marina District, the Embarcadero, and the China Basin areas. Each of these areas, to some degree, is underlain by soft soil deposits. These concentrations of damage raise important questions regarding the amplification effects of such deposits at damaging levels of motion. Unfortunately, no strong-motion recordings were obtained in these areas during the Loma Prieta earthquake and only a limited number (< 10) have been obtained on other soft soil sites in the United States. Consequently, important questions exist regarding the response of such deposits during damaging earthquakes, especially questions regarding the nonlinear soil response. Towards developing a data set to address these important questions, borehole strong-motion arrays have been installed at three locations. These arrays consist of groups of wide-dynamic-range pore-pressure transducers and three-component accelerometers, the outputs of which are recorded digitally. The arrays are designed to provide an integrated set of data on ground shaking, liquifaction-induced ground failure, and structural response. This report describes the detailed geologic, seismic, and material-property determinations derived at each of these sites.

Analysis of the Seismic Activity During the Preparatory Phase of the Mw 8.2 Iquique Earthquake, Chile 2014

NASA Astrophysics Data System (ADS)

Aden-Antoniow, F.; Satriano, C.; Poiata, N.; Bernard, P.; Vilotte, J. P.; Aissaoui, E. M.; Ruiz, S.; Schurr, B.; Sobiesiak, M.

2015-12-01

The 2014 Iquique seismic crisis, culminating with the main Mw 8.2 Iquique earthquake (Chile), 1st of April 2014, and the largest Mw 7.7 aftershock, 3rd of April, highlighted a complex unlocking of the North Chile subduction interface. Indeed, during many months preceding this event, at least three large seismic clusters have been observed, in July 2013, in January and in March 2014. Their location and final migration towards the mainshock rupture area represents the main motivation of this work.We built a new, more complete catalogue for the period over December 2013 to March 2014 in Northern Chile, using a new automated array method for earthquake detection and location [Poiata et al. 2015]. With the data-set provided by the IPOC and ILN networks, we detected an average of 8000 events per month, forty times more than the catalogue produced by Centro Sismologico National del Chile. The new catalogue decreases the magnitude of completeness by more than two units, from 3.3 to 1.2. We observe two shallow clusters offshore of the cities of Iquique and Pisagua in January 2014, and a strong one covering the rupture zone of Mw 8.2 mainshock in March. A spatial-temporal statistical analysis of these three clusters allows us to better characterize the whole preparatory phase. We interpret our results in light of the location, timing and energy of several aseismic slip events, evidenced by Boudin et al. [AGU 2014], which coincide with the seismic clusters. We propose that the preparatory phase of the Iquique earthquake consists of a complex interplay of seismic and aseismic slip along the subduction surface. Furthermore, our analysis raises new questions regarding the complex slip during the Mw 7.7 aftershock, and the spatial variation of the effective coupling along the subduction interface, imaged by GPS studies, suggesting new research direction that will be outlined.

Detection and Identification of Small Seismic Events Following the 3 September 2017 UNT Around North Korean Nuclear Test Site

NASA Astrophysics Data System (ADS)

Kim, W. Y.; Richards, P. G.

2017-12-01

At least four small seismic events were detected around the North Korean nuclear test site following the 3 September 2017 underground nuclear test. The magnitude of these shocks range from 2.6 to 3.5. Based on their proximity to the September 3 UNT, these shocks may be considered as aftershocks of the UNT. We assess the best method to classify these small events based on spectral amplitude ratios of regional P and S wave from the shocks. None of these shocks are classified as explosion-like based on P/S spectral amplitude ratios. We examine additional possible small seismic events around the North Korean test site by using seismic data from stations in southern Korea and northeastern China including IMS seismic arrays, GSN stations, and regional network stations in the region.

High resolution mapping of seismic properties across upper mantle discontinuities in the stagnant slab region beneath Korea

NASA Astrophysics Data System (ADS)

Kim, Y.; Shen, X.; Song, T. R. A.; Lim, H.

2016-12-01

Plate tectonic processes operating over much of the Earth's history induce long-term mantle mixing of chemical heterogeneities, recycling of volatiles into the mantle and regulate basalt geochemistry. Fundamental questions relevant to the mantle transition zone concern the nature of phase transition, the distribution of chemical heterogeneities (e.g., harzburgite, basalt), the temperature gradient, as well as the degree and extent of hydration and melting. One particularly important question is how the slab stagnation may be influenced by hydration or/and basalt enrichment in the mantle transition zone. To help answer these questions, we aim to detail upper mantle seismic discontinuity properties, including the shear velocity contrast, the density contrast, the transition sharpness and the gradient using high quality receiver functions using broadband data in South Korea, which is located in the immediate vicinity of the imaged stagnant slab near northeast China. Our approach involves broadband observation and amplitude analysis of direct converted waves (Pds) and multiples (PpPds) from the 410 and 660 seismic discontinuities, following our previous effort in a similar analysis in China. We processed waveforms from 52 broadband seismic stations of the Korea seismic array using an automatic scheme to remove noisy waveforms and retained close to 12,000 high quality receiver functions. After gathering receiver functions as a function of epicentral distance, we perform slowness stacking of direct converted waves and the multiples, respectively, at several discrete frequency bands between 1 sec and 15 sec. To avoid interferences from other mantle waves (PP, PPP, PcP, PP410s, PP660s), we stack receive functions across epicentral distances of 74-90 (62-76) degrees for the 410 (660) seismic discontinuity and obtain amplitude estimates and uncertainties through the bootstrap method. To properly calibrate the amplitudes of receiver functions, we take into account the effect of incoherent stacking due to discontinuity topography and frequency-dependent attenuation. Preliminary result will be presented and contrasted against our previous work in east China.

Seismicity And Accretion Processes Along The Mid-Atlantic Ridge south of the Azores using data from the MARCHE Autonomous Hydrophone Array

NASA Astrophysics Data System (ADS)

Perrot, Julie; Cevatoglu, Melis; Cannat, Mathilde; Escartin, Javier; Maia, Marcia; Tisseau, Chantal; Dziak, Robert; Goslin, Jean

2013-04-01

The seismicity of the South Atlantic Ocean has been recorded by the MARCHE network of 4 autonomous underwater hydrophones (AUH) moored within the SOFAR channel on the flanks of the Mid-Atlantic Ridge (MAR). The instruments were deployed south of the Azores Plateau between 32° and 39°N from July 2005 to August 2008. The low attenuation properties of the SOFAR channel for earthquake T-wave propagation result in a detection threshold reduction from a magnitude completeness level (Mc) of ~4.3 for MAR events recorded by the land-based seismic networks to Mc=2.1 using this hydrophone array. A spatio-temporal analysis has been performed among the 5600 events recorded inside the MARCHE array. Most events are distributed along the ridge between lat. 39°N on the Azores Platform and the Rainbow (36°N) segment. In the hydrophone catalogue, acoustic magnitude (Source Level, SL) is used as a measure of earthquake size. The source level above which the data set is complete is SLc=205 dB. We look for seismic swarms using the cluster software of the SEISAN package. The criterion used are a minimum SL of 210 to detect a possible mainshock, and a radius of 30 km and a time window of 40 days after this mainshock (Cevatoglu, 2010, Goslin et al., 2012). 7 swarms with more than 15 events are identified using this approach between 32°et 39°N of latitude. The maximum number of earthquake in a swarm is 57 events. This result differs from the study of Simao et al. (2010) as we processed a further year of data and selected sequences with fewer events. Looking at the distribution of the SL as a function of time after the mainshock, we discuss the possible mechanism of these earthquakes : tectonic events with a "mainshock-aftershock" distribution fitting a modified Omori law or volcanic events showing more constant SL values. We also present the geophysical setting of these 7 swarms, using gravity, bathymetry, and available local geological data. This study illustrates the potential of hydrophone data to monitor segment-scale ridges processes in the vicinity of the Lucky Strike seafloor observatory (lat. 37°20'N), the Azores node of the EMSO (European Multidiciplinary Subsea Observatory) system. - M. Cevatoglu, Analyse de la sismicité médio-atlantique et son apport dans la compréhension des processus d'accrétion : Expérience MARCHE3, master's thesis , IUEM, University of Brest, 52 p., june 2010. - J. Goslin, J. Perrot, J.-Y. Royer, C. Martin, N. Lourenco, J. Luis, R. P. Dziak, H. Matsumoto, J. Haxel, M. J. Fowler, C. G. Fox, A. T.-K. Lau and S.Bazin. Spatiotemporal distribution of the seismicity along the Mid-Atlantic Ridge north of the Azores from hydroacoustic data: Insights into seismogenic processes in a ridge-hot spot context, 2012, Geochem. Geophys. Geosyst., 13, Q02010, doi:10.1029/2011GC003828. - N. Simao and J. Escartin and J. Goslin and J. Haxel and M. Cannat and R. Dziak, Regional Seismicity of the Mid-Atlantic Ridge: Observations from autonomous hydrophone arrays, 2010, Geophys. J. Int., 183, 1559-1578.

Relationships between Induced Seismicity and Fluid Injection: Development of Strategies to Manage Injection

NASA Astrophysics Data System (ADS)

Eichhubl, Peter; Frohlich, Cliff; Gale, Julia; Olson, Jon; Fan, Zhiqiang; Gono, Valerie

2014-05-01

Induced seismicity during or following the subsurface injection of waste fluids such as well stimulation flow back and production fluids has recently received heightened public and industry attention. It is understood that induced seismicity occurs by reactivation of existing faults that are generally present in the injection intervals. We seek to address the question why fluid injection triggers earthquakes in some areas and not in others, with the aim toward improved injection methods that optimize injection volume and cost while avoiding induced seismicity. A GIS database has been built of natural and induced earthquakes in four hydrocarbon-producing basins: the Fort Worth Basin, South Texas, East Texas/Louisiana, and the Williston Basin. These areas are associated with disposal from the Barnett, Eagle Ford, Bakken, and Haynesville Shales respectively. In each region we analyzed data that were been collected using temporary seismographs of the National Science Foundation's USArray Transportable Array. Injection well locations, formations, histories, and volumes are also mapped using public and licensed datasets. Faults are mapped at a range of scales for selected areas that show different levels of seismic activity, and scaling relationships used to extrapolate between the seismic and wellbore scale. Reactivation potential of these faults is assessed using fault occurrence, and in-situ stress conditions, identifying areas of high and low fault reactivation potential. A correlation analysis between fault reactivation potential, induced seismicity, and fluid injection will use spatial statistics to quantify the probability of seismic fault reactivation for a given injection pressure in the studied reservoirs. The limiting conditions inducing fault reactivation will be compared to actual injection parameters (volume, rate, injection duration and frequency) where available. The objective of this project is a statistical reservoir- to basin-scale assessment of fault reactivation and seismicity induced by fluid injection. By assessing the occurrence of earthquakes (M>2) evenly across large geographic regions, this project differs from previous studies of injection-induced seismicity that focused on earthquakes large enough to cause public concern in well-populated areas. The understanding of triggered seismicity gained through this project is expected to allow for improved design strategies for waste fluid injection to industry and public decision makers.

Seismic survey probes urban earthquake hazards in Pacific Northwest

USGS Publications Warehouse

Fisher, M.A.; Brocher, T.M.; Hyndman, R.D.; Trehu, A.M.; Weaver, C.S.; Creager, K.C.; Crosson, R.S.; Parsons, T.; Cooper, A. K.; Mosher, D.; Spence, G.; Zelt, B.C.; Hammer, P.T.; Childs, J. R.; Cochrane, G.R.; Chopra, S.; Walia, R.

1999-01-01

A multidisciplinary seismic survey earlier this year in the Pacific Northwest is expected to reveal much new information about the earthquake threat to U.S. and Canadian urban areas there. A disastrous earthquake is a very real possibility in the region. The survey, known as the Seismic Hazards Investigation in Puget Sound (SHIPS), engendered close cooperation among geologists, biologists, environmental groups, and government agencies. It also succeeded in striking a fine balance between the need to prepare for a great earthquake and the requirement to protect a coveted marine environment while operating a large airgun array.

Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica

NASA Astrophysics Data System (ADS)

Diez, A.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Anthony, R. E.; Aster, R. C.; Cai, C.; Nyblade, A.; Wiens, D. A.

2016-05-01

An L-configured, three-component short period seismic array was deployed on the Ross Ice Shelf, Antarctica during November 2014. Polarization analysis of ambient noise data from these stations shows linearly polarized waves for frequency bands between 0.2 and 2 Hz. A spectral peak at about 1.6 Hz is interpreted as the resonance frequency of the water column and is used to estimate the water layer thickness below the ice shelf. The frequency band from 4 to 18 Hz is dominated by Rayleigh and Love waves propagating from the north that, based on daily temporal variations, we conclude were generated by field camp activity. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile within the firn and ice to ˜150 m depth. The derived density profile allows estimation of the pore close-off depth and the firn-air content thickness. Separate inversions of Rayleigh and Love wave dispersion curves give different shear wave velocity profiles within the firn. We attribute this difference to an effective anisotropy due to fine layering. The layered structure of firn, ice, water and the seafloor results in a characteristic dispersion curve below 7 Hz. Forward modelling the observed Rayleigh wave dispersion curves using representative firn, ice, water and sediment structures indicates that Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. The forward modelling shows that analysis of seismic data from an ice shelf provides the possibility of resolving ice shelf thickness, water column thickness and the physical properties of the ice shelf and underlying seafloor using passive-source seismic data.

Regional Small-Event Identification Using Networks and Arrays of Seismic and Acoustic Sensors

DTIC Science & Technology

2006-04-01

ground displacement and excite infra - sonic waves in the atmosphere (Blanc, 1989) near-surface explosions are much more efficient sources of...valuable advice on the portable infrasonic deployment at MNTA. Several of the images in this report are attributable to David Anderson at Southern...populations. This study has focused on seismic observations from mining explosions. There is increasing evidence that infrasonic observations may help in

Source and Path Calibration in Regions of Poor Crustal Propagation Using Temporary, Large-Aperture, High-Resolution Seismic Arrays

DTIC Science & Technology

2013-09-06

the Nepal Himalaya and the south- central Tibetan Plateau. The 2002–2005 experiment consisted of 233 stations extending from the Himalayan foreland...into the central Tibetan Plateau. The dataset provides an opportunity to obtain accurate seismic event locations for ground truth evaluation and to...after an M=6+ earthquake in the Payang Basin . .....................................................15 Approved for public release; distribution is

SEISMIC STUDY OF THE AGUA DE PAU GEOTHERMAL PROSPECT, SAO MIGUEL, AZORES.

USGS Publications Warehouse

Dawson, Phillip B.; Rodrigues da Silva, Antonio; Iyer, H.M.; Evans, John R.

1985-01-01

A 16 station array was operated over the 200 km**2 central portion of Sao Miguel utilizing 8 permanent Instituto Nacional de Meterologia e Geofisica stations and 8 USGS portable stations. Forty four local events with well constrained solutions and 15 regional events were located. In addition, hundreds of unlocatable seismic events were recorded. The most interesting seismic activity occurred in a swarm on September 6 and 7, 1983 when over 200 events were recorded in a 16 hour period. The seismic activity around Agua de Pau was centered on the east and northeast slopes of the volcano. The data suggest a boiling hydrothermal system beneath the Agua de Pau volcano, consistent with a variety of other data.

Integration of Infrasound, Atmospheric Pressure, and Seismic Observations with the NSF EarthScope USArray Transportable Array

NASA Astrophysics Data System (ADS)

Vernon, F.; Tytell, J.; Hedlin, M. A. H.; Walker, K.; Busby, R.; Woodward, R.

2012-04-01

Earthscope's USArray Transportable Array (TA) network serves as a real-time monitoring and recording platform for both seismic and weather phenomena. To date, most of the approximately 500 TA stations have been retrofitted with VTI SCP1000 MEMS barometric pressure gauges capable of recording data at 1 sample per second (sps). Additionally, over 300 of the TA stations have also been retrofitted with Setra 278 barometric gauges and NCPA infrasound sensors capable of recording data at 1 and 40 sps. While individual seismic events have been successfully researched via the TA network, observations of powerful weather events by the TA network have yet to be embraced by the scientific community. This presentation will focus on case studies involving severe weather passage across portions of the TA network throughout 2011 in order to highlight its viability as a platform for real-time weather monitoring and research. It will also highlight the coupling of atmospheric signals into the seismic observations. Examples of gust front passages and pressure couplets from severe thunderstorms will be presented, as will observations of multiple tornados occurred in the Spring of 2011. These data will demonstrate the overall viability of the TA network for monitoring severe weather events in real-time.

Stress Regime in the Nepalese Himalaya from Recent Earthquakes.

NASA Astrophysics Data System (ADS)

Pant, M.; Karplus, M. S.; Velasco, A. A.; Nabelek, J.; Kuna, V. M.; Ghosh, A.; Mendoza, M.; Adhikari, L. B.; Sapkota, S. N.; Klemperer, S. L.; Patlan, E.

2017-12-01

The two recent earthquakes, April 25, 2015 Mw 7.8 (Gorkha earthquake) and May 12, 2015 Mw 7.2, at the Indo-Eurasian plate margin killed thousands of people and caused billion dollars of property loss. In response to these events, we deployed a dense array of seismometers to record the aftershocks along Gorkha earthquake rupture area. Our network NAMASTE (Nepal Array Measuring Aftershock Seismicity Trailing Earthquake) included 45 different seismic stations (16 short period, 25 broadband, and 4 strong motion sensors) covering a large area from north-central Nepal to south of the Main Frontal Thrust at a spacing of 20 km. The instruments recorded aftershocks from June 2015 to May 2016. We used time domain short term average (STA) and long term average (LTA) algorithms (1/10s and 4/40s) respectively to detect the arrivals and then developed an earthquake catalog containing 9300 aftershocks. We are manually picking the P-wave first motion arrival polarity to develop a catalog of focal mechanisms for the larger magnitude (>M3.0) events with adequate (>10) arrivals. We hope to characterize the seismicity and stress mechanisms of the complex fault geometries in the Nepalese Himalaya and to address the geophysical processes controlling seismic cycles in the Indo-Eurasian plate margin.

A progress report on the ARRA-funded geotechnical site characterization project

NASA Astrophysics Data System (ADS)

Martin, A. J.; Yong, A.; Stokoe, K.; Di Matteo, A.; Diehl, J.; Jack, S.

2011-12-01

For the past 18 months, the 2009 American Recovery and Reinvestment Act (ARRA) has funded geotechnical site characterizations at 189 seismographic station sites in California and the central U.S. This ongoing effort applies methods involving surface-wave techniques, which include the horizontal-to-vertical spectral ratio (HVSR) technique and one or more of the following: spectral analysis of surface wave (SASW), active and passive multi-channel analysis of surface wave (MASW) and passive array microtremor techniques. From this multi-method approach, shear-wave velocity profiles (VS) and the time-averaged shear-wave velocity of the upper 30 meters (VS30) are estimated for each site. To accommodate the variability in local conditions (e.g., rural and urban soil locales, as well as weathered and competent rock sites), conventional field procedures are often modified ad-hoc to fit the unanticipated complexity at each location. For the majority of sites (>80%), fundamental-mode Rayleigh wave dispersion-based techniques are deployed and where complex geology is encountered, multiple test locations are made. Due to the presence of high velocity layers, about five percent of the locations require multi-mode inversion of Rayleigh wave (MASW-based) data or 3-D array-based inversion of SASW dispersion data, in combination with shallow P-wave seismic refraction and/or HVSR results. Where a strong impedance contrast (i.e. soil over rock) exists at shallow depth (about 10% of sites), dominant higher modes limit the use of Rayleigh wave dispersion techniques. Here, use of the Love wave dispersion technique, along with seismic refraction and/or HVSR data, is required to model the presence of shallow bedrock. At a small percentage of the sites, surface wave techniques are found not suitable for stand-alone deployment and site characterization is limited to the use of the seismic refraction technique. A USGS Open File Report-describing the surface geology, VS profile and the calculated VS30 for each site-will be prepared after the completion of the project in November 2011.

A Fiber-Optic Borehole Seismic Vector Sensor System for Geothermal Site Characterization and Monitoring

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paulsson, Bjorn N.P.; Thornburg, Jon A.; He, Ruiqing

2015-04-21

Seismic techniques are the dominant geophysical techniques for the characterization of subsurface structures and stratigraphy. The seismic techniques also dominate the monitoring and mapping of reservoir injection and production processes. Borehole seismology, of all the seismic techniques, despite its current shortcomings, has been shown to provide the highest resolution characterization and most precise monitoring results because it generates higher signal to noise ratio and higher frequency data than surface seismic techniques. The operational environments for borehole seismic instruments are however much more demanding than for surface seismic instruments making both the instruments and the installation much more expensive. The currentmore » state-of-the-art borehole seismic instruments have not been robust enough for long term monitoring compounding the problems with expensive instruments and installations. Furthermore, they have also not been able to record the large bandwidth data available in boreholes or having the sensitivity allowing them to record small high frequency micro seismic events with high vector fidelity. To reliably achieve high resolution characterization and long term monitoring of Enhanced Geothermal Systems (EGS) sites a new generation of borehole seismic instruments must therefore be developed and deployed. To address the critical site characterization and monitoring needs for EGS programs, US Department of Energy (DOE) funded Paulsson, Inc. in 2010 to develop a fiber optic based ultra-large bandwidth clamped borehole seismic vector array capable of deploying up to one thousand 3C sensor pods suitable for deployment into ultra-high temperature and high pressure boreholes. Tests of the fiber optic seismic vector sensors developed on the DOE funding have shown that the new borehole seismic sensor technology is capable of generating outstanding high vector fidelity data with extremely large bandwidth: 0.01 – 6,000 Hz. Field tests have shown that the system can record events at magnitudes much smaller than M-2.6 at frequencies up to 2,000 Hz. The sensors have also proved to be about 100 times more sensitive than the regular coil geophones that are used in borehole seismic systems today. The fiber optic seismic sensors have furthermore been qualified to operate at temperatures over 300°C (572°F). Simultaneously with the fiber optic based seismic 3C vector sensors we are using the lead-in fiber to acquire Distributed Acoustic Sensor (DAS) data from the surface to the bottom of the vector array. While the DAS data is of much lower quality than the vector sensor data it provides a 1 m spatial sampling of the downgoing wavefield which will be used to build the high resolution velocity model which is an essential component in high resolution imaging and monitoring.« less

Analysis and localization of blue whale vocalizations in the Solomon Sea using waveform amplitude data.

PubMed

Frank, Scott D; Ferris, Aaron N

2011-08-01

During the Woodlark Basin seismic experiment in eastern Papua New Guinea (1999-2000), an ocean-bottom seismic array recorded marine mammal vocalizations along with target earthquake signals. The array consisted of 14 instruments, 7 of which were three-component seismometers with a fourth component hydrophone. They were deployed at 2.0-3.2 km water depth and operated from September 1999 through February 2000. While whale vocalizations were recorded throughout the deployment, this study focuses on 3 h from December 21, 1999 during which the signals are particularly clear. The recordings show a blue whale song composed of a three-unit phrase. That song does not match vocalization characteristics of other known Pacific subpopulations and may represent a previously undocumented blue whale song. Animal tracking and source level estimates are obtained with a Bayesian inversion method that generates probabilistic source locations. The Bayesian method is augmented to include travel time estimates from seismometers and hydrophones and acoustic signal amplitude. Tracking results show the whale traveled northeasterly over the course of 3 h, covering approximately 27 km. The path followed the edge of the Woodlark Basin along a shelf that separates the shallow waters of the Trobriand platform from the deep waters of the basin.

Ground Motion Analysis of Co-Located DAS and Seismometer Sensors

NASA Astrophysics Data System (ADS)

Wang, H. F.; Fratta, D.; Lord, N. E.; Lancelle, C.; Thurber, C. H.; Zeng, X.; Parker, L.; Chalari, A.; Miller, D.; Feigl, K. L.; Team, P.

2016-12-01

The PoroTomo research team deployed 8700-meters of Distributed Acoustic Sensing (DAS) cable in a shallow trench and 400-meters in a borehole at Brady Hot Springs, Nevada in March 2016 together with an array of 246, three-component geophones. The seismic sensors occupied a natural laboratory 1500 x 500 x 400 meters overlying the Brady geothermal field. The DAS cable was laid out in three parallel zig-zag lines with line segments approximately 100-meters in length and geophones were spaced at approximately 50-m intervals. In several line segments, geophones were co-located within one meter of the DAS cable. Both DAS and the conventional geophones recorded continuously over 15 days. A large Vibroseis truck (T-Rex) provided the seismic source at approximately 250 locations outside and within the array. The Vibroseis protocol called for excitation in one vertical and two orthogonal horizontal directions at each location. For each mode, three, 5-to-80-Hz upsweeps were made over 20 seconds. In addition, a moderate-sized earthquake with a local magnitude of 4.3 was recorded on March 21, 2016. Its epicenter was approximately 150-km away. Several DAS line segments with co-located geophone stations were used to test relationships between the strain rate recorded by DAS and ground velocity recorded by the geophones.

Oceanic crust in the mid-mantle beneath Central-West Pacific subduction zones: Evidence from S-to-P converted waveforms

NASA Astrophysics Data System (ADS)

He, X.

2015-12-01

The fate of subducted slabs is enigmatic, yet intriguing. We analyze seismic arrivals at ~20-50 s after the direct P wave in an array in northeast China (NECESSArray) recordings of four deep earthquakes occurring beneath the west-central Pacific subduction zones (from the eastern Indonesia to Tonga region). We employ the array analyzing techniques of 4th root vespagram and beam-form analysis to constrain the slowness and back azimuth of later arrivals. Our analyses reveal that these arrivals have a slightly lower slowness value than the direct P wave and the back azimuth deviates slightly from the great-circle direction. Along with calculation of one-dimensional synthetic seismograms, we conclude that the later arrival is corresponding to an energy of S-to-P converted at a scatterer below the sources. Total five scatterers are detected at depths varying from ~700 to 1110 km in the study region. The past subducted oceanic crust most likely accounts for the seismic scatterers trapped in the mid-mantle beneath the west-central subduction zones. Our observation in turn reflects that oceanic crust at least partly separated from subducted oceanic lithosphere and may be trapped substantially in the mid-mantle surrounding subduction zones, in particular in the western Pacific subduction zones.

Southern Mariana OBS Experiment and Preliminary Results of Passive-Source Investigations

NASA Astrophysics Data System (ADS)

Le, B. M.; Lin, J.; Yang, T.; Shiyan 3, S. P. O. R.

2017-12-01

The Southern Mariana OBS Experiment (SMOE) was one of the first seismic experiments targeting the deepest part of Earth's surface. During the Phase I experiment in December 2016, an array of OBS instruments were deployed across the Challenger Deep that recorded both active-source and passive-source data. During the Phase II experiment in December 2016-June 2017, passive-source data were recorded. We have retrieved earthquake signals and processed the waveforms from the recorded global, regional and local events, respectively, during the Phase I experiment. Most of the waveforms recorded by the OBS array have fairly good quality with discernible main phases. Rayleigh waves from many earthquakes were analyzed using the frequency-time analysis and their group velocities at different periods were obtained. The dispersion curves from different Rayleigh wave propagating paths would be valuable for inverting the structure of the subducting Pacific and overriding Philippine Sea plates. Furthermore, we applied the ambient noise cross-correlation method and retrieved high-quality coherence surface wave waveforms. With its relatively high frequencies, the surface waves can be used to study the crustal structure of the region. Together with the Phase II data, we expect that this seismic experiment will provide unprecedented constraints on the structure and geodynamic processes of the southern Mariana trench.

Observations of the R Reflector and Sediment Interface Reflection at the Shallow Water 󈧊 Central Site

DTIC Science & Technology

2008-08-28

line array position of Woods Hole Oceanographic Institution (WHOI) during the SWARM experiment by 26 km, and southeast of the AMCOR borehole No. 6010...guided by the stratigraphic constraints provided by closely spaced 50 m chirp seismic reflection profiles that provide pseudo three-dimensional... array is at the center of set of stations at location M. c Geometry showing source position R/V KNORR with respect to the receiving array and the

New Constraints on Upper Mantle Structure Underlying the Diamondiferous Central Slave Craton, Canada, from Teleseismic Body Wave Tomography

NASA Astrophysics Data System (ADS)

Esteve, C.; Schaeffer, A. J.; Audet, P.

2017-12-01

Over the past number of decades, the Slave Craton (Canada) has been extensively studied for its diamondiferous kimberlites. Not only are diamonds a valuable resource, but their kimberlitic host rocks provide an otherwise unique direct source of information on the deep upper mantle (and potentially transition zone). Many of the Canadian Diamond mines are located within the Slave Craton. As a result of the propensity for diamondiferous kimberlites, it is imperative to probe the deep mantle structure beneath the Slave Craton. This work is further motivated by the increase in high-quality broadband seismic data across the Northern Canadian Cordillera over the past decade. To this end we have generated a P and S body wave tomography model of the Slave Craton and its surroundings. Furthermore, tomographic inversion techniques are growing ever more capable of producing high resolution Earth models which capture detailed structure and dynamics across a range of scale lengths. Here, we present preliminary results on the structure of the upper mantle underlying the Slave Craton. These results are generated using data from eight different seismic networks such as the Canadian National Seismic Network (CNSN), Yukon Northwest Seismic Network (YNSN), older Portable Observatories for Lithospheric Analysis and Reseach Investigating Seismicity (POLARIS), Regional Alberta Observatory for Earthquake Studies Network (RV), USArray Transportable Array (TA), older Canadian Northwest Experiment (CANOE), Batholith Broadband (XY) and the Yukon Observatory (YO). This regional model brings new insights about the upper mantle structure beneath the Slave Craton, Canada.

Acquisition and deconvolution of seismic signals by different methods to perform direct ground-force measurements

NASA Astrophysics Data System (ADS)

Poletto, Flavio; Schleifer, Andrea; Zgauc, Franco; Meneghini, Fabio; Petronio, Lorenzo

2016-12-01

We present the results of a novel borehole-seismic experiment in which we used different types of onshore-transient-impulsive and non-impulsive-surface sources together with direct ground-force recordings. The ground-force signals were obtained by baseplate load cells located beneath the sources, and by buried soil-stress sensors installed in the very shallow-subsurface together with accelerometers. The aim was to characterize the source's emission by its complex impedance, function of the near-field vibrations and soil stress components, and above all to obtain appropriate deconvolution operators to remove the signature of the sources in the far-field seismic signals. The data analysis shows the differences in the reference measurements utilized to deconvolve the source signature. As downgoing waves, we process the signals of vertical seismic profiles (VSP) recorded in the far-field approximation by an array of permanent geophones cemented at shallow-medium depth outside the casing of an instrumented well. We obtain a significant improvement in the waveform of the radiated seismic-vibrator signals deconvolved by ground force, similar to that of the seismograms generated by the impulsive sources, and demonstrates that the results obtained by different sources present low values in their repeatability norm. The comparison evidences the potentiality of the direct ground-force measurement approach to effectively remove the far-field source signature in VSP onshore data, and to increase the performance of permanent acquisition installations for time-lapse application purposes.

Improving time-lapse seismic repeatability: CO2CRC Otway site permanent geophone array field trials

NASA Astrophysics Data System (ADS)

Pevzner, Roman; Dupuis, Christian; Shulakova, Valeriya; Urosevic, Milovan; Lumley, David

2013-04-01

The proposed Stage 2C of the CO2CRC Otway project involves injection of a small amount (around 15,000 tonnes) of CO2/CH4 gas mixture into saline acquifer (Paaratte formation) at the depth of ~1.5 km. The seismic time-lapse signal will depend largely on the formation properties and the injection scenario, but is likely to be relatively weak. In order to improve time-lapse seismic monitoring capabilities by decreasing the noise level, a buried receiver arrays can be used. A small-scale trial of such an array was conducted at Otway site in June 2012. A set of 25 geophones was installed in 3 m deep boreholes in parallel to the same number of surface geophones. In addition, four geophones were placed into boreholes of 1 to 12 m depth. In order to assess the gain in the signal-to-noise ratio and repeatability, both active and passive seismic surveys were carried out. The surveys were conducted in relatively poor weather conditions, with rain, strong wind and thunderstorms increasing the noise level. We found that noise level for buried geophones is on average 20 dB lower compared to the surface ones. Furthermore, the combination of active and passive experiments has allowed us to perform a detailed classification of various noise sources. Acknowledgement The authors acknowledge the funding provided by the Australian government through its CRC program to support this CO2CRC research project. We also acknowledge the CO2CRC's corporate sponsors and the financial assistance provided through Australian National Low Emissions Coal Research and Development (ANLEC R&D). ANLEC R&D is supported by Australian Coal Association Low Emissions Technology Limited and the Australian Government through the Clean Energy Initiative.

Characterization of the San Andreas Fault at Parkfield Using a Massive 3D VSP

NASA Astrophysics Data System (ADS)

Chavarria, J.; Goertz, A.; Karrenbach, M.; Milligan, P.; Paulsson, B.

2005-12-01

In preparation for the drilling of SAFOD's Phase II we installed an 80 level array of 3C seismometers inside the well. The goal of the array was to refine the existing velocity model to better locate the target events, and to monitor the local seismicity. The array, with sensors laying mostly within the deviated portion of the well, spans depths ranging from 2.7 to 1.5 km with levels every 15 m. It is this dense spacing what makes 3D VSP capable of bridging the gap between drill-hole observations and observations from the surface like 2D seismics. During April and May 2005 we recorded thirteen far offset shots surrounding the SAFOD site and target event area. Data from these shots was simultaneously recorded by the surface networks and used for better location of the target events. In addition to these, a zero offset shot at SAFOD was generated to refine the structure surrounding the well. The 1D velocity model inverted from the zero offset is representative of the current geologic model at SAFOD. The complexity of the velocity model for this segment of the fault can be inferred from deviations between the zero offset model and the shorter wavelength model derived from well logs. In addition to strong changes in velocity, both zero offset and far offset shots show the presence of strong scattered phases associated to the complex geologic structure of the San Andreas Fault Zone. In addition to the active portion of the experiment we monitored the local seismicity (i.e. aftershocks from the Parkfield 2004 event) over a period of 13 days. During this period of time we recorded continuously at high sampling rates (4kHz) a large number of events, some of which were located by the surface networks and felt onsite. The quiet environment in the borehole enabled us to record microearthquakes that were not present in the NCEDC catalog. In some cases these small events were not even recorded along the entire array. Besides its high level of event detection, the high vector fidelity of the 3C geophones allowed for precise particle motion analysis of first arrivals to determine the location of microearthquakes recorded during this effort.

Seismic Noise Analysis and Reduction through Utilization of Collocated Seismic and Atmospheric Sensors at the GRO Chile Seismic Network

NASA Astrophysics Data System (ADS)

Farrell, M. E.; Russo, R. M.

2013-12-01

The installation of Earthscope Transportable Array-style geophysical observatories in Chile expands open data seismic recording capabilities in the southern hemisphere by nearly 30%, and has nearly tripled the number of seismic stations providing freely-available data in southern South America. Through the use of collocated seismic and atmospheric sensors at these stations we are able to analyze how local atmospheric conditions generate seismic noise, which can degrade data in seismic frequency bands at stations in the ';roaring forties' (S latitudes). Seismic vaults that are climate-controlled and insulated from the local environment are now employed throughout the world in an attempt to isolate seismometers from as many noise sources as possible. However, this is an expensive solution that is neither practical nor possible for all seismic deployments; and also, the increasing number and scope of temporary seismic deployments has resulted in the collection and archiving of terabytes of seismic data that is affected to some degree by natural seismic noise sources such as wind and atmospheric pressure changes. Changing air pressure can result in a depression and subsequent rebound of Earth's surface - which generates low frequency noise in seismic frequency bands - and even moderate winds can apply enough force to ground-coupled structures or to the surface above the seismometers themselves, resulting in significant noise. The 10 stations of the permanent Geophysical Reporting Observatories (GRO Chile), jointly installed during 2011-12 by IRIS and the Chilean Servicio Sismológico, include instrumentation in addition to the standard three seismic components. These stations, spaced approximately 300 km apart along the length of the country, continuously record a variety of atmospheric data including infrasound, air pressure, wind speed, and wind direction. The collocated seismic and atmospheric sensors at each station allow us to analyze both datasets together, to gain insight into how local atmospheric conditions couple with the ground to generate seismic noise, and to explore strategies for reducing this noise post data collection. Comparison of spectra of atmospheric data streams to the three broadband seismic channels for continuous signals recorded during May and June of 2013 shows high coherence between infrasound signals and time variation of air pressure (dP/dt) that we calculated from the air pressure data stream. Coherence between these signals is greatest for the east-west component of the seismic data in northern Chile. Although coherence between seismic, infrasound, and dP/dt is lower for all three seismic channels at other GRO Chile stations, for some of the data streams coherence can jump as much as 6 fold for certain frequency bands, with a common 3-fold increase for periods shorter than 10 seconds and the occasional 6-fold increase at long or very long periods.

Earthquake source imaging by high-resolution array analysis at regional distances: the 2010 M7 Haiti earthquake as seen by the Venezuela National Seismic Network

NASA Astrophysics Data System (ADS)

Meng, L.; Ampuero, J. P.; Rendon, H.

2010-12-01

Back projection of teleseismic waves based on array processing has become a popular technique for earthquake source imaging,in particular to track the areas of the source that generate the strongest high frequency radiation. The technique has been previously applied to study the rupture process of the Sumatra earthquake and the supershear rupture of the Kunlun earthquakes. Here we attempt to image the Haiti earthquake using the data recorded by Venezuela National Seismic Network (VNSN). The network is composed of 22 broad-band stations with an East-West oriented geometry, and is located approximately 10 degrees away from Haiti in the perpendicular direction to the Enriquillo fault strike. This is the first opportunity to exploit the privileged position of the VNSN to study large earthquake ruptures in the Caribbean region. This is also a great opportunity to explore the back projection scheme of the crustal Pn phase at regional distances,which provides unique complementary insights to the teleseismic source inversions. The challenge in the analysis of the 2010 M7.0 Haiti earthquake is its very compact source region, possibly shorter than 30km, which is below the resolution limit of standard back projection techniques based on beamforming. Results of back projection analysis using the teleseismic USarray data reveal little details of the rupture process. To overcome the classical resolution limit we explored the Multiple Signal Classification method (MUSIC), a high-resolution array processing technique based on the signal-noise orthognality in the eigen space of the data covariance, which achieves both enhanced resolution and better ability to resolve closely spaced sources. We experiment with various synthetic earthquake scenarios to test the resolution. We find that MUSIC provides at least 3 times higher resolution than beamforming. We also study the inherent bias due to the interferences of coherent Green’s functions, which leads to a potential quantification of biased uncertainty of the back projection. Preliminary results from the Venezuela data set shows an East to West rupture propagation along the fault with sub-Rayleigh rupture speed, consistent with a compact source with two significant asperities which are confirmed by source time function obtained from Green’s function deconvolution and other source inversion results. These efforts could lead the Venezuela National Seismic Network to play a prominent role in the timely characterization of the rupture process of large earthquakes in the Caribbean, including the future ruptures along the yet unbroken segments of the Enriquillo fault system.

Quantitative measures of air-gun pulses recorded on sperm whales (Physeter macrocephalus) using acoustic tags during controlled exposure experiments.

PubMed

Madsen, P T; Johnson, M; Miller, P J O; Aguilar Soto, N; Lynch, J; Tyack, P

2006-10-01

The widespread use of powerful, low-frequency air-gun pulses for seismic seabed exploration has raised concern about their potential negative effects on marine wildlife. Here, we quantify the sound exposure levels recorded on acoustic tags attached to eight sperm whales at ranges between 1.4 and 12.6 km from controlled air-gun array sources operated in the Gulf of Mexico. Due to multipath propagation, the animals were exposed to multiple sound pulses during each firing of the array with received levels of analyzed pulses falling between 131-167 dB re. 1 microPa (pp) [111-147 dB re. 1 microPa (rms) and 100-135 dB re. 1 microPa2 s] after compensation for hearing sensitivity using the M-weighting. Received levels varied widely with range and depth of the exposed animal precluding reliable estimation of exposure zones based on simple geometric spreading laws. When whales were close to the surface, the first arrivals of air-gun pulses contained most energy between 0.3 and 3 kHz, a frequency range well beyond the normal frequencies of interest in seismic exploration. Therefore air-gun arrays can generate significant sound energy at frequencies many octaves higher than the frequencies of interest for seismic exploration, which increases concern of the potential impact on odontocetes with poor low frequency hearing.

Noise Configuration and fault zone anisotropy investigation from Taiwan Chelungpu-fault Deep Borehole Array

NASA Astrophysics Data System (ADS)

Hung, R. J.; Ma, K. F.; Song, T. R. A.; Nishida, K.; Lin, Y. Y.

2016-12-01

The Taiwan Chelungpu-fault Drilling Project was operated to understand the fault zone characteristics associated with the 1999 Chichi earthquake. Seven Borehole Seismometers (TCDPBHS) were installed through the identified fault zone to monitor the micro-seismic activities, as well as the fault-zone seismic structure properties. To understand the fault zone anisotropy and its possible temporal variations after the Chichi earthquake, we calculated cross-correlations of the noise at different stations to obtain cross correlation functions (CCFs) of the ambient noise field between every pair of the stations. The result shows that TCDP well site suffers from complex wavefield, and phase traveltime from CCF can't provide explicit result to determine the dominated wavefield. We first analyze the power density spectra and probability density functions of this array. We observe that the spectra show diurnal variation in the frequency band 1-25 Hz, suggesting human-generated sources are dominated in this frequency band. Then, we focus on the particle motion analysis at each CCF. We assume one component at a station plays as a visual source and compute the CCF tensor in other station components. The particle motion traces show high linearity which indicate that the dominated wavefield in our study area is body wave signals with the azimuth approximate to 60° from north. We also analyze the Fourier spectral amplitudes by rotating every 5 degrees in time domain to search for the maximum background energy distribution. The result shows that the spectral amplitudes are stronger at NE-SW direction, with shallow incident angles which are comparable with the CCF particle motion measurement. In order to obtain higher resolution about the dominated wavefield in our study area, we also used beamforming from surface station array to validate our results from CCF analysis. In addition to the CCF analysis to provide the noise configuration at the TCDPBHS site for further analysis on fault zone anisotropy using ambient noise, we also analyze fault zone anisotropy using the events data recorded by TCDPBHS. The identified event clusters through the borehole data enhance the consistency in results to give hints on fault zone anisotropy.

The Seismic component of the IBERARRAY: Placing constraints on the Lithosphere and Mantle.

NASA Astrophysics Data System (ADS)

Carbonell, R.; Diaz, J.; Villaseñor, A.; Gallart, J.; Morales, J.; Pazos, A.; Cordoba, D.; Pulgar, J.; Garcia-Lobon, J.; Harnafi, M.

2008-12-01

TOPOIBERIA, is a multidisciplinary large scale research project which aims to study the links between the deep and superficial processes within the Iberian Peninsula.One of its main experimental components is the deployment of the IBERARRAY seismic network. This is a dense array (60x60 km) of new generation dataloggers equipped with broad-band seismometers which will cover Iberia and North Morocco in three successive deployments, each lasting for about 18 months. The first leg, deployed since late 2007, covers the southern part of Iberia (35 stations) and northern Morocco (20 stations). Two data centers have been established one at the CSIC-Institute of Earth Sciences (CSIC-Barcelona) and a second at the Geologic and Mining Insititute (IGME-Madrid) the data follows a standard-conventional flow from recovery to archival. The field teams collect the recorded hard disk on the field and send data and metadata to a processing center, where raw data is collected and stored and a quality control checking is performed. This include a systematic inspection of the experimental parameters (batteries charge, thermal insulation, time adjustments, geophone leveling etc), the visual verification of the seismic waveforms and the analysis, using power density spectra (PSD), of the noise level of each station. All this information is disseminated between the research teams involved in the project using a dedicated website and the continuous seismic data is made accessible through FTP and CWQ servers. Some of the nodes of the theoretical network are covered by permanent stations of the national broad-band network (IGN) or other networks operating in the region (IAG-UGR, ROA). Data from those stations will also be integrated to the Iberarray database. This Iberarray network will provide a large database of both waveform and catalogued events, with an unprecedented resolution. Earthquake data at local, regional and teleseismic scales will be analyzed using different methodologies. The first result would be an increase in the accuracy of the location of regional seismicity and the termination of focal mechanisms. A special emphasis will be attributed to seismic tomographic techniques using travel times and waveforms of P and S arrivals at different scales as well as surface waves, using dispersion measurements as well as studies dealing with background/environmental noise. In addition, receiver function analysis for seismic imaging of deep lithospheric features and splitting analysis of shear-wave arrivals will also be developed.

Passive seismic imaging based on seismic interferometry: method and its application to image the structure around the 2013 Mw6.6 Lushan earthquake

NASA Astrophysics Data System (ADS)

Gu, N.; Zhang, H.

2017-12-01

Seismic imaging of fault zones generally involves seismic velocity tomography using first arrival times or full waveforms from earthquakes occurring around the fault zones. However, in most cases seismic velocity tomography only gives smooth image of the fault zone structure. To get high-resolution structure of the fault zones, seismic migration using active seismic data needs to be used. But it is generally too expensive to conduct active seismic surveys, even for 2D. Here we propose to apply the passive seismic imaging method based on seismic interferometry to image fault zone detailed structures. Seismic interferometry generally refers to the construction of new seismic records for virtual sources and receivers by cross correlating and stacking the seismic records on physical receivers from physical sources. In this study, we utilize seismic waveforms recorded on surface seismic stations for each earthquake to construct zero-offset seismic record at each earthquake location as if there was a virtual receiver at each earthquake location. We have applied this method to image the fault zone structure around the 2013 Mw6.6 Lushan earthquake. After the occurrence of the mainshock, a 29-station temporary array is installed to monitor aftershocks. In this study, we first select aftershocks along several vertical cross sections approximately normal to the fault strike. Then we create several zero-offset seismic reflection sections by seismic interferometry with seismic waveforms from aftershocks around each section. Finally we migrate these zero-offset sections to create seismic structures around the fault zones. From these migration images, we can clearly identify strong reflectors, which correspond to major reverse fault where the mainshock occurs. This application shows that it is possible to image detailed fault zone structures with passive seismic sources.

Estimation of velocity structure around a natural gas reservoir at Yufutsu, Japan, by microtremor survey

NASA Astrophysics Data System (ADS)

Shiraishi, H.; Asanuma, H.; Tezuka, K.

2010-12-01

Seismic reflection survey has been commonly used for exploration and time-lapse monitoring of oil/gas resources. Seismic reflection images typically have reasonable reliability and resolution for commercial production. However, cost consideration sometimes avoids deployment of widely distributed array or repeating survey in cases of time lapse monitoring or exploration of small-scale reservoir. Hence, technologies to estimate structures and physical properties around the reservoir with limited cost would be effectively used. Microtremor survey method (MSM) has an ability to realize long-term monitoring of reservoir with low cost, because this technique has a passive nature and minimum numbers of the monitoring station is four. MSM has been mainly used for earthquake disaster prevention, because velocity structure of S-wave is directly estimated from velocity dispersion of the Rayleigh wave. The authors experimentally investigated feasibility of the MSM survey for exploration of oil/gas reservoir. The field measurement was carried out around natural gas reservoir at Yufutsu, Hokkaido, Japan. Four types of arrays with array radii of 30m, 100m, 300m and 600m are deployed in each area. Dispersion curves of the velocity of Rayleigh wave were estimated from observed microtremors, and S-wave velocity structures were estimated by an inverse analysis of the dispersion curves with genetic algorism (GA). The estimated velocity structures showed good consistency with one dimensional velocity structure by previous reflection surveys up to 4-5 km. We also found from the field experiment that a data of 40min is effective to estimate the velocity structure even the seismometers are deployed along roads with heavy traffic.

Anomalous Induced Seismicity due to Hydraulic Fracturing. Case of study in the Montney Formation, Northeast British Columbia.

NASA Astrophysics Data System (ADS)

Longobardi, M.; Bustin, A. M. M.; Johansen, K.; Bustin, R. M.

2017-12-01

One of our goals is to investigate the variables and processes controlling the anomalous induced seismicity and its associated ground motions, to better understand the anomalous induced seismicity (AIS) due to hydraulic fracturing in Northeast British Columbia. Our other main objective is to optimize-completions and well design. Although the vast majority of earthquakes that occur in the world each year have natural causes, some of these earthquakes and a number of lesser magnitude seismic events are induced by human activities. The recorded induced seismicity resulting from the fluid injection during hydraulic fracturing is generally small in magnitude (< M 1). Shale gas operations in Northeast British Columbia (BC) have induced the largest recorded occurrence and magnitude of AIS because of hydraulic fracturing. Anomalous induced seismicity have been recorded in seven clusters within the Montney area, with magnitudes up to ML 4.6. Five of these clusters have been linked to hydraulic fracturing. To analyse our AIS data, we first have calculated the earthquakes hypocenters. The data was recorded on an array of real-time accelerometers. We built the array based on our modified design from the early earthquake detectors installed in BC schools for the Earthquake Early Warning System for British Columbia. We have developed a new technique for locating hypocenters and applied it to our dataset. The technique will enable near real-time event location, aiding in both mitigating induced events and adjusting completions to optimize the stimulation. Our hypocenter program assumes to consider a S wave speed, fitting the arrival times to the hypocenter, and using an "amoebae method" multivariate. We have used this method because it is well suited to minimizing of the chi-squared function of the arrival time deviation. We show some preliminary results on the Montney dataset.

Non-double-couple mechanisms of microearthquakes induced by hydraulic fracturing

USGS Publications Warehouse

Sileny, J.; Hill, D.P.; Eisner, Leo; Cornet, F.H.

2009-01-01

We have inverted polarity and amplitude information of representative microearthquakes to investigate source mechanisms of seismicity induced by hydraulic fracturing in the Carthage Cotton Valley, east Texas, gas field. With vertical arrays of four and eight three-component geophones in two monitoring wells, respectively, we were able to reliably determine source mechanisms of the strongest events with the best signal-to-noise ratio. Our analysis indicates predominantly non-double-couple source mechanisms with positive volumetric component consistent with opening cracks oriented close to expected hydraulic fracture orientation. Our observations suggest the induced events are directly the result of opening cracks by fluid injection, in contrast to many previous studies where the seismicity is interpreted to be primarily shearing caused by pore pressure diffusion into the surrounding rock or associated with shear stresses created at the hydraulic fracture tip. Copyright 2009 by the American Geophysical Union.

A wireless sensor network for monitoring volcanic tremors

NASA Astrophysics Data System (ADS)

Lopes Pereira, R.; Trindade, J.; Gonçalves, F.; Suresh, L.; Barbosa, D.; Vazão, T.

2013-08-01

Monitoring of volcanic activity is important to learn about the properties of each volcano and provide early warning systems to the population. Monitoring equipment can be expensive and thus, the degree of monitoring varies from volcano to volcano and from country to country, with many volcanoes not being monitored at all. This paper describes the development of a Wireless Sensor Network (WSN) capable of collecting geophysical measurements on remote active volcanoes. Our main goals were to create a flexible, easy to deploy and maintain, adaptable, low-cost WSN for temporary or permanent monitoring of seismic tremor. The WSN enables the easy installation of a sensor array on an area of tens of thousand of m2, allowing the location of the magma movements causing the seismic tremor to be calculated. This WSN can be used by recording data locally for latter analysis or by continuously transmitting it in real time to a remote laboratory for real-time analyses.

Experimental Evidence of Volcanic Earthquakes Induced by Different Fluid Types

NASA Astrophysics Data System (ADS)

Clarke, J. A.; Adam, L.; Sarout, J.; van Wijk, K.; Dautriat, J. D.; Kennedy, B.

2017-12-01

Low Frequency volcanic seismicity has long been associated with resonance in fluid-filled cracks or conduits driven by pressure perturbations at depth. In volcano monitoring, fluid movement, fracturing and the conduit geometry are interpreted based on field observations, laboratory experiments, and numerical models. Fluids in a volcanic environment include gasses, brine and magmas with different viscosities. Magma viscosity is a key influence on eruptive behaviour. For example, increasing magma viscosity is known to favour explosive eruptions. How different fluids affect volcano seismicity is not well understood. Here, we explore the effects of fluid type on volcano seismic signals. Frequency content in the signal, frequency of the events, source mechanism and quality factor are studied. We simulate volcano tectonic (fracturing) and volcano seismic (fluid movement) signatures in a controlled laboratory environment using a range of rock samples, fluid types and pressure conditions. The viscosity of the fluids spans six orders of magnitude, representing realistic volcanic fluids. Microseismicity is generated by venting pressurised fluids through pre-generated fracture networks in cylindrical rock core samples and detected by an array of 18 ultrasonic transducers. We fracture samples of two lithologies: 1) low porosity impermeable granite samples and 2) a permeable volcanic ash tuff sample. Permeability and porosity in the granites are due to a fracture network, while in the tuff a high porosity matrix ( 40 %) and a fracture network interact. The fluids used are nitrogen gas, water, and mixtures of water and glycerol. We generate and detect a myriad of seismic event types, some of which resemble well-known families of volcano-tectonic, low-frequency, hybrid and tremor-type seismicity. Samples with fluids of lower density and viscosity generate a higher number of seismic events. We will present an integrated analysis of the event types, frequency content, source locations and mechanisms. In addition, we explore the importance of seismic wave attenuation by studying the relationship between wave path and event frequency content.

Extraction of Pn seismic signals from air-gun shots recorded by the Cascadia Amphibious seismic experiment

NASA Astrophysics Data System (ADS)

Rathnayaka, S.; Gao, H.

2017-12-01

The goal of this study is to extract Pn (head wave) seismic waveforms recorded by both offshore and onshore (broadband and short period) seismic stations and evaluate the data quality. Two offshore active-source seismic experiments, MGL 1211 and MGL 1212, were conducted from 13th June to 24th July 2012, during the first year deployment of the Cascadia Initiative Amphibious Array. In total, we choose 110 ocean bottom seismometers and 209 inland stations that are located along the entire Cascadia subduction zone. We first remove the instrument response, and then explore the potential frequency ranges and the diurnal effect. We make the common receiver gathering for each seismic station and filter the seismic waveforms at multiple frequency bands, ranging from 3-5 Hz, 5-10 Hz, 10-20 Hz, to 20-40 Hz, respectively. To quantitatively evaluate the data quality, we calculate the signal-to-noise ratio (SNR) of the waveforms for usable stations that record clear Pn arrivals at multiple frequency bands. Our results show that most offshore stations located at deep water (>1.5 km) record clear air-gun shot signals at frequencies higher than 3 Hz and up to 550 km away from the source. For most stations located on the shallow continental shelf, the seismic recordings appear much noisier at all the frequencies compared to stations at deep water. Three general trends are observed for the SNR distribution; First, the SNR ratio increases from lower to higher frequency bands; Second, the ratio decreases with the increasing source-to-receiver distance; And third, the ratio increases from shallow to deep water. We also observe a rough negative relationship of the signal-to-noise ratio with the thickness of the marine sediment. Only 5 inland stations record clear air-gun shot arrivals up to 200 km away from the source. More detailed data quality analysis with more results will also be present.

Infrasound associated with 2004-2005 large Sumatra earthquakes and tsunami

NASA Astrophysics Data System (ADS)

Le Pichon, A.; Herry, P.; Mialle, P.; Vergoz, J.; Brachet, N.; Garcés, M.; Drob, D.; Ceranna, L.

2005-10-01

Large earthquakes that occurred in the Sumatra region in 2004 and 2005 generated acoustic waves recorded by the Diego Garcia infrasound array. The Progressive Multi-Channel Correlation (PMCC) analysis is performed to detect the seismic and infrasound signals associated with these events. The study is completed by an inverse location procedure that permitted reconstruction of the source location of the infrasonic waves. The results show that ground motion near the epicenter and vibrations of nearby land masses efficiently produced infrasound. The analysis also reveals unique evidence of long period pressure waves from the tsunami earthquake (M9.0) of December 26, 2004.

Evaluation of seismic hazard of the Gökova bay in terms of seismotectonics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erkoç, Ebru Aktepe, E-mail: ebru.aktepe@deu.edu.tr; Uluğ, Atilla, E-mail: atilla.ulug@deu.edu.tr

While discovering the seismicity of our country, knowing the array of earthquake occurrence which reflects the characteristic tectonic features of each region makes vital contributions to the earthquakes that have occurred and to the pursuit of the processes which might occur in the future. When considering the region’s seismic activity, the presence of active faults that create earthquake within the bay is obvious. Many active fault parts in the Gulf of Gökova region continues their seismic activity with the opening effect that is generally prevailing in Western Anatolia. The region has generally been continuing its seismic activity under the controlmore » of normal faults. Considering the marine studies that are made and marine continuity of the faults which are on land in addition to the seismological and tectonic studies, the determination of seismic hazard in the Gulf of Gökova and its surroundings is also important in terms of introducing the earthquake scenarios with minimized errors.« less

Lunar seismic profiling experiment natural activity study

NASA Technical Reports Server (NTRS)

Duennebier, F. K.

1976-01-01

The Lunar Seismic Experiment Natural Activity Study has provided a unique opportunity to study the high frequency (4-20 Hz) portion to the seismic spectrum on the moon. The data obtained from the LSPE was studied to evaluate the origin and importance of the process that generates thermal moonquakes and the characteristics of the seismic scattering zone at the lunar surface. The detection of thermal moonquakes by the LSPE array made it possible to locate the sources of many events and determine that they are definitely not generated by astronaut activities but are the result of a natural process on the moon. The propagation of seismic waves in the near-surface layers was studied in a qualitative manner. In the absence of an adequate theoretical model for the propagation of seismic waves in the moon, it is not possible to assign a depth for the scattering layer. The LSPE data does define several parameters which must be satisfied by any model developed in the future.

Revised self-noise estimates for Güralp broadband seismometers concerning ambient noise levels of the UK mainland: implications for detectability of induced seismic events

NASA Astrophysics Data System (ADS)

Hicks, S. P.; Hill, P.; Goessen, S.; Rietbrock, A.; Garth, T.

2016-12-01

The self-noise level of a broadband seismometer sensor is a commonly-used parameter used to evaluate instrument performance. There are several independent studies of various instruments' self-noise (e.g. Ringler & Hutt, 2010; Tasič & Runovc, 2012). However, due to ongoing developments in instrument design (i.e. mechanics and electronics), it is essential to regularly assess any changes in self-noise, which could indicate improvements/deterioration in instrument design and performance over time. We present new self-noise estimates for a range of Güralp broadband seismometers (3T, 3ESPC, 40T, 6T). We use the three-channel coherence analysis estimate of Sleeman et al. (2006) to measure self-noise of these instruments. Based on coherency analysis, we also perform a mathematical rotation of measured waveforms to account for any relative sensor misalignment errors, which can cause artefacts of amplified self-noise around the microseismic peak (Tasič & Runovc, 2012). The instruments were tested for a period of several months at a seismic vault located at the Eskdalemuir array in southern Scotland. We discuss the implications of these self-noise estimates within the framework of the ambient noise level across the mainland United Kingdom. Using attenuation relationships derived for the United Kingdom, we investigate the detection capability thresholds of the UK National Seismic Network within the framework of a Traffic Light System (TLS) that has been proposed for monitoring of induced seismic events due to shale gas extraction.

Characteristics of Tremor During the Entire July 2004 Cascadia Episodic Tremor and Slip event

NASA Astrophysics Data System (ADS)

McCausland, W. A.; Malone, S.; La Rocca, M.; Creager, K.

2005-12-01

The July 2004 Cascadia episodic tremor and slip (ETS) event was recorded and analyzed using three geographically distributed small aperture seismic arrays (600m) located near Sooke, BC, Sequim, WA, and on Lopez Island, WA. We analyzed the tremor sequence in the 1 to 6 Hz frequency band in overlapping windows (12s length)using zero-lag cross correlation and polarization analysis in order to obtain a continuous record of the back-azimuth, slowness, and particle motion of tremor sources throughout the ETS episode. During periods without tremor, the average interstation correlations for each array range between 0.2 and 0.4, and observed azimuths are randomly distributed. During periods of strong tremor, the average correlation for each array is typically between 0.5 and 0.8, and azimuths are stable over periods of minutes. Observed apparent velocities are greater than 4 km/s and polarization analysis indicates that the wave-field is composed primarily of SH-waves, both of which are consistent with a deep source of shear wave energy. Azimuths and slownesses are consistent with previously obtained hypocentral locations and apparent velocities calculated using the relative arrival times of energy bursts on Pacific Northwest Seismograph Network.

Solar-Array Deployment Test for InSight

NASA Image and Video Library

2015-05-27

Engineers and technicians at Lockheed Martin Space Systems, Denver, run a test of deploying the solar arrays on NASA's InSight lander in this April 30, 2015 image. InSight, for Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport, is scheduled for launch in March 2016 and landing in September 2016. It will study the deep interior of Mars to advance understanding of the early history of all rocky planets, including Earth. Note: After thorough examination, NASA managers have decided to suspend the planned March 2016 launch of the Interior Exploration using Seismic Investigations Geodesy and Heat Transport (InSight) mission. The decision follows unsuccessful attempts to repair a leak in a section of the prime instrument in the science payload. http://photojournal.jpl.nasa.gov/catalog/PIA19665

Toward 2D Seismic Wavefield Monitoring: Seismic Gradiometry for Long-Period Seismogram and Short-Period Seismogram Envelope applied to the Hi-net Array

NASA Astrophysics Data System (ADS)

Maeda, T.; Nishida, K.; Takagi, R.; Obara, K.

2015-12-01

The high-sensitive seismograph network Japan (Hi-net) operated by National Research Institute for Earth Science and Disaster Prevention (NIED) has about 800 stations with average separation of 20 km. We can observe long-period seismic wave propagation as a 2D wavefield with station separations shorter than wavelength. In contrast, short-period waves are quite incoherent at stations, however, their envelope shapes resemble at neighbor stations. Therefore, we may be able to extract seismic wave energy propagation by seismogram envelope analysis. We attempted to characterize seismic waveform at long-period and its envelope at short-period as 2D wavefield by applying seismic gradiometry. We applied the seismic gradiometry to a synthetic long-period (20-50s) dataset prepared by numerical simulation in realistic 3D medium at the Hi-net station layout. Wave amplitude and its spatial derivatives are estimated by using data at nearby stations. The slowness vector, the radiation pattern and the geometrical spreading are extracted from estimated velocity, displacement and its spatial derivatives. For short-periods at shorter than 1 s, seismogram envelope shows temporal and spatial broadening through scattering by medium heterogeneity. It is expected that envelope shape may be coherent among nearby stations. Based on this idea, we applied the same method to the time-integration of seismogram envelope to estimate its spatial derivatives. Together with seismogram envelope, we succeeded in estimating the slowness vector from the seismogram envelope as well as long-period waveforms by synthetic test, without using phase information. Our preliminarily results show that the seismic gradiometry suits the Hi-net to extract wave propagation characteristics both at long and short periods. This method is appealing that it can estimate waves at homogeneous grid to monitor seismic wave as a wavefield. It is promising to obtain phase velocity variation from direct waves, and to grasp wave packets originating from scattering from coda, by applying the seismic gradiometry to the Hi-net.

Spatial-temporal variations of seismic noise and their relation to wind, rivers, and basins in central Alaska

NASA Astrophysics Data System (ADS)

Smith, K.; Tape, C.; Bruton, C. P.; West, M. E.

2016-12-01

Continuous seismic recordings-or ambient noise-provide means for time-dependent monitoring of site conditions. Frequency-domain amplitude spectra of seismic recordings can be used to characterize time-dependent variations as a function of period (or frequency). Spatial variations can be characterized by using a set of stations across a large region. We analyze time-dependent ambient noise spectra from stations across central Alaska with three purposes. First, we are interested in monitoring the station performance and quality of a new array (FLATS) of 13 posthole seismometers near the Tanana River in Minto Flats. Second, we want to understand time-dependent threshold levels for earthquake detection: when noise is high, earthquake detections are low. Third, we are interested in identifying the effects of nature and Earth structure on seismic stations at different spatial-temporal scales. Our results show that seismic stations are sensitive to variations in wind speed and river flow. Correlations between wind speed and long-period (>10 seconds) seismic noise variations are probably due to tilt effects that have been previously documented. We identify a seismic signal at 10 Hz that is present only on stations close (<100 m) to the main channel of the Tanana river. The 10-Hz signal is strongly correlated with river gage height during summer and weakly correlated during the winter, when the river surface is covered in 1 m of ice. Spatial correlations among stations reveal large variations at shorter time scales (days); these could be due to weather anomalies. The amplitude of seismic noise at periods 2-10 s is strongly influenced by the thickness of sediment, which ranges from 0 m at bedrock sites to 6000 m at sites in the deepest part of Nenana basin. Our analysis allows us to better monitor the performance of temporary and permanent seismic stations, and to understand the physical causes of time-dependent noise variations in Alaska. Our findings show that seismic stations near rivers can potentially be used to monitor the flow of the river during summer and during ice-covered winter, raising the possibility for monitoring river ice break-up during April.

Synthetic Seismogram Modeling.

DTIC Science & Technology

1982-11-15

various phases ( designated A, B, C, etc.) are indicated on the seismic record section at the top of the diagram. The observed travel times show a good...structure of the Yellowstone aperture seismic array (LAS), Moatana, U.S. region and experiment design , J. Geophys. Geol. Suwv. Open File Rep. 1671, 1972. Res...also display little For clarity in both typography and conitext, we coherence in waveform or even in the envelope of shall henceforth write -P-bar in

The CAFE Experiment: A Joint Seismic and MT Investigation of the Cascadia Subduction System

DTIC Science & Technology

2013-02-01

In this thesis we present results from inversion of data using dense arrays of collocated seismic and magnetotelluric stations located in the Cascadia...implicit in the standard MT inversion provides tools that enable us to generate a more accurate MT model. This final MT model clearly demonstrates...references within, Hacker, 2008) have given us the tools to better interpret geophysical evidence. Improvements in the thermal modeling of subduction zones

EarthScope Transportable Array Siting Outreach Activities in Alaska and Western Canada

NASA Astrophysics Data System (ADS)

Dorr, P. M.; Gardine, L.; Tape, C.; McQuillan, P.; Cubley, J. F.; Samolczyk, M. A.; Taber, J.; West, M. E.; Busby, R.

2015-12-01

The EarthScope Transportable Array is deploying about 260 stations in Alaska and western Canada. IRIS and EarthScope are partnering with the Alaska Earthquake Center, part of the University of Alaska's Geophysical Institute, and Yukon College to spread awareness of earthquakes in Alaska and western Canada and the benefits of the Transportable Array for people living in these regions. We provide an update of ongoing education and outreach activities in Alaska and Canada as well as continued efforts to publicize the Transportable Array in the Lower 48. Nearly all parts of Alaska and portions of western Canada are tectonically active. The tectonic and seismic variability of Alaska, in particular, requires focused attention at the regional level, and the remoteness and inaccessibility of most Alaskan and western Canadian villages and towns often makes frequent visits difficult. When a community is accessible, every opportunity to engage the residents is made. Booths at state fairs and large cultural gatherings, such as the annual convention of the Alaska Federation of Natives, are excellent venues to distribute earthquake information and to demonstrate a wide variety of educational products and web-based applications related to seismology and the Transportable Array that residents can use in their own communities. Meetings and interviews with Alaska Native Elders and tribal councils discussing past earthquakes has led to a better understanding of how Alaskans view and understand earthquakes. Region-specific publications have been developed to tie in a sense of place for residents of Alaska and the Yukon. The Alaska content for IRIS's Active Earth Monitor emphasizes the widespread tectonic and seismic features and offers not just Alaska residents, but anyone interested in Alaska, a glimpse into what is going on beneath their feet. The concerted efforts of the outreach team will have lasting effects on Alaskan and Canadian understanding of the seismic hazard and tectonics of the region.

Ice shelf structure from dispersion curve analysis of passive-source seismic data, Ross Ice Shelf, Antarctica

NASA Astrophysics Data System (ADS)

Diez, A.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Anthony, R. E.; Aster, R. C.; Cai, C.; Nyblade, A.; Wiens, D.

2015-12-01

An L-shaped array of three-component short period seismic stations was deployed at the Ross Ice Shelf, Antarctica approximately 100 km south of the ice edge, near 180° longitude, from November 18 through 28, 2014. Polarization analysis of data from these stations clearly shows propagating waves from below the ice shelf for frequencies below 2 Hz. Energy above 2 Hz is dominated by Rayleigh and Love waves propagating from the north. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile, from which we derive a density profile. The derived shear wave velocity profiles differ within the firn for the inversions using Rayleigh and Love wave dispersion curves. This difference is attributed to an effective anisotropy due to fine layering. The layered structure of firn, ice, water, and ocean floor results in a characteristic dispersion curve pattern below 7 Hz. We investigate the observed structures in more detail by forward modeling of Rayleigh wave dispersion curves for representative firn, ice, water, sediment structures. Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. Our results show that the analysis of high frequency Rayleigh waves on an ice shelf has the ability to resolve ice shelf thickness, water column thickness, and the physical properties of the underlying ocean floor using passive-source seismic data.

Preliminary results of the Source China Sea passive source OBS array experiment

NASA Astrophysics Data System (ADS)

Yang, T.; Liu, C.; Pei, Y.; Xia, S.

2013-12-01

The Scarborough, or Huangyan, Seamount chain in South China Sea (SCS) represents an extreme case of the global mid-ocean ridge system where the magmatism continues for many million years after the cessation of spreading. To understand this unique process, the South China Sea Deep (SCSD) program funded an experiment deploying a passive source OBS array to image the lithospheric structure beneath the extinct ridge. In April 2012, 18 passive source OBSs, including 15 Guralp CMG-40T OBS and 3 I-4C OBS, were deployed around the Huangyan Island for one year. 11 OBSs were successfully recovered this April, and their data are being processed. Here we present some preliminary results from analyses of this dataset, including the general quality of three-component seismograms, characteristics of seafloor ambient noise spectra, determining the OBS orientation from the Rayleigh wave polarization, and the dispersion analysis of Rayleigh waves. We found that, for most stations, seismograms from teleseismic, regional and local events are generally good with the horizontal records being comparable with vertical component. The noise levels in these seafloor stations are much higher than land-based stations, especially in shorter periods, likely suggesting the direct and stronger impact from the tempestuous SCS. Applications of more sophisticated seismic techniques such as surface wave tomography, seismic anisotropy, receiver function and ambient noise cross-correlation are underway. In addition to the low recovery rate, there are other lessons learned from this experiment. For example, at least two stations have detectable timing problems; Airgun shots should have been used to constrain the timings and orientations in both deployment and recovery. It is still challenging and costly to carry out long-term passive source seismic observations in deep sea.

Recorded earthquake responses from the integrated seismic monitoring network of the Atwood Building, Anchorage, Alaska

USGS Publications Warehouse

Celebi, M.

2006-01-01

An integrated seismic monitoring system with a total of 53 channels of accelerometers is now operating in and at the nearby free-field site of the 20-story steel-framed Atwood Building in highly seismic Anchorage, Alaska. The building has a single-story basement and a reinforced concrete foundation without piles. The monitoring system comprises a 32-channel structural array and a 21-channel site array. Accelerometers are deployed on 10 levels of the building to assess translational, torsional, and rocking motions, interstory drift (displacement) between selected pairs of adjacent floors, and average drift between floors. The site array, located approximately a city block from the building, comprises seven triaxial accelerometers, one at the surface and six in boreholes ranging in depths from 15 to 200 feet (???5-60 meters). The arrays have already recorded low-amplitude shaking responses of the building and the site caused by numerous earthquakes at distances ranging from tens to a couple of hundred kilometers. Data from an earthquake that occurred 186 km away traces the propagation of waves from the deepest borehole to the roof of the building in approximately 0.5 seconds. Fundamental structural frequencies [0.58 Hz (NS) and 0.47 Hz (EW)], low damping percentages (2-4%), mode coupling, and beating effects are identified. The fundamental site frequency at approximately 1.5 Hz is close to the second modal frequencies (1.83 Hz NS and 1.43 EW) of the building, which may cause resonance of the building. Additional earthquakes prove repeatability of these characteristics; however, stronger shaking may alter these conclusions. ?? 2006, Earthquake Engineering Research Institute.

Comparisons of Low-Strain Amplification at Soft-Sediment, Hard-Rock, Topographic, and Fault-Zone Sites in the Hayward Fault Zone, California

NASA Astrophysics Data System (ADS)

Catchings, R.; Strayer, L. M.; Goldman, M.

2014-12-01

We used a temporary network of approximately 600 seismographs to record a seismic source generated by the collapse of a 13-story building near the active trace of the Hayward Fault. These data allow us to evaluate variations in ground shaking across a series of 30 2-km-long radial arrays centered on the seismic source. Individual seismographs were spaced at 200-m intervals, forming a series of 360°concentric arrays around the seismic source. The data show variations in amplification caused by (1) soft sediments within the East Bay alluvial plain (EBAP), (2) hard rocks within the East Bay hills (EBH), (3) low-velocity rocks within the Hayward Fault zone (HFZ), and (4) topography. Given that ground shaking varies strongly with distance from the source, the concentric arrays allowed us to measure variations in ground shaking as a function of azimuth at fixed distances from the source. On individual linear profiles within the concentric arrays, we observed decreases in peak ground velocity (PGV) across the HFZ and other faults within the EBH. However, for a given distance from the source, we observe four to five fold amplification from the EBAP sites compared to most sites in the EBH. Topographic and fault-zone amplification effects within the EBH, however, are greater than the EBAP sediment amplification. Thus, for future earthquakes, shaking at many sites within the EBH may be significantly stronger than many sites within the EBAP. These observations suggest amplification can be expected in unconsolidated sediments, but topographic and fault-zone amplification can be larger. This confirms the importance of site effects for hazard mitigation and in interpreting MMI for future and historical earthquakes.

Increasing diversity in the geosciences through the AfricaArray geophysics field course

NASA Astrophysics Data System (ADS)

Vallejo, G.; Emry, E.; Galindo, B. L.; Carranza, V.; Gomez, C. D.; Ortiz, K.; Castro, J. G.; Guandique, J.; Falzone, C.; Webb, S. J.; Manzi, M.; Mngadi, S. B.; Stephens, K.; Chinamora, B.; Whitehead, R.; de Villiers, D. P.; Tshitlho, K.; Delhaye, R. P.; Smith, J. A.; Nyblade, A.

2014-12-01

For the past nine years, the AfricaArray diversity program, sponsored by industry, the National Science Foundation, and several partnering universities have supported outstanding U.S. STEM underrepresented minority undergraduates to gain field experience in near-surface geophysical techniques during an 8-week summer program at Penn State University and the University of Witwatersrand (Wits). The AfricaArray geophysics field school, which is run by Wits, has been teaching field-based geophysics to African students for over a decade. In the first 2-3 weeks of the program, the U.S. students are given basic instruction in near-surface geophysics, South African geology, and South African history and culture. The students then join the Wits AfricaArray geophysics field school - working alongside Wits students and students from several other African universities to map the shallow subsurface in prospective areas of South Africa for platinum mining. In addition to the primary goals of collecting and interpreting gravity, magnetic, resistivity, seismic refraction, seismic reflection, and EM data, students spend time mapping geologic units and gathering information on the physical properties of the rocks in the region (i.e. seismic velocity, density, and magnetic susceptibility). Subsurface targets include mafic dikes, faults, the water table, and overburden thickness. Upon returning to the U.S., students spend 2-3 weeks finalizing their project reports and presentations. The program has been effective at not only providing students with fundamental skills in applied geophysics, but also in fostering multicultural relationships, preparing students for graduate work in the geosciences, and attracting STEM students into the geosciences. Student presenters will discuss their experiences gained through the field school and give their impressions about how the program works towards the goal of increasing diversity in the geosciences in the U.S.

Seismic Tomography

NASA Astrophysics Data System (ADS)

Nowack, Robert L.; Li, Cuiping

The inversion of seismic travel-time data for radially varying media was initially investigated by Herglotz, Wiechert, and Bateman (the HWB method) in the early part of the 20th century [1]. Tomographic inversions for laterally varying media began in seismology starting in the 1970’s. This included early work by Aki, Christoffersson, and Husebye who developed an inversion technique for estimating lithospheric structure beneath a seismic array from distant earthquakes (the ACH method) [2]. Also, Alekseev and others in Russia performed early inversions of refraction data for laterally varying upper mantle structure [3]. Aki and Lee [4] developed an inversion technique using travel-time data from local earthquakes.

Methods for use in detecting seismic waves in a borehole

DOEpatents

West, Phillip B.; Fincke, James R.; Reed, Teddy R.

2007-02-20

The invention provides methods and apparatus for detecting seismic waves propagating through a subterranean formation surrounding a borehole. In a first embodiment, a sensor module uses the rotation of bogey wheels to extend and retract a sensor package for selective contact and magnetic coupling to casing lining the borehole. In a second embodiment, a sensor module is magnetically coupled to the casing wall during its travel and dragged therealong while maintaining contact therewith. In a third embodiment, a sensor module is interfaced with the borehole environment to detect seismic waves using coupling through liquid in the borehole. Two or more of the above embodiments may be combined within a single sensor array to provide a resulting seismic survey combining the optimum of the outputs of each embodiment into a single data set.

Seismic Waveform Modeling of Broadband Data From a Temporary High-Density Deployment in the Los Angeles Basin

NASA Astrophysics Data System (ADS)

Herrman, M.; Polet, J.

2016-12-01

A total of 73 broadband seismometers were deployed for a passive source seismic experiment called the Los Angeles Syncline Seismic Interferometry Experiment (LASSIE) from September to November of 2014. The purpose of this experiment was to collect high density seismic data for the Los Angeles Basin (LAB) to better understand basin structure and response. This research will use the data collected from LASSIE to assess and refine current velocity models of the LAB using a full waveform modeling approach. To this end we will compare seismograms recorded by LASSIE for a subset of the 53 earthquakes and quarry blasts located by the Southern California Seismic Network (SCSN) that occurred within or near the LAB during the deployment period to synthetic seismograms generated by the Frequency-Wavenumber (FK) code developed by Zhu and Rivera (2002). A first analysis of the data indicates that roughly 25 of the 53 events have waveforms with sufficiently high signal to noise ratio, providing approximately 500 seismograms that are of suitable quality for comparison. We observe significant changes in waveform characteristics between stations with a very small separation distance of approximately 1 km. Focal mechanisms for most of these events have been obtained from Dr. Egill Hauksson (personal communication). We will show comparisons between the broadband velocity waveforms recorded by stations across the LASSIE array and FK synthetics determined for a variety of 1D velocity models that have been developed for the LAB area (such as Hadley and Kanamori, 1977; Hauksson, 1989, 1995 and Magistrale, 1992). The results of these comparisons will be analyzed to provide additional constraints on the subsurface seismic velocity structure within the Los Angeles basin.

Seismic While Drilling Case Study in Shengli Oilfield, Eastern China

NASA Astrophysics Data System (ADS)

Wang, L.; Liu, H.; Tong, S.; Zou, Z.

2015-12-01

Seismic while drilling (SWD) is a promising borehole seismic technique with reduction of drilling risk, cost savings and increased efficiency. To evaluate the technical and economic benefits of this new technique, we carried out SWD survey at well G130 in Shengli Oilfield of Eastern China. Well G130 is an evaluation well, located in Dongying depression at depth more than 3500m. We used an array of portable seismometers to record the surface SWD-data, during the whole drilling progress. The pilot signal was being recorded continuously, by an accelerometer mounted on the top of the drill string. There were also two seismometers buried in the drill yard, one near diesel engine and another near derrick. All the data was being recorded continuously. According to mud logging data, we have processed and analyzed all the data. It demonstrates the drill yard noise is the primary noise among the whole surface wavefield and its dominant frequency is about 20Hz. Crosscorrelation of surface signal with the pilot signal shows its SNR is severely low and there is no any obvious event of drill-bit signals. Fortunately, the autocorrelation of the pilot signal shows clear BHA multiple and drill string multiple. The period of drill string multiple can be used for establishing the reference time (so-called zero time). We identified and removed different noises from the surface SWD-data, taking advantages of wavefield analysis. The drill-bit signal was retrieved from surface SWD-data, using seismic interferometry. And a reverse vertical seismic profile (RVSP) data set for the continuous drilling depth was established. The subsurface images derived from these data compare well with the corresponding images of 3D surface seismic survey cross the well.

Seismic probing of continental subduction zones

NASA Astrophysics Data System (ADS)

Zhao, Liang; Xu, Xiaobing; Malusà, Marco G.

2017-09-01

High-resolution images of Earth's interior provide pivotal information for the understanding of a range of geodynamic processes, including continental subduction and exhumation of ultrahigh-pressure (UHP) metamorphic rocks. Here we present a synthesis of available global seismic observations on continental subduction zones, and selected examples of seismic probing from the European Alps, the Himalaya-Tibet and the Qinling-Dabie orogenic belts. Our synthesis and examples show that slabs recognized beneath exhumed continental UHP terranes generally have shallow dip angles (<45°) at depths <100 km, to become much steeper at depths >100 km. Slabs underlined by a clear high velocity anomaly from Earth's surface to the mantle are generally Cenozoic in age. Some of these slabs are continuous, whereas other continental subduction zones are located above discontinuous high velocity anomalies possibly suggesting slab breakoff. The density of seismic stations and the quality of recordings are of primary importance to get high-resolution images of the upper mantle to be used as a starting point to provide reliable geodynamic interpretations. In some cases, areas previously indicated as possible site of slab breakoff, such as the European Alps, have been later proven to be located above a continuous slab by using higher quality travel time data from denser seismic arrays. Discriminating between oceanic and continental slabs can be challenging, but valuable information can be provided by combining teleseismic tomography and receiver function analysis. The upper mantle beneath most continental UHP terranes generally shows complex seismic anisotropy patterns that are potentially preserved even in pre-Cenozoic subduction zones. These patterns can be used to provide information on continental slabs that are no longer highlighted by a clear high-velocity anomaly.

New seismic images of the crust across the Rivera Plate and Jalisco Block (Mexico)

NASA Astrophysics Data System (ADS)

Cordoba, Diego; Núñez-Cornú, Francisco Javier; Bartolomé, Rafael; José Dañobeitia, Juan; Bandy, William Lee; Núñez, Diana; Prada, Manel; Escudero-Ayala, Christian; Espíndola, Juan Manuel; Zamora, Araceli; Gómez, Adán; Ortiz, Modesto; Tsujal Working Group

2015-04-01

During the spring and summer of 2014, we achieved an extensive offshore geophysical experiment at West Coast of México entitled "Crustal characterization of the Rivera Plate-Jalisco Block boundary and its implications for seismic and tsunami hazard assessment (TSUJAL)". The project is the result of continuous scientific collaboration between institutions in Mexico and Spain, whose main objective is to study the lithospheric structure at the collision zone between Rivera, North America Plates and the Jalisco Block, and identifying submarine structures which can potentially be tsunamigenic sources The active phase of this project carried out in February and March of 2014, we acquired around 5200 km of Multichannel Seismic Reflection (MCS) together with multibeam bathymetry and potential fields (gravity and magnetism) data. Moreover, a wide angle experiment was performed, deploying 16 OBS in 32 locations in Jalisco and Nayarit offshore regions, also recorded on a terrestrial network of 100 portable seismic stations in 240 locations across 5 seismic profiles of 200-300 km in length combined with the Seismological Network of the State of Jalisco (SisVOc). In addition, 8 land seismic stations were installed in Marías Islands and Isabel Island. These instruments registered, in continuous mode, the airgun shots generated by airgun array of 5800 ci, shooting every 120 s. The UK vessel RRS James Cook participated in this project as a part of the exchange program between Spanish and English scientific vessels, she was responsible of marine seismic experiment (MCS & WA) using a 6 km length streamer and a high capacity airgun array. Furthermore, the ARM Holzinger and RV El Puma participated in this project and were provided by the Mexican Navy and UNAM, respectively. The second phase of this project was achieved in June 2014, where 100 short period seismic stations were installed along a 200 km seismic profile from La Caldera de la Primavera (Guadalajara) to Barra de Navidad (Jalisco coast).These instruments registered 3 borehole explosions of 1000 kg specially made for this project, in the northern, central and southern parts of this profile. These new data provide a dense sampling of tectonic plates, W Mexico, and give new seismic constraints on the deformation along and across the subduction zone, accretionary wedge size, at contact between Rivera and North American Plates and, in the transition zone between oceanic and continental crust.

GNSS seismometer: Seismic phase recognition of real-time high-rate GNSS deformation waves

NASA Astrophysics Data System (ADS)

Nie, Zhaosheng; Zhang, Rui; Liu, Gang; Jia, Zhige; Wang, Dijin; Zhou, Yu; Lin, Mu

2016-12-01

High-rate global navigation satellite systems (GNSS) can potentially be used as seismometers to capture short-period instantaneous dynamic deformation waves from earthquakes. However, the performance and seismic phase recognition of the GNSS seismometer in the real-time mode, which plays an important role in GNSS seismology, are still uncertain. By comparing the results of accuracy and precision of the real-time solution using a shake table test, we found real-time solutions to be consistent with post-processing solutions and independent of sampling rate. In addition, we analyzed the time series of real-time solutions for shake table tests and recent large earthquakes. The results demonstrated that high-rate GNSS have the ability to retrieve most types of seismic waves, including P-, S-, Love, and Rayleigh waves. The main factor limiting its performance in recording seismic phases is the widely used 1-Hz sampling rate. The noise floor also makes recognition of some weak seismic phases difficult. We concluded that the propagation velocities and path of seismic waves, macro characteristics of the high-rate GNSS array, spatial traces of seismic phases, and incorporation of seismographs are all useful in helping to retrieve seismic phases from the high-rate GNSS time series.

Seismo-Acoustic Generation by Earthquakes and Explosions and Near-Regional Propagation

DTIC Science & Technology

2009-09-30

earthquakes generate infrasound . Three infrasonic arrays in Utah (BGU, EPU, and NOQ), one in Nevada (NVIAR), and one in Wyoming (PDIAR) recorded...Katz, and C. Hayward (2009b). The F-detector Revisited: An Improved Strategy for Signal Detection at Seismic and Infrasound Arrays , Bull. Seism. Soc...sources. RESEARCH ACCOMPLISHED Infrasound Observations of the Wells Earthquake Most studies documenting earthquake - generated infrasound are based

Testing of Streckeisen STS-5A and Nanometrics Trillium 120PH Sensors for the Alaska Transportable Array

NASA Astrophysics Data System (ADS)

Abbasi Baghbadorani, A.; Aderhold, K.; Bloomquist, D.; Frassetto, A.; Miller, P. E.; Busby, R. W.

2017-12-01

Starting in 2014, the IRIS Transportable Array facility began to install and operate seismic stations in Alaska and western Canada. By the end of the project, the full deployment of the array will cover a grid of 280 stations spaced about 85 km apart covering all of mainland Alaska and parts of the Yukon, British Columbia, and the Northwest Territories. Approximately 200 stations will be operated directly by IRIS through at least 2019. A key aspect of the Alaska TA is the need for stations to operate autonomously, on account of the high cost of installation and potential subsequent visits to remote field-sites to repair equipment. The TA is using newly developed broadband seismometers Streckeisen STS-5A and Nanometrics Trillium-120PH, designed for installation in shallow posthole emplacements. These new instruments were extensively vetted beforehand, but they are still relatively new to the TA inventory. Here we will assess their performance under deployment conditions and after repeated commercial shipping and travel to the field. Our objective is to provide a thorough accounting of the identified failures of the existing inventory of posthole instruments. We will assess the practices and results of instrument testing by the PASSCAL Instrument Center/Array Operations Facility (PIC/AOF), Alaska Operations Center (AOC), and broadband seismic sensor manufacturers (Streckeisen, Nanometrics) in order to document potential factors in and stages during the process for instrument failures. This will help to quantify the overall reliability of the TA seismic sensors and quality of TA practices and data collection, and identify potential considerations in future TA operations. Our results show that the overall rate of failure of all posthole instruments is <4% out of 260. This is lower than the rates seen for vault sensor failures in the operation of the Lower 48 Transportable Array. For telemetered stations such as these installed in the TA Alaska array, we also show that noise analyses can capture a failed emplaced sensor and reveal improved station performance after sensor replacement, and that these are key elements in assessing whether or not a sensor should be replaced in the field.

Imaging subsurface hydrothermal structure using a dense geophone array in Yellowstone

NASA Astrophysics Data System (ADS)

Wu, S. M.; Lin, F. C.; Farrell, J.; Smith, R. B.

2016-12-01

The recent development of ambient noise cross-correlation and the availability of large N seismic arrays allow for the study of detailed shallow crustal structure. In this study, we apply multi-component noise cross-correlation to explore shallow hydrothermal structure near Old Faithful geyser in Yellowstone National Park using a temporary geophone array. The array was composed of 133 three-component 5-Hz geophones and was deployed for two weeks during November 2015. The average station spacing is 50 meters and the full aperture of the array is around 1 km with good azimuthal and spatial coverage. The Upper Geyser Basin, where Old Faithful is located, has the largest concentration of geysers in the world. This unique active hydrothermal environment and hence the extremely inhomogeneous noise source distribution makes the construction of empirical Green's functions difficult based on the traditional noise cross-correlation method. In this presentation, we show examples of the constructed cross-correlation functions and demonstrate their spatial and temporal relationships with known hydrothermal activity. We also demonstrate how useful seismic signals can be extracted from these cross-correlation functions and used for subsurface imaging. In particular, we will discuss the existence of a recharge cavity beneath Old Faithful revealed by the noise cross-correlations. In addition, we also investigated the temporal structure variation based on time-lapse noise cross-correlations and these preliminary results will also be discussed.

PICTURES (Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source): seismic imaging of the source region of the April 1, 2014 Mw 8.2 earthquake offshore northern Chile

NASA Astrophysics Data System (ADS)

Trehu, A. M.

2017-12-01

The 2014 event partially filled a well-recognized seismic gap that had not experienced a large earthquake since a pair of devastating M9 events in 1868 and 1877. The rupture sequence was marked by an unusually long and distinct precursory period that was well recorded by onshore seismic and geodetic instruments of the Integrated Plate Boundary Observatory Chile (IPOC). The pattern of foreshock activity, which defined a "classic" Mogi donut, is correlated with a circular residual gravity high that surrounds the patch of greatest slip during the main shock. Aftershocks generally propagated to the south and stopped in a region of relatively low pre-earthquake coupling. The remaining nearly 300-km long seismic gap is correlated with a distinct forearc residual gravity high. The correlation between the pre-, syn- and post-earthquake deformation patterns and the residual gravity anomalies indicates that crustal structure affects the distribution of seismic and aseismic deformation in response to plate convergence. Because the non-uniqueness inherent in modeling gravity data does not allow for a detailed geologic interpretation of the correlation between structure and slip, we conducted an ambitious seismic experiment using the R/V Marcus Langseth to acquire 5000 km of multichannel seismic seismic data using an 8-12.5-km long streamer and a 6600 cubic inch tuned air-gun array. The 45000 shots were also recorded on 70 ocean-bottom and 50 land-based seismometers. Shipboard analysis of the data indicates that the Moho of the Nazca plate is well imaged west of the trench, that deformation is distributed throughout the outer 10 km of the accretionary wedge as the rough topography of the Nazca plate is subducted, and that a reflection tentatively interpreted to be the plate boundary can be imaged continuously from the trench to the coast on at least one transect across the margin. Post-cruise data analysis is underway to process the MCS data using various techniques to determine along-strike continuity of plate boundary reflectivity and to use OBS and onshore large-aperture data to obtain high-resolution models of the crustal velocity structure of the subducting and overriding plates. The PICTURES Science Team incudes investigators in the US, Chile, Germany, France and the UK.

Fault structure in the Nepal Himalaya as illuminated by aftershocks of the 2015 Mw 7.8 Gorkha earthquake recorded by the local NAMASTE network

NASA Astrophysics Data System (ADS)

Ghosh, A.; Mendoza, M.; LI, B.; Karplus, M. S.; Nabelek, J.; Sapkota, S. N.; Adhikari, L. B.; Klemperer, S. L.; Velasco, A. A.

2017-12-01

Geometry of the Main Himalayan Thrust (MHT), that accommodates majority of the plate motion between Indian and Eurasian plate, is being debated for a long time. Different models have been proposed; some of them are significantly different from others. Obtaining a well constrained geometry of the MHT is challenging mainly because of the lack of high quality data, inherent low resolution and non-uniqueness of the models. We used a dense local seismic network - NAMASTE - to record and analyze a prolific aftershock sequence following the 2015 Mw 7.8 Gorkha earthquake, and determine geometry of the MHT constrained by precisely located well-constrained aftershocks. We detected and located more than 15,000 aftershocks of the Gorkha earthquake using Hypoinverse and then relatively relocated using HypoDD algorithm. We selected about 7,000 earthquakes that are particularly well constrained to analyze the geometry of the megathrust. They illuminate fault structure in this part of the Himalaya with unprecedented detail. The MHT shows two subhorizontal planes connected by a duplex structure. The duplex structure is characterized by multiple steeply dipping planes. In addition, we used four large-aperture continental-scale seismic arrays at teleseismic distances to backproject high-frequency seismic radiation. Moreover, we combined all arrays to significantly increase the resolution and detectability. We imaged rupture propagation of the mainshock showing complexity near the end of the rupture that might help arresting of the rupture to the east. Furthermore, we continuously scanned teleseismic data for two weeks starting from immediately after the mainshock to detect and locate aftershock activity only using the arrays. Spatial pattern of the aftershocks was similar to the existing global catalog using conventional seismic network and technique. However, we detected more than twice as many aftershocks using the array technique compared to the global catalog including many aftershocks that were undetected by the global network. This method might provide new tool to rapidly detect aftershock activity immediately after a large damaging earthquake to guide fast and more effective disaster response.

Seismic Strong Motion Array Project (SSMAP) to Record Future Large Earthquakes in the Nicoya Peninsula area, Costa Rica

NASA Astrophysics Data System (ADS)

Simila, G.; Lafromboise, E.; McNally, K.; Quintereo, R.; Segura, J.

2007-12-01

The seismic strong motion array project (SSMAP) for the Nicoya Peninsula in northwestern Costa Rica is composed of 10 - 13 sites including Geotech A900/A800 accelerographs (three-component), Ref-Teks (three- component velocity), and Kinemetric Episensors. The main objectives of the array are to: 1) record and locate strong subduction zone mainshocks [and foreshocks, "early aftershocks", and preshocks] in Nicoya Peninsula, at the entrance of the Nicoya Gulf, and in the Papagayo Gulf regions of Costa Rica, and 2) record and locate any moderate to strong upper plate earthquakes triggered by a large subduction zone earthquake in the above regions. Our digital accelerograph array has been deployed as part of our ongoing research on large earthquakes in conjunction with the Earthquake and Volcano Observatory (OVSICORI) at the Universidad Nacional in Costa Rica. The country wide seismographic network has been operating continuously since the 1980's, with the first earthquake bulletin published more than 20 years ago, in 1984. The recording of seismicity and strong motion data for large earthquakes along the Middle America Trench (MAT) has been a major research project priority over these years, and this network spans nearly half the time of a "repeat cycle" (~ 50 years) for large (Ms ~ 7.5- 7.7) earthquakes beneath the Nicoya Peninsula, with the last event in 1950. Our long time co- collaborators include the seismology group OVSICORI, with coordination for this project by Dr. Ronnie Quintero and Mr. Juan Segura. The major goal of our project is to contribute unique scientific information pertaining to a large subduction zone earthquake and its related seismic activity when the next large earthquake occurs in Nicoya. We are now collecting a database of strong motion records for moderate sized events to document this last stage prior to the next large earthquake. A recent event (08/18/06; M=4.3) located 20 km northwest of Samara was recorded by two stations (Playa Carrillo and Nicoya) at distances of 25-30 km with maximum acceleration of 0.2g.

3D P and S Wave Velocity Structure and Tremor Locations in the Parkfield Region

NASA Astrophysics Data System (ADS)

Zeng, X.; Thurber, C. H.; Shelly, D. R.; Bennington, N. L.; Cochran, E. S.; Harrington, R. M.

2014-12-01

We have assembled a new dataset to refine the 3D seismic velocity model in the Parkfield region. The S arrivals from 184 earthquakes recorded by the Parkfield Experiment to Record MIcroseismicity and Tremor array (PERMIT) during 2010-2011 were picked by a new S wave picker, which is based on machine learning. 74 blasts have been assigned to four quarries, whose locations were identified with Google Earth. About 1000 P and S wave arrivals from these blasts at permanent seismic network were also incorporated. Low frequency earthquakes (LFEs) occurring within non-volcanic tremor (NVT) are valuable for improving the precision of NVT location and the seismic velocity model at greater depths. Based on previous work (Shelley and Hardebeck, 2010), waveforms of hundreds of LFEs in same family were stacked to improve signal qualify. In a previous study (McClement et al., 2013), stacked traces of more than 30 LFE families at the Parkfileld Array Seismic Observatory (PASO) have been picked. We expanded our work to include LFEs recorded by the PERMIT array. The time-frequency Phase Weight Stacking (tf-PWS) method was introduced to improve the stack quality, as direct stacking does not produce clear S-wave arrivals on the PERMIT stations. This technique uses the coherence of the instantaneous phase among the stacked signals to enhance the signal-to-noise ratio (SNR) of the stack. We found that it is extremely effective for picking LFE arrivals (Thurber et al., 2014). More than 500 P and about 1000 S arrivals from 58 LFE families were picked at the PERMIT and PASO arrays. Since the depths of LFEs are much deeper than earthquakes, we are able to extend model resolution to lower crustal depths. Both P and S wave velocity structure have been obtained with the tomoDD method. The result suggests that there is a low velocity zone (LVZ) in the lower crust and the location of the LVZ is consistent with the high conductivity zone beneath the southern segment of the Rinconada fault that was revealed in the 3D magnetotelluric inversion of Tietze and Ritter(2013).

Wide-angle seismic recordings from the 1998 Seismic Hazards Investigation of Puget Sound (SHIPS), western Washington and British Columbia

USGS Publications Warehouse

Brocher, Thomas M.; Parsons, Tom; Creager, Ken C.; Crosson, Robert S.; Symons, Neill P.; Spence, George D.; Zelt, Barry C.; Hammer, Philip T.C.; Hyndman, Roy D.; Mosher, David C.; Tréhu, Anne M.; Miller, Kate C.; ten Brink, Uri S.; Fisher, Michael A.; Pratt, Thomas L.; Alvarez, Marcos G.; Beaudoin, Bruce C.; Louden, Keith E.; Weaver, Craig S.

1999-01-01

This report describes the acquisition and processing of deep-crustal wide-angle seismic reflection and refraction data obtained in the vicinity of Puget Lowland, the Strait of Juan de Fuca, and Georgia Strait, western Washington and southwestern British Columbia, in March 1998 during the Seismic Hazards Investigation of Puget Sound (SHIPS). As part of a larger initiative to better understand lateral variations in crustal structure along the Cascadia margin, SHIPS participants acquired 1000 km of deep-crustal multichannel seismic-reflection profiles and 1300 km of wideangle airgun shot lines in this region using the R/V Thompson and R/V Tully. The Tully was used to record airgun shots fired by the Thompson in two different geometries: (1) expanding spread profiles (ESPs) and (2) constant offset profiles (COPs). Prior to this reflection survey, we deployed 257 Reftek and 15 ocean-bottom seismic recorders to record the airgun signals at far offsets. All data were recorded digitally on large-capacity hard disks. Although most of these stations only recorded the vertical component of motion, 95 of these seismographs recorded signals from an oriented 3-component seismometer. By recording signals generated by the Thompson's marine air gun array, operated in two differing geometries having a total volume of 110 and 79 liters (6730 and 4838 cu. in.), respectively, the arrays of wide-angle recorders were designed to (1) image the crustal structure, particularly in the vicinity of crustal faults and Cenozoic sedimentary basins, (2) determine the geometry of the Moho, and (3) image the subducting Gorda and Juan de Fuca plates. Nearly 33,300 air gun shots were recorded along several seismic lines. In this report, we illustrate the expanding spread profiles acquired using the Thompson and Tully, describe the land and ocean-bottom recording of the air gun signals, discuss the processing of the land recorder data into common receiver gathers, and illustrate the processed wide-angle seismic data collected using the Refteks and ocean-bottom seismometers. We also describe the format and content of the archival tapes containing the SEGY-formated, common-receiver gathers for the Reftek data. Data quality is variable but SHIPS appears to have successfully obtained useful data from almost all the stations deployed to record the airgun shots. Several interesting arrivals were observed: including refractions from the sedimentary basin fill in several basins, refractions from basement rocks forming the upper crust, Pg, refractions from the upper mantle, Pn, as well as reflections from within the crust and from the top of the upper mantle, PmP. We separately archived more than 30 local earthquakes recorded by the Reftek array during our deployment.

Further Constraints and Uncertainties on the Deep Seismic Structure of the Moon

NASA Technical Reports Server (NTRS)

Lin, Pei-Ying Patty; Weber, Renee C.; Garnero, Ed J.; Schmerr, Nicholas C.

2011-01-01

The Apollo Passive Seismic Experiment (APSE) consisted of four 3-component seismometers deployed between 1969 and 1972, that continuously recorded lunar ground motion until late 1977. The APSE data provide a unique opportunity for investigating the interior of a planet other than Earth, generating the most direct constraints on the elastic structure, and hence the thermal and compositional evolution of the Moon. Owing to the lack of far side moonquakes, past seismic models of the lunar interior were unable to constrain the lowermost 500 km of the interior. Recently, array methodologies aimed at detecting deep lunar seismic reflections found evidence for a lunar core, providing an elastic model of the deepest lunar interior consistent with geodetic parameters. Here we study the uncertainties in these models associated with the double array stacking of deep moonquakes for imaging deep reflectors in the Moon. We investigate the dependency of the array stacking results on a suite of parameters, including amplitude normalization assumptions, polarization filters, assumed velocity structure, and seismic phases that interfere with our desired target phases. These efforts are facilitated by the generation of synthetic seismograms at high frequencies (approx. 1Hz), allowing us to directly study the trade-offs between different parameters. We also investigate expected amplitudes of deep reflections relative to direct P and S arrivals, including predictions from arbitrarily oriented focal mechanisms in our synthetics. Results from separate versus combined station stacking help to establish the robustness of stacks. Synthetics for every path geometry of data were processed identically to that done with data. Different experiments were aimed at examining various processing assumptions, such as adding random noise to synthetics and mixing 3 components to some degree. The principal stacked energy peaks put forth in recent work persist, but their amplitude (which maps into reflector impedance contrast) and timing (which maps into reflector depth) depend on factors that are not well constrained -- most notably, the velocity structure of the overlying lunar interior. Thus, while evidence for the lunar core remains strong, the depths of imaged reflectors have associated uncertainties that will require new seismic data and observations to constrain. These results strongly advocate further investigations on the Moon to better resolve the interior (e.g., Selene missions), for the Moon apparently has a rich history of construction and evolution that is inextricably tied to that of Earth.

A seismic search for the paleoshorelines of Lake Otero beneath White Sands Dune Field, New Mexico

NASA Astrophysics Data System (ADS)

Wagner, P. F.; Reece, R.; Ewing, R. C.

2014-12-01

The Tularosa Basin, which now houses White Sands Dune Field, was once occupied by Pleistocene Lake Otero. Several paleoshorelines of Lake Otero have been identified throughout the basin by field surveys and remote sensing using digital elevation models. Up to four shorelines may be buried beneath White Sands Dune Field and it has been posited that the current upwind margin of White Sands coincides with a one of these shorelines. Here we employ a novel geophysical instrument and method to image the subsurface: the seismic land streamer. The land streamer utilizes weighted base plates and one-component vertical geophones in a towed array. With a seisgun acoustic source, we imaged in the Alkali Flats area near the upwind margin, one potential location of paleoshorelines, as well as the Film Lot closer to the center of the dune field. Surfaces in both locations are indurated gypsum playa, which made seismic imaging possible and successful. We collected one SW-NE trending seismic line at each location, which matches the dominant wind and dune migration directions. Based on initial data analysis we find some subsurface structure that may coincide with the paleo lake bed of Lake Otero. The successful demonstration of this new method provides the foundation for an expanded regional subsurface study to image the strata and structure of the Tularosa Basin.

Seismicity and structure of Nazca Plate subduction zone in southern Peru

NASA Astrophysics Data System (ADS)

Lim, H.; Kim, Y.; Clayton, R. W.; Thurber, C. H.

2016-12-01

We define subducting plate geometries in the Nazca subduction zone by (re)locating intra-slab earthquakes in southern Peru (2-18°S) and taking previously published converted phase analysis results, to clarify the slab geometry and inferred relationships to the seismicity. We also provide both P- and S-wave velocities of the subducting Nazca Plate and mantle wedge portions close to the slab using double-difference tomography (Zhang and Thurber, 2003) to understand upper plate volcanism and subduction process. A total of 492 regional earthquakes from August 2008 to February 2013 recorded from the dense seismic array (PeruSE, 2013) are selected for the relocation and tomography. The relocated seismicity shows a smooth contortion in the slab-dip transition zone for 400 km between the shallow (25°)-to-flat dipping interface in the north and 40°-dipping interface in the south. We find a significant slab-dip difference (up to 10°) between our results and previously published slab models along the profile region sampling the normal-dip slab at depth (>100 km). Robust features in both P- and S-wave tomography inversions are dipping low-velocity slabs down to 100 km transitioning to higher-velocities at 100-140 km in both flat slab and dipping slab regions. Differences in the velocities of the mantle wedge between the two regions may indicate different hydration states in the wedge.

Infrasound Observation of the Apparent North Korean Nuclear Test of 25 May 2009

NASA Astrophysics Data System (ADS)

Jeon, J.; Che, I.; Kim, T.; Lee, H.

2009-12-01

On 25 May 2009, a seismic event (mb 4.6) was recorded from a source in northeastern North Korea, close to the location of a previous seismic event on 9 October 2006. Both events have been declared to be nuclear tests. Five seismo-acoustic arrays in South Korea recorded epicentral infrasonic signals for the more recent test following the strong seismic waves from the explosion. This study describes the characteristics of the nuclear test-generated infrasound signals observed at infrasound arrays located from 304 to 528 km from the source. The signals were characterized by stratospheric returns with amplitudes from 0.16 to 0.35 microbar and dominant frequencies between 1.0 and 4.3 Hz. Celerities determined for the arrivals suggest that most of the infrasonic energy travelled as a stratospheric phase. The inferred infrasonic location was offset about 15.7 km from the reference seismic location. On the basis of observed amplitudes of the stratospheric phases and corrections based on prevailing winds, the epicentral infrasonic energy was estimated to be equivalent to that expected from about 2.2 ton surface detonation of conventional explosives. We conclude that this small energy estimate is related to the partitioning of the contained explosive energy resulting from the interaction of strong ground motion at the surface with the atmosphere rather than the direct transfer of explosion energy to the air. This relatively small energy ratio between the infrasonic energy and the seismic energy could be used to distinguish the event from a common surface explosion.

Spatial extent of a hydrothermal system at Kilauea Volcano, Hawaii, determined from array analyses of shallow long-period seismicity 2. Results

USGS Publications Warehouse

Almendros, J.; Chouet, B.; Dawson, P.

2001-01-01

Array data from a seismic experiment carried out at Kilauea Volcano, Hawaii, in February 1997, are analyzed by the frequency-slowness method. The slowness vectors are determined at each of three small-aperture seismic antennas for the first arrivals of 1129 long-period (LP) events and 147 samples of volcanic tremor. The source locations are determined by using a probabilistic method which compares the event azimuths and slownesses with a slowness vector model. The results show that all the LP seismicity, including both discrete LP events and tremor, was generated in the same source region along the east flank of the Halemaumau pit crater, demonstrating the strong relation that exists between the two types of activities. The dimensions of the source region are approximately 0.6 X 1.0 X 0.5 km. For LP events we are able to resolve at least three different clusters of events. The most active cluster is centered ???200 m northeast of Halemaumau at depths shallower than 200 m beneath the caldera floor. A second cluster is located beneath the northeast quadrant of Halemaumau at a depth of ???400 m. The third cluster is <200 m deep and extends southeastward from the northeast quadrant of Halemaumau. Only one source zone is resolved for tremor. This zone is coincident with the most active source zone of LP events, northeast of Halemaumau. The location, depth, and size of the source region suggest a hydrothermal origin for all the analyzed LP seismicity. Copyright 2001 by the American Geophysical Union.

Imaging a Fault Boundary System Using Controlled-Source Data Recorded on a Large-N Seismic Array

NASA Astrophysics Data System (ADS)

Paschall, O. C.; Chen, T.; Snelson, C. M.; Ralston, M. D.; Rowe, C. A.

2016-12-01

The Source Physics Experiment (SPE) is a series of chemical explosions conducted in southern Nevada with an objective of improving nuclear explosion monitoring. Five chemical explosions have occurred thus far in granite, the most recent being SPE-5 on April 26, 2016. The SPE series will improve our understanding of seismic wave propagation (primarily S-waves) due to explosions, and allow better discrimination of background seismicity such as earthquakes and explosions. The Large-N portion of the project consists of 996 receiver stations. Half of the stations were vertical component and the other half were three-component geophones. All receivers were deployed for 30 days and recorded the SPE-5 shot, earthquakes, noise, and an additional controlled-source: a large weight-drop, which is a 13,000 kg modified industrial pile driver. In this study, we undertake reflection processing of waveforms from the weight-drop, as recorded by a line of sensors extracted from the Large-N array. The profile is 1.2 km in length with 25 m station spacing and 100 m shot point spacing. This profile crosses the Boundary Fault that separates granite body and an alluvium basin, a strong acoustic impedance boundary that scatters seismic energy into S-waves and coda. The data were processed with traditional seismic reflection processing methods that include filtering, deconvolution, and stacking. The stack will be used to extract the location of the splays of the Boundary Fault and provide geologic constraints to the modeling and simulation teams within the SPE project.

The Larderello-Travale geothermal field (Tuscany, central Italy): seismic imaging as a tool for the analysis and assessment of the reservoir

NASA Astrophysics Data System (ADS)

Anselmi, M.; Piccinini, D.; Casini, M.; Spinelli, E.; Ciuffi, S.; De Gori, P.; Saccorotti, G.; chiarabba, C.

2013-12-01

The Larderello-Travale is a geothermal field with steam-dominated reservoirs (1300 kg/s of steam and running capacity of 700 MWatt), which is exploited by Enel Green Power, the electric company involved in the renewable energy and resources. The area is located in the pre-Apennine belt of southern Tuscany and has been characterized by extensional tectonics and sporadic events of compression. The result of these tectonic phases is a block-faulting structure with NW-SE trending horsts and basins. Small post-orogenic granitic stocks were emplaced along the main axes of the uplifted structures, causing the anomalous heat flow that marks the area. Results from seismic reflection lines crossing the study area show the presence of the top of a discontinuous reflector in the 3-8 km depth range and with thickness up to ~1 km, referred to as the ';K-horizon'. In this framework we present the results obtained by the processing of a high-quality local earthquake dataset, recorded during the 1977-2005 time interval by the seismic network managed by Enel Green Power. The geothermal target volume was parameterized using a 3-D grid for both Vp (P-wave velocities) and Qp (quality factor of P-waves). Grid nodes are spaced by 5 and 2 km along the two horizontal and vertical directions, respectively. The tomographic Vp images show an overall velocity increase with depth down to the K-horizon. Conversely, some characteristic features are observed in the distribution of Qp anomalies, with high Qp values in the 300-600 range located just below the K-horizon. The relationship between K-horizon and the seismicity distribution doesn't show a clear and homogeneous coupling: the bulk of re-located earthquakes are placed either above or below the top of the K-horizon in the shallower 8 km depth, with an abrupt cut-off at depth greater than 10 km. We then present the preliminary result from the G.A.P.S.S. (Geothermal Area Passive Seismic Sources) experiment, a project that the Istituto Nazionale di Geofisica e Vulcanologia (I.N.G.V.) is conducting since May, 2012. The GAPSS experiment consists of a large aperture seismic array composed by 20 temporary and 2 permanent broad-band seismic stations. Besides the characterization of the seismic release of the geothermal field, our purpose is to investigate in depth the geothermal field applying cost-effective passive seismic techniques, such as local earthquake tomography, attenuation tomography, shear wave splitting analysis and surface-wave dispersion from noise correlation analysis.