Foreshocks and aftershocks locations of the 2014 Pisagua, N. Chile earthquake: history of a megathrust earthquake nucleation

NASA Astrophysics Data System (ADS)

Fuenzalida Velasco, Amaya; Rietbrock, Andreas; Tavera, Hernando; Ryder, Isabelle; Ruiz, Sergio; Thomas, Reece; De Angelis, Silvio; Bondoux, Francis

2015-04-01

The April 2014 Mw 8.1 Pisagua earthquake occurred in the Northern Chile seismic gap: a region of the South American subduction zone lying between Arica city and the Mejillones Peninsula. It is believed that this part of the subduction zone has not experienced a large earthquake since 1877. Thanks to the identification of this seismic gap, the north of Chile was well instrumented before the Pisagua earthquake, including the Integrated Plate boundary Observatory Chile (IPOC) network and the Chilean local network installed by the Centro Sismologico Nacional (CSN). These instruments were able to record the full foreshock and aftershock sequences, allowing a unique opportunity to study the nucleation process of large megathrust earthquakes. To improve azimuthal coverage of the Pisagua seismic sequence, after the earthquake, in collaboration with the Instituto Geofisico del Peru (IGP) we installed a temporary seismic network in south of Peru. The network comprised 12 short-period stations located in the coastal area between Moquegua and Tacna and they were operative from 1st May 2014. We also installed three stations on the slopes of the Ticsiani volcano to monitor any possible change in volcanic activity following the Pisagua earthquake. In this work we analysed the continuous seismic data recorded by CSN and IPOC networks from 1 March to 30 June to obtain the catalogue of the sequence, including foreshocks and aftershocks. Using an automatic algorithm based in STA/LTA we obtained the picks for P and S waves. Association in time and space defined the events and computed an initial location using Hypo71 and the 1D local velocity model. More than 11,000 events were identified with this method for the whole period, but we selected the best resolved events that include more than 7 observed arrivals with at least 2 S picks of them, to relocate these events using NonLinLoc software. For the main events of the sequence we carefully estimate event locations and we obtained

Controls of repeating earthquakes' location from a- and b- values imaging

NASA Astrophysics Data System (ADS)

Chen, K. H.; Kawamura, M.

2017-12-01

The locations where creeping and locked fault areas abut have commonly found to be delineated by the foci of small repeating earthquakes (REs). REs not only represent the finer structure of high creep-rate location, they also function as fault slip-rate indicators. Knowledge of the expected location of REs therefore, is crucial for fault deformation monitoring and assessment of earthquake potential. However, a precise description of factors determining REs locations is lacking. To explore where earthquakes tend to recur, we statistically investigated repeating earthquake catalogs and background seismicity from different regions including six fault segments in California and Taiwan. We show that the location of repeating earthquakes can be mapped using the spatial distribution of the seismic a- and b-values obtained from the background seismicity. Molchan's error diagram statistically confirmed that repeating earthquakes occur within areas with high a-values (2.8-3.8) and high b-values (0.9-1.1) on both strike-slip and thrust fault segments. However, no significant association held true for fault segments with more complicated geometry or for wider areas with a complex fault network. The productivity of small earthquakes responsible for high a- and b-values may thus be the most important factor controlling the location of repeating earthquakes. We hypothesize that, given that the deformation conditions within a fault zone are suitable for a planar fault plane, the location of repeating earthquakes can be best described by a-value 3 and b-value 1. This feature of a- and b-values may be useful for foresee the location of REs for measuring creep rate at depth. Further investigation of REs-rich areas may allow testing of this hypothesis.

Development a heuristic method to locate and allocate the medical centers to minimize the earthquake relief operation time.

PubMed

Aghamohammadi, Hossein; Saadi Mesgari, Mohammad; Molaei, Damoon; Aghamohammadi, Hasan

2013-01-01

Location-allocation is a combinatorial optimization problem, and is defined as Non deterministic Polynomial Hard (NP) hard optimization. Therefore, solution of such a problem should be shifted from exact to heuristic or Meta heuristic due to the complexity of the problem. Locating medical centers and allocating injuries of an earthquake to them has high importance in earthquake disaster management so that developing a proper method will reduce the time of relief operation and will consequently decrease the number of fatalities. This paper presents the development of a heuristic method based on two nested genetic algorithms to optimize this location allocation problem by using the abilities of Geographic Information System (GIS). In the proposed method, outer genetic algorithm is applied to the location part of the problem and inner genetic algorithm is used to optimize the resource allocation. The final outcome of implemented method includes the spatial location of new required medical centers. The method also calculates that how many of the injuries at each demanding point should be taken to any of the existing and new medical centers as well. The results of proposed method showed high performance of designed structure to solve a capacitated location-allocation problem that may arise in a disaster situation when injured people has to be taken to medical centers in a reasonable time.

Comparing methods for Earthquake Location

NASA Astrophysics Data System (ADS)

Turkaya, Semih; Bodin, Thomas; Sylvander, Matthieu; Parroucau, Pierre; Manchuel, Kevin

2017-04-01

There are plenty of methods available for locating small magnitude point source earthquakes. However, it is known that these different approaches produce different results. For each approach, results also depend on a number of parameters which can be separated into two main branches: (1) parameters related to observations (number and distribution of for example) and (2) parameters related to the inversion process (velocity model, weighting parameters, initial location etc.). Currently, the results obtained from most of the location methods do not systematically include quantitative uncertainties. The effect of the selected parameters on location uncertainties is also poorly known. Understanding the importance of these different parameters and their effect on uncertainties is clearly required to better constrained knowledge on fault geometry, seismotectonic processes and at the end to improve seismic hazard assessment. In this work, realized in the frame of the SINAPS@ research program (http://www.institut-seism.fr/projets/sinaps/), we analyse the effect of different parameters on earthquakes location (e.g. type of phase, max. hypocentral separation etc.). We compare several codes available (Hypo71, HypoDD, NonLinLoc etc.) and determine their strengths and weaknesses in different cases by means of synthetic tests. The work, performed for the moment on synthetic data, is planned to be applied, in a second step, on data collected by the Midi-Pyrénées Observatory (OMP).

Probablilistic evaluation of earthquake detection and location capability for Illinois, Indiana, Kentucky, Ohio, and West Virginia

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

Mauk, F.J.; Christensen, D.H.

1980-09-01

Probabilistic estimations of earthquake detection and location capabilities for the states of Illinois, Indiana, Kentucky, Ohio and West Virginia are presented in this document. The algorithm used in these epicentrality and minimum-magnitude estimations is a version of the program NETWORTH by Wirth, Blandford, and Husted (DARPA Order No. 2551, 1978) which was modified for local array evaluation at the University of Michigan Seismological Observatory. Estimations of earthquake detection capability for the years 1970 and 1980 are presented in four regional minimum m/sub b/ magnitude contour maps. Regional 90% confidence error ellipsoids are included for m/sub b/ magnitude events from 2.0more » through 5.0 at 0.5 m/sub b/ unit increments. The close agreement between these predicted epicentral 90% confidence estimates and the calculated error ellipses associated with actual earthquakes within the studied region suggest that these error determinations can be used to estimate the reliability of epicenter location. 8 refs., 14 figs., 2 tabs.« less

Novel Algorithms Enabling Rapid, Real-Time Earthquake Monitoring and Tsunami Early Warning Worldwide

NASA Astrophysics Data System (ADS)

Lomax, A.; Michelini, A.

2012-12-01

We have introduced recently new methods to determine rapidly the tsunami potential and magnitude of large earthquakes (e.g., Lomax and Michelini, 2009ab, 2011, 2012). To validate these methods we have implemented them along with other new algorithms within the Early-est earthquake monitor at INGV-Rome (http://early-est.rm.ingv.it, http://early-est.alomax.net). Early-est is a lightweight software package for real-time earthquake monitoring (including phase picking, phase association and event detection, location, magnitude determination, first-motion mechanism determination, ...), and for tsunami early warning based on discriminants for earthquake tsunami potential. In a simulation using archived broadband seismograms for the devastating M9, 2011 Tohoku earthquake and tsunami, Early-est determines: the epicenter within 3 min after the event origin time, discriminants showing very high tsunami potential within 5-7 min, and magnitude Mwpd(RT) 9.0-9.2 and a correct shallow-thrusting mechanism within 8 min. Real-time monitoring with Early-est givess similar results for most large earthquakes using currently available, real-time seismogram data. Here we summarize some of the key algorithms within Early-est that enable rapid, real-time earthquake monitoring and tsunami early warning worldwide: >>> FilterPicker - a general purpose, broad-band, phase detector and picker (http://alomax.net/FilterPicker); >>> Robust, simultaneous association and location using a probabilistic, global-search; >>> Period-duration discriminants TdT0 and TdT50Ex for tsunami potential available within 5 min; >>> Mwpd(RT) magnitude for very large earthquakes available within 10 min; >>> Waveform P polarities determined on broad-band displacement traces, focal mechanisms obtained with the HASH program (Hardebeck and Shearer, 2002); >>> SeisGramWeb - a portable-device ready seismogram viewer using web-services in a browser (http://alomax.net/webtools/sgweb/info.html). References (see also: http

Precisely locating the Klamath Falls, Oregon, earthquakes

USGS Publications Warehouse

Qamar, A.; Meagher, K.L.

1993-01-01

In this article we present preliminary results of a close-in, instrumental study of the Klamath Falls earthquake sequence, carried as a cooperative effort by scientists from the U.S Geological Survey (USGS) and universities in Washington, Orgeon, and California. In addition to obtaining much mroe accurate earthquake locations, this study has improved our understanding of the relationship between seismicity and mapped faults in the region. 

Development of double-pair double difference location algorithm and its application to the regular earthquakes and non-volcanic tremors

NASA Astrophysics Data System (ADS)

Guo, H.; Zhang, H.

2016-12-01

Relocating high-precision earthquakes is a central task for monitoring earthquakes and studying the structure of earth's interior. The most popular location method is the event-pair double-difference (DD) relative location method, which uses the catalog and/or more accurate waveform cross-correlation (WCC) differential times from event pairs with small inter-event separations to the common stations to reduce the effect of the velocity uncertainties outside the source region. Similarly, Zhang et al. [2010] developed a station-pair DD location method which uses the differential times from common events to pairs of stations to reduce the effect of the velocity uncertainties near the source region, to relocate the non-volcanic tremors (NVT) beneath the San Andreas Fault (SAF). To utilize advantages of both DD location methods, we have proposed and developed a new double-pair DD location method to use the differential times from pairs of events to pairs of stations. The new method can remove the event origin time and station correction terms from the inversion system and cancel out the effects of the velocity uncertainties near and outside the source region simultaneously. We tested and applied the new method on the northern California regular earthquakes to validate its performance. In comparison, among three DD location methods, the new double-pair DD method can determine more accurate relative locations and the station-pair DD method can better improve the absolute locations. Thus, we further proposed a new location strategy combining station-pair and double-pair differential times to determine accurate absolute and relative locations at the same time. For NVTs, it is difficult to pick the first arrivals and derive the WCC event-pair differential times, thus the general practice is to measure station-pair envelope WCC differential times. However, station-pair tremor locations are scattered due to the low-precision relative locations. The ability that double-pair data

An Envelope Based Feedback Control System for Earthquake Early Warning: Reality Check Algorithm

NASA Astrophysics Data System (ADS)

Heaton, T. H.; Karakus, G.; Beck, J. L.

2016-12-01

Earthquake early warning systems are, in general, designed to be open loop control systems in such a way that the output, i.e., the warning messages, only depend on the input, i.e., recorded ground motions, up to the moment when the message is issued in real-time. We propose an algorithm, which is called Reality Check Algorithm (RCA), which would assess the accuracy of issued warning messages, and then feed the outcome of the assessment back into the system. Then, the system would modify its messages if necessary. That is, we are proposing to convert earthquake early warning systems into feedback control systems by integrating them with RCA. RCA works by continuously monitoring and comparing the observed ground motions' envelopes to the predicted envelopes of Virtual Seismologist (Cua 2005). Accuracy of magnitude and location (both spatial and temporal) estimations of the system are assessed separately by probabilistic classification models, which are trained by a Sparse Bayesian Learning technique called Automatic Relevance Determination prior.

ISC-GEM: Global Instrumental Earthquake Catalogue (1900-2009), II. Location and seismicity patterns

NASA Astrophysics Data System (ADS)

Bondár, I.; Engdahl, E. Robert; Villaseñor, A.; Harris, James; Storchak, D.

2015-02-01

We present the final results of a two-year project sponsored by the Global Earthquake Model (GEM) Foundation. The ISC-GEM global catalogue consists of some 19 thousand instrumentally recorded, moderate to large earthquakes, spanning 110 years of seismicity. We relocated all events in the catalogue using a two-tier approach. The EHB location methodology (Engdahl et al., 1998) was applied first to obtain improved hypocentres with special focus on the depth determination. The locations were further refined in the next step by fixing the depths to those from the EHB analysis and applying the new International Seismological Centre (ISC) location algorithm (Bondár and Storchak, 2011) that reduces location bias by accounting for correlated travel-time prediction error structure. To facilitate the relocation effort, some one million seismic P and S wave arrival-time data were added to the ISC database for the period between 1904 and 1970, either from original station bulletins in the ISC archive or by digitizing the scanned images of the International Seismological Summary (ISS) bulletin (Villaseñor and Engdahl, 2005, 2007). Although no substantial amount of new phase data were acquired for the modern period (1964-2009), the number of phases used in the location has still increased by three millions, owing to fact that both the EHB and ISC locators use most well-recorded ak135 (Kennett et al., 1995) phases in the location. We show that the relocation effort yielded substantially improved locations, especially in the first half of the 20th century; we demonstrate significant improvements in focal depth estimates in subduction zones and other seismically active regions; and we show that the ISC-GEM catalogue provides an improved view of 110 years of global seismicity of the Earth. The ISC-GEM Global Instrumental Earthquake Catalogue represents the final product of one of the ten global components in the GEM program, and is available to researchers at the ISC (http://www.isc.ac.uk).

Revision of earthquake hypocenter locations in GEOFON bulletin data using global source-specific station terms technique

NASA Astrophysics Data System (ADS)

Nooshiri, N.; Saul, J.; Heimann, S.; Tilmann, F. J.; Dahm, T.

2015-12-01

The use of a 1D velocity model for seismic event location is often associated with significant travel-time residuals. Particularly for regional stations in subduction zones, where the velocity structure strongly deviates from the assumed 1D model, residuals of up to ±10 seconds are observed even for clear arrivals, which leads to strongly biased locations. In fact, due to mostly regional travel-time anomalies, arrival times at regional stations do not match the location obtained with teleseismic picks, and vice versa. If the earthquake is weak and only recorded regionally, or if fast locations based on regional stations are needed, the location may be far off the corresponding teleseismic location. In this case, implementation of travel-time corrections may leads to a reduction of the travel-time residuals at regional stations and, in consequence, significantly improve the relative location accuracy. Here, we have extended the source-specific station terms (SSST) technique to regional and teleseismic distances and adopted the algorithm for probabilistic, non-linear, global-search earthquake location. The method has been applied to specific test regions using P and pP phases from the GEOFON bulletin data for all available station networks. By using this method, a set of timing corrections has been calculated for each station varying as a function of source position. In this way, an attempt is made to correct for the systematic errors, introduced by limitations and inaccuracies in the assumed velocity structure, without solving for a new earth model itself. In this presentation, we draw on examples of the application of this global SSST technique to relocate earthquakes from the Tonga-Fiji subduction zone and from the Chilean margin. Our results have been showing a considerable decrease of the root-mean-square (RMS) residual in earthquake location final catalogs, a major reduction of the median absolute deviation (MAD) of the travel

Magnitude and location of historical earthquakes in Japan and implications for the 1855 Ansei Edo earthquake

USGS Publications Warehouse

Bakun, W.H.

2005-01-01

Japan Meteorological Agency (JMA) intensity assignments IJMA are used to derive intensity attenuation models suitable for estimating the location and an intensity magnitude Mjma for historical earthquakes in Japan. The intensity for shallow crustal earthquakes on Honshu is equal to -1.89 + 1.42MJMA - 0.00887?? h - 1.66log??h, where MJMA is the JMA magnitude, ??h = (??2 + h2)1/2, and ?? and h are epicentral distance and focal depth (km), respectively. Four earthquakes located near the Japan Trench were used to develop a subducting plate intensity attenuation model where intensity is equal to -8.33 + 2.19MJMA -0.00550??h - 1.14 log ?? h. The IJMA assignments for the MJMA7.9 great 1923 Kanto earthquake on the Philippine Sea-Eurasian plate interface are consistent with the subducting plate model; Using the subducting plate model and 226 IJMA IV-VI assignments, the location of the intensity center is 25 km north of the epicenter, Mjma is 7.7, and MJMA is 7.3-8.0 at the 1?? confidence level. Intensity assignments and reported aftershock activity for the enigmatic 11 November 1855 Ansei Edo earthquake are consistent with an MJMA 7.2 Philippine Sea-Eurasian interplate source or Philippine Sea intraslab source at about 30 km depth. If the 1855 earthquake was a Philippine Sea-Eurasian interplate event, the intensity center was adjacent to and downdip of the rupture area of the great 1923 Kanto earthquake, suggesting that the 1855 and 1923 events ruptured adjoining sections of the Philippine Sea-Eurasian plate interface.

Improving automatic earthquake locations in subduction zones: a case study for GEOFON catalog of Tonga-Fiji region

NASA Astrophysics Data System (ADS)

Nooshiri, Nima; Heimann, Sebastian; Saul, Joachim; Tilmann, Frederik; Dahm, Torsten

2015-04-01

Automatic earthquake locations are sometimes associated with very large residuals up to 10 s even for clear arrivals, especially for regional stations in subduction zones because of their strongly heterogeneous velocity structure associated. Although these residuals are most likely not related to measurement errors but unmodelled velocity heterogeneity, these stations are usually removed from or down-weighted in the location procedure. While this is possible for large events, it may not be useful if the earthquake is weak. In this case, implementation of travel-time station corrections may significantly improve the automatic locations. Here, the shrinking box source-specific station term method (SSST) [Lin and Shearer, 2005] has been applied to improve relative location accuracy of 1678 events that occurred in the Tonga subduction zone between 2010 and mid-2014. Picks were obtained from the GEOFON earthquake bulletin for all available station networks. We calculated a set of timing corrections for each station which vary as a function of source position. A separate time correction was computed for each source-receiver path at the given station by smoothing the residual field over nearby events. We begin with a very large smoothing radius essentially encompassing the whole event set and iterate by progressively shrinking the smoothing radius. In this way, we attempted to correct for the systematic errors, that are introduced into the locations by the inaccuracies in the assumed velocity structure, without solving for a new velocity model itself. One of the advantages of the SSST technique is that the event location part of the calculation is separate from the station term calculation and can be performed using any single event location method. In this study, we applied a non-linear, probabilistic, global-search earthquake location method using the software package NonLinLoc [Lomax et al., 2000]. The non-linear location algorithm implemented in NonLinLoc is less

Automatic Earthquake Detection and Location by Waveform coherency in Alentejo (South Portugal) Using CatchPy

NASA Astrophysics Data System (ADS)

Custodio, S.; Matos, C.; Grigoli, F.; Cesca, S.; Heimann, S.; Rio, I.

2015-12-01

Seismic data processing is currently undergoing a step change, benefitting from high-volume datasets and advanced computer power. In the last decade, a permanent seismic network of 30 broadband stations, complemented by dense temporary deployments, covered mainland Portugal. This outstanding regional coverage currently enables the computation of a high-resolution image of the seismicity of Portugal, which contributes to fitting together the pieces of the regional seismo-tectonic puzzle. Although traditional manual inspections are valuable to refine automatic results they are impracticable with the big data volumes now available. When conducted alone they are also less objective since the criteria is defined by the analyst. In this work we present CatchPy, a scanning algorithm to detect earthquakes in continuous datasets. Our main goal is to implement an automatic earthquake detection and location routine in order to have a tool to quickly process large data sets, while at the same time detecting low magnitude earthquakes (i.e. lowering the detection threshold). CatchPY is designed to produce an event database that could be easily located using existing location codes (e.g.: Grigoli et al. 2013, 2014). We use CatchPy to perform automatic detection and location of earthquakes that occurred in Alentejo region (South Portugal), taking advantage of a dense seismic network deployed in the region for two years during the DOCTAR experiment. Results show that our automatic procedure is particularly suitable for small aperture networks. The event detection is performed by continuously computing the short-term-average/long-term-average of two different characteristic functions (CFs). For the P phases we used a CF based on the vertical energy trace while for S phases we used a CF based on the maximum eigenvalue of the instantaneous covariance matrix (Vidale 1991). Seismic event location is performed by waveform coherence analysis, scanning different hypocentral coordinates

An automatic procedure for high-resolution earthquake locations: a case study from the TABOO near fault observatory (Northern Apennines, Italy)

NASA Astrophysics Data System (ADS)

Valoroso, Luisa; Chiaraluce, Lauro; Di Stefano, Raffaele; Latorre, Diana; Piccinini, Davide

2014-05-01

The characterization of the geometry, kinematics and rheology of fault zones by seismological data depends on our capability of accurately locate the largest number of low-magnitude seismic events. To this aim, we have been working for the past three years to develop an advanced modular earthquake location procedure able to automatically retrieve high-resolution earthquakes catalogues directly from continuous waveforms data. We use seismograms recorded at about 60 seismic stations located both at surface and at depth. The network covers an area of about 80x60 km with a mean inter-station distance of 6 km. These stations are part of a Near fault Observatory (TABOO; http://taboo.rm.ingv.it/), consisting of multi-sensor stations (seismic, geodetic, geochemical and electromagnetic). This permanent scientific infrastructure managed by the INGV is devoted to studying the earthquakes preparatory phase and the fast/slow (i.e., seismic/aseismic) deformation process active along the Alto Tiberina fault (ATF) located in the northern Apennines (Italy). The ATF is potentially one of the rare worldwide examples of active low-angle (< 15°) normal fault accommodating crustal extension and characterized by a regular occurrence of micro-earthquakes. The modular procedure combines: i) a sensitive detection algorithm optimized to declare low-magnitude events; ii) an accurate picking procedure that provides consistently weighted P- and S-wave arrival times, P-wave first motion polarities and the maximum waveform amplitude for local magnitude calculation; iii) both linearized iterative and non-linear global-search earthquake location algorithms to compute accurate absolute locations of single-events in a 3D geological model (see Latorre et al. same session); iv) cross-correlation and double-difference location methods to compute high-resolution relative event locations. This procedure is now running off-line with a delay of 1 week to the real-time. We are now implementing this

Locating Local Earthquakes Using Single 3-Component Broadband Seismological Data

NASA Astrophysics Data System (ADS)

Das, S. B.; Mitra, S.

2015-12-01

We devised a technique to locate local earthquakes using single 3-component broadband seismograph and analyze the factors governing the accuracy of our result. The need for devising such a technique arises in regions of sparse seismic network. In state-of-the-art location algorithms, a minimum of three station recordings are required for obtaining well resolved locations. However, the problem arises when an event is recorded by less than three stations. This may be because of the following reasons: (a) down time of stations in a sparse network; (b) geographically isolated regions with limited logistic support to setup large network; (c) regions of insufficient economy for financing multi-station network and (d) poor signal-to-noise ratio for smaller events at most stations, except the one in its closest vicinity. Our technique provides a workable solution to the above problematic scenarios. However, our methodology is strongly dependent on the velocity model of the region. Our method uses a three step processing: (a) ascertain the back-azimuth of the event from the P-wave particle motion recorded on the horizontal components; (b) estimate the hypocentral distance using the S-P time; and (c) ascertain the emergent angle from the vertical and radial components. Once this is obtained, one can ray-trace through the 1-D velocity model to estimate the hypocentral location. We test our method on synthetic data, which produces results with 99% precision. With observed data, the accuracy of our results are very encouraging. The precision of our results depend on the signal-to-noise ratio (SNR) and choice of the right band-pass filter to isolate the P-wave signal. We used our method on minor aftershocks (3 < mb < 4) of the 2011 Sikkim earthquake using data from the Sikkim Himalayan network. Location of these events highlight the transverse strike-slip structure within the Indian plate, which was observed from source mechanism study of the mainshock and larger aftershocks.

The Mw=8.8 Maule earthquake aftershock sequence, event catalog and locations

NASA Astrophysics Data System (ADS)

Meltzer, A.; Benz, H.; Brown, L.; Russo, R. M.; Beck, S. L.; Roecker, S. W.

2011-12-01

The aftershock sequence of the Mw=8.8 Maule earthquake off the coast of Chile in February 2010 is one of the most well-recorded aftershock sequences from a great megathrust earthquake. Immediately following the Maule earthquake, teams of geophysicists from Chile, France, Germany, Great Britain and the United States coordinated resources to capture aftershocks and other seismic signals associated with this significant earthquake. In total, 91 broadband, 48 short period, and 25 accelerometers stations were deployed above the rupture zone of the main shock from 33-38.5°S and from the coast to the Andean range front. In order to integrate these data into a unified catalog, the USGS National Earthquake Information Center develop procedures to use their real-time seismic monitoring system (Bulletin Hydra) to detect, associate, location and compute earthquake source parameters from these stations. As a first step in the process, the USGS has built a seismic catalog of all M3.5 or larger earthquakes for the time period of the main aftershock deployment from March 2010-October 2010. The catalog includes earthquake locations, magnitudes (Ml, Mb, Mb_BB, Ms, Ms_BB, Ms_VX, Mc), associated phase readings and regional moment tensor solutions for most of the M4 or larger events. Also included in the catalog are teleseismic phases and amplitude measures and body-wave MT and CMT solutions for the larger events, typically M5.5 and larger. Tuning of automated detection and association parameters should allow a complete catalog of events to approximately M2.5 or larger for that dataset of more than 164 stations. We characterize the aftershock sequence in terms of magnitude, frequency, and location over time. Using the catalog locations and travel times as a starting point we use double difference techniques to investigate relative locations and earthquake clustering. In addition, phase data from candidate ground truth events and modeling of surface waves can be used to calibrate the

Earthquake location in transversely isotropic media with a tilted symmetry axis

NASA Astrophysics Data System (ADS)

Zhao, Aihua; Ding, Zhifeng

2009-04-01

The conventional intersection method for earthquake location in isotropic media is developed in the case of transversely isotropic media with a tilted symmetry axis (TTI media). The hypocenter is determined using its loci, which are calculated through a minimum travel time tree algorithm for ray tracing in TTI media. There are no restrictions on the structural complexity of the model or on the anisotropy strength of the medium. The location method is validated by its application to determine the hypocenter and origin time of an event in a complex TTI structure, in accordance with four hypotheses or study cases: (a) accurate model and arrival times, (b) perturbed model with randomly variable elastic parameter, (c) noisy arrival time data, and (d) incomplete set of observations from the seismic stations. Furthermore, several numerical tests demonstrate that the orientation of the symmetry axis has a significant effect on the hypocenter location when the seismic anisotropy is not very weak. Moreover, if the hypocentral determination is based on an isotropic reference model while the real medium is anisotropic, the resultant location errors can be considerable even though the anisotropy strength does not exceed 6.10%.

Intensity, magnitude, location and attenuation in India for felt earthquakes since 1762

USGS Publications Warehouse

Szeliga, Walter; Hough, Susan; Martin, Stacey; Bilham, Roger

2010-01-01

A comprehensive, consistently interpreted new catalog of felt intensities for India (Martin and Szeliga, 2010, this issue) includes intensities for 570 earthquakes; instrumental magnitudes and locations are available for 100 of these events. We use the intensity values for 29 of the instrumentally recorded events to develop new intensity versus attenuation relations for the Indian subcontinent and the Himalayan region. We then use these relations to determine the locations and magnitudes of 234 historical events, using the method of Bakun and Wentworth (1997). For the remaining 336 events, intensity distributions are too sparse to determine magnitude or location. We evaluate magnitude and location accuracy of newly located events by comparing the instrumental- with the intensity-derived location for 29 calibration events, for which more than 15 intensity observations are available. With few exceptions, most intensity-derived locations lie within a fault length of the instrumentally determined location. For events in which the azimuthal distribution of intensities is limited, we conclude that the formal error bounds from the regression of Bakun and Wentworth (1997) do not reflect the true uncertainties. We also find that the regression underestimates the uncertainties of the location and magnitude of the 1819 Allah Bund earthquake, for which a location has been inferred from mapped surface deformation. Comparing our inferred attenuation relations to those developed for other regions, we find that attenuation for Himalayan events is comparable to intensity attenuation in California (Bakun and Wentworth, 1997), while intensity attenuation for cratonic events is higher than intensity attenuation reported for central/eastern North America (Bakun et al., 2003). Further, we present evidence that intensities of intraplate earthquakes have a nonlinear dependence on magnitude such that attenuation relations based largely on small-to-moderate earthquakes may significantly

Intensity, magnitude, location, and attenuation in India for felt earthquakes since 1762

USGS Publications Warehouse

Szeliga, W.; Hough, S.; Martin, S.; Bilham, R.

2010-01-01

A comprehensive, consistently interpreted new catalog of felt intensities for India (Martin and Szeliga, 2010, this issue) includes intensities for 570 earth-quakes; instrumental magnitudes and locations are available for 100 of these events. We use the intensity values for 29 of the instrumentally recorded events to develop new intensity versus attenuation relations for the Indian subcontinent and the Himalayan region. We then use these relations to determine the locations and magnitudes of 234 historical events, using the method of Bakun and Wentworth (1997). For the remaining 336 events, intensity distributions are too sparse to determine magnitude or location. We evaluate magnitude and location accuracy of newly located events by comparing the instrumental-with the intensity-derived location for 29 calibration events, for which more than 15 intensity observations are available. With few exceptions, most intensity-derived locations lie within a fault length of the instrumentally determined location. For events in which the azimuthal distribution of intensities is limited, we conclude that the formal error bounds from the regression of Bakun and Wentworth (1997) do not reflect the true uncertainties. We also find that the regression underestimates the uncertainties of the location and magnitude of the 1819 Allah Bund earthquake, for which a location has been inferred from mapped surface deformation. Comparing our inferred attenuation relations to those developed for other regions, we find that attenuation for Himalayan events is comparable to intensity attenuation in California (Bakun and Wentworth, 1997), while intensity attenuation for cratonic events is higher than intensity attenuation reported for central/eastern North America (Bakun et al., 2003). Further, we present evidence that intensities of intraplate earth-quakes have a nonlinear dependence on magnitude such that attenuation relations based largely on small-to-moderate earthquakes may significantly

Epistemic uncertainty in the location and magnitude of earthquakes in Italy from Macroseismic data

USGS Publications Warehouse

Bakun, W.H.; Gomez, Capera A.; Stucchi, M.

2011-01-01

Three independent techniques (Bakun and Wentworth, 1997; Boxer from Gasperini et al., 1999; and Macroseismic Estimation of Earthquake Parameters [MEEP; see Data and Resources section, deliverable D3] from R.M.W. Musson and M.J. Jimenez) have been proposed for estimating an earthquake location and magnitude from intensity data alone. The locations and magnitudes obtained for a given set of intensity data are almost always different, and no one technique is consistently best at matching instrumental locations and magnitudes of recent well-recorded earthquakes in Italy. Rather than attempting to select one of the three solutions as best, we use all three techniques to estimate the location and the magnitude and the epistemic uncertainties among them. The estimates are calculated using bootstrap resampled data sets with Monte Carlo sampling of a decision tree. The decision-tree branch weights are based on goodness-of-fit measures of location and magnitude for recent earthquakes. The location estimates are based on the spatial distribution of locations calculated from the bootstrap resampled data. The preferred source location is the locus of the maximum bootstrap location spatial density. The location uncertainty is obtained from contours of the bootstrap spatial density: 68% of the bootstrap locations are within the 68% confidence region, and so on. For large earthquakes, our preferred location is not associated with the epicenter but with a location on the extended rupture surface. For small earthquakes, the epicenters are generally consistent with the location uncertainties inferred from the intensity data if an epicenter inaccuracy of 2-3 km is allowed. The preferred magnitude is the median of the distribution of bootstrap magnitudes. As with location uncertainties, the uncertainties in magnitude are obtained from the distribution of bootstrap magnitudes: the bounds of the 68% uncertainty range enclose 68% of the bootstrap magnitudes, and so on. The instrumental

A Kinesthetic Demonstration for Locating Earthquake Epicenters

NASA Astrophysics Data System (ADS)

Keyantash, J.; Sperber, S.

2005-12-01

During Spring 2005, an inquiry-based curriculum for plate tectonics was developed for implementation in sixth-grade classrooms within the Los Angeles Unified School District (LAUSD). Two cohorts of LAUSD teachers received training and orientation to the plate tectonics unit during one week workshops in July 2005. However, during the training workshops, it was observed that there was considerable confusion among the teachers as to how the traditional "textbook" explanation of the time lag between P and S waves on a seismogram could possibly be used to determine the epicenter of an earthquake. One of the State of California science content standards for sixth grade students is that they understand how the epicenters of earthquakes are determined, so it was critical that the teachers themselves grasped the concept. In response to the adult learner difficulties, the classroom explanation of earthquake epicenter location was supplemented with an outdoor kinesthetic activity. Based upon the experience of the kinesthetic model, it was found that the hands-on model greatly cemented the teachers' understanding of the underlying theory. This paper details the steps of the kinesthetic demonstration for earthquake epicenter identification, as well as offering extended options for its classroom implementation.

Revision of earthquake hypocentre locations in global bulletin data sets using source-specific station terms

NASA Astrophysics Data System (ADS)

Nooshiri, Nima; Saul, Joachim; Heimann, Sebastian; Tilmann, Frederik; Dahm, Torsten

2017-02-01

Global earthquake locations are often associated with very large systematic travel-time residuals even for clear arrivals, especially for regional and near-regional stations in subduction zones because of their strongly heterogeneous velocity structure. Travel-time corrections can drastically reduce travel-time residuals at regional stations and, in consequence, improve the relative location accuracy. We have extended the shrinking-box source-specific station terms technique to regional and teleseismic distances and adopted the algorithm for probabilistic, nonlinear, global-search location. We evaluated the potential of the method to compute precise relative hypocentre locations on a global scale. The method has been applied to two specific test regions using existing P- and pP-phase picks. The first data set consists of 3103 events along the Chilean margin and the second one comprises 1680 earthquakes in the Tonga-Fiji subduction zone. Pick data were obtained from the GEOFON earthquake bulletin, produced using data from all available, global station networks. A set of timing corrections varying as a function of source position was calculated for each seismic station. In this way, we could correct the systematic errors introduced into the locations by the inaccuracies in the assumed velocity structure without explicitly solving for a velocity model. Residual statistics show that the median absolute deviation of the travel-time residuals is reduced by 40-60 per cent at regional distances, where the velocity anomalies are strong. Moreover, the spread of the travel-time residuals decreased by ˜20 per cent at teleseismic distances (>28°). Furthermore, strong variations in initial residuals as a function of recording distance are smoothed out in the final residuals. The relocated catalogues exhibit less scattered locations in depth and sharper images of the seismicity associated with the subducting slabs. Comparison with a high-resolution local catalogue reveals that

Locations and magnitudes of historical earthquakes in the Sierra of Ecuador (1587-1996)

NASA Astrophysics Data System (ADS)

Beauval, Céline; Yepes, Hugo; Bakun, William H.; Egred, José; Alvarado, Alexandra; Singaucho, Juan-Carlos

2010-06-01

The whole territory of Ecuador is exposed to seismic hazard. Great earthquakes can occur in the subduction zone (e.g. Esmeraldas, 1906, Mw 8.8), whereas lower magnitude but shallower and potentially more destructive earthquakes can occur in the highlands. This study focuses on the historical crustal earthquakes of the Andean Cordillera. Several large cities are located in the Interandean Valley, among them Quito, the capital (~2.5 millions inhabitants). A total population of ~6 millions inhabitants currently live in the highlands, raising the seismic risk. At present, precise instrumental data for the Ecuadorian territory is not available for periods earlier than 1990 (beginning date of the revised instrumental Ecuadorian seismic catalogue); therefore historical data are of utmost importance for assessing seismic hazard. In this study, the Bakun & Wentworth method is applied in order to determine magnitudes, locations, and associated uncertainties for historical earthquakes of the Sierra over the period 1587-1976. An intensity-magnitude equation is derived from the four most reliable instrumental earthquakes (Mw between 5.3 and 7.1). Intensity data available per historical earthquake vary between 10 (Quito, 1587, Intensity >=VI) and 117 (Riobamba, 1797, Intensity >=III). The bootstrap resampling technique is coupled to the B&W method for deriving geographical confidence contours for the intensity centre depending on the data set of each earthquake, as well as confidence intervals for the magnitude. The extension of the area delineating the intensity centre location at the 67 per cent confidence level (+/-1σ) depends on the amount of intensity data, on their internal coherence, on the number of intensity degrees available, and on their spatial distribution. Special attention is dedicated to the few earthquakes described by intensities reaching IX, X and XI degrees. Twenty-five events are studied, and nineteen new epicentral locations are obtained, yielding

Improvements to Earthquake Location with a Fuzzy Logic Approach

NASA Astrophysics Data System (ADS)

Gökalp, Hüseyin

2018-01-01

In this study, improvements to the earthquake location method were investigated using a fuzzy logic approach proposed by Lin and Sanford (Bull Seismol Soc Am 91:82-93, 2001). The method has certain advantages compared to the inverse methods in terms of eliminating the uncertainties of arrival times and reading errors. In this study, adopting this approach, epicentral locations were determined based on the results of a fuzzy logic space concerning the uncertainties in the velocity models. To map the uncertainties in arrival times into the fuzzy logic space, a trapezoidal membership function was constructed by directly using the travel time difference between the two stations for the P- and S-arrival times instead of the P- and S-wave models to eliminate the need for obtaining information concerning the velocity structure of the study area. The results showed that this method worked most effectively when earthquakes occurred away from a network or when the arrival time data contained phase reading errors. In this study, to resolve the problems related to determining the epicentral locations of the events, a forward modeling method like the grid search technique was used by applying different logical operations (i.e., intersection, union, and their combination) with a fuzzy logic approach. The locations of the events were depended on results of fuzzy logic outputs in fuzzy logic space by searching in a gridded region. The process of location determination with the defuzzification of only the grid points with the membership value of 1 obtained by normalizing all the maximum fuzzy output values of the highest values resulted in more reliable epicentral locations for the earthquakes than the other approaches. In addition, throughout the process, the center-of-gravity method was used as a defuzzification operation.

Two-year survey comparing earthquake activity and injection-well locations in the Barnett Shale, Texas

PubMed Central

Frohlich, Cliff

2012-01-01

Between November 2009 and September 2011, temporary seismographs deployed under the EarthScope USArray program were situated on a 70-km grid covering the Barnett Shale in Texas, recording data that allowed sensing and locating regional earthquakes with magnitudes 1.5 and larger. I analyzed these data and located 67 earthquakes, more than eight times as many as reported by the National Earthquake Information Center. All 24 of the most reliably located epicenters occurred in eight groups within 3.2 km of one or more injection wells. These included wells near Dallas–Fort Worth and Cleburne, Texas, where earthquakes near injection wells were reported by the media in 2008 and 2009, as well as wells in six other locations, including several where no earthquakes have been reported previously. This suggests injection-triggered earthquakes are more common than is generally recognized. All the wells nearest to the earthquake groups reported maximum monthly injection rates exceeding 150,000 barrels of water per month (24,000 m3/mo) since October 2006. However, while 9 of 27 such wells in Johnson County were near earthquakes, elsewhere no earthquakes occurred near wells with similar injection rates. A plausible hypothesis to explain these observations is that injection only triggers earthquakes if injected fluids reach and relieve friction on a suitably oriented, nearby fault that is experiencing regional tectonic stress. Testing this hypothesis would require identifying geographic regions where there is interpreted subsurface structure information available to determine whether there are faults near seismically active and seismically quiescent injection wells. PMID:22869701

Mexican Seismic Alert System's SAS-I algorithm review considering strong earthquakes felt in Mexico City since 1985

NASA Astrophysics Data System (ADS)

Cuellar Martinez, A.; Espinosa Aranda, J.; Suarez, G.; Ibarrola Alvarez, G.; Ramos Perez, S.; Camarillo Barranco, L.

2013-05-01

The Seismic Alert System of Mexico (SASMEX) uses three algorithms for alert activation that involve the distance between the seismic sensing field station (FS) and the city to be alerted; and the forecast for earthquake early warning activation in the cities integrated to the system, for example in Mexico City, the earthquakes occurred with the highest accelerations, were originated in the Pacific Ocean coast, whose distance this seismic region and the city, favors the use of algorithm called Algorithm SAS-I. This algorithm, without significant changes since its beginning in 1991, employs the data that generate one or more FS during P wave detection until S wave detection plus a period equal to the time employed to detect these phases; that is the double S-P time, called 2*(S-P). In this interval, the algorithm performs an integration process of quadratic samples from FS which uses a triaxial accelerometer to get two parameters: amplitude and growth rate measured until 2*(S-P) time. The parameters in SAS-I are used in a Magnitude classifier model, which was made from Guerrero Coast earthquakes time series, with reference to Mb magnitude mainly. This algorithm activates a Public or Preventive Alert if the model predicts whether Strong or Moderate earthquake. The SAS-I algorithm has been operating for over 23 years in the subduction zone of the Pacific Coast of Mexico, initially in Guerrero and followed by Oaxaca; and since March 2012 in the seismic region of Pacific covering the coasts among Jalisco, Colima, Michoacan, Guerrero and Oaxaca, where this algorithm has issued 16 Public Alert and 62 Preventive Alerts to the Mexico City where its soil conditions increase damages by earthquake such as the occurred in September 1985. This work shows the review of the SAS-I algorithm and possible alerts that it could generate from major earthquakes recordings detected by FS or seismometers near the earthquakes, coming from Pacific Ocean Coast whose have been felt in Mexico

A phase coherence approach to identifying co-located earthquakes and tremor

NASA Astrophysics Data System (ADS)

Hawthorne, J. C.; Ampuero, J.-P.

2018-05-01

We present and use a phase coherence approach to identify seismic signals that have similar path effects but different source time functions: co-located earthquakes and tremor. The method used is a phase coherence-based implementation of empirical matched field processing, modified to suit tremor analysis. It works by comparing the frequency-domain phases of waveforms generated by two sources recorded at multiple stations. We first cross-correlate the records of the two sources at a single station. If the sources are co-located, this cross-correlation eliminates the phases of the Green's function. It leaves the relative phases of the source time functions, which should be the same across all stations so long as the spatial extent of the sources are small compared with the seismic wavelength. We therefore search for cross-correlation phases that are consistent across stations as an indication of co-located sources. We also introduce a method to obtain relative locations between the two sources, based on back-projection of interstation phase coherence. We apply this technique to analyse two tremor-like signals that are thought to be composed of a number of earthquakes. First, we analyse a 20 s long seismic precursor to a M 3.9 earthquake in central Alaska. The analysis locates the precursor to within 2 km of the mainshock, and it identifies several bursts of energy—potentially foreshocks or groups of foreshocks—within the precursor. Second, we examine several minutes of volcanic tremor prior to an eruption at Redoubt Volcano. We confirm that the tremor source is located close to repeating earthquakes identified earlier in the tremor sequence. The amplitude of the tremor diminishes about 30 s before the eruption, but the phase coherence results suggest that the tremor may persist at some level through this final interval.

Locations and magnitudes of historical earthquakes in the Sierra of Ecuador (1587–1996)

USGS Publications Warehouse

Beauval, Celine; Yepes, Hugo; Bakun, William H.; Egred, Jose; Alvarado, Alexandra; Singaucho, Juan-Carlos

2010-01-01

The whole territory of Ecuador is exposed to seismic hazard. Great earthquakes can occur in the subduction zone (e.g. Esmeraldas, 1906, Mw8.8), whereas lower magnitude but shallower and potentially more destructive earthquakes can occur in the highlands. This study focuses on the historical crustal earthquakes of the Andean Cordillera. Several large cities are located in the Interandean Valley, among them Quito, the capital (∼2.5 millions inhabitants). A total population of ∼6 millions inhabitants currently live in the highlands, raising the seismic risk. At present, precise instrumental data for the Ecuadorian territory is not available for periods earlier than 1990 (beginning date of the revised instrumental Ecuadorian seismic catalogue); therefore historical data are of utmost importance for assessing seismic hazard. In this study, the Bakun & Wentworth method is applied in order to determine magnitudes, locations, and associated uncertainties for historical earthquakes of the Sierra over the period 1587–1976. An intensity-magnitude equation is derived from the four most reliable instrumental earthquakes (Mwbetween 5.3 and 7.1). Intensity data available per historical earthquake vary between 10 (Quito, 1587, Intensity ≥VI) and 117 (Riobamba, 1797, Intensity ≥III). The bootstrap resampling technique is coupled to the B&W method for deriving geographical confidence contours for the intensity centre depending on the data set of each earthquake, as well as confidence intervals for the magnitude. The extension of the area delineating the intensity centre location at the 67 per cent confidence level (±1σ) depends on the amount of intensity data, on their internal coherence, on the number of intensity degrees available, and on their spatial distribution. Special attention is dedicated to the few earthquakes described by intensities reaching IX, X and XI degrees. Twenty-five events are studied, and nineteen new epicentral locations are obtained, yielding

Fault structure and mechanics of the Hayward Fault, California from double-difference earthquake locations

USGS Publications Warehouse

Waldhauser, F.; Ellsworth, W.L.

2002-01-01

The relationship between small-magnitude seismicity and large-scale crustal faulting along the Hayward Fault, California, is investigated using a double-difference (DD) earthquake location algorithm. We used the DD method to determine high-resolution hypocenter locations of the seismicity that occurred between 1967 and 1998. The DD technique incorporates catalog travel time data and relative P and S wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events. The relocated seismicity reveals a narrow, near-vertical fault zone at most locations. This zone follows the Hayward Fault along its northern half and then diverges from it to the east near San Leandro, forming the Mission trend. The relocated seismicity is consistent with the idea that slip from the Calaveras Fault is transferred over the Mission trend onto the northern Hayward Fault. The Mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the Calaveras Fault at Calaveras Reservoir. In some locations, discrete structures adjacent to the main trace are seen, features that were previously hidden in the uncertainty of the network locations. The fine structure of the seismicity suggest that the fault surface on the northern Hayward Fault is curved or that the events occur on several substructures. Near San Leandro, where the more westerly striking trend of the Mission seismicity intersects with the surface trace of the (aseismic) southern Hayward Fault, the seismicity remains diffuse after relocation, with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation. The seismicity is highly organized in space, especially on the northern Hayward Fault, where it forms horizontal, slip-parallel streaks of hypocenters of only a few tens of meters width, bounded by areas almost absent of seismic activity. During the interval from 1984 to 1998, when digital

Improvements of the Ray-Tracing Based Method Calculating Hypocentral Loci for Earthquake Location

NASA Astrophysics Data System (ADS)

Zhao, A. H.

2014-12-01

Hypocentral loci are very useful to reliable and visual earthquake location. However, they can hardly be analytically expressed when the velocity model is complex. One of methods numerically calculating them is based on a minimum traveltime tree algorithm for tracing rays: a focal locus is represented in terms of ray paths in its residual field from the minimum point (namely initial point) to low residual points (referred as reference points of the focal locus). The method has no restrictions on the complexity of the velocity model but still lacks the ability of correctly dealing with multi-segment loci. Additionally, it is rather laborious to set calculation parameters for obtaining loci with satisfying completeness and fineness. In this study, we improve the ray-tracing based numerical method to overcome its advantages. (1) Reference points of a hypocentral locus are selected from nodes of the model cells that it goes through, by means of a so-called peeling method. (2) The calculation domain of a hypocentral locus is defined as such a low residual area that its connected regions each include one segment of the locus and hence all the focal locus segments are respectively calculated with the minimum traveltime tree algorithm for tracing rays by repeatedly assigning the minimum residual reference point among those that have not been traced as an initial point. (3) Short ray paths without branching are removed to make the calculated locus finer. Numerical tests show that the improved method becomes capable of efficiently calculating complete and fine hypocentral loci of earthquakes in a complex model.

Joint probabilistic determination of earthquake location and velocity structure: application to local and regional events

NASA Astrophysics Data System (ADS)

Beucler, E.; Haugmard, M.; Mocquet, A.

2016-12-01

The most widely used inversion schemes to locate earthquakes are based on iterative linearized least-squares algorithms and using an a priori knowledge of the propagation medium. When a small amount of observations is available for moderate events for instance, these methods may lead to large trade-offs between outputs and both the velocity model and the initial set of hypocentral parameters. We present a joint structure-source determination approach using Bayesian inferences. Monte-Carlo continuous samplings, using Markov chains, generate models within a broad range of parameters, distributed according to the unknown posterior distributions. The non-linear exploration of both the seismic structure (velocity and thickness) and the source parameters relies on a fast forward problem using 1-D travel time computations. The a posteriori covariances between parameters (hypocentre depth, origin time and seismic structure among others) are computed and explicitly documented. This method manages to decrease the influence of the surrounding seismic network geometry (sparse and/or azimuthally inhomogeneous) and a too constrained velocity structure by inferring realistic distributions on hypocentral parameters. Our algorithm is successfully used to accurately locate events of the Armorican Massif (western France), which is characterized by moderate and apparently diffuse local seismicity.

Absolute earthquake locations using 3-D versus 1-D velocity models below a local seismic network: example from the Pyrenees

NASA Astrophysics Data System (ADS)

Theunissen, T.; Chevrot, S.; Sylvander, M.; Monteiller, V.; Calvet, M.; Villaseñor, A.; Benahmed, S.; Pauchet, H.; Grimaud, F.

2018-03-01

Local seismic networks are usually designed so that earthquakes are located inside them (primary azimuthal gap <<180°) and close to the seismic stations (0-100 km). With these local or near-regional networks (0°-5°), many seismological observatories still routinely locate earthquakes using 1-D velocity models. Moving towards 3-D location algorithms requires robust 3-D velocity models. This work takes advantage of seismic monitoring spanning more than 30 yr in the Pyrenean region. We investigate the influence of a well-designed 3-D model with station corrections including basins structure and the geometry of the Mohorovicic discontinuity on earthquake locations. In the most favourable cases (GAP < 180° and distance to the first station lower than 15 km), results using 1-D velocity models are very similar to 3-D results. The horizontal accuracy in the 1-D case can be higher than in the 3-D case if lateral variations in the structure are not properly resolved. Depth is systematically better resolved in the 3-D model even on the boundaries of the seismic network (GAP > 180° and distance to the first station higher than 15 km). Errors on velocity models and accuracy of absolute earthquake locations are assessed based on a reference data set made of active seismic, quarry blasts and passive temporary experiments. Solutions and uncertainties are estimated using the probabilistic approach of the NonLinLoc (NLLoc) software based on Equal Differential Time. Some updates have been added to NLLoc to better focus on the final solution (outlier exclusion, multiscale grid search, S-phases weighting). Errors in the probabilistic approach are defined to take into account errors on velocity models and on arrival times. The seismicity in the final 3-D catalogue is located with a horizontal uncertainty of about 2.0 ± 1.9 km and a vertical uncertainty of about 3.0 ± 2.0 km.

Repeating Earthquakes on the Queen Charlotte Plate Boundary

NASA Astrophysics Data System (ADS)

Hayward, T. W.; Bostock, M. G.

2015-12-01

The Queen Charlotte Fault (QCF) is a major plate boundary located off the northwest coast of North America that has produced large earthquakes in 1949 (M8.1) and more recently in October, 2012 (M7.8). The 2012 event was dominated by thrusting despite the fact that plate motions at the boundary are nearly transcurrent. It is now widely believed that the plate boundary comprises the QCF (i.e., a dextral strike-slip fault) as well as an element of subduction of the Pacific Plate beneath the North American Plate. Repeating earthquakes and seismic tremor have been observed in the vicinity of the QCF; providing insight into the spatial and temporal characteristics of repeating earthquakes is the goal of this research. Due to poor station coverage and data quality, traditional methods of locating earthquakes are not applicable to these events. Instead, we have implemented an algorithm to locate local (i.e., < 100 km distance to epicenter) earthquakes using a single, three-component seismogram. This algorithm relies on the P-wave polarization and, through comparison with larger local events in the Geological Survey of Canada catalogue, is shown to yield epicentral locations accurate to within 5-10 km. A total of 24 unique families of repeating earthquakes has been identified, and 4 of these families have been located with high confidence. Their epicenters locate directly on the trace of the QCF and their depths are shallow (i.e., 5-15 km), consistent with the proposed depth of the QCF. Analysis of temporal recurrence leading up to the 2012 M7.8 event reveals a non-random pattern, with an approximately 15 day periodicity. Further analysis is planned to study whether this behaviour persists after the 2012 event and to gain insight into the effects of the 2012 event on the stress field and frictional properties of the plate boundary.

Combining multiple earthquake models in real time for earthquake early warning

USGS Publications Warehouse

Minson, Sarah E.; Wu, Stephen; Beck, James L; Heaton, Thomas H.

2017-01-01

The ultimate goal of earthquake early warning (EEW) is to provide local shaking information to users before the strong shaking from an earthquake reaches their location. This is accomplished by operating one or more real‐time analyses that attempt to predict shaking intensity, often by estimating the earthquake’s location and magnitude and then predicting the ground motion from that point source. Other EEW algorithms use finite rupture models or may directly estimate ground motion without first solving for an earthquake source. EEW performance could be improved if the information from these diverse and independent prediction models could be combined into one unified, ground‐motion prediction. In this article, we set the forecast shaking at each location as the common ground to combine all these predictions and introduce a Bayesian approach to creating better ground‐motion predictions. We also describe how this methodology could be used to build a new generation of EEW systems that provide optimal decisions customized for each user based on the user’s individual false‐alarm tolerance and the time necessary for that user to react.

Nonexposure Accurate Location K-Anonymity Algorithm in LBS

PubMed Central

2014-01-01

This paper tackles location privacy protection in current location-based services (LBS) where mobile users have to report their exact location information to an LBS provider in order to obtain their desired services. Location cloaking has been proposed and well studied to protect user privacy. It blurs the user's accurate coordinate and replaces it with a well-shaped cloaked region. However, to obtain such an anonymous spatial region (ASR), nearly all existent cloaking algorithms require knowing the accurate locations of all users. Therefore, location cloaking without exposing the user's accurate location to any party is urgently needed. In this paper, we present such two nonexposure accurate location cloaking algorithms. They are designed for K-anonymity, and cloaking is performed based on the identifications (IDs) of the grid areas which were reported by all the users, instead of directly on their accurate coordinates. Experimental results show that our algorithms are more secure than the existent cloaking algorithms, need not have all the users reporting their locations all the time, and can generate smaller ASR. PMID:24605060

Estimating earthquake location and magnitude from seismic intensity data

USGS Publications Warehouse

Bakun, W.H.; Wentworth, C.M.

1997-01-01

Analysis of Modified Mercalli intensity (MMI) observations for a training set of 22 California earthquakes suggests a strategy for bounding the epicentral region and moment magnitude M from MMI observations only. We define an intensity magnitude MI that is calibrated to be equal in the mean to M. MI = mean (Mi), where Mi = (MMIi + 3.29 + 0.0206 * ??i)/1.68 and ??i is the epicentral distance (km) of observation MMIi. The epicentral region is bounded by contours of rms [MI] = rms (MI - Mi) - rms0 (MI - Mi-), where rms is the root mean square, rms0 (MI - Mi) is the minimum rms over a grid of assumed epicenters, and empirical site corrections and a distance weighting function are used. Empirical contour values for bounding the epicenter location and empirical bounds for M estimated from MI appropriate for different levels of confidence and different quantities of intensity observations are tabulated. The epicentral region bounds and MI obtained for an independent test set of western California earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes. The analysis strategy is particularly appropriate for the evaluation of pre-1900 earthquakes for which the only available data are a sparse set of intensity observations.

Precise relative locations for earthquakes in the northeast Pacific region

DOE PAGES

Cleveland, K. Michael; VanDeMark, Thomas F.; Ammon, Charles J.

2015-10-09

We report that double-difference methods applied to cross-correlation measured Rayleigh wave time shifts are an effective tool to improve epicentroid locations and relative origin time shifts in remote regions. We apply these methods to seismicity offshore of southwestern Canada and the U.S. Pacific Northwest, occurring along the boundaries of the Pacific and Juan de Fuca (including the Explorer Plate and Gorda Block) Plates. The Blanco, Mendocino, Revere-Dellwood, Nootka, and Sovanco fracture zones host the majority of this seismicity, largely consisting of strike-slip earthquakes. The Explorer, Juan de Fuca, and Gorda spreading ridges join these fracture zones and host normal faultingmore » earthquakes. Our results show that at least the moderate-magnitude activity clusters along fault strike, supporting suggestions of large variations in seismic coupling along oceanic transform faults. Our improved relative locations corroborate earlier interpretations of the internal deformation in the Explorer and Gorda Plates. North of the Explorer Plate, improved locations support models that propose northern extension of the Revere-Dellwood fault. Relocations also support interpretations that favor multiple parallel active faults along the Blanco Transform Fault Zone. Seismicity of the western half of the Blanco appears more scattered and less collinear than the eastern half, possibly related to fault maturity. We use azimuthal variations in the Rayleigh wave cross-correlation amplitude to detect and model rupture directivity for a moderate size earthquake along the eastern Blanco Fault. Lastly, the observations constrain the seismogenic zone geometry and suggest a relatively narrow seismogenic zone width of 2 to 4 km.« less

Co-located ionospheric and geomagnetic disturbances caused by great earthquakes

NASA Astrophysics Data System (ADS)

Hao, Yongqiang; Zhang, Donghe; Xiao, Zuo

2016-07-01

Despite primary energy disturbances from the Sun, oscillations of the Earth surface due to a large earthquake will couple with the atmosphere and therefore the ionosphere, to generate so-called coseismic ionospheric disturbances (CIDs). In the cases of 2008 Wenchuan and 2011 Tohoku earthquakes, infrasonic waves accompanying the propagation of seismic Rayleigh waves were observed in the ionosphere by a combination of techniques, total electron content, HF Doppler, and ground magnetometer. This is the very first report to present CIDs recorded by different techniques at co-located sites and profiled with regard to changes of both ionospheric plasma and current (geomagnetic field) simultaneously. Comparison between the oceanic (2011 Tohoku) and inland (2008 Wenchuan) earthquakes revealed that the main directional lobe of latter case is more distinct which is perpendicular to the direction of the fault rupture. We argue that the different fault slip (inland or submarine) may affect the way of couplings of lithosphere with atmosphere. Zhao, B., and Y. Hao (2015), Ionospheric and geomagnetic disturbances caused by the 2008 Wenchuan earthquake: A revisit, J. Geophys. Res., doi:10.1002/2015JA021035. Hao, Y. Q., et al. (2013), Teleseismic magnetic effects (TMDs) of 2011 Tohoku earthquake, J. Geophys. Res., doi:10.1002/jgra.50326. Hao, Y. Q., et al. (2012), Multi-instrument observation on co-seismic ionospheric effects after great Tohoku earthquake, J. Geophys. Res., doi:10.1029/2011JA017036.

Fine-scale structure of the San Andreas fault zone and location of the SAFOD target earthquakes

USGS Publications Warehouse

Thurber, C.; Roecker, S.; Zhang, H.; Baher, S.; Ellsworth, W.

2004-01-01

We present results from the tomographic analysis of seismic data from the Parkfield area using three different inversion codes. The models provide a consistent view of the complex velocity structure in the vicinity of the San Andreas, including a sharp velocity contrast across the fault. We use the inversion results to assess our confidence in the absolute location accuracy of a potential target earthquake. We derive two types of accuracy estimates, one based on a consideration of the location differences from the three inversion methods, and the other based on the absolute location accuracy of "virtual earthquakes." Location differences are on the order of 100-200 m horizontally and up to 500 m vertically. Bounds on the absolute location errors based on the "virtual earthquake" relocations are ??? 50 m horizontally and vertically. The average of our locations places the target event epicenter within about 100 m of the SAF surface trace. Copyright 2004 by the American Geophysical Union.

Assessing the location and magnitude of the 20 October 1870 Charlevoix, Quebec, earthquake

USGS Publications Warehouse

Ebel, John E.; Dupuy, Megan; Bakun, William H.

2013-01-01

The Charlevoix, Quebec, earthquake of 20 October 1870 caused damage to several towns in Quebec and was felt throughout much of southeastern Canada and along the U.S. Atlantic seaboard from Maine to Maryland. Site‐specific damage and felt reports from Canadian and U.S. cities and towns were used in analyses of the location and magnitude of the earthquake. The macroseismic center of the earthquake was very close to Baie‐St‐Paul, where the greatest damage was reported, and the intensity magnitude MI was found to be 5.8, with a 95% probability range of 5.5–6.0. After corrections for epicentral‐distance differences are applied, the modified Mercalli intensity (MMI) data for the 1870 earthquake and for the moment magnitude M 6.2 Charlevoix earthquake of 1925 at common sites show that on average, the MMI readings are about 0.8 intensity units smaller for the 1870 earthquake than for the 1925 earthquake, suggesting that the 1870 earthquake was MI 5.7. A similar comparison of the MMI data for the 1870 earthquake with the corresponding data for the M 5.9 1988 Saguenay event suggests that the 1870 earthquake was MI 6.0. These analyses all suggest that the magnitude of the 1870 Charlevoix earthquake is between MI 5.5 and MI 6.0, with a best estimate of MI 5.8.

Combining Multiple Rupture Models in Real-Time for Earthquake Early Warning

NASA Astrophysics Data System (ADS)

Minson, S. E.; Wu, S.; Beck, J. L.; Heaton, T. H.

2015-12-01

The ShakeAlert earthquake early warning system for the west coast of the United States is designed to combine information from multiple independent earthquake analysis algorithms in order to provide the public with robust predictions of shaking intensity at each user's location before they are affected by strong shaking. The current contributing analyses come from algorithms that determine the origin time, epicenter, and magnitude of an earthquake (On-site, ElarmS, and Virtual Seismologist). A second generation of algorithms will provide seismic line source information (FinDer), as well as geodetically-constrained slip models (BEFORES, GPSlip, G-larmS, G-FAST). These new algorithms will provide more information about the spatial extent of the earthquake rupture and thus improve the quality of the resulting shaking forecasts.Each of the contributing algorithms exploits different features of the observed seismic and geodetic data, and thus each algorithm may perform differently for different data availability and earthquake source characteristics. Thus the ShakeAlert system requires a central mediator, called the Central Decision Module (CDM). The CDM acts to combine disparate earthquake source information into one unified shaking forecast. Here we will present a new design for the CDM that uses a Bayesian framework to combine earthquake reports from multiple analysis algorithms and compares them to observed shaking information in order to both assess the relative plausibility of each earthquake report and to create an improved unified shaking forecast complete with appropriate uncertainties. We will describe how these probabilistic shaking forecasts can be used to provide each user with a personalized decision-making tool that can help decide whether or not to take a protective action (such as opening fire house doors or stopping trains) based on that user's distance to the earthquake, vulnerability to shaking, false alarm tolerance, and time required to act.

Testing continuous earthquake detection and location in Alentejo (South Portugal) by waveform coherency analysis

NASA Astrophysics Data System (ADS)

Matos, Catarina; Grigoli, Francesco; Cesca, Simone; Custódio, Susana

2015-04-01

In the last decade a permanent seismic network of 30 broadband stations, complemented by dense temporary deployments, covered Portugal. This extraordinary network coverage enables now the computation of a high-resolution image of the seismicity of Portugal, which in turn will shed light on the seismotectonics of Portugal. The large data volumes available cannot be analyzed by traditional time-consuming manual location procedures. In this presentation we show first results on the automatic detection and location of earthquakes occurred in a selected region in the south of Portugal Our main goal is to implement an automatic earthquake detection and location routine in order to have a tool to quickly process large data sets, while at the same time detecting low magnitude earthquakes (i.e., lowering the detection threshold). We present a modified version of the automatic seismic event location by waveform coherency analysis developed by Grigoli et al. (2013, 2014), designed to perform earthquake detections and locations in continuous data. The event detection is performed by continuously computing the short-term-average/long-term-average of two different characteristic functions (CFs). For the P phases we used a CF based on the vertical energy trace, while for S phases we used a CF based on the maximum eigenvalue of the instantaneous covariance matrix (Vidale 1991). Seismic event detection and location is obtained by performing waveform coherence analysis scanning different hypocentral coordinates. We apply this technique to earthquakes in the Alentejo region (South Portugal), taking advantage from a small aperture seismic network installed in the south of Portugal for two years (2010 - 2011) during the DOCTAR experiment. In addition to the good network coverage, the Alentejo region was chosen for its simple tectonic setting and also because the relationship between seismicity, tectonics and local lithospheric structure is intriguing and still poorly understood. Inside

An Impact-Location Estimation Algorithm for Subsonic Uninhabited Aircraft

NASA Technical Reports Server (NTRS)

Bauer, Jeffrey E.; Teets, Edward

1997-01-01

An impact-location estimation algorithm is being used at the NASA Dryden Flight Research Center to support range safety for uninhabited aerial vehicle flight tests. The algorithm computes an impact location based on the descent rate, mass, and altitude of the vehicle and current wind information. The predicted impact location is continuously displayed on the range safety officer's moving map display so that the flightpath of the vehicle can be routed to avoid ground assets if the flight must be terminated. The algorithm easily adapts to different vehicle termination techniques and has been shown to be accurate to the extent required to support range safety for subsonic uninhabited aerial vehicles. This paper describes how the algorithm functions, how the algorithm is used at NASA Dryden, and how various termination techniques are handled by the algorithm. Other approaches to predicting the impact location and the reasons why they were not selected for real-time implementation are also discussed.

Regional intensity attenuation models for France and the estimation of magnitude and location of historical earthquakes

USGS Publications Warehouse

Bakun, W.H.; Scotti, O.

2006-01-01

Intensity assignments for 33 calibration earthquakes were used to develop intensity attenuation models for the Alps, Armorican, Provence, Pyrenees and Rhine regions of France. Intensity decreases with ?? most rapidly in the French Alps, Provence and Pyrenees regions, and least rapidly in the Armorican and Rhine regions. The comparable Armorican and Rhine region attenuation models are aggregated into a French stable continental region model and the comparable Provence and Pyrenees region models are aggregated into a Southern France model. We analyse MSK intensity assignments using the technique of Bakun & Wentworth, which provides an objective method for estimating epicentral location and intensity magnitude MI. MI for the 1356 October 18 earthquake in the French stable continental region is 6.6 for a location near Basle, Switzerland, and moment magnitude M is 5.9-7.2 at the 95 per cent (??2??) confidence level. MI for the 1909 June 11 Trevaresse (Lambesc) earthquake near Marseilles in the Southern France region is 5.5, and M is 4.9-6.0 at the 95 per cent confidence level. Bootstrap resampling techniques are used to calculate objective, reproducible 67 per cent and 95 per cent confidence regions for the locations of historical earthquakes. These confidence regions for location provide an attractive alternative to the macroseismic epicentre and qualitative location uncertainties used heretofore. ?? 2006 The Authors Journal compilation ?? 2006 RAS.

Earthquake Relocation in the Middle East with Geodetically-Calibrated Events

NASA Astrophysics Data System (ADS)

Brengman, C.; Barnhart, W. D.

2017-12-01

Regional and global earthquake catalogs in tectonically active regions commonly contain mislocated earthquakes that impede efforts to address first order characteristics of seismogenic strain release and to monitor anthropogenic seismic events through the Comprehensive Nuclear-Test-Ban Treaty. Earthquake mislocations are particularly limiting in the plate boundary zone between the Arabia and Eurasia plates of Iran, Pakistan, and Turkey where earthquakes are commonly mislocated by 20+ kilometers and hypocentral depths are virtually unconstrained. Here, we present preliminary efforts to incorporate calibrated earthquake locations derived from Interferometric Synthetic Aperture Radar (InSAR) observations into a relocated catalog of seismicity in the Middle East. We use InSAR observations of co-seismic deformation to determine the locations, geometries, and slip distributions of small to moderate magnitude (M4.8+) crustal earthquakes. We incorporate this catalog of calibrated event locations, along with other seismologically-calibrated earthquake locations, as "priors" into a fully Bayesian multi-event relocation algorithm that relocates all teleseismically and regionally recorded earthquakes over the time span 1970-2017, including calibrated and uncalibrated events. Our relocations are conducted using cataloged phase picks and BayesLoc. We present a suite of sensitivity tests for the time span of 2003-2014 to explore the impacts of our input parameters (i.e., how a point source is defined from a finite fault inversion) on the behavior of the event relocations, potential improvements to depth estimates, the ability of the relocation to recover locations outside of the time span in which there are InSAR observations, and the degree to which our relocations can recover "known" calibrated earthquake locations that are not explicitly included as a-priori constraints. Additionally, we present a systematic comparison of earthquake relocations derived from phase picks of two

Earthquake Forecasting Methodology Catalogue - A collection and comparison of the state-of-the-art in earthquake forecasting and prediction methodologies

NASA Astrophysics Data System (ADS)

Schaefer, Andreas; Daniell, James; Wenzel, Friedemann

2015-04-01

Earthquake forecasting and prediction has been one of the key struggles of modern geosciences for the last few decades. A large number of approaches for various time periods have been developed for different locations around the world. A categorization and review of more than 20 of new and old methods was undertaken to develop a state-of-the-art catalogue in forecasting algorithms and methodologies. The different methods have been categorised into time-independent, time-dependent and hybrid methods, from which the last group represents methods where additional data than just historical earthquake statistics have been used. It is necessary to categorize in such a way between pure statistical approaches where historical earthquake data represents the only direct data source and also between algorithms which incorporate further information e.g. spatial data of fault distributions or which incorporate physical models like static triggering to indicate future earthquakes. Furthermore, the location of application has been taken into account to identify methods which can be applied e.g. in active tectonic regions like California or in less active continental regions. In general, most of the methods cover well-known high-seismicity regions like Italy, Japan or California. Many more elements have been reviewed, including the application of established theories and methods e.g. for the determination of the completeness magnitude or whether the modified Omori law was used or not. Target temporal scales are identified as well as the publication history. All these different aspects have been reviewed and catalogued to provide an easy-to-use tool for the development of earthquake forecasting algorithms and to get an overview in the state-of-the-art.

Multiple-Threshold Event Detection and Other Enhancements to the Virtual Seismologist (VS) Earthquake Early Warning Algorithm

NASA Astrophysics Data System (ADS)

Fischer, M.; Caprio, M.; Cua, G. B.; Heaton, T. H.; Clinton, J. F.; Wiemer, S.

2009-12-01

The Virtual Seismologist (VS) algorithm is a Bayesian approach to earthquake early warning (EEW) being implemented by the Swiss Seismological Service at ETH Zurich. The application of Bayes’ theorem in earthquake early warning states that the most probable source estimate at any given time is a combination of contributions from a likelihood function that evolves in response to incoming data from the on-going earthquake, and selected prior information, which can include factors such as network topology, the Gutenberg-Richter relationship or previously observed seismicity. The VS algorithm was one of three EEW algorithms involved in the California Integrated Seismic Network (CISN) real-time EEW testing and performance evaluation effort. Its compelling real-time performance in California over the last three years has led to its inclusion in the new USGS-funded effort to develop key components of CISN ShakeAlert, a prototype EEW system that could potentially be implemented in California. A significant portion of VS code development was supported by the SAFER EEW project in Europe. We discuss recent enhancements to the VS EEW algorithm. We developed and continue to test a multiple-threshold event detection scheme, which uses different association / location approaches depending on the peak amplitudes associated with an incoming P pick. With this scheme, an event with sufficiently high initial amplitudes can be declared on the basis of a single station, maximizing warning times for damaging events for which EEW is most relevant. Smaller, non-damaging events, which will have lower initial amplitudes, will require more picks to be declared an event to reduce false alarms. This transforms the VS codes from a regional EEW approach reliant on traditional location estimation (and it requirement of at least 4 picks as implemented by the Binder Earthworm phase associator) to a hybrid on-site/regional approach capable of providing a continuously evolving stream of EEW

Repeating Earthquakes Following an Mw 4.4 Earthquake Near Luther, Oklahoma

NASA Astrophysics Data System (ADS)

Clements, T.; Keranen, K. M.; Savage, H. M.

2015-12-01

An Mw 4.4 earthquake on April 16, 2013 near Luther, OK was one of the earliest M4+ earthquakes in central Oklahoma, following the Prague sequence in 2011. A network of four local broadband seismometers deployed within a day of the Mw 4.4 event, along with six Oklahoma netquake stations, recorded more than 500 aftershocks in the two weeks following the Luther earthquake. Here we use HypoDD (Waldhauser & Ellsworth, 2000) and waveform cross-correlation to obtain precise aftershock locations. The location uncertainty, calculated using the SVD method in HypoDD, is ~15 m horizontally and ~ 35 m vertically. The earthquakes define a near vertical, NE-SW striking fault plane. Events occur at depths from 2 km to 3.5 km within the granitic basement, with a small fraction of events shallower, near the sediment-basement interface. Earthquakes occur within a zone of ~200 meters thickness on either side of the best-fitting fault surface. We use an equivalency class algorithm to identity clusters of repeating events, defined as event pairs with median three-component correlation > 0.97 across common stations (Aster & Scott, 1993). Repeating events occur as doublets of only two events in over 50% of cases; overall, 41% of earthquakes recorded occur as repeating events. The recurrence intervals for the repeating events range from minutes to days, with common recurrence intervals of less than two minutes. While clusters occur in tight dimensions, commonly of 80 m x 200 m, aftershocks occur in 3 distinct ~2km x 2km-sized patches along the fault. Our analysis suggests that with rapidly deployed local arrays, the plethora of ~Mw 4 earthquakes occurring in Oklahoma and Southern Kansas can be used to investigate the earthquake rupture process and the role of damage zones.

Automatic arrival time detection for earthquakes based on Modified Laplacian of Gaussian filter

NASA Astrophysics Data System (ADS)

Saad, Omar M.; Shalaby, Ahmed; Samy, Lotfy; Sayed, Mohammed S.

2018-04-01

Precise identification of onset time for an earthquake is imperative in the right figuring of earthquake's location and different parameters that are utilized for building seismic catalogues. P-wave arrival detection of weak events or micro-earthquakes cannot be precisely determined due to background noise. In this paper, we propose a novel approach based on Modified Laplacian of Gaussian (MLoG) filter to detect the onset time even in the presence of very weak signal-to-noise ratios (SNRs). The proposed algorithm utilizes a denoising-filter algorithm to smooth the background noise. In the proposed algorithm, we employ the MLoG mask to filter the seismic data. Afterward, we apply a Dual-threshold comparator to detect the onset time of the event. The results show that the proposed algorithm can detect the onset time for micro-earthquakes accurately, with SNR of -12 dB. The proposed algorithm achieves an onset time picking accuracy of 93% with a standard deviation error of 0.10 s for 407 field seismic waveforms. Also, we compare the results with short and long time average algorithm (STA/LTA) and the Akaike Information Criterion (AIC), and the proposed algorithm outperforms them.

Dynamic Source Inversion of a M6.5 Intraslab Earthquake in Mexico: Application of a New Parallel Genetic Algorithm

NASA Astrophysics Data System (ADS)

Díaz-Mojica, J. J.; Cruz-Atienza, V. M.; Madariaga, R.; Singh, S. K.; Iglesias, A.

2013-05-01

We introduce a novel approach for imaging the earthquakes dynamics from ground motion records based on a parallel genetic algorithm (GA). The method follows the elliptical dynamic-rupture-patch approach introduced by Di Carli et al. (2010) and has been carefully verified through different numerical tests (Díaz-Mojica et al., 2012). Apart from the five model parameters defining the patch geometry, our dynamic source description has four more parameters: the stress drop inside the nucleation and the elliptical patches; and two friction parameters, the slip weakening distance and the change of the friction coefficient. These parameters are constant within the rupture surface. The forward dynamic source problem, involved in the GA inverse method, uses a highly accurate computational solver for the problem, namely the staggered-grid split-node. The synthetic inversion presented here shows that the source model parameterization is suitable for the GA, and that short-scale source dynamic features are well resolved in spite of low-pass filtering of the data for periods comparable to the source duration. Since there is always uncertainty in the propagation medium as well as in the source location and the focal mechanisms, we have introduced a statistical approach to generate a set of solution models so that the envelope of the corresponding synthetic waveforms explains as much as possible the observed data. We applied the method to the 2012 Mw6.5 intraslab Zumpango, Mexico earthquake and determined several fundamental source parameters that are in accordance with different and completely independent estimates for Mexican and worldwide earthquakes. Our weighted-average final model satisfactorily explains eastward rupture directivity observed in the recorded data. Some parameters found for the Zumpango earthquake are: Δτ = 30.2+/-6.2 MPa, Er = 0.68+/-0.36x10^15 J, G = 1.74+/-0.44x10^15 J, η = 0.27+/-0.11, Vr/Vs = 0.52+/-0.09 and Mw = 6.64+/-0.07; for the stress drop

Seismicity in 2010 and major earthquakes recorded and located in Costa Rica from 1983 until 2012, by the local OVSICORI-UNA seismic network

NASA Astrophysics Data System (ADS)

Ronnie, Q.; Segura, J.; Burgoa, B.; Jimenez, W.; McNally, K. C.

2013-05-01

This work is the result of the analysis of existing information in the earthquake database of the Observatorio Sismológico y Vulcanológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), and seeks disclosure of basic seismological information recorded and processed in 2010. In this year there was a transition between the software used to record, store and locate earthquakes. During the first three months of 2010, we used Earthworm (http://folkworm.ceri.memphis.edu/ew-doc), SEISAN (Haskov y Ottemoller, 1999) and Hypocenter (Lienert y Haskov, 1995) to capture, store and locate the earthquakes, respectively; in April 2010, ANTELOPE (http://www.brtt.com/software.html) start to be used for recording and storing and GENLOC (Fan at al, 2006) and LOCSAT (Bratt and Bache 1988), to locate earthquakes. GENLOC was used for local events and LOCSAT for regional and distant earthquakes. The local earthquakes were located using the 1D velocity model of Quintero and Kissling (2001) and for regional and distant earthquakes IASPEI91 (Kennett and Engdahl, 1991) was used. All the events for 2010 and shown in this work were rechecked by the authors. We located 3903 earthquakes in and around Costa Rica and 746 regional and distant seismic events were recorded (see Figure 1). In this work we also give a summary of major earthquakes recorded and located by OVSICORI-UNA network between 1983 and 2012. Seismicity recorded by OVSICORI-UNA network in 2010

Twitter earthquake detection: Earthquake monitoring in a social world

USGS Publications Warehouse

Earle, Paul S.; Bowden, Daniel C.; Guy, Michelle R.

2011-01-01

The U.S. Geological Survey (USGS) is investigating how the social networking site Twitter, a popular service for sending and receiving short, public text messages, can augment USGS earthquake response products and the delivery of hazard information. Rapid detection and qualitative assessment of shaking events are possible because people begin sending public Twitter messages (tweets) with in tens of seconds after feeling shaking. Here we present and evaluate an earthquake detection procedure that relies solely on Twitter data. A tweet-frequency time series constructed from tweets containing the word "earthquake" clearly shows large peaks correlated with the origin times of widely felt events. To identify possible earthquakes, we use a short-term-average, long-term-average algorithm. When tuned to a moderate sensitivity, the detector finds 48 globally-distributed earthquakes with only two false triggers in five months of data. The number of detections is small compared to the 5,175 earthquakes in the USGS global earthquake catalog for the same five-month time period, and no accurate location or magnitude can be assigned based on tweet data alone. However, Twitter earthquake detections are not without merit. The detections are generally caused by widely felt events that are of more immediate interest than those with no human impact. The detections are also fast; about 75% occur within two minutes of the origin time. This is considerably faster than seismographic detections in poorly instrumented regions of the world. The tweets triggering the detections also provided very short first-impression narratives from people who experienced the shaking.

hypoDD-A Program to Compute Double-Difference Hypocenter Locations

USGS Publications Warehouse

Waldhauser, Felix

2001-01-01

HypoDD is a Fortran computer program package for relocating earthquakes with the double-difference algorithm of Waldhauser and Ellsworth (2000). This document provides a brief introduction into how to run and use the programs ph2dt and hypoDD to compute double-difference (DD) hypocenter locations. It gives a short overview of the DD technique, discusses the data preprocessing using ph2dt, and leads through the earthquake relocation process using hypoDD. The appendices include the reference manuals for the two programs and a short description of auxiliary programs and example data. Some minor subroutines are presently in the c language, and future releases will be in c. Earthquake location algorithms are usually based on some form of Geiger’s method, the linearization of the travel time equation in a first order Taylor series that relates the difference between the observed and predicted travel time to unknown adjustments in the hypocentral coordinates through the partial derivatives of travel time with respect to the unknowns. Earthquakes can be located individually with this algorithm, or jointly when other unknowns link together the solutions to indivdual earthquakes, such as station corrections in the joint hypocenter determination (JHD) method, or the earth model in seismic tomography. The DD technique (described in detail in Waldhauser and Ellsworth, 2000) takes advantage of the fact that if the hypocentral separation between two earthquakes is small compared to the event-station distance and the scale length of velocity heterogeneity, then the ray paths between the source region and a common station are similar along almost the entire ray path (Fréchet, 1985; Got et al., 1994). In this case, the difference in travel times for two events observed at one station can be attributed to the spatial offset between the events with high accuracy. DD equations are built by differencing Geiger’s equation for earthquake location. In this way, the residual between

Genetic algorithm for TEC seismo-ionospheric anomalies detection around the time of the Solomon (Mw = 8.0) earthquake of 06 February 2013

NASA Astrophysics Data System (ADS)

Akhoondzadeh, M.

2013-08-01

On 6 February 2013, at 12:12:27 local time (01:12:27 UTC) a seismic event registering Mw 8.0 struck the Solomon Islands, located at the boundaries of the Australian and Pacific tectonic plates. Time series prediction is an important and widely interesting topic in the research of earthquake precursors. This paper describes a new computational intelligence approach to detect the unusual variations of the total electron content (TEC) seismo-ionospheric anomalies induced by the powerful Solomon earthquake using genetic algorithm (GA). The GA detected a considerable number of anomalous occurrences on earthquake day and also 7 and 8 days prior to the earthquake in a period of high geomagnetic activities. In this study, also the detected TEC anomalies using the proposed method are compared to the results dealing with the observed TEC anomalies by applying the mean, median, wavelet, Kalman filter, ARIMA, neural network and support vector machine methods. The accordance in the final results of all eight methods is a convincing indication for the efficiency of the GA method. It indicates that GA can be an appropriate non-parametric tool for anomaly detection in a non linear time series showing the seismo-ionospheric precursors variations.

Determining on-fault earthquake magnitude distributions from integer programming

NASA Astrophysics Data System (ADS)

Geist, Eric L.; Parsons, Tom

2018-02-01

Earthquake magnitude distributions among faults within a fault system are determined from regional seismicity and fault slip rates using binary integer programming. A synthetic earthquake catalog (i.e., list of randomly sampled magnitudes) that spans millennia is first formed, assuming that regional seismicity follows a Gutenberg-Richter relation. Each earthquake in the synthetic catalog can occur on any fault and at any location. The objective is to minimize misfits in the target slip rate for each fault, where slip for each earthquake is scaled from its magnitude. The decision vector consists of binary variables indicating which locations are optimal among all possibilities. Uncertainty estimates in fault slip rates provide explicit upper and lower bounding constraints to the problem. An implicit constraint is that an earthquake can only be located on a fault if it is long enough to contain that earthquake. A general mixed-integer programming solver, consisting of a number of different algorithms, is used to determine the optimal decision vector. A case study is presented for the State of California, where a 4 kyr synthetic earthquake catalog is created and faults with slip ≥3 mm/yr are considered, resulting in >106 variables. The optimal magnitude distributions for each of the faults in the system span a rich diversity of shapes, ranging from characteristic to power-law distributions.

Determining on-fault earthquake magnitude distributions from integer programming

USGS Publications Warehouse

Geist, Eric L.; Parsons, Thomas E.

2018-01-01

Earthquake magnitude distributions among faults within a fault system are determined from regional seismicity and fault slip rates using binary integer programming. A synthetic earthquake catalog (i.e., list of randomly sampled magnitudes) that spans millennia is first formed, assuming that regional seismicity follows a Gutenberg-Richter relation. Each earthquake in the synthetic catalog can occur on any fault and at any location. The objective is to minimize misfits in the target slip rate for each fault, where slip for each earthquake is scaled from its magnitude. The decision vector consists of binary variables indicating which locations are optimal among all possibilities. Uncertainty estimates in fault slip rates provide explicit upper and lower bounding constraints to the problem. An implicit constraint is that an earthquake can only be located on a fault if it is long enough to contain that earthquake. A general mixed-integer programming solver, consisting of a number of different algorithms, is used to determine the optimal decision vector. A case study is presented for the State of California, where a 4 kyr synthetic earthquake catalog is created and faults with slip ≥3 mm/yr are considered, resulting in >106  variables. The optimal magnitude distributions for each of the faults in the system span a rich diversity of shapes, ranging from characteristic to power-law distributions. 

An improved data integration algorithm to constrain the 3D displacement field induced by fast deformation phenomena tested on the Napa Valley earthquake

NASA Astrophysics Data System (ADS)

Polcari, Marco; Fernández, José; Albano, Matteo; Bignami, Christian; Palano, Mimmo; Stramondo, Salvatore

2017-12-01

In this work, we propose an improved algorithm to constrain the 3D ground displacement field induced by fast surface deformations due to earthquakes or landslides. Based on the integration of different data, we estimate the three displacement components by solving a function minimization problem from the Bayes theory. We exploit the outcomes from SAR Interferometry (InSAR), Global Positioning System (GNSS) and Multiple Aperture Interferometry (MAI) to retrieve the 3D surface displacement field. Any other source of information can be added to the processing chain in a simple way, being the algorithm computationally efficient. Furthermore, we use the intensity Pixel Offset Tracking (POT) to locate the discontinuity produced on the surface by a sudden deformation phenomenon and then improve the GNSS data interpolation. This approach allows to be independent from other information such as in-situ investigations, tectonic studies or knowledge of the data covariance matrix. We applied such a method to investigate the ground deformation field related to the 2014 Mw 6.0 Napa Valley earthquake, occurred few kilometers from the San Andreas fault system.

Robust method to detect and locate local earthquakes by means of amplitude measurements.

NASA Astrophysics Data System (ADS)

del Puy Papí Isaba, María; Brückl, Ewald

2016-04-01

In this study we present a robust new method to detect and locate medium and low magnitude local earthquakes. This method is based on an empirical model of the ground motion obtained from amplitude data of earthquakes in the area of interest, which were located using traditional methods. The first step of our method is the computation of maximum resultant ground velocities in sliding time windows covering the whole period of interest. In the second step, these maximum resultant ground velocities are back-projected to every point of a grid covering the whole area of interest while applying the empirical amplitude - distance relations. We refer to these back-projected ground velocities as pseudo-magnitudes. The number of operating seismic stations in the local network equals the number of pseudo-magnitudes at each grid-point. Our method introduces the new idea of selecting the minimum pseudo-magnitude at each grid-point for further analysis instead of searching for a minimum of the L2 or L1 norm. In case no detectable earthquake occurred, the spatial distribution of the minimum pseudo-magnitudes constrains the magnitude of weak earthquakes hidden in the ambient noise. In the case of a detectable local earthquake, the spatial distribution of the minimum pseudo-magnitudes shows a significant maximum at the grid-point nearest to the actual epicenter. The application of our method is restricted to the area confined by the convex hull of the seismic station network. Additionally, one must ensure that there are no dead traces involved in the processing. Compared to methods based on L2 and even L1 norms, our new method is almost wholly insensitive to outliers (data from locally disturbed seismic stations). A further advantage is the fast determination of the epicenter and magnitude of a seismic event located within a seismic network. This is possible due to the method of obtaining and storing a back-projected matrix, independent of the registered amplitude, for each seismic

Prioritizing earthquake and tsunami alerting efforts

NASA Astrophysics Data System (ADS)

Allen, R. M.; Allen, S.; Aranha, M. A.; Chung, A. I.; Hellweg, M.; Henson, I. H.; Melgar, D.; Neuhauser, D. S.; Nof, R. N.; Strauss, J. A.

2015-12-01

The timeline of hazards associated with earthquakes ranges from seconds for the strong shaking at the epicenter, to minutes for strong shaking at more distant locations in big quakes, to tens of minutes for a local tsunami. Earthquake and tsunami warning systems must therefore include very fast initial alerts, while also taking advantage of available time in bigger and tsunami-generating quakes. At the UC Berkeley Seismological Laboratory we are developing a suite of algorithms to provide the fullest possible information about earthquake shaking and tsunami inundation from seconds to minutes after a quake. The E-larmS algorithm uses the P-wave to rapidly detect an earthquake and issue a warning. It is currently issuing alerts to test users in as little as 3 sec after the origin time. Development of a new waveform detector may lead to even faster alerts. G-larmS uses permanent deformation estimates from GNSS stations to estimate the geometry and extent of rupture underway providing more accurate ground shaking estimates in big (M>~7) earthquakes. It performed well in the M6.0 2014 Napa earthquake. T-larmS is a new algorithm designed to extend alert capabilities to tsunami inundation. Rapid estimates of source characteristics for subduction zones event can not only be used to warn of the shaking hazard, but also the local tsunami inundation hazard. These algorithms are being developed, implemented and tested with a focus on the western US, but are also now being tested in other parts of the world including Israel, Turkey, Korea and Chile. Beta users in the Bay Area are receiving the alerts and beginning to implement automated actions. They also provide feedback on users needs, which has led to the development of the MyEEW smartphone app. This app allows beta users to receive the alerts on their cell phones. All these efforts feed into our ongoing assessment of directions and priorities for future development and implementation efforts.

Earthquakes along the Azores-Iberia plate boundary revisited

NASA Astrophysics Data System (ADS)

Batlló, Josep; Matos, Catarina; Torres, Ricardo; Cruz, Jorge; Custódio, Susana

2017-04-01

been consigned in the resulting catalogue. Earthquakes were re-located using both a 1D velocity structure and a linear inversion procedure (Hypocenter) and using a 3D structure developed for the region and a non-linear inversion algorithm (NonLinLoc). The results are interpreted in light of the most recent knowledge of geological structures, precise earthquake locations obtained for the most recent decades, which identify belts of preferential clustering of earthquakes, focal mechanisms and gravity anomalies.

Offline Performance of the Filter Bank EEW Algorithm in the 2014 M6.0 South Napa Earthquake

NASA Astrophysics Data System (ADS)

Meier, M. A.; Heaton, T. H.; Clinton, J. F.

2014-12-01

Medium size events like the M6.0 South Napa earthquake are very challenging for EEW: the damage such events produce can be severe, but it is generally confined to relatively small zones around the epicenter and the shaking duration is short. This leaves a very short window for timely EEW alerts. Algorithms that wait for several stations to trigger before sending out EEW alerts are typically not fast enough for these kind of events because their blind zone (the zone where strong ground motions start before the warnings arrive) typically covers all or most of the area that experiences strong ground motions. At the same time, single station algorithms are often too unreliable to provide useful alerts. The filter bank EEW algorithm is a new algorithm that is designed to provide maximally accurate and precise earthquake parameter estimates with minimum data input, with the goal of producing reliable EEW alerts when only a very small number of stations have been reached by the p-wave. It combines the strengths of single station and network based algorithms in that it starts parameter estimates as soon as 0.5 seconds of data are available from the first station, but then perpetually incorporates additional data from the same or from any number of other stations. The algorithm analyzes the time dependent frequency content of real time waveforms with a filter bank. It then uses an extensive training data set to find earthquake records from the past that have had similar frequency content at a given time since the p-wave onset. The source parameters of the most similar events are used to parameterize a likelihood function for the source parameters of the ongoing event, which can then be maximized to find the most likely parameter estimates. Our preliminary results show that the filter bank EEW algorithm correctly estimated the magnitude of the South Napa earthquake to be ~M6 with only 1 second worth of data at the nearest station to the epicenter. This estimate is then

Precise hypocenter locations of midcrustal low-frequency earthquakes beneath Mt. Fuji, Japan

USGS Publications Warehouse

Nakamichi, H.; Ukawa, M.; Sakai, S.

2004-01-01

Midcrustal low-frequency earthquakes (MLFs) have been observed at seismic stations around Mt. Fuji, Japan. In September - December 2000 and April - May 2001, abnormally high numbers of MLFs occurred. We located hypocenters for the 80 MLFs during 1998-2003 by using the hypoDD earthquake location program (Waldhauser and Ellsworth, 2000). The MLF hypocenters define an ellipsoidal volume some 5 km in diameter ranging from 11 to 16 km in focal depth. This volume is centered 3 km northeast of the summit and its long axis is directed NW-SE. The direction of the axis coincides with the major axis of tectonic compression around Mt. Fuji. The center of the MLF epicenters gradually migrated upward and 2-3 km from southeast to northwest during 1998-2001. We interpret that the hypocentral migration of MLFs reflects magma movement associated with a NW-SE oriented dike beneath Mt. Fuji. Copyright ?? The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences.

Fast Ss-Ilm a Computationally Efficient Algorithm to Discover Socially Important Locations

NASA Astrophysics Data System (ADS)

Dokuz, A. S.; Celik, M.

2017-11-01

Socially important locations are places which are frequently visited by social media users in their social media lifetime. Discovering socially important locations provide several valuable information about user behaviours on social media networking sites. However, discovering socially important locations are challenging due to data volume and dimensions, spatial and temporal calculations, location sparseness in social media datasets, and inefficiency of current algorithms. In the literature, several studies are conducted to discover important locations, however, the proposed approaches do not work in computationally efficient manner. In this study, we propose Fast SS-ILM algorithm by modifying the algorithm of SS-ILM to mine socially important locations efficiently. Experimental results show that proposed Fast SS-ILM algorithm decreases execution time of socially important locations discovery process up to 20 %.

An efficient algorithm for double-difference tomography and location in heterogeneous media, with an application to the Kilauea volcano

USGS Publications Warehouse

Monteiller, V.; Got, J.-L.; Virieux, J.; Okubo, P.

2005-01-01

Improving our understanding of crustal processes requires a better knowledge of the geometry and the position of geological bodies. In this study we have designed a method based upon double-difference relocation and tomography to image, as accurately as possible, a heterogeneous medium containing seismogenic objects. Our approach consisted not only of incorporating double difference in tomography but also partly in revisiting tomographic schemes for choosing accurate and stable numerical strategies, adapted to the use of cross-spectral time delays. We used a finite difference solution to the eikonal equation for travel time computation and a Tarantola-Valette approach for both the classical and double-difference three-dimensional tomographic inversion to find accurate earthquake locations and seismic velocity estimates. We estimated efficiently the square root of the inverse model's covariance matrix in the case of a Gaussian correlation function. It allows the use of correlation length and a priori model variance criteria to determine the optimal solution. Double-difference relocation of similar earthquakes is performed in the optimal velocity model, making absolute and relative locations less biased by the velocity model. Double-difference tomography is achieved by using high-accuracy time delay measurements. These algorithms have been applied to earthquake data recorded in the vicinity of Kilauea and Mauna Loa volcanoes for imaging the volcanic structures. Stable and detailed velocity models are obtained: the regional tomography unambiguously highlights the structure of the island of Hawaii and the double-difference tomography shows a detailed image of the southern Kilauea caldera-upper east rift zone magmatic complex. Copyright 2005 by the American Geophysical Union.

Earthquake detection through computationally efficient similarity search

PubMed Central

Yoon, Clara E.; O’Reilly, Ossian; Bergen, Karianne J.; Beroza, Gregory C.

2015-01-01

Seismology is experiencing rapid growth in the quantity of data, which has outpaced the development of processing algorithms. Earthquake detection—identification of seismic events in continuous data—is a fundamental operation for observational seismology. We developed an efficient method to detect earthquakes using waveform similarity that overcomes the disadvantages of existing detection methods. Our method, called Fingerprint And Similarity Thresholding (FAST), can analyze a week of continuous seismic waveform data in less than 2 hours, or 140 times faster than autocorrelation. FAST adapts a data mining algorithm, originally designed to identify similar audio clips within large databases; it first creates compact “fingerprints” of waveforms by extracting key discriminative features, then groups similar fingerprints together within a database to facilitate fast, scalable search for similar fingerprint pairs, and finally generates a list of earthquake detections. FAST detected most (21 of 24) cataloged earthquakes and 68 uncataloged earthquakes in 1 week of continuous data from a station located near the Calaveras Fault in central California, achieving detection performance comparable to that of autocorrelation, with some additional false detections. FAST is expected to realize its full potential when applied to extremely long duration data sets over a distributed network of seismic stations. The widespread application of FAST has the potential to aid in the discovery of unexpected seismic signals, improve seismic monitoring, and promote a greater understanding of a variety of earthquake processes. PMID:26665176

Seismic swarm associated with the 2008 eruption of Kasatochi Volcano, Alaska: earthquake locations and source parameters

USGS Publications Warehouse

Ruppert, Natalia G.; Prejean, Stephanie G.; Hansen, Roger A.

2011-01-01

An energetic seismic swarm accompanied an eruption of Kasatochi Volcano in the central Aleutian volcanic arc in August of 2008. In retrospect, the first earthquakes in the swarm were detected about 1 month prior to the eruption onset. Activity in the swarm quickly intensified less than 48 h prior to the first large explosion and subsequently subsided with decline of eruptive activity. The largest earthquake measured as moment magnitude 5.8, and a dozen additional earthquakes were larger than magnitude 4. The swarm exhibited both tectonic and volcanic characteristics. Its shear failure earthquake features were b value = 0.9, most earthquakes with impulsive P and S arrivals and higher-frequency content, and earthquake faulting parameters consistent with regional tectonic stresses. Its volcanic or fluid-influenced seismicity features were volcanic tremor, large CLVD components in moment tensor solutions, and increasing magnitudes with time. Earthquake location tests suggest that the earthquakes occurred in a distributed volume elongated in the NS direction either directly under the volcano or within 5-10 km south of it. Following the MW 5.8 event, earthquakes occurred in a new crustal volume slightly east and north of the previous earthquakes. The central Aleutian Arc is a tectonically active region with seismicity occurring in the crusts of the Pacific and North American plates in addition to interplate events. We postulate that the Kasatochi seismic swarm was a manifestation of the complex interaction of tectonic and magmatic processes in the Earth's crust. Although magmatic intrusion triggered the earthquakes in the swarm, the earthquakes failed in context of the regional stress field.

Aftershocks, earthquake effects, and the location of the large 14 December 1872 earthquake near Entiat, central Washington

USGS Publications Warehouse

Brocher, Thomas M.; Hopper, Margaret G.; Algermissen, S.T. Ted; Perkins, David M.; Brockman, Stanley R.; Arnold, Edouard P.

2017-01-01

Reported aftershock durations, earthquake effects, and other observations from the large 14 December 1872 earthquake in central Washington are consistent with an epicenter near Entiat, Washington. Aftershocks were reported for more than 3 months only near Entiat. Modal intensity data described in this article are consistent with an Entiat area epicenter, where the largest modified Mercalli intensities, VIII, were assigned between Lake Chelan and Wenatchee. Although ground failures and water effects were widespread, there is a concentration of these features along the Columbia River and its tributaries in the Entiat area. Assuming linear ray paths, misfits from 23 reports of the directions of horizontal shaking have a local minima at Entiat, assuming the reports are describing surface waves, but the region having comparable misfit is large. Broadband seismograms recorded for comparable ray paths provide insight into the reasons why possible S–P times estimated from felt reports at two locations are several seconds too small to be consistent with an Entiat area epicenter.

Comparison of optimized algorithms in facility location allocation problems with different distance measures

NASA Astrophysics Data System (ADS)

Kumar, Rakesh; Chandrawat, Rajesh Kumar; Garg, B. P.; Joshi, Varun

2017-07-01

Opening the new firm or branch with desired execution is very relevant to facility location problem. Along the lines to locate the new ambulances and firehouses, the government desires to minimize average response time for emergencies from all residents of cities. So finding the best location is biggest challenge in day to day life. These type of problems were named as facility location problems. A lot of algorithms have been developed to handle these problems. In this paper, we review five algorithms that were applied to facility location problems. The significance of clustering in facility location problems is also presented. First we compare Fuzzy c-means clustering (FCM) algorithm with alternating heuristic (AH) algorithm, then with Particle Swarm Optimization (PSO) algorithms using different type of distance function. The data was clustered with the help of FCM and then we apply median model and min-max problem model on that data. After finding optimized locations using these algorithms we find the distance from optimized location point to the demanded point with different distance techniques and compare the results. At last, we design a general example to validate the feasibility of the five algorithms for facilities location optimization, and authenticate the advantages and drawbacks of them.

Seismic swarm associated with the 2008 eruption of Kasatochi Volcano, Alaska: Earthquake locations and source parameters

USGS Publications Warehouse

Ruppert, N.A.; Prejean, S.; Hansen, R.A.

2011-01-01

An energetic seismic swarm accompanied an eruption of Kasatochi Volcano in the central Aleutian volcanic arc in August of 2008. In retrospect, the first earthquakes in the swarm were detected about 1 month prior to the eruption onset. Activity in the swarm quickly intensified less than 48 h prior to the first large explosion and subsequently subsided with decline of eruptive activity. The largest earthquake measured as moment magnitude 5.8, and a dozen additional earthquakes were larger than magnitude 4. The swarm exhibited both tectonic and volcanic characteristics. Its shear failure earthquake features were b value = 0.9, most earthquakes with impulsive P and S arrivals and higher-frequency content, and earthquake faulting parameters consistent with regional tectonic stresses. Its volcanic or fluid-influenced seismicity features were volcanic tremor, large CLVD components in moment tensor solutions, and increasing magnitudes with time. Earthquake location tests suggest that the earthquakes occurred in a distributed volume elongated in the NS direction either directly under the volcano or within 5-10 km south of it. Following the MW 5.8 event, earthquakes occurred in a new crustal volume slightly east and north of the previous earthquakes. The central Aleutian Arc is a tectonically active region with seismicity occurring in the crusts of the Pacific and North American plates in addition to interplate events. We postulate that the Kasatochi seismic swarm was a manifestation of the complex interaction of tectonic and magmatic processes in the Earth's crust. Although magmatic intrusion triggered the earthquakes in the swarm, the earthquakes failed in context of the regional stress field. Copyright ?? 2011 by the American Geophysical Union.

A new algorithm to detect earthquakes outside the seismic network: preliminary results

NASA Astrophysics Data System (ADS)

Giudicepietro, Flora; Esposito, Antonietta Maria; Ricciolino, Patrizia

2017-04-01

In this text we are going to present a new technique for detecting earthquakes outside the seismic network, which are often the cause of fault of automatic analysis system. Our goal is to develop a robust method that provides the discrimination result as quickly as possible. We discriminate local earthquakes from regional earthquakes, both recorded at SGG station, equipped with short period sensors, operated by Osservatorio Vesuviano (INGV) in the Southern Apennines (Italy). The technique uses a Multi Layer Perceptron (MLP) neural network with an architecture composed by an input layer, a hidden layer and a single node output layer. We pre-processed the data using the Linear Predictive Coding (LPC) technique to extract the spectral features of the signals in a compact form. We performed several experiments by shortening the signal window length. In particular, we used windows of 4, 2 and 1 seconds containing the onset of the local and the regional earthquakes. We used a dataset of 103 local earthquakes and 79 regional earthquakes, most of which occurred in Greece, Albania and Crete. We split the dataset into a training set, for the network training, and a testing set to evaluate the network's capacity of discrimination. In order to assess the network stability, we repeated this procedure six times, randomly changing the data composition of the training and testing set and the initial weights of the net. We estimated the performance of this method by calculating the average of correct detection percentages obtained for each of the six permutations. The average performances are 99.02%, 98.04% and 98.53%, which concern respectively the experiments carried out on 4, 2 and 1 seconds signal windows. The results show that our method is able to recognize the earthquakes outside the seismic network using only the first second of the seismic records, with a suitable percentage of correct detection. Therefore, this algorithm can be profitably used to make earthquake automatic

Temporal Variation of Tectonic Tremor Activity Associated with Nearby Earthquakes

NASA Astrophysics Data System (ADS)

Chao, K.; Van der Lee, S.; Hsu, Y. J.; Pu, H. C.

2017-12-01

Tectonic tremor and slow slip events, located downdip from the seismogenic zone, hold the key to recurring patterns of typical earthquakes. Several findings of slow aseismic slip during the prenucletion processes of nearby earthquakes have provided new insight into the study of stress transform of slow earthquakes in fault zones prior to megathrust earthquakes. However, how tectonic tremor is associated with the occurrence of nearby earthquakes remains unclear. To enhance our understanding of the stress interaction between tremor and earthquakes, we developed an algorithm for the automatic detection and location of tectonic tremor in the collisional tectonic environment in Taiwan. Our analysis of a three-year data set indicates a short-term increase in the tremor rate starting at 19 days before the 2010 ML6.4 Jiashian main shock (Chao et al., JGR, 2017). Around the time when the tremor rate began to rise, one GPS station recorded a flip in its direction of motion. We hypothesize that tremor is driven by a slow-slip event that preceded the occurrence of the shallower nearby main shock, even though the inferred slip is too small to be observed by all GPS stations. To better quantify what the necessary condition for tremor to response to nearby earthquakes is, we obtained a 13-year ambient tremor catalog from 2004 to 2016 in the same region. We examine the spatiotemporal relationship between tremor and 37 ML>=5.0 (seven events with ML>=6.0) nearby earthquakes located within 0.5 degrees to the active tremor sources. The findings from this study can enhance our understanding of the interaction among tremor, slow slip, and nearby earthquakes in the high seismic hazard regions.

Algorithms for System Identification and Source Location.

NASA Astrophysics Data System (ADS)

Nehorai, Arye

This thesis deals with several topics in least squares estimation and applications to source location. It begins with a derivation of a mapping between Wiener theory and Kalman filtering for nonstationary autoregressive moving average (ARMO) processes. Applying time domain analysis, connections are found between time-varying state space realizations and input-output impulse response by matrix fraction description (MFD). Using these connections, the whitening filters are derived by the two approaches, and the Kalman gain is expressed in terms of Wiener theory. Next, fast estimation algorithms are derived in a unified way as special cases of the Conjugate Direction Method. The fast algorithms included are the block Levinson, fast recursive least squares, ladder (or lattice) and fast Cholesky algorithms. The results give a novel derivation and interpretation for all these methods, which are efficient alternatives to available recursive system identification algorithms. Multivariable identification algorithms are usually designed only for left MFD models. In this work, recursive multivariable identification algorithms are derived for right MFD models with diagonal denominator matrices. The algorithms are of prediction error and model reference type. Convergence analysis results obtained by the Ordinary Differential Equation (ODE) method are presented along with simulations. Sources of energy can be located by estimating time differences of arrival (TDOA's) of waves between the receivers. A new method for TDOA estimation is proposed for multiple unknown ARMA sources and additive correlated receiver noise. The method is based on a formula that uses only the receiver cross-spectra and the source poles. Two algorithms are suggested that allow tradeoffs between computational complexity and accuracy. A new time delay model is derived and used to show the applicability of the methods for non -integer TDOA's. Results from simulations illustrate the performance of the

Propagation of the velocity model uncertainties to the seismic event location

NASA Astrophysics Data System (ADS)

Gesret, A.; Desassis, N.; Noble, M.; Romary, T.; Maisons, C.

2015-01-01

Earthquake hypocentre locations are crucial in many domains of application (academic and industrial) as seismic event location maps are commonly used to delineate faults or fractures. The interpretation of these maps depends on location accuracy and on the reliability of the associated uncertainties. The largest contribution to location and uncertainty errors is due to the fact that the velocity model errors are usually not correctly taken into account. We propose a new Bayesian formulation that integrates properly the knowledge on the velocity model into the formulation of the probabilistic earthquake location. In this work, the velocity model uncertainties are first estimated with a Bayesian tomography of active shot data. We implement a sampling Monte Carlo type algorithm to generate velocity models distributed according to the posterior distribution. In a second step, we propagate the velocity model uncertainties to the seismic event location in a probabilistic framework. This enables to obtain more reliable hypocentre locations as well as their associated uncertainties accounting for picking and velocity model uncertainties. We illustrate the tomography results and the gain in accuracy of earthquake location for two synthetic examples and one real data case study in the context of induced microseismicity.

Inverting the parameters of an earthquake-ruptured fault with a genetic algorithm

NASA Astrophysics Data System (ADS)

Yu, Ting-To; Fernàndez, Josè; Rundle, John B.

1998-03-01

Natural selection is the spirit of the genetic algorithm (GA): by keeping the good genes in the current generation, thereby producing better offspring during evolution. The crossover function ensures the heritage of good genes from parent to offspring. Meanwhile, the process of mutation creates a special gene, the character of which does not exist in the parent generation. A program based on genetic algorithms using C language is constructed to invert the parameters of an earthquake-ruptured fault. The verification and application of this code is shown to demonstrate its capabilities. It is determined that this code is able to find the global extreme and can be used to solve more practical problems with constraints gathered from other sources. It is shown that GA is superior to other inverting schema in many aspects. This easy handling and yet powerful algorithm should have many suitable applications in the field of geosciences.

Aftershock Distribution of the Mw=7.8 April 16, 2016 Pedernales Ecuador Subduction Earthquake: Constraints from 3D Earthquake Locations

NASA Astrophysics Data System (ADS)

Font, Y.; Agurto-Detzel, H.; Alvarado, A. P.; Regnier, M. M.; Rolandone, F.; Charvis, P.; Mothes, P. A.; Nocquet, J. M.; Jarrin, P.; Ambrois, D.; Maron, C.; Deschamps, A.; Cheze, J.; Peix, F., Sr.; Ruiz, M. C.; Gabriela, P.; Acero, W.; Singaucho, J. C.; Viracucha, C.; Vasconez, F.; De Barros, L.; Mercerat, D.; Courboulex, F.; Galve, A.; Godano, M.; Monfret, T.; Ramos, C.; Martin, X.; Rietbrock, A.; Beck, S. L.; Metlzer, A.

2017-12-01

The Mw7.8 Pedernales earthquake is associated with the subduction of the Nazca Plate beneath the South American Plate. The mainshock caused many casualties and widespread damage across the Manabi province. The 150 km-long coseismic rupture area extends beneath the coastline, near 25 km depth. The rupture propagated southward and involved the successive rupture of two discrete asperities, with a maximum slip ( 5 m) on the southern patch. The rupture area is consistent with the highly locked regions observed on interseismic coupling models, overlaps the 7.2 Mw rupture zone, and terminates near where the 1906 Mw 8.8 megathrust earthquake rupture zone is estimated to have ended. Two neighboring highly coupled patches remain locked: (A) south and updip of the coseismic rupture zone and (B) north and downdip. In this study, we are working on the earthquake locations of the first month of aftershocks and compare the seismicity distribution to the interseismic coupling, the rupture area and to early afterslip. We use continuous seismic traces recorded on the permanent network partly installed in the framework of the collaboration between l'Institut de Recherche pour le Développement (France) and the Instituto Geofísico, Escuela Politécnica Nacional (IGEPN), Quito, Ecuador. Detections are conducted using Seiscomp in play-back mode and arrival-times are manually picked. To improve earthquake locations, we use the MAXi technique and a heterogeneous a priori P-wave velocity model that approximates the large velocity variations of the Ecuadorian subduction system. Aftershocks align along 3 to 4 main clusters that strike perpendicularly to the trench, and mostly updip of the co-seismic rupture. Seismicity develops over portions of plate interface that are known to be strongly locked or almost uncoupled. The seismicity pattern is similar to the one observed during a decade of observation during the interseismic period with swarms such as the Galera alignment, Jama and Cabo

Connecting slow earthquakes to huge earthquakes.

PubMed

Obara, Kazushige; Kato, Aitaro

2016-07-15

Slow earthquakes are characterized by a wide spectrum of fault slip behaviors and seismic radiation patterns that differ from those of traditional earthquakes. However, slow earthquakes and huge megathrust earthquakes can have common slip mechanisms and are located in neighboring regions of the seismogenic zone. The frequent occurrence of slow earthquakes may help to reveal the physics underlying megathrust events as useful analogs. Slow earthquakes may function as stress meters because of their high sensitivity to stress changes in the seismogenic zone. Episodic stress transfer to megathrust source faults leads to an increased probability of triggering huge earthquakes if the adjacent locked region is critically loaded. Careful and precise monitoring of slow earthquakes may provide new information on the likelihood of impending huge earthquakes. Copyright © 2016, American Association for the Advancement of Science.

Automatic Earthquake Detection by Active Learning

NASA Astrophysics Data System (ADS)

Bergen, K.; Beroza, G. C.

2017-12-01

In recent years, advances in machine learning have transformed fields such as image recognition, natural language processing and recommender systems. Many of these performance gains have relied on the availability of large, labeled data sets to train high-accuracy models; labeled data sets are those for which each sample includes a target class label, such as waveforms tagged as either earthquakes or noise. Earthquake seismologists are increasingly leveraging machine learning and data mining techniques to detect and analyze weak earthquake signals in large seismic data sets. One of the challenges in applying machine learning to seismic data sets is the limited labeled data problem; learning algorithms need to be given examples of earthquake waveforms, but the number of known events, taken from earthquake catalogs, may be insufficient to build an accurate detector. Furthermore, earthquake catalogs are known to be incomplete, resulting in training data that may be biased towards larger events and contain inaccurate labels. This challenge is compounded by the class imbalance problem; the events of interest, earthquakes, are infrequent relative to noise in continuous data sets, and many learning algorithms perform poorly on rare classes. In this work, we investigate the use of active learning for automatic earthquake detection. Active learning is a type of semi-supervised machine learning that uses a human-in-the-loop approach to strategically supplement a small initial training set. The learning algorithm incorporates domain expertise through interaction between a human expert and the algorithm, with the algorithm actively posing queries to the user to improve detection performance. We demonstrate the potential of active machine learning to improve earthquake detection performance with limited available training data.

Short-term volcano-tectonic earthquake forecasts based on a moving mean recurrence time algorithm: the El Hierro seismo-volcanic crisis experience

NASA Astrophysics Data System (ADS)

García, Alicia; De la Cruz-Reyna, Servando; Marrero, José M.; Ortiz, Ramón

2016-05-01

Under certain conditions, volcano-tectonic (VT) earthquakes may pose significant hazards to people living in or near active volcanic regions, especially on volcanic islands; however, hazard arising from VT activity caused by localized volcanic sources is rarely addressed in the literature. The evolution of VT earthquakes resulting from a magmatic intrusion shows some orderly behaviour that may allow the occurrence and magnitude of major events to be forecast. Thus governmental decision makers can be supplied with warnings of the increased probability of larger-magnitude earthquakes on the short-term timescale. We present here a methodology for forecasting the occurrence of large-magnitude VT events during volcanic crises; it is based on a mean recurrence time (MRT) algorithm that translates the Gutenberg-Richter distribution parameter fluctuations into time windows of increased probability of a major VT earthquake. The MRT forecasting algorithm was developed after observing a repetitive pattern in the seismic swarm episodes occurring between July and November 2011 at El Hierro (Canary Islands). From then on, this methodology has been applied to the consecutive seismic crises registered at El Hierro, achieving a high success rate in the real-time forecasting, within 10-day time windows, of volcano-tectonic earthquakes.

Statistical validation of earthquake related observations

NASA Astrophysics Data System (ADS)

Kossobokov, V. G.

2011-12-01

The confirmed fractal nature of earthquakes and their distribution in space and time implies that many traditional estimations of seismic hazard (from term-less to short-term ones) are usually based on erroneous assumptions of easy tractable or, conversely, delicately-designed models. The widespread practice of deceptive modeling considered as a "reasonable proxy" of the natural seismic process leads to seismic hazard assessment of unknown quality, which errors propagate non-linearly into inflicted estimates of risk and, eventually, into unexpected societal losses of unacceptable level. The studies aimed at forecast/prediction of earthquakes must include validation in the retro- (at least) and, eventually, in prospective tests. In the absence of such control a suggested "precursor/signal" remains a "candidate", which link to target seismic event is a model assumption. Predicting in advance is the only decisive test of forecast/predictions and, therefore, the score-card of any "established precursor/signal" represented by the empirical probabilities of alarms and failures-to-predict achieved in prospective testing must prove statistical significance rejecting the null-hypothesis of random coincidental occurrence in advance target earthquakes. We reiterate suggesting so-called "Seismic Roulette" null-hypothesis as the most adequate undisturbed random alternative accounting for the empirical spatial distribution of earthquakes: (i) Consider a roulette wheel with as many sectors as the number of earthquake locations from a sample catalog representing seismic locus, a sector per each location and (ii) make your bet according to prediction (i.e., determine, which locations are inside area of alarm, and put one chip in each of the corresponding sectors); (iii) Nature turns the wheel; (iv) accumulate statistics of wins and losses along with the number of chips spent. If a precursor in charge of prediction exposes an imperfection of Seismic Roulette then, having in mind

The Improved Locating Algorithm of Particle Filter Based on ROS Robot

NASA Astrophysics Data System (ADS)

Fang, Xun; Fu, Xiaoyang; Sun, Ming

2018-03-01

This paperanalyzes basic theory and primary algorithm of the real-time locating system and SLAM technology based on ROS system Robot. It proposes improved locating algorithm of particle filter effectively reduces the matching time of laser radar and map, additional ultra-wideband technology directly accelerates the global efficiency of FastSLAM algorithm, which no longer needs searching on the global map. Meanwhile, the re-sampling has been largely reduced about 5/6 that directly cancels the matching behavior on Roboticsalgorithm.

A Bayesian Approach to Real-Time Earthquake Phase Association

NASA Astrophysics Data System (ADS)

Benz, H.; Johnson, C. E.; Earle, P. S.; Patton, J. M.

2014-12-01

Real-time location of seismic events requires a robust and extremely efficient means of associating and identifying seismic phases with hypothetical sources. An association algorithm converts a series of phase arrival times into a catalog of earthquake hypocenters. The classical approach based on time-space stacking of the locus of possible hypocenters for each phase arrival using the principal of acoustic reciprocity has been in use now for many years. One of the most significant problems that has emerged over time with this approach is related to the extreme variations in seismic station density throughout the global seismic network. To address this problem we have developed a novel, Bayesian association algorithm, which looks at the association problem as a dynamically evolving complex system of "many to many relationships". While the end result must be an array of one to many relations (one earthquake, many phases), during the association process the situation is quite different. Both the evolving possible hypocenters and the relationships between phases and all nascent hypocenters is many to many (many earthquakes, many phases). The computational framework we are using to address this is a responsive, NoSQL graph database where the earthquake-phase associations are represented as intersecting Bayesian Learning Networks. The approach directly addresses the network inhomogeneity issue while at the same time allowing the inclusion of other kinds of data (e.g., seismic beams, station noise characteristics, priors on estimated location of the seismic source) by representing the locus of intersecting hypothetical loci for a given datum as joint probability density functions.

Outward-dipping ring-fault structure at rabaul caldera as shown by earthquake locations.

PubMed

Mori, J; McKee, C

1987-01-09

The locations of a large number of earthquakes recorded at Rabaul caldera in Papua New Guinea from late 1983 to mid-1985 have produced a picture of this active caldera's structural boundary. The earthquake epicenters form an elliptical annulus about 10 kilometers long by 4 kilometers wide, centered in the southern part of the Rabaul volcanic complex. A set of events with well-constrained depth determinations shows a ring-fault structure that extends from the surface to a depth of about 4 kilometers and slopes steeply outward from the center of the caldera. This is the first geophysical data set that clearly outlines the orientation of an active caldera's bounding faults. This orientation, however, conflicts with the configuration of many other calderas and is not in keeping with currently preferred models of caldera formation.

Estimating the Locations of Past and Future Large Earthquake Ruptures using Recent M4 and Greater Events

NASA Astrophysics Data System (ADS)

Ebel, J.; Chambers, D. W.

2017-12-01

Although most aftershock activity dies away within months or a few years of a mainshock, there is evidence that aftershocks still occur decades or even centuries after mainshocks, particularly in areas of low background seismicity such as stable continental regions. There also is evidence of long-lasting aftershock sequences in California. New work to study the occurrences of recent M≥4 in California shows that these events occur preferentially at the edges of past major ruptures, with the effect lessening with decreasing magnitude below M4. Prior to several California mainshocks, the M≥4 seismicity was uniformly spread along the future fault ruptures without concentrations at the fault ends. On these faults, the rates of the M≥4 earthquakes prior to the mainshocks were much greater than the rates of the recent M≥4 earthquakes. These results suggest that the spatial patterns and rates of M≥4 earthquakes may help identify which faults are most prone to rupturing in the near future. Using this idea, speculation on which faults in California may be the next ones to experience major earthquakes is presented. Some Japanese earthquakes were also tested for the patterns of M≥4 earthquake seen in California. The 2000 Mw6.6 Western Tottori earthquake shows a premonitory pattern similar to the patterns seen in California, and there have not been any M≥4 earthquakes in the fault vicinity since 2010. The 1995 Mw6.9 Kobe earthquake had little M≥4 seismicity in the years prior to the mainshock, and the M≥4 seismicity since 2000 has been scattered along the fault rupture. Both the 2016 M7.3 Kumamoto, Kyushu earthquake and the 2016 Mw6.2 Central Tottori earthquake had some M≥4 earthquakes along the fault in the two decades before the mainshocks. The results of these analyses suggest that the locations of recent M≥4 earthquakes may be useful for determining the spatial extents of past earthquake ruptures and also may help indicate which faults may have strong

Application of genetic algorithms to focal mechanism determination

NASA Astrophysics Data System (ADS)

Kobayashi, Reiji; Nakanishi, Ichiro

1994-04-01

Genetic algorithms are a new class of methods for global optimization. They resemble Monte Carlo techniques, but search for solutions more efficiently than uniform Monte Carlo sampling. In the field of geophysics, genetic algorithms have recently been used to solve some non-linear inverse problems (e.g., earthquake location, waveform inversion, migration velocity estimation). We present an application of genetic algorithms to focal mechanism determination from first-motion polarities of P-waves and apply our method to two recent large events, the Kushiro-oki earthquake of January 15, 1993 and the SW Hokkaido (Japan Sea) earthquake of July 12, 1993. Initial solution and curvature information of the objective function that gradient methods need are not required in our approach. Moreover globally optimal solutions can be efficiently obtained. Calculation of polarities based on double-couple models is the most time-consuming part of the source mechanism determination. The amount of calculations required by the method designed in this study is much less than that of previous grid search methods.

Earthquake prediction in California using regression algorithms and cloud-based big data infrastructure

NASA Astrophysics Data System (ADS)

Asencio-Cortés, G.; Morales-Esteban, A.; Shang, X.; Martínez-Álvarez, F.

2018-06-01

Earthquake magnitude prediction is a challenging problem that has been widely studied during the last decades. Statistical, geophysical and machine learning approaches can be found in literature, with no particularly satisfactory results. In recent years, powerful computational techniques to analyze big data have emerged, making possible the analysis of massive datasets. These new methods make use of physical resources like cloud based architectures. California is known for being one of the regions with highest seismic activity in the world and many data are available. In this work, the use of several regression algorithms combined with ensemble learning is explored in the context of big data (1 GB catalog is used), in order to predict earthquakes magnitude within the next seven days. Apache Spark framework, H2 O library in R language and Amazon cloud infrastructure were been used, reporting very promising results.

Disease and injury trends among evacuees in a shelter located at the epicenter of the 2016 Kumamoto earthquakes, Japan.

PubMed

Yorifuji, Takashi; Sato, Takushi; Yoneda, Toru; Kishida, Yoshiomi; Yamamoto, Sumie; Sakai, Taro; Sashiyama, Hiroshi; Takahashi, Shuko; Orui, Hayato; Kato, Daisuke; Hasegawa, Taro; Suzuki, Yoshihiro; Okamoto, Maki; Hayashi, Hideki; Suganami, Shigeru

2017-06-16

Two huge earthquakes struck Kumamoto, Japan, in April 2016, forcing residents to evacuate. Few studies have reported early-phase disease and injury trends among evacuees following major inland earthquakes. We evaluated the trends among evacuees who visited a medical clinic in a shelter located at the epicenter of the 2016 Kumamoto earthquakes. The clinic opened on April 15, the day after the foreshock, and closed 3 weeks later. We reviewed medical charts related to 929 outpatient visits and conducted descriptive analyses. The evacuees experienced mild injuries and common diseases. The types of diseases changed weekly. Elderly people needed medical support for longer than other age groups. Future earthquakes may be inevitable, but establishing arrangements for medical needs or making precautions for infectious diseases in shelters could reduce the effects of earthquake-related health problems.

Constraining Source Locations of Shallow Subduction Megathrust Earthquakes in 1-D and 3-D Velocity Models - A Case Study of the 2002 Mw=6.4 Osa Earthquake, Costa Rica

NASA Astrophysics Data System (ADS)

Grevemeyer, I.; Arroyo, I. G.

2015-12-01

Earthquake source locations are generally routinely constrained using a global 1-D Earth model. However, the source location might be associated with large uncertainties. This is definitively the case for earthquakes occurring at active continental margins were thin oceanic crust subducts below thick continental crust and hence large lateral changes in crustal thickness occur as a function of distance to the deep-sea trench. Here, we conducted a case study of the 2002 Mw 6.4 Osa thrust earthquake in Costa Rica that was followed by an aftershock sequence. Initial relocations indicated that the main shock occurred fairly trenchward of most large earthquakes along the Middle America Trench off central Costa Rica. The earthquake sequence occurred while a temporary network of ocean-bottom-hydrophones and land stations 80 km to the northwest were deployed. By adding readings from permanent Costa Rican stations, we obtain uncommon P wave coverage of a large subduction zone earthquake. We relocated this catalog using a nonlinear probabilistic approach using a 1-D and two 3-D P-wave velocity models. The 3-D model was either derived from 3-D tomography based on onshore stations and a priori model based on seismic refraction data. All epicentres occurred close to the trench axis, but depth estimates vary by several tens of kilometres. Based on the epicentres and constraints from seismic reflection data the main shock occurred 25 km from the trench and probably along the plate interface at 5-10 km depth. The source location that agreed best with the geology was based on the 3-D velocity model derived from a priori data. Aftershocks propagated downdip to the area of a 1999 Mw 6.9 sequence and partially overlapped it. The results indicate that underthrusting of the young and buoyant Cocos Ridge has created conditions for interpolate seismogenesis shallower and closer to the trench axis than elsewhere along the central Costa Rica margin.

Study on Earthquake Emergency Evacuation Drill Trainer Development

NASA Astrophysics Data System (ADS)

ChangJiang, L.

2016-12-01

With the improvement of China's urbanization, to ensure people survive the earthquake needs scientific routine emergency evacuation drills. Drawing on cellular automaton, shortest path algorithm and collision avoidance, we designed a model of earthquake emergency evacuation drill for school scenes. Based on this model, we made simulation software for earthquake emergency evacuation drill. The software is able to perform the simulation of earthquake emergency evacuation drill by building spatial structural model and selecting the information of people's location grounds on actual conditions of constructions. Based on the data of simulation, we can operate drilling in the same building. RFID technology could be used here for drill data collection which read personal information and send it to the evacuation simulation software via WIFI. Then the simulation software would contrast simulative data with the information of actual evacuation process, such as evacuation time, evacuation path, congestion nodes and so on. In the end, it would provide a contrastive analysis report to report assessment result and optimum proposal. We hope the earthquake emergency evacuation drill software and trainer can provide overall process disposal concept for earthquake emergency evacuation drill in assembly occupancies. The trainer can make the earthquake emergency evacuation more orderly, efficient, reasonable and scientific to fulfill the increase in coping capacity of urban hazard.

Seismicity, faulting, and structure of the Koyna-Warna seismic region, Western India from local earthquake tomography and hypocenter locations

NASA Astrophysics Data System (ADS)

Dixit, Madan M.; Kumar, Sanjay; Catchings, R. D.; Suman, K.; Sarkar, Dipankar; Sen, M. K.

2014-08-01

Although seismicity near Koyna Reservoir (India) has persisted for ~50 years and includes the largest induced earthquake (M 6.3) reported worldwide, the seismotectonic framework of the area is not well understood. We recorded ~1800 earthquakes from 6 January 2010 to 28 May 2010 and located a subset of 343 of the highest-quality earthquakes using the tomoDD code of Zhang and Thurber (2003) to better understand the framework. We also inverted first arrivals for 3-D Vp, Vs, and Vp/Vs and Poisson's ratio tomography models of the upper 12 km of the crust. Epicenters for the recorded earthquakes are located south of the Koyna River, including a high-density cluster that coincides with a shallow depth (<1.5 km) zone of relatively high Vp and low Vs (also high Vp/Vs and Poisson's ratios) near Warna Reservoir. This anomalous zone, which extends near vertically to at least 8 km depth and laterally northward at least 15 km, is likely a water-saturated zone of faults under high pore pressures. Because many of the earthquakes occur on the periphery of the fault zone, rather than near its center, the observed seismicity-velocity correlations are consistent with the concept that many of the earthquakes nucleate in fractures adjacent to the main fault zone due to high pore pressure. We interpret our velocity images as showing a series of northwest trending faults locally near the central part of Warna Reservoir and a major northward trending fault zone north of Warna Reservoir.

The Development of Several Electromagnetic Monitoring Strategies and Algorithms for Validating Pre-Earthquake Electromagnetic Signals

NASA Astrophysics Data System (ADS)

Bleier, T. E.; Dunson, J. C.; Roth, S.; Mueller, S.; Lindholm, C.; Heraud, J. A.

2012-12-01

QuakeFinder, a private research group in California, reports on the development of a 100+ station network consisting of 3-axis induction magnetometers, and air conductivity sensors to collect and characterize pre-seismic electromagnetic (EM) signals. These signals are combined with daily Infra Red signals collected from the GOES weather satellite infrared (IR) instrument to compare and correlate with the ground EM signals, both from actual earthquakes and boulder stressing experiments. This presentation describes the efforts QuakeFinder has undertaken to automatically detect these pulse patterns using their historical data as a reference, and to develop other discriminative algorithms that can be used with air conductivity sensors, and IR instruments from the GOES satellites. The overall big picture results of the QuakeFinder experiment are presented. In 2007, QuakeFinder discovered the occurrence of strong uni-polar pulses in their magnetometer coil data that increased in tempo dramatically prior to the M5.1 earthquake at Alum Rock, California. Suggestions that these pulses might have been lightning or power-line arcing did not fit with the data actually recorded as was reported in Bleier [2009]. Then a second earthquake occurred near the same site on January 7, 2010 as was reported in Dunson [2011], and the pattern of pulse count increases before the earthquake occurred similarly to the 2007 event. There were fewer pulses, and the magnitude of them was decreased, both consistent with the fact that the earthquake was smaller (M4.0 vs M5.4) and farther away (7Km vs 2km). At the same time similar effects were observed at the QuakeFinder Tacna, Peru site before the May 5th, 2010 M6.2 earthquake and a cluster of several M4-5 earthquakes.

Bayesian historical earthquake relocation: an example from the 1909 Taipei earthquake

USGS Publications Warehouse

Minson, Sarah E.; Lee, William H.K.

2014-01-01

Locating earthquakes from the beginning of the modern instrumental period is complicated by the fact that there are few good-quality seismograms and what traveltimes do exist may be corrupted by both large phase-pick errors and clock errors. Here, we outline a Bayesian approach to simultaneous inference of not only the hypocentre location but also the clock errors at each station and the origin time of the earthquake. This methodology improves the solution for the source location and also provides an uncertainty analysis on all of the parameters included in the inversion. As an example, we applied this Bayesian approach to the well-studied 1909 Mw 7 Taipei earthquake. While our epicentre location and origin time for the 1909 Taipei earthquake are consistent with earlier studies, our focal depth is significantly shallower suggesting a higher seismic hazard to the populous Taipei metropolitan area than previously supposed.

Earthquake source parameters from GPS-measured static displacements with potential for real-time application

NASA Astrophysics Data System (ADS)

O'Toole, Thomas B.; Valentine, Andrew P.; Woodhouse, John H.

2013-01-01

We describe a method for determining an optimal centroid-moment tensor solution of an earthquake from a set of static displacements measured using a network of Global Positioning System receivers. Using static displacements observed after the 4 April 2010, MW 7.2 El Mayor-Cucapah, Mexico, earthquake, we perform an iterative inversion to obtain the source mechanism and location, which minimize the least-squares difference between data and synthetics. The efficiency of our algorithm for forward modeling static displacements in a layered elastic medium allows the inversion to be performed in real-time on a single processor without the need for precomputed libraries of excitation kernels; we present simulated real-time results for the El Mayor-Cucapah earthquake. The only a priori information that our inversion scheme needs is a crustal model and approximate source location, so the method proposed here may represent an improvement on existing early warning approaches that rely on foreknowledge of fault locations and geometries.

Application of the region-time-length algorithm to study of earthquake precursors in the Thailand-Laos-Myanmar borders

NASA Astrophysics Data System (ADS)

Puangjaktha, P.; Pailoplee, S.

2018-04-01

In order to examine the precursory seismic quiescence of upcoming hazardous earthquakes, the seismicity data available in the vicinity of the Thailand-Laos-Myanmar borders was analyzed using the Region-Time-Length (RTL) algorithm based statistical technique. The utilized earthquake data were obtained from the International Seismological Centre. Thereafter, the homogeneity and completeness of the catalogue were improved. After performing iterative tests with different values of the r0 and t0 parameters, those of r0 = 120 km and t0 = 2 yr yielded reasonable estimates of the anomalous RTL scores, in both temporal variation and spatial distribution, of a few years prior to five out of eight strong-to-major recognized earthquakes. Statistical evaluation of both the correlation coefficient and stochastic process for the RTL were checked and revealed that the RTL score obtained here excluded artificial or random phenomena. Therefore, the prospective earthquake sources mentioned here should be recognized and effective mitigation plans should be provided.

A novel tree-based algorithm to discover seismic patterns in earthquake catalogs

NASA Astrophysics Data System (ADS)

Florido, E.; Asencio-Cortés, G.; Aznarte, J. L.; Rubio-Escudero, C.; Martínez-Álvarez, F.

2018-06-01

A novel methodology is introduced in this research study to detect seismic precursors. Based on an existing approach, the new methodology searches for patterns in the historical data. Such patterns may contain statistical or soil dynamics information. It improves the original version in several aspects. First, new seismicity indicators have been used to characterize earthquakes. Second, a machine learning clustering algorithm has been applied in a very flexible way, thus allowing the discovery of new data groupings. Third, a novel search strategy is proposed in order to obtain non-overlapped patterns. And, fourth, arbitrary lengths of patterns are searched for, thus discovering long and short-term behaviors that may influence in the occurrence of medium-large earthquakes. The methodology has been applied to seven different datasets, from three different regions, namely the Iberian Peninsula, Chile and Japan. Reported results show a remarkable improvement with respect to the former version, in terms of all evaluated quality measures. In particular, the number of false positives has decreased and the positive predictive values increased, both of them in a very remarkable manner.

NASA Spacecraft Image Shows Location of Iranian Earthquake

NASA Image and Video Library

2017-12-08

On April 9, 2013 at 11:52 GMT, a magnitude 6.3 earthquake hit southwestern Iran's Bushehr province near the town of Kaki. Preliminary information is that several villages have been destroyed and many people have died, as reported by BBC News. This perspective view of the region was acquired Nov. 17, 2012, by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra spacecraft. The location of the earthquake's epicenter is marked with a yellow star. Vegetation is displayed in red; the vertical exaggeration of the topography is 2X. The image is centered near 28.5 degrees north latitude, 51.6 degrees east longitude. With its 14 spectral bands from the visible to the thermal infrared wavelength region and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER images Earth to map and monitor the changing surface of our planet. ASTER is one of five Earth-observing instruments launched Dec. 18, 1999, on Terra. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and data products. The broad spectral coverage and high spectral resolution of ASTER provides scientists in numerous disciplines with critical information for surface mapping and monitoring of dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; wetlands evaluation; thermal pollution monitoring; coral reef degradation; surface temperature mapping of soils and geology; and measuring surface heat balance. The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate, Washington, D.C. More information about ASTER is available at asterweb.jpl.nasa.gov/. Image Credit: NASA

Optimizing the real-time automatic location of the events produced in Romania using an advanced processing system

NASA Astrophysics Data System (ADS)

Neagoe, Cristian; Grecu, Bogdan; Manea, Liviu

2016-04-01

National Institute for Earth Physics (NIEP) operates a real time seismic network which is designed to monitor the seismic activity on the Romanian territory, which is dominated by the intermediate earthquakes (60-200 km) from Vrancea area. The ability to reduce the impact of earthquakes on society depends on the existence of a large number of high-quality observational data. The development of the network in recent years and an advanced seismic acquisition are crucial to achieving this objective. The software package used to perform the automatic real-time locations is Seiscomp3. An accurate choice of the Seiscomp3 setting parameters is necessary to ensure the best performance of the real-time system i.e., the most accurate location for the earthquakes and avoiding any false events. The aim of this study is to optimize the algorithms of the real-time system that detect and locate the earthquakes in the monitored area. This goal is pursued by testing different parameters (e.g., STA/LTA, filters applied to the waveforms) on a data set of representative earthquakes of the local seismicity. The results are compared with the locations from the Romanian Catalogue ROMPLUS.

Rapid Estimates of Rupture Extent for Large Earthquakes Using Aftershocks

NASA Astrophysics Data System (ADS)

Polet, J.; Thio, H. K.; Kremer, M.

2009-12-01

The spatial distribution of aftershocks is closely linked to the rupture extent of the mainshock that preceded them and a rapid analysis of aftershock patterns therefore has potential for use in near real-time estimates of earthquake impact. The correlation between aftershocks and slip distribution has frequently been used to estimate the fault dimensions of large historic earthquakes for which no, or insufficient, waveform data is available. With the advent of earthquake inversions that use seismic waveforms and geodetic data to constrain the slip distribution, the study of aftershocks has recently been largely focused on enhancing our understanding of the underlying mechanisms in a broader earthquake mechanics/dynamics framework. However, in a near real-time earthquake monitoring environment, in which aftershocks of large earthquakes are routinely detected and located, these data may also be effective in determining a fast estimate of the mainshock rupture area, which would aid in the rapid assessment of the impact of the earthquake. We have analyzed a considerable number of large recent earthquakes and their aftershock sequences and have developed an effective algorithm that determines the rupture extent of a mainshock from its aftershock distribution, in a fully automatic manner. The algorithm automatically removes outliers by spatial binning, and subsequently determines the best fitting “strike” of the rupture and its length by projecting the aftershock epicenters onto a set of lines that cross the mainshock epicenter with incremental azimuths. For strike-slip or large dip-slip events, for which the surface projection of the rupture is recti-linear, the calculated strike correlates well with the strike of the fault and the corresponding length, determined from the distribution of aftershocks projected onto the line, agrees well with the rupture length. In the case of a smaller dip-slip rupture with an aspect ratio closer to 1, the procedure gives a measure

Seismicity, faulting, and structure of the Koyna-Warna seismic region, Western India from local earthquake tomography and hypocenter locations

USGS Publications Warehouse

Dixit, Madan M.; Kumar, Sanjay; Catchings, Rufus D.; Suman, K.; Sarkar, Dipankar; Sen, M.K.

2014-01-01

Although seismicity near Koyna Reservoir (India) has persisted for ~50 years and includes the largest induced earthquake (M 6.3) reported worldwide, the seismotectonic framework of the area is not well understood. We recorded ~1800 earthquakes from 6 January 2010 to 28 May 2010 and located a subset of 343 of the highest-quality earthquakes using the tomoDD code of Zhang and Thurber (2003) to better understand the framework. We also inverted first arrivals for 3-D Vp, Vs, and Vp/Vs and Poisson's ratio tomography models of the upper 12 km of the crust. Epicenters for the recorded earthquakes are located south of the Koyna River, including a high-density cluster that coincides with a shallow depth (<1.5 km) zone of relatively high Vp and low Vs (also high Vp/Vs and Poisson's ratios) near Warna Reservoir. This anomalous zone, which extends near vertically to at least 8 km depth and laterally northward at least 15 km, is likely a water-saturated zone of faults under high pore pressures. Because many of the earthquakes occur on the periphery of the fault zone, rather than near its center, the observed seismicity-velocity correlations are consistent with the concept that many of the earthquakes nucleate in fractures adjacent to the main fault zone due to high pore pressure. We interpret our velocity images as showing a series of northwest trending faults locally near the central part of Warna Reservoir and a major northward trending fault zone north of Warna Reservoir.

A Benders based rolling horizon algorithm for a dynamic facility location problem

DOE PAGES

Marufuzzaman,, Mohammad; Gedik, Ridvan; Roni, Mohammad S.

2016-06-28

This study presents a well-known capacitated dynamic facility location problem (DFLP) that satisfies the customer demand at a minimum cost by determining the time period for opening, closing, or retaining an existing facility in a given location. To solve this challenging NP-hard problem, this paper develops a unique hybrid solution algorithm that combines a rolling horizon algorithm with an accelerated Benders decomposition algorithm. Extensive computational experiments are performed on benchmark test instances to evaluate the hybrid algorithm’s efficiency and robustness in solving the DFLP problem. Computational results indicate that the hybrid Benders based rolling horizon algorithm consistently offers high qualitymore » feasible solutions in a much shorter computational time period than the standalone rolling horizon and accelerated Benders decomposition algorithms in the experimental range.« less

Using a modified time-reverse imaging technique to locate low-frequency earthquakes on the San Andreas Fault near Cholame, California

USGS Publications Warehouse

Horstmann, Tobias; Harrington, Rebecca M.; Cochran, Elizabeth S.

2015-01-01

We present a new method to locate low-frequency earthquakes (LFEs) within tectonic tremor episodes based on time-reverse imaging techniques. The modified time-reverse imaging technique presented here is the first method that locates individual LFEs within tremor episodes within 5 km uncertainty without relying on high-amplitude P-wave arrivals and that produces similar hypocentral locations to methods that locate events by stacking hundreds of LFEs without having to assume event co-location. In contrast to classic time-reverse imaging algorithms, we implement a modification to the method that searches for phase coherence over a short time period rather than identifying the maximum amplitude of a superpositioned wavefield. The method is independent of amplitude and can help constrain event origin time. The method uses individual LFE origin times, but does not rely on a priori information on LFE templates and families.We apply the method to locate 34 individual LFEs within tremor episodes that occur between 2010 and 2011 on the San Andreas Fault, near Cholame, California. Individual LFE location accuracies range from 2.6 to 5 km horizontally and 4.8 km vertically. Other methods that have been able to locate individual LFEs with accuracy of less than 5 km have mainly used large-amplitude events where a P-phase arrival can be identified. The method described here has the potential to locate a larger number of individual low-amplitude events with only the S-phase arrival. Location accuracy is controlled by the velocity model resolution and the wavelength of the dominant energy of the signal. Location results are also dependent on the number of stations used and are negligibly correlated with other factors such as the maximum gap in azimuthal coverage, source–station distance and signal-to-noise ratio.

Calculation of earthquake rupture histories using a hybrid global search algorithm: Application to the 1992 Landers, California, earthquake

USGS Publications Warehouse

Hartzell, S.; Liu, P.

1996-01-01

A method is presented for the simultaneous calculation of slip amplitudes and rupture times for a finite fault using a hybrid global search algorithm. The method we use combines simulated annealing with the downhill simplex method to produce a more efficient search algorithm then either of the two constituent parts. This formulation has advantages over traditional iterative or linearized approaches to the problem because it is able to escape local minima in its search through model space for the global optimum. We apply this global search method to the calculation of the rupture history for the Landers, California, earthquake. The rupture is modeled using three separate finite-fault planes to represent the three main fault segments that failed during this earthquake. Both the slip amplitude and the time of slip are calculated for a grid work of subfaults. The data used consist of digital, teleseismic P and SH body waves. Long-period, broadband, and short-period records are utilized to obtain a wideband characterization of the source. The results of the global search inversion are compared with a more traditional linear-least-squares inversion for only slip amplitudes. We use a multi-time-window linear analysis to relax the constraints on rupture time and rise time in the least-squares inversion. Both inversions produce similar slip distributions, although the linear-least-squares solution has a 10% larger moment (7.3 ?? 1026 dyne-cm compared with 6.6 ?? 1026 dyne-cm). Both inversions fit the data equally well and point out the importance of (1) using a parameterization with sufficient spatial and temporal flexibility to encompass likely complexities in the rupture process, (2) including suitable physically based constraints on the inversion to reduce instabilities in the solution, and (3) focusing on those robust rupture characteristics that rise above the details of the parameterization and data set.

G-FAST Early Warning Potential for Great Earthquakes in Chile

NASA Astrophysics Data System (ADS)

Crowell, B.; Schmidt, D. A.; Baker, B. I.; Bodin, P.; Vidale, J. E.

2016-12-01

The importance of GNSS-based earthquake early warning for modeling large earthquakes has been studied extensively over the past decade and several such systems are currently under development. In the Pacific Northwest, we have developed the G-FAST GNSS-based earthquake early warning module for eventual inclusion in the US West-Coast wide ShakeAlert system. We have also created a test system that allows us to replay past and synthetic earthquakes to identify problems with both the network architecture and the algorithms. Between 2010 and 2016, there have been seven M > 8 earthquakes across the globe, of which three struck offshore Chile; the 27 February 2010 Mw 8.8 Maule, the 1 April 2014 Mw 8.2 Iquique, and the 16 September 2015 Mw 8.3 Illapel. Subsequent to these events, the Chilean national GNSS network operated by the Centro Sismologico Nacional (http://www.sismologia.cl/) greatly expanded to over 150 continuous GNSS stations, providing the best recordings of great earthquakes with GNSS outside of Japan. Here we report on retrospective G-FAST performance for those three great earthquakes in Chile. We discuss the interplay of location errors, latency, and data completeness with respect to the precision and timing of G-FAST earthquake source alerts as well as the computational demands of the system.

A General Event Location Algorithm with Applications to Eclipse and Station Line-of-Sight

NASA Technical Reports Server (NTRS)

Parker, Joel J. K.; Hughes, Steven P.

2011-01-01

A general-purpose algorithm for the detection and location of orbital events is developed. The proposed algorithm reduces the problem to a global root-finding problem by mapping events of interest (such as eclipses, station access events, etc.) to continuous, differentiable event functions. A stepping algorithm and a bracketing algorithm are used to detect and locate the roots. Examples of event functions and the stepping/bracketing algorithms are discussed, along with results indicating performance and accuracy in comparison to commercial tools across a variety of trajectories.

A General Event Location Algorithm with Applications to Eclispe and Station Line-of-Sight

NASA Technical Reports Server (NTRS)

Parker, Joel J. K.; Hughes, Steven P.

2011-01-01

A general-purpose algorithm for the detection and location of orbital events is developed. The proposed algorithm reduces the problem to a global root-finding problem by mapping events of interest (such as eclipses, station access events, etc.) to continuous, differentiable event functions. A stepping algorithm and a bracketing algorithm are used to detect and locate the roots. Examples of event functions and the stepping/bracketing algorithms are discussed, along with results indicating performance and accuracy in comparison to commercial tools across a variety of trajectories.

Delineation of Rupture Propagation of Large Earthquakes Using Source-Scanning Algorithm: A Control Study

NASA Astrophysics Data System (ADS)

Kao, H.; Shan, S.

2004-12-01

Determination of the rupture propagation of large earthquakes is important and of wide interest to the seismological research community. The conventional inversion method determines the distribution of slip at a grid of subfaults whose orientations are predefined. As a result, difference choices of fault geometry and dimensions often result in different solutions. In this study, we try to reconstruct the rupture history of an earthquake using the newly developed Source-Scanning Algorithm (SSA) without imposing any a priori constraints on the fault's orientation and dimension. The SSA identifies the distribution of seismic sources in two steps. First, it calculates the theoretical arrival times from all grid points inside the model space to all seismic stations by assuming an origin time. Then, the absolute amplitudes of the observed waveforms at the predicted arrival times are added to give the "brightness" of each time-space pair, and the brightest spots mark the locations of sources. The propagation of the rupture is depicted by the migration of the brightest spots throughout a prescribed time window. A series of experiments are conducted to test the resolution of the SSA inversion. Contrary to the conventional wisdom that seismometers should be placed as close as possible to the fault trace to give the best resolution in delineating rupture details, we found that the best results are obtained if the seismograms are recorded at a distance about half of the total rupture length away from the fault trace. This is especially true when the rupture duration is longer than ~10 s. A possible explanation is that the geometric spreading effects for waveforms from different segments of the rupture are about the same if the stations are sufficiently away from the fault trace, thus giving a uniform resolution to the entire rupture history.

PAGER--Rapid assessment of an earthquake?s impact

USGS Publications Warehouse

Wald, D.J.; Jaiswal, K.; Marano, K.D.; Bausch, D.; Hearne, M.

2010-01-01

PAGER (Prompt Assessment of Global Earthquakes for Response) is an automated system that produces content concerning the impact of significant earthquakes around the world, informing emergency responders, government and aid agencies, and the media of the scope of the potential disaster. PAGER rapidly assesses earthquake impacts by comparing the population exposed to each level of shaking intensity with models of economic and fatality losses based on past earthquakes in each country or region of the world. Earthquake alerts--which were formerly sent based only on event magnitude and location, or population exposure to shaking--now will also be generated based on the estimated range of fatalities and economic losses.

Geodetic Finite-Fault-based Earthquake Early Warning Performance for Great Earthquakes Worldwide

NASA Astrophysics Data System (ADS)

Ruhl, C. J.; Melgar, D.; Grapenthin, R.; Allen, R. M.

2017-12-01

GNSS-based earthquake early warning (EEW) algorithms estimate fault-finiteness and unsaturated moment magnitude for the largest, most damaging earthquakes. Because large events are infrequent, algorithms are not regularly exercised and insufficiently tested on few available datasets. The Geodetic Alarm System (G-larmS) is a GNSS-based finite-fault algorithm developed as part of the ShakeAlert EEW system in the western US. Performance evaluations using synthetic earthquakes offshore Cascadia showed that G-larmS satisfactorily recovers magnitude and fault length, providing useful alerts 30-40 s after origin time and timely warnings of ground motion for onshore urban areas. An end-to-end test of the ShakeAlert system demonstrated the need for GNSS data to accurately estimate ground motions in real-time. We replay real data from several subduction-zone earthquakes worldwide to demonstrate the value of GNSS-based EEW for the largest, most damaging events. We compare predicted ground acceleration (PGA) from first-alert-solutions with those recorded in major urban areas. In addition, where applicable, we compare observed tsunami heights to those predicted from the G-larmS solutions. We show that finite-fault inversion based on GNSS-data is essential to achieving the goals of EEW.

Links Between Earthquake Characteristics and Subducting Plate Heterogeneity in the 2016 Pedernales Ecuador Earthquake Rupture Zone

NASA Astrophysics Data System (ADS)

Bai, L.; Mori, J. J.

2016-12-01

The collision between the Indian and Eurasian plates formed the Himalayas, the largest orogenic belt on the Earth. The entire region accommodates shallow earthquakes, while intermediate-depth earthquakes are concentrated at the eastern and western Himalayan syntaxis. Here we investigate the focal depths, fault plane solutions, and source rupture process for three earthquake sequences, which are located at the western, central and eastern regions of the Himalayan orogenic belt. The Pamir-Hindu Kush region is located at the western Himalayan syntaxis and is characterized by extreme shortening of the upper crust and strong interaction of various layers of the lithosphere. Many shallow earthquakes occur on the Main Pamir Thrust at focal depths shallower than 20 km, while intermediate-deep earthquakes are mostly located below 75 km. Large intermediate-depth earthquakes occur frequently at the western Himalayan syntaxis about every 10 years on average. The 2015 Nepal earthquake is located in the central Himalayas. It is a typical megathrust earthquake that occurred on the shallow portion of the Main Himalayan Thrust (MHT). Many of the aftershocks are located above the MHT and illuminate faulting structures in the hanging wall with dip angles that are steeper than the MHT. These observations provide new constraints on the collision and uplift processes for the Himalaya orogenic belt. The Indo-Burma region is located south of the eastern Himalayan syntaxis, where the strike of the plate boundary suddenly changes from nearly east-west at the Himalayas to nearly north-south at the Burma Arc. The Burma arc subduction zone is a typical oblique plate convergence zone. The eastern boundary is the north-south striking dextral Sagaing fault, which hosts many shallow earthquakes with focal depth less than 25 km. In contrast, intermediate-depth earthquakes along the subduction zone reflect east-west trending reverse faulting.

An improvement of the Earthworm Based Earthquake Alarm Reporting system in Taiwan

NASA Astrophysics Data System (ADS)

Chen, D. Y.; Hsiao, N. C.; Yih-Min, W.

2017-12-01

The Central Weather Bureau of Taiwan (CWB) has operated the Earthworm Based Earthquake Alarm Reporting (eBEAR) system for the purpose of earthquake early warning (EEW). The system has been used to report EEW messages to the general public since 2016 through text message from the mobile phones and the television programs. The system for inland earthquakes is able to provide accurate and fast warnings. The average epicenter error is about 5 km and the processing time is about 15 seconds. The epicenter error is defined as the distance between the epicenter estimated by the EEW system and the epicenter estimated by man. The processing time is defined as the time difference between the time earthquakes occurred and the time the system issued warning. The CWB seismic network consist about 200 seismic stations. In some area of Taiwan the distance between each seismic station is about 10 km. It means that when an earthquake occurred the seismic P wave is able to propagate through 6 stations, which is the minimum number of required stations in the EEW system, within 20 km. If the latency of data transmitting is about 1 sec, the P-wave velocity is about 6 km per sec and we take 3-sec length time window to estimate earthquake magnitude, then the processing should be around 8 sec. In fact, however, the average processing time is larger than this figure. Because some outliers of P-wave onset picks may exist in the beginning of the earthquake occurrence, the Geiger's method we used in the EEW system for earthquake location is not stable. It usually takes more time to wait for enough number of good picks. In this study we used grid search method to improve the estimations of earthquake location. The MAXEL algorithm (Sheen et al., 2015, 2016) was tested in the EEW system by simulating historical earthquakes occurred in Taiwan. The results show the processing time can be reduced and the location accuracy is acceptable for EEW purpose.

Active accommodation of plate convergence in Southern Iran: Earthquake locations, triggered aseismic slip, and regional strain rates

NASA Astrophysics Data System (ADS)

Barnhart, William D.; Lohman, Rowena B.; Mellors, Robert J.

2013-10-01

We present a catalog of interferometric synthetic aperture radar (InSAR) constraints on deformation that occurred during earthquake sequences in southern Iran between 1992 and 2011, and explore the implications on the accommodation of large-scale continental convergence between Saudi Arabia and Eurasia within the Zagros Mountains. The Zagros Mountains, a salt-laden fold-and-thrust belt involving ~10 km of sedimentary rocks overlying Precambrian basement rocks, have formed as a result of ongoing continental collision since 10-20 Ma that is currently occurring at a rate of ~3 cm/yr. We first demonstrate that there is a biased misfit in earthquake locations in global catalogs that likely results from neglect of 3-D velocity structure. Previous work involving two M ~ 6 earthquakes with well-recorded aftershocks has shown that the deformation observed with InSAR may represent triggered slip on faults much shallower than the primary earthquake, which likely occurred within the basement rocks (>10 km depth). We explore the hypothesis that most of the deformation observed with InSAR spanning earthquake sequences is also due to shallow, triggered slip above a deeper earthquake, effectively doubling the moment release for each event. We quantify the effects that this extra moment release would have on the discrepancy between seismically and geodetically constrained moment rates in the region, finding that even with the extra triggered fault slip, significant aseismic deformation during the interseismic period is necessary to fully explain the convergence between Eurasia and Saudi Arabia.

Earthquake triggering in southeast Africa following the 2012 Indian Ocean earthquake

NASA Astrophysics Data System (ADS)

Neves, Miguel; Custódio, Susana; Peng, Zhigang; Ayorinde, Adebayo

2018-02-01

In this paper we present evidence of earthquake dynamic triggering in southeast Africa. We analysed seismic waveforms recorded at 53 broad-band and short-period stations in order to identify possible increases in the rate of microearthquakes and tremor due to the passage of teleseismic waves generated by the Mw8.6 2012 Indian Ocean earthquake. We found evidence of triggered local earthquakes and no evidence of triggered tremor in the region. We assessed the statistical significance of the increase in the number of local earthquakes using β-statistics. Statistically significant dynamic triggering of local earthquakes was observed at 7 out of the 53 analysed stations. Two of these stations are located in the northeast coast of Madagascar and the other five stations are located in the Kaapvaal Craton, southern Africa. We found no evidence of dynamically triggered seismic activity in stations located near the structures of the East African Rift System. Hydrothermal activity exists close to the stations that recorded dynamic triggering, however, it also exists near the East African Rift System structures where no triggering was observed. Our results suggest that factors other than solely tectonic regime and geothermalism are needed to explain the mechanisms that underlie earthquake triggering.

Characterizing the structural maturity of fault zones using high-resolution earthquake locations.

NASA Astrophysics Data System (ADS)

Perrin, C.; Waldhauser, F.; Scholz, C. H.

2017-12-01

We use high-resolution earthquake locations to characterize the three-dimensional structure of active faults in California and how it evolves with fault structural maturity. We investigate the distribution of aftershocks of several recent large earthquakes that occurred on immature faults (i.e., slow moving and small cumulative displacement), such as the 1992 (Mw7.3) Landers and 1999 (Mw7.1) Hector Mine events, and earthquakes that occurred on mature faults, such as the 1984 (Mw6.2) Morgan Hill and 2004 (Mw6.0) Parkfield events. Unlike previous studies which typically estimated the width of fault zones from the distribution of earthquakes perpendicular to the surface fault trace, we resolve fault zone widths with respect to the 3D fault surface estimated from principal component analysis of local seismicity. We find that the zone of brittle deformation around the fault core is narrower along mature faults compared to immature faults. We observe a rapid fall off of the number of events at a distance range of 70 - 100 m from the main fault surface of mature faults (140-200 m fault zone width), and 200-300 m from the fault surface of immature faults (400-600 m fault zone width). These observations are in good agreement with fault zone widths estimated from guided waves trapped in low velocity damage zones. The total width of the active zone of deformation surrounding the main fault plane reach 1.2 km and 2-4 km for mature and immature faults, respectively. The wider zone of deformation presumably reflects the increased heterogeneity in the stress field along complex and discontinuous faults strands that make up immature faults. In contrast, narrower deformation zones tend to align with well-defined fault planes of mature faults where most of the deformation is concentrated. Our results are in line with previous studies suggesting that surface fault traces become smoother, and thus fault zones simpler, as cumulative fault slip increases.

Simulating Earthquake Early Warning Systems in the Classroom as a New Approach to Teaching Earthquakes

NASA Astrophysics Data System (ADS)

D'Alessio, M. A.

2010-12-01

A discussion of P- and S-waves seems an ubiquitous part of studying earthquakes in the classroom. Textbooks from middle school through university level typically define the differences between the waves and illustrate the sense of motion. While many students successfully memorize the differences between wave types (often utilizing the first letter as a memory aide), textbooks rarely give tangible examples of how the two waves would "feel" to a person sitting on the ground. One reason for introducing the wave types is to explain how to calculate earthquake epicenters using seismograms and travel time charts -- very abstract representations of earthquakes. Even when the skill is mastered using paper-and-pencil activities or one of the excellent online interactive versions, locating an epicenter simply does not excite many of our students because it evokes little emotional impact, even in students located in earthquake-prone areas. Despite these limitations, huge numbers of students are mandated to complete the task. At the K-12 level, California requires that all students be able to locate earthquake epicenters in Grade 6; in New York, the skill is a required part of the Regent's Examination. Recent innovations in earthquake early warning systems around the globe give us the opportunity to address the same content standard, but with substantially more emotional impact on students. I outline a lesson about earthquakes focused on earthquake early warning systems. The introductory activities include video clips of actual earthquakes and emphasize the differences between the way P- and S-waves feel when they arrive (P arrives first, but is weaker). I include an introduction to the principle behind earthquake early warning (including a summary of possible uses of a few seconds warning about strong shaking) and show examples from Japan. Students go outdoors to simulate P-waves, S-waves, and occupants of two different cities who are talking to one another on cell phones

Accuracy of algorithms to predict accessory pathway location in children with Wolff-Parkinson-White syndrome.

PubMed

Wren, Christopher; Vogel, Melanie; Lord, Stephen; Abrams, Dominic; Bourke, John; Rees, Philip; Rosenthal, Eric

2012-02-01

The aim of this study was to examine the accuracy in predicting pathway location in children with Wolff-Parkinson-White syndrome for each of seven published algorithms. ECGs from 100 consecutive children with Wolff-Parkinson-White syndrome undergoing electrophysiological study were analysed by six investigators using seven published algorithms, six of which had been developed in adult patients. Accuracy and concordance of predictions were adjusted for the number of pathway locations. Accessory pathways were left-sided in 49, septal in 20 and right-sided in 31 children. Overall accuracy of prediction was 30-49% for the exact location and 61-68% including adjacent locations. Concordance between investigators varied between 41% and 86%. No algorithm was better at predicting septal pathways (accuracy 5-35%, improving to 40-78% including adjacent locations), but one was significantly worse. Predictive accuracy was 24-53% for the exact location of right-sided pathways (50-71% including adjacent locations) and 32-55% for the exact location of left-sided pathways (58-73% including adjacent locations). All algorithms were less accurate in our hands than in other authors' own assessment. None performed well in identifying midseptal or right anteroseptal accessory pathway locations.

Delineating Concealed Faults within Cogdell Oil Field via Earthquake Detection

NASA Astrophysics Data System (ADS)

Aiken, C.; Walter, J. I.; Brudzinski, M.; Skoumal, R.; Savvaidis, A.; Frohlich, C.; Borgfeldt, T.; Dotray, P.

2016-12-01

Cogdell oil field, located within the Permian Basin of western Texas, has experienced several earthquakes ranging from magnitude 1.7 to 4.6, most of which were recorded since 2006. Using the Earthscope USArray, Gan and Frohlich [2013] relocated some of these events and found a positive correlation in the timing of increased earthquake activity and increased CO2 injection volume. However, focal depths of these earthquakes are unknown due to 70 km station spacing of the USArray. Accurate focal depths as well as new detections can delineate subsurface faults and establish whether earthquakes are occurring in the shallow sediments or in the deeper basement. To delineate subsurface fault(s) in this region, we first detect earthquakes not currently listed in the USGS catalog by applying continuous waveform-template matching algorithms to multiple seismic data sets. We utilize seismic data spanning the time frame of 2006 to 2016 - which includes data from the U.S. Geological Survey Global Seismographic Network, the USArray, and the Sweetwater, TX broadband and nodal array located 20-40 km away. The catalog of earthquakes enhanced by template matching reveals events that were well recorded by the large-N Sweetwater array, so we are experimenting with strategies for optimizing template matching using different configurations of many stations. Since earthquake activity in the Cogdell oil field is on-going (a magnitude 2.6 occurred on May 29, 2016), a temporary deployment of TexNet seismometers has been planned for the immediate vicinity of Cogdell oil field in August 2016. Results on focal depths and detection of small magnitude events are pending this small local network deployment.

Characterize kinematic rupture history of large earthquakes with Multiple Haskell sources

NASA Astrophysics Data System (ADS)

Jia, Z.; Zhan, Z.

2017-12-01

Earthquakes are often regarded as continuous rupture along a single fault, but the occurrence of complex large events involving multiple faults and dynamic triggering challenges this view. Such rupture complexities cause difficulties in existing finite fault inversion algorithms, because they rely on specific parameterizations and regularizations to obtain physically meaningful solutions. Furthermore, it is difficult to assess reliability and uncertainty of obtained rupture models. Here we develop a Multi-Haskell Source (MHS) method to estimate rupture process of large earthquakes as a series of sub-events of varying location, timing and directivity. Each sub-event is characterized by a Haskell rupture model with uniform dislocation and constant unilateral rupture velocity. This flexible yet simple source parameterization allows us to constrain first-order rupture complexity of large earthquakes robustly. Additionally, relatively few parameters in the inverse problem yields improved uncertainty analysis based on Markov chain Monte Carlo sampling in a Bayesian framework. Synthetic tests and application of MHS method on real earthquakes show that our method can capture major features of large earthquake rupture process, and provide information for more detailed rupture history analysis.

OMG Earthquake! Can Twitter improve earthquake response?

NASA Astrophysics Data System (ADS)

Earle, P. S.; Guy, M.; Ostrum, C.; Horvath, S.; Buckmaster, R. A.

2009-12-01

The U.S. Geological Survey (USGS) is investigating how the social networking site Twitter, a popular service for sending and receiving short, public, text messages, can augment its earthquake response products and the delivery of hazard information. The goal is to gather near real-time, earthquake-related messages (tweets) and provide geo-located earthquake detections and rough maps of the corresponding felt areas. Twitter and other social Internet technologies are providing the general public with anecdotal earthquake hazard information before scientific information has been published from authoritative sources. People local to an event often publish information within seconds via these technologies. In contrast, depending on the location of the earthquake, scientific alerts take between 2 to 20 minutes. Examining the tweets following the March 30, 2009, M4.3 Morgan Hill earthquake shows it is possible (in some cases) to rapidly detect and map the felt area of an earthquake using Twitter responses. Within a minute of the earthquake, the frequency of “earthquake” tweets rose above the background level of less than 1 per hour to about 150 per minute. Using the tweets submitted in the first minute, a rough map of the felt area can be obtained by plotting the tweet locations. Mapping the tweets from the first six minutes shows observations extending from Monterey to Sacramento, similar to the perceived shaking region mapped by the USGS “Did You Feel It” system. The tweets submitted after the earthquake also provided (very) short first-impression narratives from people who experienced the shaking. Accurately assessing the potential and robustness of a Twitter-based system is difficult because only tweets spanning the previous seven days can be searched, making a historical study impossible. We have, however, been archiving tweets for several months, and it is clear that significant limitations do exist. The main drawback is the lack of quantitative information

USGS Tweet Earthquake Dispatch (@USGSted): Using Twitter for Earthquake Detection and Characterization

NASA Astrophysics Data System (ADS)

Liu, S. B.; Bouchard, B.; Bowden, D. C.; Guy, M.; Earle, P.

2012-12-01

The U.S. Geological Survey (USGS) is investigating how online social networking services like Twitter—a microblogging service for sending and reading public text-based messages of up to 140 characters—can augment USGS earthquake response products and the delivery of hazard information. The USGS Tweet Earthquake Dispatch (TED) system is using Twitter not only to broadcast seismically-verified earthquake alerts via the @USGSted and @USGSbigquakes Twitter accounts, but also to rapidly detect widely felt seismic events through a real-time detection system. The detector algorithm scans for significant increases in tweets containing the word "earthquake" or its equivalent in other languages and sends internal alerts with the detection time, tweet text, and the location of the city where most of the tweets originated. It has been running in real-time for 7 months and finds, on average, two or three felt events per day with a false detection rate of less than 10%. The detections have reasonable coverage of populated areas globally. The number of detections is small compared to the number of earthquakes detected seismically, and only a rough location and qualitative assessment of shaking can be determined based on Tweet data alone. However, the Twitter detections are generally caused by widely felt events that are of more immediate interest than those with no human impact. The main benefit of the tweet-based detections is speed, with most detections occurring between 19 seconds and 2 minutes from the origin time. This is considerably faster than seismic detections in poorly instrumented regions of the world. Going beyond the initial detection, the USGS is developing data mining techniques to continuously archive and analyze relevant tweets for additional details about the detected events. The information generated about an event is displayed on a web-based map designed using HTML5 for the mobile environment, which can be valuable when the user is not able to access a

Location of early aftershocks of the 2004 Mid-Niigata Prefecture Earthquake (M = 6.8) in central Japan using seismogram envelopes as templates

NASA Astrophysics Data System (ADS)

Kosuga, M.

2013-12-01

The location of early aftershocks is very important to obtain information of mainshock fault, however, it is often difficult due to the long-lasting coda wave of mainshock and successive occurrence of afterrshocks. To overcome this difficulty, we developed a method of location using seismogram envelopes as templates, and applied the method to the early aftershock sequence of the 2004 Mid-Niigata Prefecture (Chuetsu) Earthquake (M = 6.8) in central Japan. The location method composes of three processes. The first process is the calculation of cross-correlation coefficients between a continuous (target) and template envelopes. We prepare envelopes by taking the logarithm of root-mean-squared amplitude of band-pass filtered seismograms. We perform the calculation by shifting the time window to obtain a set of cross-correlation values for each template. The second process is the event detection (selection of template) and magnitude estimate. We search for the events in descending order of cross-correlation in a time window excluding the dead times around the previously detected events. Magnitude is calculated by the amplitude ratio of target and template envelopes. The third process is the relative event location to the selected template. We applied this method to the Chuetsu earthquake, a large inland earthquake with extensive aftershock activity. The number of detected events depends on the number of templates, frequency range, and the threshold value of cross-correlation. We set the threshold as 0.5 by referring to the histogram of cross-correlation. During a period of one-hour from the mainshock, we could detect more events than the JMA catalog. The location of events is generally near the catalog location. Though we should improve the methods of relative location and magnitude estimate, we conclude that the proposed method works adequately even just after the mainshock of large inland earthquake. Acknowledgement: We thank JMA, NIED, and the University of Tokyo for

A revised “earthquake report” questionaire

USGS Publications Warehouse

Stover, C.; Reagor, G.; Simon, R.

1976-01-01

The U.S geological Survey is responsible for conducting intensity and damage surveys following felt or destructive earthquakes in the United States. Shortly after a felt or damaging earthquake occurs, a canvass of the affected area is made. Specially developed questionnaires are mailed to volunteer observers located within the estimated felt area. These questionnaires, "Earthquake Reports," are filled out by the observers and returned to the Survey's National Earthquake Information Service, which is located in Colorado. They are then evaluated, and, based on answers to questions about physical effects seen or felt, each canvassed location is assigned to the various locations, they are plotted on an intensity distribution map. When all of the intensity data have been plotted, isoseismals can then be contoured through places where equal intensity was experienced. The completed isoseismal map yields a detailed picture of the earthquake, its effects, and its felt area. All of the data and maps are published quarterly in a U.S Geological Survey Circular series entitled "Earthquakes in the United States".  

An interdisciplinary approach for earthquake modelling and forecasting

NASA Astrophysics Data System (ADS)

Han, P.; Zhuang, J.; Hattori, K.; Ogata, Y.

2016-12-01

Earthquake is one of the most serious disasters, which may cause heavy casualties and economic losses. Especially in the past two decades, huge/mega earthquakes have hit many countries. Effective earthquake forecasting (including time, location, and magnitude) becomes extremely important and urgent. To date, various heuristically derived algorithms have been developed for forecasting earthquakes. Generally, they can be classified into two types: catalog-based approaches and non-catalog-based approaches. Thanks to the rapid development of statistical seismology in the past 30 years, now we are able to evaluate the performances of these earthquake forecast approaches quantitatively. Although a certain amount of precursory information is available in both earthquake catalogs and non-catalog observations, the earthquake forecast is still far from satisfactory. In most case, the precursory phenomena were studied individually. An earthquake model that combines self-exciting and mutually exciting elements was developed by Ogata and Utsu from the Hawkes process. The core idea of this combined model is that the status of the event at present is controlled by the event itself (self-exciting) and all the external factors (mutually exciting) in the past. In essence, the conditional intensity function is a time-varying Poisson process with rate λ(t), which is composed of the background rate, the self-exciting term (the information from past seismic events), and the external excitation term (the information from past non-seismic observations). This model shows us a way to integrate the catalog-based forecast and non-catalog-based forecast. Against this background, we are trying to develop a new earthquake forecast model which combines catalog-based and non-catalog-based approaches.

High resolution strain sensor for earthquake precursor observation and earthquake monitoring

NASA Astrophysics Data System (ADS)

Zhang, Wentao; Huang, Wenzhu; Li, Li; Liu, Wenyi; Li, Fang

2016-05-01

We propose a high-resolution static-strain sensor based on a FBG Fabry-Perot interferometer (FBG-FP) and a wavelet domain cross-correlation algorithm. This sensor is used for crust deformation measurement, which plays an important role in earthquake precursor observation. The Pound-Drever-Hall (PDH) technique based on a narrow-linewidth tunable fiber laser is used to interrogate the FBG-FPs. A demodulation algorithm based on wavelet domain cross-correlation is used to calculate the wavelength difference. The FBG-FP sensor head is fixed on the two steel alloy rods which are installed in the bedrock. The reference FBG-FP is placed in a strain-free state closely to compensate the environment temperature fluctuation. A static-strain resolution of 1.6 n(epsilon) can be achieved. As a result, clear solid tide signals and seismic signals can be recorded, which suggests that the proposed strain sensor can be applied to earthquake precursor observation and earthquake monitoring.

Prompt identification of tsunamigenic earthquakes from 3-component seismic data

NASA Astrophysics Data System (ADS)

Kundu, Ajit; Bhadauria, Y. S.; Basu, S.; Mukhopadhyay, S.

2016-10-01

An Artificial Neural Network (ANN) based algorithm for prompt identification of shallow focus (depth < 70 km) tsunamigenic earthquakes at a regional distance is proposed in the paper. The promptness here refers to decision making as fast as 5 min after the arrival of LR phase in the seismogram. The root mean square amplitudes of seismic phases recorded by a single 3-component station have been considered as inputs besides location and magnitude. The trained ANN has been found to categorize 100% of the new earthquakes successfully as tsunamigenic or non-tsunamigenic. The proposed method has been corroborated by an alternate mapping technique of earthquake category estimation. The second method involves computation of focal parameters, estimation of water volume displaced at the source and eventually deciding category of the earthquake. The method has been found to identify 95% of the new earthquakes successfully. Both the methods have been tested using three component broad band seismic data recorded at PALK (Pallekele, Sri Lanka) station provided by IRIS for earthquakes originating from Sumatra region of magnitude 6 and above. The fair agreement between the methods ensures that a prompt alert system could be developed based on proposed method. The method would prove to be extremely useful for the regions that are not adequately instrumented for azimuthal coverage.

Earthquake activity along the Himalayan orogenic belt

NASA Astrophysics Data System (ADS)

Bai, L.; Mori, J. J.

2017-12-01

The collision between the Indian and Eurasian plates formed the Himalayas, the largest orogenic belt on the Earth. The entire region accommodates shallow earthquakes, while intermediate-depth earthquakes are concentrated at the eastern and western Himalayan syntaxis. Here we investigate the focal depths, fault plane solutions, and source rupture process for three earthquake sequences, which are located at the western, central and eastern regions of the Himalayan orogenic belt. The Pamir-Hindu Kush region is located at the western Himalayan syntaxis and is characterized by extreme shortening of the upper crust and strong interaction of various layers of the lithosphere. Many shallow earthquakes occur on the Main Pamir Thrust at focal depths shallower than 20 km, while intermediate-deep earthquakes are mostly located below 75 km. Large intermediate-depth earthquakes occur frequently at the western Himalayan syntaxis about every 10 years on average. The 2015 Nepal earthquake is located in the central Himalayas. It is a typical megathrust earthquake that occurred on the shallow portion of the Main Himalayan Thrust (MHT). Many of the aftershocks are located above the MHT and illuminate faulting structures in the hanging wall with dip angles that are steeper than the MHT. These observations provide new constraints on the collision and uplift processes for the Himalaya orogenic belt. The Indo-Burma region is located south of the eastern Himalayan syntaxis, where the strike of the plate boundary suddenly changes from nearly east-west at the Himalayas to nearly north-south at the Burma Arc. The Burma arc subduction zone is a typical oblique plate convergence zone. The eastern boundary is the north-south striking dextral Sagaing fault, which hosts many shallow earthquakes with focal depth less than 25 km. In contrast, intermediate-depth earthquakes along the subduction zone reflect east-west trending reverse faulting.

Widespread Triggering of Earthquakes in the Central US by the 2011 M9.0 Tohoku-Oki Earthquake

NASA Astrophysics Data System (ADS)

Rubinstein, J. L.; Savage, H. M.

2011-12-01

The strong shaking of the 2011 M9.0 off-Tohoku earthquake triggered tectonic tremor and earthquakes in many locations around the world. We analyze broadband records from the USARRAY to identify triggered seismicity in more than 10 different locations in the Central United States. We identify triggered events in many states including: Kansas, Nebraska, Arkansas, Minnesota, and Iowa. The locally triggered earthquakes are obscured in broadband records by the Tohoku-Oki mainshock but can be revealed with high-pass filtering. With the exception of one location (central Arkansas), the triggered seismicity occurred in regions that are seismically quiet. The coincidence of this seismicity with the Tohoku-Oki event suggests that these earthquakes were triggered. The triggered seismicity in Arkansas occurred in a region where there has been an active swarm of seismicity since August 2010. There are two lines of evidence to indicate that the seismicity in Arkansas is triggered instead of part of the swarm: (1) we observe two earthquakes that initiate coincident with the arrival of shear wave and Love wave; (2) the seismicity rate increased dramatically following the Tohoku-Oki mainshock. Our observations of widespread earthquake triggering in regions thought to be seismically quiet remind us that earthquakes can occur in most any location. Studying additional teleseismic events has the potential to reveal regions with a propensity for earthquake triggering.

Characterization of the Virginia earthquake effects and source parameters from website traffic analysis

NASA Astrophysics Data System (ADS)

Bossu, R.; Lefebvre, S.; Mazet-Roux, G.; Roussel, F.

2012-12-01

This paper presents an after the fact study of the Virginia earthquake of 2011 August 23 using only the traffic observed on the EMSC website within minutes of its occurrence. Although the EMSC real time information services remain poorly identified in the US, a traffic surge was observed immediately after the earthquake's occurrence. Such surges, known as flashcrowd and commonly observed on our website after felt events within the Euro-Med region are caused by eyewitnesses looking for information about the shaking they have just felt. EMSC developed an approach named flashsourcing to map the felt area, and in some circumstances, the regions affected by severe damage or network disruption. The felt area is mapped simply by locating the Internet Protocol (IP) addresses of the visitors to the website during these surges while the existence of network disruption is detected by the instantaneous loss at the time of earthquake's occurrence of existing Internet sessions originating from the impacted area. For the Virginia earthquake, which was felt at large distances, the effects of the waves propagation are clearly observed. We show that the visits to our website are triggered by the P waves arrival: the first visitors from a given locality reach our website 90s after their location was shaken by the P waves. From a processing point of view, eyewitnesses can then be considered as ground motion detectors. By doing so, the epicentral location is determined through a simple dedicated location algorithm within 2 min of the earthquake's occurrence and 30 km accuracy. The magnitude can be estimated in similar time frame by using existing empirical relationships between the surface of the felt area and the magnitude. Concerning the effects of the earthquake, we check whether one can discriminate localities affected by strong shaking from web traffic analysis. This is actually the case. Localities affected by strong level of shaking exhibit higher ratio of visitors to the number

Earthquake classification, location, and error analysis in a volcanic environment: implications for the magmatic system of the 1989-1990 eruptions at redoubt volcano, Alaska

USGS Publications Warehouse

Lahr, J.C.; Chouet, B.A.; Stephens, C.D.; Power, J.A.; Page, R.A.

1994-01-01

Determination of the precise locations of seismic events associated with the 1989-1990 eruptions of Redoubt Volcano posed a number of problems, including poorly known crustal velocities, a sparse station distribution, and an abundance of events with emergent phase onsets. In addition, the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm. This algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations. The velocity model was calibrated on the basis of a posteruptive seismic survey, in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice. The model consists of a stack of homogeneous horizontal layers; setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice. Detailed analysis of hypocentral errors shows that the long-period (LP) events constituting the vigorous 23-hour swarm that preceded the initial eruption on December 14 could have originated from a point 1.4 km below the crater floor. A similar analysis of LP events in the swarm preceding the major eruption on January 2 shows they also could have originated from a point, the location of which is shifted 0.8 km northwest and 0.7 km deeper than the source of the initial swarm. We suggest this shift in LP activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of December. Volcano-tectonic (VT) earthquakes did not occur until after the initial 23-hour-long swarm. They began slowly just below the LP source and their rate of occurrence increased after the eruption of 01:52 AST on December 15, when they shifted to depths of 6 to 10 km. After January 2 the VT activity migrated gradually northward; this migration suggests northward propagating withdrawal of

A firefly algorithm for solving competitive location-design problem: a case study

NASA Astrophysics Data System (ADS)

Sadjadi, Seyed Jafar; Ashtiani, Milad Gorji; Ramezanian, Reza; Makui, Ahmad

2016-12-01

This paper aims at determining the optimal number of new facilities besides specifying both the optimal location and design level of them under the budget constraint in a competitive environment by a novel hybrid continuous and discrete firefly algorithm. A real-world application of locating new chain stores in the city of Tehran, Iran, is used and the results are analyzed. In addition, several examples have been solved to evaluate the efficiency of the proposed model and algorithm. The results demonstrate that the performed method provides good-quality results for the test problems.

Rapid Tsunami Inundation Forecast from Near-field or Far-field Earthquakes using Pre-computed Tsunami Database: Pelabuhan Ratu, Indonesia

NASA Astrophysics Data System (ADS)

Gusman, A. R.; Setiyono, U.; Satake, K.; Fujii, Y.

2017-12-01

We built pre-computed tsunami inundation database in Pelabuhan Ratu, one of tsunami-prone areas on the southern coast of Java, Indonesia. The tsunami database can be employed for a rapid estimation of tsunami inundation during an event. The pre-computed tsunami waveforms and inundations are from a total of 340 scenarios ranging from 7.5 to 9.2 in moment magnitude scale (Mw), including simple fault models of 208 thrust faults and 44 tsunami earthquakes on the plate interface, as well as 44 normal faults and 44 reverse faults in the outer-rise region. Using our tsunami inundation forecasting algorithm (NearTIF), we could rapidly estimate the tsunami inundation in Pelabuhan Ratu for three different hypothetical earthquakes. The first hypothetical earthquake is a megathrust earthquake type (Mw 9.0) offshore Sumatra which is about 600 km from Pelabuhan Ratu to represent a worst-case event in the far-field. The second hypothetical earthquake (Mw 8.5) is based on a slip deficit rate estimation from geodetic measurements and represents a most likely large event near Pelabuhan Ratu. The third hypothetical earthquake is a tsunami earthquake type (Mw 8.1) which often occur south off Java. We compared the tsunami inundation maps produced by the NearTIF algorithm with results of direct forward inundation modeling for the hypothetical earthquakes. The tsunami inundation maps produced from both methods are similar for the three cases. However, the tsunami inundation map from the inundation database can be obtained in much shorter time (1 min) than the one from a forward inundation modeling (40 min). These indicate that the NearTIF algorithm based on pre-computed inundation database is reliable and useful for tsunami warning purposes. This study also demonstrates that the NearTIF algorithm can work well even though the earthquake source is located outside the area of fault model database because it uses a time shifting procedure for the best-fit scenario searching.

Discussion of New Approaches to Medium-Short-Term Earthquake Forecast in Practice of The Earthquake Prediction in Yunnan

NASA Astrophysics Data System (ADS)

Hong, F.

2017-12-01

After retrospection of years of practice of the earthquake prediction in Yunnan area, it is widely considered that the fixed-point earthquake precursory anomalies mainly reflect the field information. The increase of amplitude and number of precursory anomalies could help to determine the original time of earthquakes, however it is difficult to obtain the spatial relevance between earthquakes and precursory anomalies, thus we can hardly predict the spatial locations of earthquakes using precursory anomalies. The past practices have shown that the seismic activities are superior to the precursory anomalies in predicting earthquakes locations, resulting from the increased seismicity were observed before 80% M=6.0 earthquakes in Yunnan area. While the mobile geomagnetic anomalies are turned out to be helpful in predicting earthquakes locations in recent year, for instance, the forecasted earthquakes occurring time and area derived form the 1-year-scale geomagnetic anomalies before the M6.5 Ludian earthquake in 2014 are shorter and smaller than which derived from the seismicity enhancement region. According to the past works, the author believes that the medium-short-term earthquake forecast level, as well as objective understanding of the seismogenic mechanisms, could be substantially improved by the densely laying observation array and capturing the dynamic process of physical property changes in the enhancement region of medium to small earthquakes.

A PC-based computer package for automatic detection and location of earthquakes: Application to a seismic network in eastern sicity (Italy)

NASA Astrophysics Data System (ADS)

Patanè, Domenico; Ferrari, Ferruccio; Giampiccolo, Elisabetta; Gresta, Stefano

Few automated data acquisition and processing systems operate on mainframes, some run on UNIX-based workstations and others on personal computers, equipped with either DOS/WINDOWS or UNIX-derived operating systems. Several large and complex software packages for automatic and interactive analysis of seismic data have been developed in recent years (mainly for UNIX-based systems). Some of these programs use a variety of artificial intelligence techniques. The first operational version of a new software package, named PC-Seism, for analyzing seismic data from a local network is presented in Patanè et al. (1999). This package, composed of three separate modules, provides an example of a new generation of visual object-oriented programs for interactive and automatic seismic data-processing running on a personal computer. In this work, we mainly discuss the automatic procedures implemented in the ASDP (Automatic Seismic Data-Processing) module and real time application to data acquired by a seismic network running in eastern Sicily. This software uses a multi-algorithm approach and a new procedure MSA (multi-station-analysis) for signal detection, phase grouping and event identification and location. It is designed for an efficient and accurate processing of local earthquake records provided by single-site and array stations. Results from ASDP processing of two different data sets recorded at Mt. Etna volcano by a regional network are analyzed to evaluate its performance. By comparing the ASDP pickings with those revised manually, the detection and subsequently the location capabilities of this software are assessed. The first data set is composed of 330 local earthquakes recorded in the Mt. Etna erea during 1997 by the telemetry analog seismic network. The second data set comprises about 970 automatic locations of more than 2600 local events recorded at Mt. Etna during the last eruption (July 2001) at the present network. For the former data set, a comparison of the

Efficient Location Uncertainty Treatment for Probabilistic Modelling of Portfolio Loss from Earthquake Events

NASA Astrophysics Data System (ADS)

Scheingraber, Christoph; Käser, Martin; Allmann, Alexander

2017-04-01

Probabilistic seismic risk analysis (PSRA) is a well-established method for modelling loss from earthquake events. In the insurance industry, it is widely employed for probabilistic modelling of loss to a distributed portfolio. In this context, precise exposure locations are often unknown, which results in considerable loss uncertainty. The treatment of exposure uncertainty has already been identified as an area where PSRA would benefit from increased research attention. However, so far, epistemic location uncertainty has not been in the focus of a large amount of research. We propose a new framework for efficient treatment of location uncertainty. To demonstrate the usefulness of this novel method, a large number of synthetic portfolios resembling real-world portfolios is systematically analyzed. We investigate the effect of portfolio characteristics such as value distribution, portfolio size, or proportion of risk items with unknown coordinates on loss variability. Several sampling criteria to increase the computational efficiency of the framework are proposed and put into the wider context of well-established Monte-Carlo variance reduction techniques. The performance of each of the proposed criteria is analyzed.

One dimensional P wave velocity structure of the crust beneath west Java and accurate hypocentre locations from local earthquake inversion

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

Supardiyono; Santosa, Bagus Jaya; Physics Department, Faculty of Mathematics and Natural Sciences, Sepuluh Nopember Institute of Technology, Surabaya

A one-dimensional (1-D) velocity model and station corrections for the West Java zone were computed by inverting P-wave arrival times recorded on a local seismic network of 14 stations. A total of 61 local events with a minimum of 6 P-phases, rms 0.56 s and a maximum gap of 299 Degree-Sign were selected. Comparison with previous earthquake locations shows an improvement for the relocated earthquakes. Tests were carried out to verify the robustness of inversion results in order to corroborate the conclusions drawn out from our reasearch. The obtained minimum 1-D velocity model can be used to improve routine earthquakemore » locations and represents a further step toward more detailed seismotectonic studies in this area of West Java.« less

An efficient repeating signal detector to investigate earthquake swarms

NASA Astrophysics Data System (ADS)

Skoumal, Robert J.; Brudzinski, Michael R.; Currie, Brian S.

2016-08-01

Repetitive earthquake swarms have been recognized as key signatures in fluid injection induced seismicity, precursors to volcanic eruptions, and slow slip events preceding megathrust earthquakes. We investigate earthquake swarms by developing a Repeating Signal Detector (RSD), a computationally efficient algorithm utilizing agglomerative clustering to identify similar waveforms buried in years of seismic recordings using a single seismometer. Instead of relying on existing earthquake catalogs of larger earthquakes, RSD identifies characteristic repetitive waveforms by rapidly identifying signals of interest above a low signal-to-noise ratio and then grouping based on spectral and time domain characteristics, resulting in dramatically shorter processing time than more exhaustive autocorrelation approaches. We investigate seismicity in four regions using RSD: (1) volcanic seismicity at Mammoth Mountain, California, (2) subduction-related seismicity in Oaxaca, Mexico, (3) induced seismicity in Central Alberta, Canada, and (4) induced seismicity in Harrison County, Ohio. In each case, RSD detects a similar or larger number of earthquakes than existing catalogs created using more time intensive methods. In Harrison County, RSD identifies 18 seismic sequences that correlate temporally and spatially to separate hydraulic fracturing operations, 15 of which were previously unreported. RSD utilizes a single seismometer for earthquake detection which enables seismicity to be quickly identified in poorly instrumented regions at the expense of relying on another method to locate the new detections. Due to the smaller computation overhead and success at distances up to ~50 km, RSD is well suited for real-time detection of low-magnitude earthquake swarms with permanent regional networks.

The 7.9 Denali Fault Earthquake: Aftershock Locations, Moment Tensors and Focal Mechanisms from the Regional Seismic Network Data

NASA Astrophysics Data System (ADS)

Ratchkovski, N. A.; Hansen, R. A.; Christensen, D.; Kore, K.

2002-12-01

The largest earthquake ever recorded on the Denali fault system (magnitude 7.9) struck central Alaska on November 3, 2002. It was preceded by a magnitude 6.7 foreshock on October 23. This earlier earthquake and its zone of aftershocks were located slightly to the west of the 7.9 quake. Aftershock locations and surface slip observations from the 7.9 quake indicate that the rupture was predominately unilateral in the eastward direction. Near Mentasta Lake, a village that experienced some of the worst damage in the quake, the surface rupture scar turns from the Denali fault to the adjacent Totschunda fault, which trends toward more southeasterly toward the Canadian border. Overall, the geologists found that measurable scarps indicate that the north side of the Denali fault moved to the east and vertically up relative to the south. Maximum offsets on the Denali fault were 8.8 meters at the Tok Highway cutoff, and were 2.2 meters on the Totschunda fault. The Alaska regional seismic network consists of over 250 station sites, operated by the Alaska Earthquake Information Center (AEIC), the Alaska Volcano Observatory (AVO), and the Pacific Tsunami Warning Center (PTWC). Over 25 sites are equipped with the broad-band sensors, some of which have in addition the strong motion sensors. The rest of the stations are either 1 or 3-component short-period instruments. The data from these stations are collected, processed and archived at the AEIC. The AEIC staff installed a temporary network with over 20 instruments following the 6.7 Nenana Mountain and the 7.9 events. Prior to the M 7.9 Denali Fault event, the automatic earthquake detection system at AEIC was locating between 15 and 30 events per day. After the event, the system had over 200-400 automatic locations per day for at least 10 days following the 7.9 event. The processing of the data is ongoing with the priority given to the larger events. The cumulative length of the 6.7 and 7.9 aftershock locations along the Denali

From Tornadoes to Earthquakes: Forecast Verification for Binary Events Applied to the 1999 Chi-Chi, Taiwan, Earthquake

NASA Astrophysics Data System (ADS)

Chen, C.; Rundle, J. B.; Holliday, J. R.; Nanjo, K.; Turcotte, D. L.; Li, S.; Tiampo, K. F.

2005-12-01

Forecast verification procedures for statistical events with binary outcomes typically rely on the use of contingency tables and Relative Operating Characteristic (ROC) diagrams. Originally developed for the statistical evaluation of tornado forecasts on a county-by-county basis, these methods can be adapted to the evaluation of competing earthquake forecasts. Here we apply these methods retrospectively to two forecasts for the m = 7.3 1999 Chi-Chi, Taiwan, earthquake. These forecasts are based on a method, Pattern Informatics (PI), that locates likely sites for future large earthquakes based on large change in activity of the smallest earthquakes. A competing null hypothesis, Relative Intensity (RI), is based on the idea that future large earthquake locations are correlated with sites having the greatest frequency of small earthquakes. We show that for Taiwan, the PI forecast method is superior to the RI forecast null hypothesis. Inspection of the two maps indicates that their forecast locations are indeed quite different. Our results confirm an earlier result suggesting that the earthquake preparation process for events such as the Chi-Chi earthquake involves anomalous changes in activation or quiescence, and that signatures of these processes can be detected in precursory seismicity data. Furthermore, we find that our methods can accurately forecast the locations of aftershocks from precursory seismicity changes alone, implying that the main shock together with its aftershocks represent a single manifestation of the formation of a high-stress region nucleating prior to the main shock.

Earthquakes of Garhwal Himalaya region of NW Himalaya, India: A study of relocated earthquakes and their seismogenic source and stress

NASA Astrophysics Data System (ADS)

R, A. P.; Paul, A.; Singh, S.

2017-12-01

Since the continent-continent collision 55 Ma, the Himalaya has accommodated 2000 km of convergence along its arc. The strain energy is being accumulated at a rate of 37-44 mm/yr and releases at time as earthquakes. The Garhwal Himalaya is located at the western side of a Seismic Gap, where a great earthquake is overdue atleast since 200 years. This seismic gap (Central Seismic Gap: CSG) with 52% probability for a future great earthquake is located between the rupture zones of two significant/great earthquakes, viz. the 1905 Kangra earthquake of M 7.8 and the 1934 Bihar-Nepal earthquake of M 8.0; and the most recent one, the 2015 Gorkha earthquake of M 7.8 is in the eastern side of this seismic gap (CSG). The Garhwal Himalaya is one of the ideal locations of the Himalaya where all the major Himalayan structures and the Himalayan Seimsicity Belt (HSB) can ably be described and studied. In the present study, we are presenting the spatio-temporal analysis of the relocated local micro-moderate earthquakes, recorded by a seismicity monitoring network, which is operational since, 2007. The earthquake locations are relocated using the HypoDD (double difference hypocenter method for earthquake relocations) program. The dataset from July, 2007- September, 2015 have been used in this study to estimate their spatio-temporal relationships, moment tensor (MT) solutions for the earthquakes of M>3.0, stress tensors and their interactions. We have also used the composite focal mechanism solutions for small earthquakes. The majority of the MT solutions show thrust type mechanism and located near the mid-crustal-ramp (MCR) structure of the detachment surface at 8-15 km depth beneath the outer lesser Himalaya and higher Himalaya regions. The prevailing stress has been identified to be compressional towards NNE-SSW, which is the direction of relative plate motion between the India and Eurasia continental plates. The low friction coefficient estimated along with the stress inversions

W phase source inversion for moderate to large earthquakes (1990-2010)

USGS Publications Warehouse

Duputel, Zacharie; Rivera, Luis; Kanamori, Hiroo; Hayes, Gavin P.

2012-01-01

Rapid characterization of the earthquake source and of its effects is a growing field of interest. Until recently, it still took several hours to determine the first-order attributes of a great earthquake (e.g. Mw≥ 7.5), even in a well-instrumented region. The main limiting factors were data saturation, the interference of different phases and the time duration and spatial extent of the source rupture. To accelerate centroid moment tensor (CMT) determinations, we have developed a source inversion algorithm based on modelling of the W phase, a very long period phase (100–1000 s) arriving at the same time as the P wave. The purpose of this work is to finely tune and validate the algorithm for large-to-moderate-sized earthquakes using three components of W phase ground motion at teleseismic distances. To that end, the point source parameters of all Mw≥ 6.5 earthquakes that occurred between 1990 and 2010 (815 events) are determined using Federation of Digital Seismograph Networks, Global Seismographic Network broad-band stations and STS1 global virtual networks of the Incorporated Research Institutions for Seismology Data Management Center. For each event, a preliminary magnitude obtained from W phase amplitudes is used to estimate the initial moment rate function half duration and to define the corner frequencies of the passband filter that will be applied to the waveforms. Starting from these initial parameters, the seismic moment tensor is calculated using a preliminary location as a first approximation of the centroid. A full CMT inversion is then conducted for centroid timing and location determination. Comparisons with Harvard and Global CMT solutions highlight the robustness of W phase CMT solutions at teleseismic distances. The differences in Mw rarely exceed 0.2 and the source mechanisms are very similar to one another. Difficulties arise when a target earthquake is shortly (e.g. within 10 hr) preceded by another large earthquake, which disturbs the

Constraining the source location of the 30 May 2015 (Mw 7.9) Bonin deep-focus earthquake using seismogram envelopes of high-frequency P waveforms: Occurrence of deep-focus earthquake at the bottom of a subducting slab

NASA Astrophysics Data System (ADS)

Takemura, Shunsuke; Maeda, Takuto; Furumura, Takashi; Obara, Kazushige

2016-05-01

In this study, the source location of the 30 May 2015 (Mw 7.9) deep-focus Bonin earthquake was constrained using P wave seismograms recorded across Japan. We focus on propagation characteristics of high-frequency P wave. Deep-focus intraslab earthquakes typically show spindle-shaped seismogram envelopes with peak delays of several seconds and subsequent long-duration coda waves; however, both the main shock and aftershock of the 2015 Bonin event exhibited pulse-like P wave propagations with high apparent velocities (~12.2 km/s). Such P wave propagation features were reproduced by finite-difference method simulations of seismic wave propagation in the case of slab-bottom source. The pulse-like P wave seismogram envelopes observed from the 2015 Bonin earthquake show that its source was located at the bottom of the Pacific slab at a depth of ~680 km, rather than within its middle or upper regions.

Intrastab Earthquakes: Dehydration of the Cascadia Slab

USGS Publications Warehouse

Preston, L.A.; Creager, K.C.; Crosson, R.S.; Brocher, T.M.; Trehu, A.M.

2003-01-01

We simultaneously invert travel times of refracted and wide-angle reflected waves for three-dimensional compressional-wave velocity structure, earthquake locations, and reflector geometry in northwest Washington state. The reflector, interpreted to be the crust-mantle boundary (Moho) of the subducting Juan de Fuca plate, separates intrastab earthquakes into two groups, permitting a new understanding of the origins of intrastab earthquakes in Cascadia. Earthquakes up-dip of the Moho's 45-kilometer depth contour occur below the reflector, in the subducted oceanic mantle, consistent with serpentinite dehydration; earthquakes located down-dip occur primarily within the subducted crust, consistent with the basalt-to-eclogite transformation.

Foreshocks and aftershocks of the Great 1857 California earthquake

USGS Publications Warehouse

Meltzner, A.J.; Wald, D.J.

1999-01-01

The San Andreas fault is the longest fault in California and one of the longest strike-slip faults anywhere in the world, yet we know little about many aspects of its behavior before, during, and after large earthquakes. We conducted a study to locate and to estimate magnitudes for the largest foreshocks and aftershocks of the 1857 M 7.9 Fort Tejon earthquake on the central and southern segments of the fault. We began by searching archived first-hand accounts from 1857 through 1862, by grouping felt reports temporally, and by assigning modified Mercalli intensities to each site. We then used a modified form of the grid-search algorithm of Bakum and Wentworth, derived from empirical analysis of modern earthquakes, to find the location and magnitude most consistent with the assigned intensities for each of the largest events. The result confirms a conclusion of Sieh that at least two foreshocks ('dawn' and 'sunrise') located on or near the Parkfield segment of the San Andreas fault preceded the mainshock. We estimate their magnitudes to be M ~ 6.1 and M ~ 5.6, respectively. The aftershock rate was below average but within one standard deviation of the number of aftershocks expected based on statistics of modern southern California mainshock-aftershock sequences. The aftershocks included two significant events during the first eight days of the sequence, with magnitudes M ~ 6.25 and M ~ 6.7, near the southern half of the rupture; later aftershocks included a M ~ 6 event near San Bernardino in December 1858 and a M ~ 6.3 event near the Parkfield segment in April 1860. From earthquake logs at Fort Tejon, we conclude that the aftershock sequence lasted a minimum of 3.75 years.

Earthquakes in Arkansas and vicinity 1699-2010

USGS Publications Warehouse

Dart, Richard L.; Ausbrooks, Scott M.

2011-01-01

This map summarizes approximately 300 years of earthquake activity in Arkansas. It is one in a series of similar State earthquake history maps. Work on the Arkansas map was done in collaboration with the Arkansas Geological Survey. The earthquake data plotted on the map are from several sources: the Arkansas Geological Survey, the Center for Earthquake Research and Information, the National Center for Earthquake Engineering Research, and the Mississippi Department of Environmental Quality. In addition to earthquake locations, other materials presented include seismic hazard and isoseismal maps and related text. Earthquakes are a legitimate concern in Arkansas and parts of adjacent states. Arkansas has undergone a number of significant felt earthquakes since 1811. At least two of these events caused property damage: a magnitude 4.7 earthquake in 1931, and a magnitude 4.3 earthquake in 1967. The map shows all historical and instrumentally located earthquakes in Arkansas and vicinity between 1811 and 2010. The largest historic earthquake in the vicinity of the State was an intensity XI event, on December 16, 1811; the first earthquake in the New Madrid sequence. This violent event and the earthquakes that followed caused considerable damage to the then sparsely settled region.

Logistics Distribution Center Location Evaluation Based on Genetic Algorithm and Fuzzy Neural Network

NASA Astrophysics Data System (ADS)

Shao, Yuxiang; Chen, Qing; Wei, Zhenhua

Logistics distribution center location evaluation is a dynamic, fuzzy, open and complicated nonlinear system, which makes it difficult to evaluate the distribution center location by the traditional analysis method. The paper proposes a distribution center location evaluation system which uses the fuzzy neural network combined with the genetic algorithm. In this model, the neural network is adopted to construct the fuzzy system. By using the genetic algorithm, the parameters of the neural network are optimized and trained so as to improve the fuzzy system’s abilities of self-study and self-adaptation. At last, the sampled data are trained and tested by Matlab software. The simulation results indicate that the proposed identification model has very small errors.

MyShake: A smartphone seismic network for earthquake early warning and beyond.

PubMed

Kong, Qingkai; Allen, Richard M; Schreier, Louis; Kwon, Young-Woo

2016-02-01

Large magnitude earthquakes in urban environments continue to kill and injure tens to hundreds of thousands of people, inflicting lasting societal and economic disasters. Earthquake early warning (EEW) provides seconds to minutes of warning, allowing people to move to safe zones and automated slowdown and shutdown of transit and other machinery. The handful of EEW systems operating around the world use traditional seismic and geodetic networks that exist only in a few nations. Smartphones are much more prevalent than traditional networks and contain accelerometers that can also be used to detect earthquakes. We report on the development of a new type of seismic system, MyShake, that harnesses personal/private smartphone sensors to collect data and analyze earthquakes. We show that smartphones can record magnitude 5 earthquakes at distances of 10 km or less and develop an on-phone detection capability to separate earthquakes from other everyday shakes. Our proof-of-concept system then collects earthquake data at a central site where a network detection algorithm confirms that an earthquake is under way and estimates the location and magnitude in real time. This information can then be used to issue an alert of forthcoming ground shaking. MyShake could be used to enhance EEW in regions with traditional networks and could provide the only EEW capability in regions without. In addition, the seismic waveforms recorded could be used to deliver rapid microseism maps, study impacts on buildings, and possibly image shallow earth structure and earthquake rupture kinematics.

Locating and Modeling Regional Earthquakes with Broadband Waveform Data

NASA Astrophysics Data System (ADS)

Tan, Y.; Zhu, L.; Helmberger, D.

2003-12-01

Retrieving source parameters of small earthquakes (Mw < 4.5), including mechanism, depth, location and origin time, relies on local and regional seismic data. Although source characterization for such small events achieves a satisfactory stage in some places with a dense seismic network, such as TriNet, Southern California, a worthy revisit to the historical events in these places or an effective, real-time investigation of small events in many other places, where normally only a few local waveforms plus some short-period recordings are available, is still a problem. To address this issue, we introduce a new type of approach that estimates location, depth, origin time and fault parameters based on 3-component waveform matching in terms of separated Pnl, Rayleigh and Love waves. We show that most local waveforms can be well modeled by a regionalized 1-D model plus different timing corrections for Pnl, Rayleigh and Love waves at relatively long periods, i.e., 4-100 sec for Pnl, and 8-100 sec for surface waves, except for few anomalous paths involving greater structural complexity, meanwhile, these timing corrections reveal similar azimuthal patterns for well-located cluster events, despite their different focal mechanisms. Thus, we can calibrate the paths separately for Pnl, Rayleigh and Love waves with the timing corrections from well-determined events widely recorded by a dense modern seismic network or a temporary PASSCAL experiment. In return, we can locate events and extract their fault parameters by waveform matching for available waveform data, which could be as less as from two stations, assuming timing corrections from the calibration. The accuracy of the obtained source parameters is subject to the error carried by the events used for the calibration. The detailed method requires a Green­_s function library constructed from a regionalized 1-D model together with necessary calibration information, and adopts a grid search strategy for both hypercenter and

Study of earthquakes using a borehole seismic network at Koyna, India

NASA Astrophysics Data System (ADS)

Gupta, Harsh; Satyanarayana, Hari VS; Shashidhar, Dodla; Mallika, Kothamasu; Ranjan Mahato, Chitta; Shankar Maity, Bhavani

2017-04-01

Koyna, located near the west coast of India, is a classical site of artificial water reservoir triggered earthquakes. Triggered earthquakes started soon after the impoundment of the Koyna Dam in 1962. The activity has continued till now including the largest triggered earthquake of M 6.3 in 1967; 22 earthquakes of M ≥ 5 and several thousands smaller earthquakes. The latest significant earthquake of ML 3.7 occurred on 24th November 2016. In spite of having a network of 23 broad band 3-component seismic stations in the near vicinity of the Koyna earthquake zone, locations of earthquakes had errors of 1 km. The main reason was the presence of 1 km thick very heterogeneous Deccan Traps cover that introduced noise and locations could not be improved. To improve the accuracy of location of earthquakes, a unique network of eight borehole seismic stations surrounding the seismicity was designed. Six of these have been installed at depths varying from 981 m to 1522 m during 2015 and 2016, well below the Deccan Traps cover. During 2016 a total of 2100 earthquakes were located. There has been a significant improvement in the location of earthquakes and the absolute errors of location have come down to ± 300 m. All earthquakes of ML ≥ 0.5 are now located, compared to ML ≥1.0 earlier. Based on seismicity and logistics, a block of 2 km x 2 km area has been chosen for the 3 km deep pilot borehole. The installation of the borehole seismic network has further elucidated the correspondence between rate of water loading/unloading the reservoir and triggered seismicity.

Earthquakes in Mississippi and vicinity 1811-2010

USGS Publications Warehouse

Dart, Richard L.; Bograd, Michael B.E.

2011-01-01

This map summarizes two centuries of earthquake activity in Mississippi. Work on the Mississippi map was done in collaboration with the Mississippi Department of Environmental Quality, Office of Geology. The earthquake data plotted on the map are from several sources: the Mississippi Department of Environmental Quality, the Center for Earthquake Research and Information, the National Center for Earthquake Engineering Research, and the Arkansas Geological Survey. In addition to earthquake locations, other materials include seismic hazard and isoseismal maps and related text. Earthquakes are a legitimate concern in Mississippi and parts of adjacent States. Mississippi has undergone a number of felt earthquakes since 1811. At least two of these events caused property damage: a magnitude 4.7 earthquake in 1931, and a magnitude 4.3 earthquake in 1967. The map shows all historical and instrumentally located earthquakes in Mississippi and vicinity between 1811 and 2010. The largest historic earthquake in the vicinity of the State was an intensity XI event, on December 16, 1811; the first earthquake in the New Madrid sequence. This violent event and the earthquakes that followed caused considerable damage to the then sparsely settled region.

The 2011 Eruption of Nabro Volcano (Eritrea): Earthquake Locations from a Temporary Broadband Network

NASA Astrophysics Data System (ADS)

Hamlyn, J.; Keir, D.; Hammond, J.; Wright, T.; Neuberg, J.; Kibreab, A.; Ogubazghi, G.; Goitom, B.

2012-04-01

Nabro volcano dominates the central part of the Nabro Volcanic Range (NVR), which trends SSW-NNE covering a stretch of 110 km from the SEE margin of the Afar depression to the Red Sea. Regionally, the NVR sits within the Afar triangle, the triple junction of the Somalian, Arabian and African plates. On 12th June 2011 Nabro volcano suddenly erupted after being inactive for 10, 000 years. In response, a network of 8 seismometers, were located around the active vent. The seismic signals detected by this array and those arriving at a regional seismic station (located to the north-west) were processed to provide accurate earthquake locations for the period August-October. Transects of the volcano were used to create cross sections to aid the interpretation. Typically, the majority of the seismic events are located at the active vent and on the flanks of Nabro, with fewer events dispersed around the surrounding area. However, there appears to be a smaller hub of events to the south-west of Nabro beneath the neighbouring Mallahle volcanic caldera (located on the Ethiopian side of the international border). This may imply some form of co-dependent relationship within the plumbing of the magma system beneath both calderas.

Structures vibration control via Tuned Mass Dampers using a co-evolution Coral Reefs Optimization algorithm

NASA Astrophysics Data System (ADS)

Salcedo-Sanz, S.; Camacho-Gómez, C.; Magdaleno, A.; Pereira, E.; Lorenzana, A.

2017-04-01

In this paper we tackle a problem of optimal design and location of Tuned Mass Dampers (TMDs) for structures subjected to earthquake ground motions, using a novel meta-heuristic algorithm. Specifically, the Coral Reefs Optimization (CRO) with Substrate Layer (CRO-SL) is proposed as a competitive co-evolution algorithm with different exploration procedures within a single population of solutions. The proposed approach is able to solve the TMD design and location problem, by exploiting the combination of different types of searching mechanisms. This promotes a powerful evolutionary-like algorithm for optimization problems, which is shown to be very effective in this particular problem of TMDs tuning. The proposed algorithm's performance has been evaluated and compared with several reference algorithms in two building models with two and four floors, respectively.

Recognition of strong earthquake-prone areas with a single learning class

NASA Astrophysics Data System (ADS)

Gvishiani, A. D.; Agayan, S. M.; Dzeboev, B. A.; Belov, I. O.

2017-05-01

This article presents a new Barrier recognition algorithm with learning, designed for recognition of earthquake-prone areas. In comparison to the Crust (Kora) algorithm, used by the classical EPA approach, the Barrier algorithm proceeds with learning just on one "pure" high-seismic class. The new algorithm operates in the space of absolute values of the geological-geophysical parameters of the objects. The algorithm is used for recognition of earthquake-prone areas with M ≥ 6.0 in the Caucasus region. Comparative analysis of the Crust and Barrier algorithms justifies their productive coherence.

Toward a probabilistic acoustic emission source location algorithm: A Bayesian approach

NASA Astrophysics Data System (ADS)

Schumacher, Thomas; Straub, Daniel; Higgins, Christopher

2012-09-01

Acoustic emissions (AE) are stress waves initiated by sudden strain releases within a solid body. These can be caused by internal mechanisms such as crack opening or propagation, crushing, or rubbing of crack surfaces. One application for the AE technique in the field of Structural Engineering is Structural Health Monitoring (SHM). With piezo-electric sensors mounted to the surface of the structure, stress waves can be detected, recorded, and stored for later analysis. An important step in quantitative AE analysis is the estimation of the stress wave source locations. Commonly, source location results are presented in a rather deterministic manner as spatial and temporal points, excluding information about uncertainties and errors. Due to variability in the material properties and uncertainty in the mathematical model, measures of uncertainty are needed beyond best-fit point solutions for source locations. This paper introduces a novel holistic framework for the development of a probabilistic source location algorithm. Bayesian analysis methods with Markov Chain Monte Carlo (MCMC) simulation are employed where all source location parameters are described with posterior probability density functions (PDFs). The proposed methodology is applied to an example employing data collected from a realistic section of a reinforced concrete bridge column. The selected approach is general and has the advantage that it can be extended and refined efficiently. Results are discussed and future steps to improve the algorithm are suggested.

Earthquake clustering in modern seismicity and its relationship with strong historical earthquakes around Beijing, China

NASA Astrophysics Data System (ADS)

Wang, Jian; Main, Ian G.; Musson, Roger M. W.

2017-11-01

Beijing, China's capital city, is located in a typical intraplate seismic belt, with relatively high-quality instrumental catalogue data available since 1970. The Chinese historical earthquake catalogue contains six strong historical earthquakes of Ms ≥ 6 around Beijing, the earliest in 294 AD. This poses a significant potential hazard to one of the most densely populated and economically active parts of China. In some intraplate areas, persistent clusters of events associated with historical events can occur over centuries, for example, the ongoing sequence in the New Madrid zone of the eastern US. Here we will examine the evidence for such persistent clusters around Beijing. We introduce a metric known as the `seismic density index' that quantifies the degree of clustering of seismic energy release. For a given map location, this multi-dimensional index depends on the number of events, their magnitudes, and the distances to the locations of the surrounding population of earthquakes. We apply the index to modern instrumental catalogue data between 1970 and 2014, and identify six clear candidate zones. We then compare these locations to earthquake epicentre and seismic intensity data for the six largest historical earthquakes. Each candidate zone contains one of the six historical events, and the location of peak intensity is within 5 km or so of the reported epicentre in five of these cases. In one case—the great Ms 8 earthquake of 1679—the peak is closer to the area of strongest shaking (Intensity XI or more) than the reported epicentre. The present-day event rates are similar to those predicted by the modified Omori law but there is no evidence of ongoing decay in event rates. Accordingly, the index is more likely to be picking out the location of persistent weaknesses in the lithosphere. Our results imply zones of high seismic density index could be used in principle to indicate the location of unrecorded historical of palaeoseismic events, in China and

A Report Of The December 6, 2016 Mw 6.5 Pidie Jaya, Aceh Earthquake

NASA Astrophysics Data System (ADS)

Muzli, M.; Daniarsyad, G.; Nugraha, A. D.; Muksin, U.; Widiyantoro, S.; Bradley, K.; Wang, T.; Jousset, P. G.; Erbas, K.; Nurdin, I.; Wei, S.

2017-12-01

The December 6, 2016 Mw 6.5 earthquake in Pidie Jaya, Aceh was one of the devastating inland earthquakes in Sumatra that took away more than 100 people's life. Here we present our seismological analysis of the earthquake sequence. The earthquake focal mechanism inversions using regional BMKG broadband data and teleseismic waveform data all indicate a strike-slip focal mechanism with a centroid depth of 15 km. Preliminary finite fault inversion using teleseismic body waves prefers the fault plane with strike of 45 degree and dip of 50 degree, in agreement with the surface geology and USGS aftershock distributions. Nine broadband seismic stations were installed in the source region along the coast one week after the earthquake and have collected the data for one month. The data have been used to locate aftershocks with grid search and double-difference algorithm, which results in the lineup of the seismicity in NE-SW direction, in agreement with the fault inversion and geology results. Using the M4.0 calibration earthquake that was recorded by the temporally network, we relocated the mainshock epicenter, which is also consistent with fault geometry defined by the well located aftershocks. In addition, a portion of the seismicity shows a lineation in E-W direction, indicating a secondary fault that has not been identified before. Aftershock focal mechanisms determined by the first motion reveal similar solutions as the mainshock. The observed macro intensity data shows most of the damaged buildings are distributed along the coast, approximately perpendicular to the preferred fault strike instead of parallel with it. It appears that the distribution of damage is strongly related to the site conditions, since these strong shaking/damage regions are mainly located on the costal sedimentary soils.

Improved phase arrival estimate and location for local earthquakes in South Korea

NASA Astrophysics Data System (ADS)

Morton, E. A.; Rowe, C. A.; Begnaud, M. L.

2012-12-01

The Korean Institute of Geoscience and Mineral Resources (KIGAM) and the Korean Meteorological Agency (KMA) regularly report local (distance < ~1200 km) seismicity recorded with their networks; we obtain preliminary event location estimates as well as waveform data, but no phase arrivals are reported, so the data are not immediately useful for earthquake location. Our goal is to identify seismic events that are sufficiently well-located to provide accurate seismic travel-time information for events within the KIGAM and KMA networks, and also recorded by some regional stations. Toward that end, we are using a combination of manual phase identification and arrival-time picking, with waveform cross-correlation, to cluster events that have occurred in close proximity to one another, which allows for improved phase identification by comparing the highly correlating waveforms. We cross-correlate the known events with one another on 5 seismic stations and cluster events that correlate above a correlation coefficient threshold of 0.7, which reveals few clusters containing few events each. The small number of repeating events suggests that the online catalogs have had mining and quarry blasts removed before publication, as these can contribute significantly to repeating seismic sources in relatively aseismic regions such as South Korea. The dispersed source locations in our catalog, however, are ideal for seismic velocity modeling by providing superior sampling through the dense seismic station arrangement, which produces favorable event-to-station ray path coverage. Following careful manual phase picking on 104 events chosen to provide adequate ray coverage, we re-locate the events to obtain improved source coordinates. The re-located events are used with Thurber's Simul2000 pseudo-bending local tomography code to estimate the crustal structure on the Korean Peninsula, which is an important contribution to ongoing calibration for events of interest in the region.

Contribution of the Surface and Down-Hole Seismic Networks to the Location of Earthquakes at the Soultz-sous-Forêts Geothermal Site (France)

NASA Astrophysics Data System (ADS)

Kinnaert, X.; Gaucher, E.; Kohl, T.; Achauer, U.

2018-03-01

Seismicity induced in geo-reservoirs can be a valuable observation to image fractured reservoirs, to characterize hydrological properties, or to mitigate seismic hazard. However, this requires accurate location of the seismicity, which is nowadays an important seismological task in reservoir engineering. The earthquake location (determination of the hypocentres) depends on the model used to represent the medium in which the seismic waves propagate and on the seismic monitoring network. In this work, location uncertainties and location inaccuracies are modeled to investigate the impact of several parameters on the determination of the hypocentres: the picking uncertainty, the numerical precision of picked arrival times, a velocity perturbation and the seismic network configuration. The method is applied to the geothermal site of Soultz-sous-Forêts, which is located in the Upper Rhine Graben (France) and which was subject to detailed scientific investigations. We focus on a massive water injection performed in the year 2000 to enhance the productivity of the well GPK2 in the granitic basement, at approximately 5 km depth, and which induced more than 7000 earthquakes recorded by down-hole and surface seismic networks. We compare the location errors obtained from the joint or the separate use of the down-hole and surface networks. Besides the quantification of location uncertainties caused by picking uncertainties, the impact of the numerical precision of the picked arrival times as provided in a reference catalogue is investigated. The velocity model is also modified to mimic possible effects of a massive water injection and to evaluate its impact on earthquake hypocentres. It is shown that the use of the down-hole network in addition to the surface network provides smaller location uncertainties but can also lead to larger inaccuracies. Hence, location uncertainties would not be well representative of the location errors and interpretation of the seismicity

Joint inversion of teleseismic body-waves and geodetic data for the Mw6.8 aftershock of the Balochistan earthquake with refined epicenter location

NASA Astrophysics Data System (ADS)

Wei, S.; Wang, T.; Jonsson, S.; Avouac, J. P.; Helmberger, D. V.

2014-12-01

Aftershocks of the 2013 Balochistan earthquake are mainly concentrated along the northeastern end of the mainshock rupture despite of much larger coseismic slip to the southwest. The largest event among them is an Mw6.8 earthquake which occurred three days after the mainshock. A kinematic slip model of the mainshock was obtained by joint inversion of the teleseismic body-waves and horizontal static deformation field derived from remote sensing optical and SAR data, which is composed of seven fault segments with gradually changing strikes and dips [Avouac et al., 2014]. The remote sensing data provide well constraints on the fault geometry and spatial distribution of slip but no timing information. Meanwhile, the initiation of the teleseismic waveform is very sensitive to fault geometry of the epicenter segment (strike and dip) and spatial slip distribution but much less sensitive to the absolute location of the epicenter. The combination of the two data sets allows a much better determination of the absolute epicenter location, which is about 25km to the southwest of the NEIC epicenter location. The well located mainshock epicenter is used to establish path calibrations for teleseismic P-waves, which are essential for relocating the Mw6.8 aftershock. Our grid search shows that the refined epicenter is located right at the northeastern end of the mainshock rupture. This is confirmed by the SAR offsets calculated from images acquired after the mainshock. The azimuth and range offsets display a discontinuity across the rupture trace of the mainshock. Teleseismic only and static only, as well as joint inversions all indicate that the aftershock ruptured an asperity with 25km along strike and range from 8km to 20km in depth. The earthquake was originated in a positive Coulomb stress change regime due to the mainshock and has complementary slip distribution to the mainshock rupture at the northeastern end, suggesting that the entire seismic generic zone in the crust was

The 7.9 Denali Fault, Alaska Earthquake of November 3, 2002: Aftershock Locations, Moment Tensors and Focal Mechanisms from the Regional Seismic Network Data

NASA Astrophysics Data System (ADS)

Ratchkovski, N. A.; Hansen, R. A.; Kore, K. R.

2003-04-01

The largest earthquake ever recorded on the Denali fault system (magnitude 7.9) struck central Alaska on November 3, 2002. It was preceded by a magnitude 6.7 earthquake on October 23. This earlier earthquake and its zone of aftershocks were located ~20 km to the west of the 7.9 quake. Aftershock locations and surface slip observations from the 7.9 quake indicate that the rupture was predominately unilateral in the eastward direction. The geologists mapped a ~300-km-long rupture and measured maximum offsets of 8.8 meters. The 7.9 event ruptured three different faults. The rupture began on the northeast trending Susitna Glacier Thrust fault, a splay fault south of the Denali fault. Then the rupture transferred to the Denali fault and propagated eastward for 220 km. At about 143W the rupture moved onto the adjacent southeast-trending Totschunda fault and propagated for another 55 km. The cumulative length of the 6.7 and 7.9 aftershock zones along the Denali and Totschunda faults is about 380 km. The earthquakes were recorded and processed by the Alaska Earthquake Information Center (AEIC). The AEIC acquires and processes data from the Alaska Seismic Network, consisting of over 350 seismograph stations. Nearly 40 of these sites are equipped with the broad-band sensors, some of which also have strong motion sensors. The rest of the stations are either 1 or 3-component short-period instruments. The data from these stations are collected, processed and archived at the AEIC. The AEIC staff installed a temporary seismic network of 6 instruments following the 6.7 earthquake and an additional 20 stations following the 7.9 earthquake. Prior to the 7.9 Denali Fault event, the AEIC was locating 35 to 50 events per day. After the event, the processing load increased to over 300 events per day during the first week following the event. In this presentation, we will present and interpret the aftershock location patterns, first motion focal mechanism solutions, and regional seismic

Earthquake effects at nuclear reactor facilities: San Fernando earthquake of February 9th, 1971

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

Howard, G.; Ibanez, P.; Matthiesen, F.

1972-02-01

The effects of the San Fernando earthquake of February 9, 1971 on 26 reactor facilities located in California, Arizona, and Nevada are reported. The safety performance of the facilities during the earthquake is discussed. (JWR)

Iris Location Algorithm Based on the CANNY Operator and Gradient Hough Transform

NASA Astrophysics Data System (ADS)

Zhong, L. H.; Meng, K.; Wang, Y.; Dai, Z. Q.; Li, S.

2017-12-01

In the iris recognition system, the accuracy of the localization of the inner and outer edges of the iris directly affects the performance of the recognition system, so iris localization has important research meaning. Our iris data contain eyelid, eyelashes, light spot and other noise, even the gray transformation of the images is not obvious, so the general methods of iris location are unable to realize the iris location. The method of the iris location based on Canny operator and gradient Hough transform is proposed. Firstly, the images are pre-processed; then, calculating the gradient information of images, the inner and outer edges of iris are coarse positioned using Canny operator; finally, according to the gradient Hough transform to realize precise localization of the inner and outer edge of iris. The experimental results show that our algorithm can achieve the localization of the inner and outer edges of the iris well, and the algorithm has strong anti-interference ability, can greatly reduce the location time and has higher accuracy and stability.

An efficient biological pathway layout algorithm combining grid-layout and spring embedder for complicated cellular location information

PubMed Central

2010-01-01

Background Graph drawing is one of the important techniques for understanding biological regulations in a cell or among cells at the pathway level. Among many available layout algorithms, the spring embedder algorithm is widely used not only for pathway drawing but also for circuit placement and www visualization and so on because of the harmonized appearance of its results. For pathway drawing, location information is essential for its comprehension. However, complex shapes need to be taken into account when torus-shaped location information such as nuclear inner membrane, nuclear outer membrane, and plasma membrane is considered. Unfortunately, the spring embedder algorithm cannot easily handle such information. In addition, crossings between edges and nodes are usually not considered explicitly. Results We proposed a new grid-layout algorithm based on the spring embedder algorithm that can handle location information and provide layouts with harmonized appearance. In grid-layout algorithms, the mapping of nodes to grid points that minimizes a cost function is searched. By imposing positional constraints on grid points, location information including complex shapes can be easily considered. Our layout algorithm includes the spring embedder cost as a component of the cost function. We further extend the layout algorithm to enable dynamic update of the positions and sizes of compartments at each step. Conclusions The new spring embedder-based grid-layout algorithm and a spring embedder algorithm are applied to three biological pathways; endothelial cell model, Fas-induced apoptosis model, and C. elegans cell fate simulation model. From the positional constraints, all the results of our algorithm satisfy location information, and hence, more comprehensible layouts are obtained as compared to the spring embedder algorithm. From the comparison of the number of crossings, the results of the grid-layout-based algorithm tend to contain more crossings than those of the

Improvement of Earthquake Epicentral Locations Using T-Phases: Testing by Comparison With Surface Wave Relative Event Locations

DTIC Science & Technology

2001-10-01

deployment of 51 ocean -bottom seismometers (OBS) on the seafloor spanning 800 km across the East Pacific Rise provides a unique opportunity to test the...aftershock sequence of earthquakes at the northern end of the Easter microplate . In addition, for the larger earthquakes, we can compare relative... ocean -bottom seismometers OBJECTIVES The objectives of this research are To explore the synergy between hydroacoustic and seismic techniques

Robust optimization model and algorithm for railway freight center location problem in uncertain environment.

PubMed

Liu, Xing-Cai; He, Shi-Wei; Song, Rui; Sun, Yang; Li, Hao-Dong

2014-01-01

Railway freight center location problem is an important issue in railway freight transport programming. This paper focuses on the railway freight center location problem in uncertain environment. Seeing that the expected value model ignores the negative influence of disadvantageous scenarios, a robust optimization model was proposed. The robust optimization model takes expected cost and deviation value of the scenarios as the objective. A cloud adaptive clonal selection algorithm (C-ACSA) was presented. It combines adaptive clonal selection algorithm with Cloud Model which can improve the convergence rate. Design of the code and progress of the algorithm were proposed. Result of the example demonstrates the model and algorithm are effective. Compared with the expected value cases, the amount of disadvantageous scenarios in robust model reduces from 163 to 21, which prove the result of robust model is more reliable.

Increasing critical sensitivity of the Load/Unload Response Ratio before large earthquakes with identified stress accumulation pattern

NASA Astrophysics Data System (ADS)

Yu, Huai-zhong; Shen, Zheng-kang; Wan, Yong-ge; Zhu, Qing-yong; Yin, Xiang-chu

2006-12-01

The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701-715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events.

Temporal variation of tectonic tremor activity in southern Taiwan around the 2010 ML6.4 Jiashian earthquake

NASA Astrophysics Data System (ADS)

Chao, Kevin; Peng, Zhigang; Hsu, Ya-Ju; Obara, Kazushige; Wu, Chunquan; Ching, Kuo-En; van der Lee, Suzan; Pu, Hsin-Chieh; Leu, Peih-Lin; Wech, Aaron

2017-07-01

Deep tectonic tremor, which is extremely sensitive to small stress variations, could be used to monitor fault zone processes during large earthquake cycles and aseismic processes before large earthquakes. In this study, we develop an algorithm for the automatic detection and location of tectonic tremor beneath the southern Central Range of Taiwan and examine the spatiotemporal relationship between tremor and the 4 March 2010 ML6.4 Jiashian earthquake, located about 20 km from active tremor sources. We find that tremor in this region has a relatively short duration, short recurrence time, and no consistent correlation with surface GPS data. We find a short-term increase in the tremor rate 19 days before the Jiashian main shock, and around the time when the tremor rate began to rise one GPS station recorded a flip in its direction of motion. We hypothesize that tremor is driven by a slow-slip event that preceded the occurrence of the shallower Jiashian main shock, even though the inferred slip is too small to be observed by all GPS stations. Our study shows that tectonic tremor may reflect stress variation during the prenucleation process of a nearby earthquake.

Structural features of the Pernicana Fault (M. Etna, Sicily, Italy) inferred by high precise location of the microseismicity

NASA Astrophysics Data System (ADS)

Alparone, S.; Gambino, S.; Mostaccio, A.; Spampinato, S.; Tuvè, T.; Ursino, A.

2009-04-01

The north-eastern flank of Mt. Etna is crossed by an important and active tectonic structure, the Pernicana Fault having a mean strike WNW-ESE. It links westward to the active NE Rift and seems to have an important role in controlling instability processes affecting the eastern flank of the volcano. Recent studies suggest that Pernicana Fault is very active through sinistral, oblique-slip movements and is also characterised by frequent shallow seismicity (depth < 2 km bsl) on the uphill western segment and by remarkable creeping on the downhill eastern one. The Pernicana Fault earthquakes, which can reach magnitudes up to 4.2, sometimes with coseismic surface faulting, caused severe damages to tourist resorts and villages along or close this structure. In the last years, a strong increase of seismicity, also characterized by swarms, was recorded by INGV-CT permanent local seismic network close the Pernicana Fault. A three-step procedure was applied to calculate precise hypocentre locations. In a first step, we chose to apply cross-correlation analysis, in order to easily evaluate the similarity of waveforms useful to identify earthquakes families. In a second step, we calculate probabilistic earthquake locations using the software package NONLINLOC, which includes systematic, complete grid search and global, non-linear search methods. Subsequently, we perform relative relocation of correlated event pairs using the double-difference earthquake algorithm and the program HypoDD. The double-difference algorithm minimizes the residuals between observed and calculated travel time difference for pairs of earthquakes at common stations by iteratively adjusting the vector difference between the hypocenters. We show the recognized spatial seismic clusters identifying the most active and hazarding sectors of the structure, their geometry and depth. Finally, in order to clarify the geodynamic framework of the area, we associate these results with calculated focal mechanisms

Twitter Seismology: Earthquake Monitoring and Response in a Social World

NASA Astrophysics Data System (ADS)

Bowden, D. C.; Earle, P. S.; Guy, M.; Smoczyk, G.

2011-12-01

The U.S. Geological Survey (USGS) is investigating how the social networking site Twitter, a popular service for sending and receiving short, public, text messages, can augment USGS earthquake response products and the delivery of hazard information. The potential uses of Twitter for earthquake response include broadcasting earthquake alerts, rapidly detecting widely felt events, qualitatively assessing earthquake damage effects, communicating with the public, and participating in post-event collaboration. Several seismic networks and agencies are currently distributing Twitter earthquake alerts including the European-Mediterranean Seismological Centre (@LastQuake), Natural Resources Canada (@CANADAquakes), and the Indonesian meteorological agency (@infogempabmg); the USGS will soon distribute alerts via the @USGSted and @USGSbigquakes Twitter accounts. Beyond broadcasting alerts, the USGS is investigating how to use tweets that originate near the epicenter to detect and characterize shaking events. This is possible because people begin tweeting immediately after feeling an earthquake, and their short narratives and exclamations are available for analysis within 10's of seconds of the origin time. Using five months of tweets that contain the word "earthquake" and its equivalent in other languages, we generate a tweet-frequency time series. The time series clearly shows large peaks correlated with the origin times of widely felt events. To identify possible earthquakes, we use a simple Short-Term-Average / Long-Term-Average algorithm similar to that commonly used to detect seismic phases. As with most auto-detection algorithms, the parameters can be tuned to catch more or less events at the cost of more or less false triggers. When tuned to a moderate sensitivity, the detector found 48 globally-distributed, confirmed seismic events with only 2 false triggers. A space-shuttle landing and "The Great California ShakeOut" caused the false triggers. This number of

MyShake: A smartphone seismic network for earthquake early warning and beyond

PubMed Central

Kong, Qingkai; Allen, Richard M.; Schreier, Louis; Kwon, Young-Woo

2016-01-01

Large magnitude earthquakes in urban environments continue to kill and injure tens to hundreds of thousands of people, inflicting lasting societal and economic disasters. Earthquake early warning (EEW) provides seconds to minutes of warning, allowing people to move to safe zones and automated slowdown and shutdown of transit and other machinery. The handful of EEW systems operating around the world use traditional seismic and geodetic networks that exist only in a few nations. Smartphones are much more prevalent than traditional networks and contain accelerometers that can also be used to detect earthquakes. We report on the development of a new type of seismic system, MyShake, that harnesses personal/private smartphone sensors to collect data and analyze earthquakes. We show that smartphones can record magnitude 5 earthquakes at distances of 10 km or less and develop an on-phone detection capability to separate earthquakes from other everyday shakes. Our proof-of-concept system then collects earthquake data at a central site where a network detection algorithm confirms that an earthquake is under way and estimates the location and magnitude in real time. This information can then be used to issue an alert of forthcoming ground shaking. MyShake could be used to enhance EEW in regions with traditional networks and could provide the only EEW capability in regions without. In addition, the seismic waveforms recorded could be used to deliver rapid microseism maps, study impacts on buildings, and possibly image shallow earth structure and earthquake rupture kinematics. PMID:26933682

The 2007 Boso Slow Slip Event and the associated earthquake swarm

NASA Astrophysics Data System (ADS)

Sekine, S.; Hirose, H.; Kimura, H.; Obara, K.

2007-12-01

In the Boso Peninsula, which is located in southeast of the Japan mainland, slow slip events (SSE) have been observed by the GEONET GPS array operated by the Geographical Survey Institute Japan and the NIED tiltmeter network every 6-7 years (Ozawa et al.,2003; NIED 2003). The unique characteristics of the Boso SSE are that earthquake swarm activities have also occurred in association with the SSE. The latest activity of the SSE and the earthquake swarm took place in August 2007. On 13th August, an earthquake swarm began to occur at east off Boso Peninsula and the slow tilt deformations also started. The earthquake sources migrated to the NNE direction, which is the same direction of the relative plate motion of the subducting Philippine Sea Plate with respect to the overriding plate. The largest earthquake in this episode (Mw 5.3) occurred on 16th and the second largest one (Mw 5.2) on 18th. Most of the larger earthquakes show low- angle thrust type focal mechanisms that are consistent with the plate motion and the geometry of the subduction plate interface. The tilt changes seem to stop on 17th and the activity of the swarm rapidly decreases after 19th. The maximum tilt change of 0.8 micro radian with northwest down tilting was observed at KT2H, the nearest station from the source region. Based on the tilt records around Boso Peninsula, we estimate a fault model for the SSE using genetic algorithm inversion to non-linear parameter and the weighted least squares method to linear parameters. As a result, the estimated moment magnitude and the amount of slip are 6.4 and 10 cm, respectively. The size and the location of the SSE are similar to the previous episodes. The estimated fault plane is very consistent with the configuration of the plate interface (Kimura et al., 2006). Most of the earthquakes are located on the deeper edge of the estimated SSE fault area. The coincidence of the swarm and the SSE suggests a causal relation between them and may help us to

A 3-D velocity model for earthquake location from combined geological and geophysical data: a case study from the TABOO near fault observatory (Northern Apennines, Italy)

NASA Astrophysics Data System (ADS)

Latorre, Diana; Lupattelli, Andrea; Mirabella, Francesco; Trippetta, Fabio; Valoroso, Luisa; Lomax, Anthony; Di Stefano, Raffaele; Collettini, Cristiano; Chiaraluce, Lauro

2014-05-01

Accurate hypocenter location at the crustal scale strongly depends on our knowledge of the 3D velocity structure. The integration of geological and geophysical data, when available, should contribute to a reliable seismic velocity model in order to guarantee high quality earthquake locations as well as their consistency with the geological structure. Here we present a 3D, P- and S-wave velocity model of the Upper Tiber valley region (Northern Apennines) retrieved by combining an extremely robust dataset of surface and sub-surface geological data (seismic reflection profiles and boreholes), in situ and laboratory velocity measurements, and earthquake data. The study area is a portion of the Apennine belt undergoing active extension where a set of high-angle normal faults is detached on the Altotiberina low-angle normal fault (ATF). From 2010, this area hosts a scientific infrastructure (the Alto Tiberina Near Fault Observatory, TABOO; http://taboo.rm.ingv.it/), consisting of a dense array of multi-sensor stations, devoted to studying the earthquakes preparatory phase and the deformation processes along the ATF fault system. The proposed 3D velocity model is a layered model in which irregular shaped surfaces limit the boundaries between main lithological units. The model has been constructed by interpolating depth converted seismic horizons interpreted along 40 seismic reflection profiles (down to 4s two way travel times) that have been calibrated with 6 deep boreholes (down to 5 km depth) and constrained by detailed geological maps and structural surveys data. The layers of the model are characterized by similar rock types and seismic velocity properties. The P- and S-waves velocities for each layer have been derived from velocity measurements coming from both boreholes (sonic logs) and laboratory, where measurements have been performed on analogue natural samples increasing confining pressure in order to simulate crustal conditions. In order to test the 3D velocity

A global search inversion for earthquake kinematic rupture history: Application to the 2000 western Tottori, Japan earthquake

USGS Publications Warehouse

Piatanesi, A.; Cirella, A.; Spudich, P.; Cocco, M.

2007-01-01

We present a two-stage nonlinear technique to invert strong motions records and geodetic data to retrieve the rupture history of an earthquake on a finite fault. To account for the actual rupture complexity, the fault parameters are spatially variable peak slip velocity, slip direction, rupture time and risetime. The unknown parameters are given at the nodes of the subfaults, whereas the parameters within a subfault are allowed to vary through a bilinear interpolation of the nodal values. The forward modeling is performed with a discrete wave number technique, whose Green's functions include the complete response of the vertically varying Earth structure. During the first stage, an algorithm based on the heat-bath simulated annealing generates an ensemble of models that efficiently sample the good data-fitting regions of parameter space. In the second stage (appraisal), the algorithm performs a statistical analysis of the model ensemble and computes a weighted mean model and its standard deviation. This technique, rather than simply looking at the best model, extracts the most stable features of the earthquake rupture that are consistent with the data and gives an estimate of the variability of each model parameter. We present some synthetic tests to show the effectiveness of the method and its robustness to uncertainty of the adopted crustal model. Finally, we apply this inverse technique to the well recorded 2000 western Tottori, Japan, earthquake (Mw 6.6); we confirm that the rupture process is characterized by large slip (3-4 m) at very shallow depths but, differently from previous studies, we imaged a new slip patch (2-2.5 m) located deeper, between 14 and 18 km depth. Copyright 2007 by the American Geophysical Union.

Distributing Earthquakes Among California's Faults: A Binary Integer Programming Approach

NASA Astrophysics Data System (ADS)

Geist, E. L.; Parsons, T.

2016-12-01

Statement of the problem is simple: given regional seismicity specified by a Gutenber-Richter (G-R) relation, how are earthquakes distributed to match observed fault-slip rates? The objective is to determine the magnitude-frequency relation on individual faults. The California statewide G-R b-value and a-value are estimated from historical seismicity, with the a-value accounting for off-fault seismicity. UCERF3 consensus slip rates are used, based on geologic and geodetic data and include estimates of coupling coefficients. The binary integer programming (BIP) problem is set up such that each earthquake from a synthetic catalog spanning millennia can occur at any location along any fault. The decision vector, therefore, consists of binary variables, with values equal to one indicating the location of each earthquake that results in an optimal match of slip rates, in an L1-norm sense. Rupture area and slip associated with each earthquake are determined from a magnitude-area scaling relation. Uncertainty bounds on the UCERF3 slip rates provide explicit minimum and maximum constraints to the BIP model, with the former more important to feasibility of the problem. There is a maximum magnitude limit associated with each fault, based on fault length, providing an implicit constraint. Solution of integer programming problems with a large number of variables (>105 in this study) has been possible only since the late 1990s. In addition to the classic branch-and-bound technique used for these problems, several other algorithms have been recently developed, including pre-solving, sifting, cutting planes, heuristics, and parallelization. An optimal solution is obtained using a state-of-the-art BIP solver for M≥6 earthquakes and California's faults with slip-rates > 1 mm/yr. Preliminary results indicate a surprising diversity of on-fault magnitude-frequency relations throughout the state.

Injection-induced earthquakes

USGS Publications Warehouse

Ellsworth, William L.

2013-01-01

Earthquakes in unusual locations have become an important topic of discussion in both North America and Europe, owing to the concern that industrial activity could cause damaging earthquakes. It has long been understood that earthquakes can be induced by impoundment of reservoirs, surface and underground mining, withdrawal of fluids and gas from the subsurface, and injection of fluids into underground formations. Injection-induced earthquakes have, in particular, become a focus of discussion as the application of hydraulic fracturing to tight shale formations is enabling the production of oil and gas from previously unproductive formations. Earthquakes can be induced as part of the process to stimulate the production from tight shale formations, or by disposal of wastewater associated with stimulation and production. Here, I review recent seismic activity that may be associated with industrial activity, with a focus on the disposal of wastewater by injection in deep wells; assess the scientific understanding of induced earthquakes; and discuss the key scientific challenges to be met for assessing this hazard.

Feasibility study of earthquake early warning (EEW) in Hawaii

USGS Publications Warehouse

Thelen, Weston A.; Hotovec-Ellis, Alicia J.; Bodin, Paul

2016-09-30

when using a regional network of seismometers. Given the current network, a single-station approach provides more warning for damaging earthquakes that occur close to the station, but it would have limited benefit compared to a fully implemented ShakeAlert system. For Honolulu, for example, the single-station approach provides an advantage over ShakeAlert only for earthquakes that occur in a narrow zone extending northeast and southwest of O‘ahu. Instrumentation and alarms associated with the single-station approach are typically maintained and assessed within the target facility, and thus no outside connectivity is required. A single-station approach, then, is unlikely to help broader populations beyond the individuals at the target facility, but they have the benefit of being commercially available for relatively little cost. The USGS Hawaiian Volcano Observatory (HVO) is the Advanced National Seismic System (ANSS) regional seismic network responsible for locating and characterizing earthquakes across the State of Hawaii. During 2014 and 2015, HVO tested a network-based EEW algorithm within the current seismic network in order to assess the suitability for building a full EEW system. Using the current seismic instrumentation and processing setup at HVO, it is possible for a network approach to release an alarm a little more than 3 seconds after the earthquake is recorded on the fourth seismometer. Presently, earthquakes having M≥3 detected with the ElarmS algorithm have an average location error of approximately 4.5 km and an average magnitude error of -0.3 compared to the reviewed catalog locations from the HVO. Additional stations and upgrades to existing seismic stations would serve to improve solution precision and warning times and additional staffing would be required to provide support for a robust, network-based EEW system. For a critical facility on the Island of Hawaiʻi, such as the telescopes atop Mauna Kea, one phased approach to mitigate losses

3-D P- and S-wave velocity structure and low-frequency earthquake locations in the Parkfield, California region

USGS Publications Warehouse

Zeng, Xiangfang; Thurber, Clifford H.; Shelly, David R.; Harrington, Rebecca M.; Cochran, Elizabeth S.; Bennington, Ninfa L.; Peterson, Dana; Guo, Bin; McClement, Kara

2016-01-01

To refine the 3-D seismic velocity model in the greater Parkfield, California region, a new data set including regular earthquakes, shots, quarry blasts and low-frequency earthquakes (LFEs) was assembled. Hundreds of traces of each LFE family at two temporary arrays were stacked with time–frequency domain phase weighted stacking method to improve signal-to-noise ratio. We extend our model resolution to lower crustal depth with LFE data. Our result images not only previously identified features but also low velocity zones (LVZs) in the area around the LFEs and the lower crust beneath the southern Rinconada Fault. The former LVZ is consistent with high fluid pressure that can account for several aspects of LFE behaviour. The latter LVZ is consistent with a high conductivity zone in magnetotelluric studies. A new Vs model was developed with S picks that were obtained with a new autopicker. At shallow depth, the low Vs areas underlie the strongest shaking areas in the 2004 Parkfield earthquake. We relocate LFE families and analyse the location uncertainties with the NonLinLoc and tomoDD codes. The two methods yield similar results.

CISN ShakeAlert: Improving the Virtual Seismologist (VS) earthquake early warning framework to provide faster, more robust warning information

NASA Astrophysics Data System (ADS)

Meier, M.; Cua, G. B.; Wiemer, S.; Fischer, M.

2011-12-01

The Virtual Seismologist (VS) method is a Bayesian approach to regional network-based earthquake early warning (EEW) that uses observed phase arrivals, ground motion amplitudes and selected prior information to estimate earthquake magnitude, location and origin time, and predict the distribution of peak ground motion throughout a region using envelope attenuation relationships. Implementation of the VS algorithm in California is an on-going effort of the Swiss Seismological Service (SED) at ETH Zürich. VS is one of three EEW algorithms - the other two being ElarmS (Allen and Kanamori, 2003) and On-Site (Wu and Kanamori, 2005; Boese et al., 2008) - that form the basis of the California Integrated Seismic Network ShakeAlert system, a prototype end-to-end EEW system that could potentially be implemented in California. The current prototype version of VS in California requires picks at 4 stations to initiate an event declaration. On average, taking into account data latency, variable station distribution, and processing time, this initial estimate is available about 20 seconds after the earthquake origin time, corresponding to a blind zone of about 70 km around the epicenter which would receive no warning, but where it would be the most useful. To increase the available warning time, we want to produce EEW estimates faster (with less than 4 stations). However, working with less than 4 stations with our current approach would increase the number of false alerts, for which there is very little tolerance in a useful EEW system. We explore the use of back-azimuth estimations and the Voronoi-based concept of not-yet-arrived data for reducing false alerts of the earliest VS estimates. The concept of not-yet-arrived data was originally used to provide evolutionary location estimates in EEW (Horiuchi, 2005; Cua and Heaton, 2007; Satriano et al. 2008). However, it can also be applied in discriminating between earthquake and non-earthquake signals. For real earthquakes, the

Earthquakes in South Carolina and Vicinity 1698-2009

USGS Publications Warehouse

Dart, Richard L.; Talwani, Pradeep; Stevenson, Donald

2010-01-01

This map summarizes more than 300 years of South Carolina earthquake history. It is one in a series of three similar State earthquake history maps. The current map and the previous two for Virginia and Ohio are accessible at http://pubs.usgs.gov/of/2006/1017/ and http://pubs.usgs.gov/of/2008/1221/. All three State earthquake maps were collaborative efforts between the U.S. Geological Survey and respective State agencies. Work on the South Carolina map was done in collaboration with the Department of Geological Sciences, University of South Carolina. As with the two previous maps, the history of South Carolina earthquakes was derived from letters, journals, diaries, newspaper accounts, academic journal articles, and, beginning in the early 20th century, instrumental recordings (seismograms). All historical (preinstrumental) earthquakes that were large enough to be felt have been located based on felt reports. Some of these events caused damage to buildings and their contents. The more recent widespread use of seismographs has allowed many smaller earthquakes, previously undetected, to be recorded and accurately located. The seismicity map shows historically located and instrumentally recorded earthquakes in and near South Carolina

Laser-Interferometric Broadband Seismometer for Epicenter Location Estimation

PubMed Central

Lee, Kyunghyun; Kwon, Hyungkwan; You, Kwanho

2017-01-01

In this paper, we suggest a seismic signal measurement system that uses a laser interferometer. The heterodyne laser interferometer is used as a seismometer due to its high accuracy and robustness. Seismic data measured by the laser interferometer is used to analyze crucial earthquake characteristics. To measure P-S time more precisely, the short time Fourier transform and instantaneous frequency estimation methods are applied to the intensity signal (Iy) of the laser interferometer. To estimate the epicenter location, the range difference of arrival algorithm is applied with the P-S time result. The linear matrix equation of the epicenter localization can be derived using P-S time data obtained from more than three observatories. We prove the performance of the proposed algorithm through simulation and experimental results. PMID:29065515

Catalog of earthquake hypocenters at Alaskan volcanoes: January 1 through December 31, 2006

USGS Publications Warehouse

Dixon, James P.; Stihler, Scott D.; Power, John A.; Searcy, Cheryl

2008-01-01

Between January 1 and December 31, 2006, AVO located 8,666 earthquakes of which 7,783 occurred on or near the 33 volcanoes monitored within Alaska. Monitoring highlights in 2006 include: an eruption of Augustine Volcano, a volcanic-tectonic earthquake swarm at Mount Martin, elevated seismicity and volcanic unrest at Fourpeaked Mountain, and elevated seismicity and low-level tremor at Mount Veniaminof and Korovin Volcano. A new seismic subnetwork was installed on Fourpeaked Mountain. This catalog includes: (1) descriptions and locations of seismic instrumentation deployed in the field during 2006, (2) a description of earthquake detection, recording, analysis, and data archival systems, (3) a description of seismic velocity models used for earthquake locations, (4) a summary of earthquakes located in 2006, and (5) an accompanying UNIX tar-file with a summary of earthquake origin times, hypocenters, magnitudes, phase arrival times, location quality statistics, daily station usage statistics, and all files used to determine the earthquake locations in 2006.

Earthquakes in Virginia and vicinity 1774 - 2004

USGS Publications Warehouse

Tarr, Arthur C.; Wheeler, Russell L.

2006-01-01

This map summarizes two and a third centuries of earthquake activity. The seismic history consists of letters, journals, diaries, and newspaper and scholarly articles that supplement seismograph recordings (seismograms) dating from the early twentieth century to the present. All of the pre-instrumental (historical) earthquakes were large enough to be felt by people or to cause shaking damage to buildings and their contents. Later, widespread use of seismographs meant that tremors too small or distant to be felt could be detected and accurately located. Earthquakes are a legitimate concern in Virginia and parts of adjacent States. Moderate earthquakes cause slight local damage somewhere in the map area about twice a decade on the average. Additionally, many buildings in the map area were constructed before earthquake protection was added to local building codes. The large map shows all historical and instrumentally located earthquakes from 1774 through 2004.

Deviant Earthquakes: Data-driven Constraints on the Variability in Earthquake Source Properties and Seismic Hazard

NASA Astrophysics Data System (ADS)

Trugman, Daniel Taylor

The complexity of the earthquake rupture process makes earthquakes inherently unpredictable. Seismic hazard forecasts often presume that the rate of earthquake occurrence can be adequately modeled as a space-time homogenenous or stationary Poisson process and that the relation between the dynamical source properties of small and large earthquakes obey self-similar scaling relations. While these simplified models provide useful approximations and encapsulate the first-order statistical features of the historical seismic record, they are inconsistent with the complexity underlying earthquake occurrence and can lead to misleading assessments of seismic hazard when applied in practice. The six principle chapters of this thesis explore the extent to which the behavior of real earthquakes deviates from these simplified models, and the implications that the observed deviations have for our understanding of earthquake rupture processes and seismic hazard. Chapter 1 provides a brief thematic overview and introduction to the scope of this thesis. Chapter 2 examines the complexity of the 2010 M7.2 El Mayor-Cucapah earthquake, focusing on the relation between its unexpected and unprecedented occurrence and anthropogenic stresses from the nearby Cerro Prieto Geothermal Field. Chapter 3 compares long-term changes in seismicity within California's three largest geothermal fields in an effort to characterize the relative influence of natural and anthropogenic stress transients on local seismic hazard. Chapter 4 describes a hybrid, hierarchical clustering algorithm that can be used to relocate earthquakes using waveform cross-correlation, and applies the new algorithm to study the spatiotemporal evolution of two recent seismic swarms in western Nevada. Chapter 5 describes a new spectral decomposition technique that can be used to analyze the dynamic source properties of large datasets of earthquakes, and applies this approach to revisit the question of self-similar scaling of

Earthquake precursors: spatial-temporal gravity changes before the great earthquakes in the Sichuan-Yunnan area

NASA Astrophysics Data System (ADS)

Zhu, Yi-Qing; Liang, Wei-Feng; Zhang, Song

2018-01-01

Using multiple-scale mobile gravity data in the Sichuan-Yunnan area, we systematically analyzed the relationships between spatial-temporal gravity changes and the 2014 Ludian, Yunnan Province Ms6.5 earthquake and the 2014 Kangding Ms6.3, 2013 Lushan Ms7.0, and 2008 Wenchuan Ms8.0 earthquakes in Sichuan Province. Our main results are as follows. (1) Before the occurrence of large earthquakes, gravity anomalies occur in a large area around the epicenters. The directions of gravity change gradient belts usually agree roughly with the directions of the main fault zones of the study area. Such gravity changes might reflect the increase of crustal stress, as well as the significant active tectonic movements and surface deformations along fault zones, during the period of gestation of great earthquakes. (2) Continuous significant changes of the multiple-scale gravity fields, as well as greater gravity changes with larger time scales, can be regarded as medium-range precursors of large earthquakes. The subsequent large earthquakes always occur in the area where the gravity changes greatly. (3) The spatial-temporal gravity changes are very useful in determining the epicenter of coming large earthquakes. The large gravity networks are useful to determine the general areas of coming large earthquakes. However, the local gravity networks with high spatial-temporal resolution are suitable for determining the location of epicenters. Therefore, denser gravity observation networks are necessary for better forecasts of the epicenters of large earthquakes. (4) Using gravity changes from mobile observation data, we made medium-range forecasts of the Kangding, Ludian, Lushan, and Wenchuan earthquakes, with especially successful forecasts of the location of their epicenters. Based on the above discussions, we emphasize that medium-/long-term potential for large earthquakes might exist nowadays in some areas with significant gravity anomalies in the study region. Thus, the monitoring

Scaling of seismic memory with earthquake size

NASA Astrophysics Data System (ADS)

Zheng, Zeyu; Yamasaki, Kazuko; Tenenbaum, Joel; Podobnik, Boris; Tamura, Yoshiyasu; Stanley, H. Eugene

2012-07-01

It has been observed that discrete earthquake events possess memory, i.e., that events occurring in a particular location are dependent on the history of that location. We conduct an analysis to see whether continuous real-time data also display a similar memory and, if so, whether such autocorrelations depend on the size of earthquakes within close spatiotemporal proximity. We analyze the seismic wave form database recorded by 64 stations in Japan, including the 2011 “Great East Japan Earthquake,” one of the five most powerful earthquakes ever recorded, which resulted in a tsunami and devastating nuclear accidents. We explore the question of seismic memory through use of mean conditional intervals and detrended fluctuation analysis (DFA). We find that the wave form sign series show power-law anticorrelations while the interval series show power-law correlations. We find size dependence in earthquake autocorrelations: as the earthquake size increases, both of these correlation behaviors strengthen. We also find that the DFA scaling exponent α has no dependence on the earthquake hypocenter depth or epicentral distance.

Earthquakes in Ohio and Vicinity 1776-2007

USGS Publications Warehouse

Dart, Richard L.; Hansen, Michael C.

2008-01-01

This map summarizes two and a third centuries of earthquake activity. The seismic history consists of letters, journals, diaries, and newspaper and scholarly articles that supplement seismograph recordings (seismograms) dating from the early twentieth century to the present. All of the pre-instrumental (historical) earthquakes were large enough to be felt by people or to cause shaking damage to buildings and their contents. Later, widespread use of seismographs meant that tremors too small or distant to be felt could be detected and accurately located. Earthquakes are a legitimate concern in Ohio and parts of adjacent States. Ohio has experienced more than 160 felt earthquakes since 1776. Most of these events caused no damage or injuries. However, 15 Ohio earthquakes resulted in property damage and some minor injuries. The largest historic earthquake in the state occurred in 1937. This event had an estimated magnitude of 5.4 and caused considerable damage in the town of Anna and in several other western Ohio communities. The large map shows all historical and instrumentally located earthquakes from 1776 through 2007.

CyberTEAM Interactive Epicenter Locator Tool

NASA Astrophysics Data System (ADS)

Ouyang, Y.; Hayden, K.; Lehmann, M.; Kilb, D.

2008-12-01

News coverage showing collapsed buildings, broken bridges and smashed cars help middle school students visualize the hazardous nature of earthquakes. However, few students understand how scientists investigate earthquakes through analysis of data collected using technology devices from around the world. The important findings by Muawia Barazangi and James Dorman in 1969 revealed how earthquakes charted between 1961 and 1967 delineated narrow belts of seismicity. This important discovery prompted additional research that eventually led to the theory of plate tectonics. When a large earthquake occurs, people from distances near and far can feel it to varying degrees. But how do scientists examine data to identify the locations of earthquake epicenters? The scientific definition of an earthquake: "a movement within the Earth's crust or mantle, caused by the sudden rupture or repositioning of underground material as they release stress" can be confusing for students first studying Earth science in 6th grade. Students struggle with understanding how scientists can tell when and where a rupture occurs, when the inner crust and mantle are not visible to us. Our CyberTEAM project provides 6th grade teachers with the opportunity to engage adolescents in activities that make textbooks come alive as students manipulate the same data that today's scientists use. We have developed an Earthquake Epicenter Location Tool that includes two Flash-based interactive learning objects that can be used to study basic seismology concepts and lets the user determine earthquake epicenters from current data. Through the Wilber II system maintained at the IRIS (Incorporated Research Institutions for Seismology) Web site, this project retrieves seismic data of recent earthquakes and makes them available to the public. Students choose an earthquake to perform further explorations. For each earthquake, a selection of USArray seismic stations are marked on a Google Map. Picking a station on the

Aftershock locations and rupture characteristics of the 2006 May 27, Yogyakarta-Indonesia earthquake

NASA Astrophysics Data System (ADS)

Irwan, M.; Ando, M.; Kimata, F.; Tadokoro, K.; Nakamichi, H.; Muto, D.; Okuda, T.; Hasanuddin, A.; Mipi A., K.; Setyadji, B.; Andreas, H.; Gamal, M.; Arif, R.

2006-12-01

A strong earthquake (M6.3) rocked the Bantul district, south of Yogyakarta Special Province (DIY) on the morningof May 27, 2006. We installed a temporary array of 6 seismographs to record aftershocks of the earthquake. The area of aftershocks, which may be interpreted as mainshock ruptured area has dimensions of about 25 km length and 20 km width, in the N48E direction. At depth the seismicity mainly concentrated between 5 to 15 km. The distribution of aftershock does not appear to come very close to the surface. There is no obvious surface evidence of causative fault in this area, though we find many crack and fissures that seem to have produced by the strong ground motion. We used the orientation and size of the fault determined from our aftershock results to carry out an inversion of teleseismic data for the slip distribution. We used broad- band seismograms of the IRIS network with epicentral distances between 30 and 90 degrees. We assume a single fault plane, strike 48 degree and dip 80 degree, which is inferred from the aftershock distribution. The total seismic moment is 0.369 x 10(19) Nm with maximum slip 0.4 meters. The asperity is located about 5 km away southwest of USGS estimated epicenter. Although the distances from the seismic source to heavily damaged areas Bantul and Klaten are 10 to 50 km, soft sedimentary soil likely to have generated very damaging motions within the area.

Integrated Land- and Underwater-Based Sensors for a Subduction Zone Earthquake Early Warning System

NASA Astrophysics Data System (ADS)

Pirenne, B.; Rosenberger, A.; Rogers, G. C.; Henton, J.; Lu, Y.; Moore, T.

2016-12-01

Ocean Networks Canada (ONC — oceannetworks.ca/ ) operates cabled ocean observatories off the coast of British Columbia (BC) to support research and operational oceanography. Recently, ONC has been funded by the Province of BC to deliver an earthquake early warning (EEW) system that integrates offshore and land-based sensors to deliver alerts of incoming ground shaking from the Cascadia Subduction Zone. ONC's cabled seismic network has the unique advantage of being located offshore on either side of the surface expression of the subduction zone. The proximity of ONC's sensors to the fault can result in faster, more effective warnings, which translates into more lives saved, injuries avoided and more ability for mitigative actions to take place.ONC delivers near real-time data from various instrument types simultaneously, providing distinct advantages to seismic monitoring and earthquake early warning. The EEW system consists of a network of sensors, located on the ocean floor and on land, that detect and analyze the initial p-wave of an earthquake as well as the crustal deformation on land during the earthquake sequence. Once the p-wave is detected and characterized, software systems correlate the data streams of the various sensors and deliver alerts to clients through a Common Alerting Protocol-compliant data package. This presentation will focus on the development of the earthquake early warning capacity at ONC. It will describe the seismic sensors and their distribution, the p-wave detection algorithms selected and the overall architecture of the system. It will further overview the plan to achieve operational readiness at project completion.

Results of the Regional Earthquake Likelihood Models (RELM) test of earthquake forecasts in California.

PubMed

Lee, Ya-Ting; Turcotte, Donald L; Holliday, James R; Sachs, Michael K; Rundle, John B; Chen, Chien-Chih; Tiampo, Kristy F

2011-10-04

The Regional Earthquake Likelihood Models (RELM) test of earthquake forecasts in California was the first competitive evaluation of forecasts of future earthquake occurrence. Participants submitted expected probabilities of occurrence of M ≥ 4.95 earthquakes in 0.1° × 0.1° cells for the period 1 January 1, 2006, to December 31, 2010. Probabilities were submitted for 7,682 cells in California and adjacent regions. During this period, 31 M ≥ 4.95 earthquakes occurred in the test region. These earthquakes occurred in 22 test cells. This seismic activity was dominated by earthquakes associated with the M = 7.2, April 4, 2010, El Mayor-Cucapah earthquake in northern Mexico. This earthquake occurred in the test region, and 16 of the other 30 earthquakes in the test region could be associated with it. Nine complete forecasts were submitted by six participants. In this paper, we present the forecasts in a way that allows the reader to evaluate which forecast is the most "successful" in terms of the locations of future earthquakes. We conclude that the RELM test was a success and suggest ways in which the results can be used to improve future forecasts.

Results of the Regional Earthquake Likelihood Models (RELM) test of earthquake forecasts in California

PubMed Central

Lee, Ya-Ting; Turcotte, Donald L.; Holliday, James R.; Sachs, Michael K.; Rundle, John B.; Chen, Chien-Chih; Tiampo, Kristy F.

2011-01-01

The Regional Earthquake Likelihood Models (RELM) test of earthquake forecasts in California was the first competitive evaluation of forecasts of future earthquake occurrence. Participants submitted expected probabilities of occurrence of M≥4.95 earthquakes in 0.1° × 0.1° cells for the period 1 January 1, 2006, to December 31, 2010. Probabilities were submitted for 7,682 cells in California and adjacent regions. During this period, 31 M≥4.95 earthquakes occurred in the test region. These earthquakes occurred in 22 test cells. This seismic activity was dominated by earthquakes associated with the M = 7.2, April 4, 2010, El Mayor–Cucapah earthquake in northern Mexico. This earthquake occurred in the test region, and 16 of the other 30 earthquakes in the test region could be associated with it. Nine complete forecasts were submitted by six participants. In this paper, we present the forecasts in a way that allows the reader to evaluate which forecast is the most “successful” in terms of the locations of future earthquakes. We conclude that the RELM test was a success and suggest ways in which the results can be used to improve future forecasts. PMID:21949355

Magnitudes and locations of the 1811-1812 New Madrid, Missouri, and the 1886 Charleston, South Carolina, earthquakes

USGS Publications Warehouse

Bakun, W.H.; Hopper, M.G.

2004-01-01

We estimate locations and moment magnitudes M and their uncertainties for the three largest events in the 1811-1812 sequence near New Madrid, Missouri, and for the 1 September 1886 event near Charleston, South Carolina. The intensity magnitude M1, our preferred estimate of M, is 7.6 for the 16 December 1811 event that occurred in the New Madrid seismic zone (NMSZ) on the Bootheel lineament or on the Blytheville seismic zone. M1, is 7.5 for the 23 January 1812 event for a location on the New Madrid north zone of the NMSZ and 7.8 for the 7 February 1812 event that occurred on the Reelfoot blind thrust of the NMSZ. Our preferred locations for these events are located on those NMSZ segments preferred by Johnston and Schweig (1996). Our estimates of M are 0.1-0.4 M units less than those of Johnston (1996b) and 0.3-0.5 M units greater than those of Hough et al. (2000). M1 is 6.9 for the 1 September 1886 event for a location at the Summerville-Middleton Place cluster of recent small earthquakes located about 30 km northwest of Charleston.

PPP Sliding Window Algorithm and Its Application in Deformation Monitoring.

PubMed

Song, Weiwei; Zhang, Rui; Yao, Yibin; Liu, Yanyan; Hu, Yuming

2016-05-31

Compared with the double-difference relative positioning method, the precise point positioning (PPP) algorithm can avoid the selection of a static reference station and directly measure the three-dimensional position changes at the observation site and exhibit superiority in a variety of deformation monitoring applications. However, because of the influence of various observing errors, the accuracy of PPP is generally at the cm-dm level, which cannot meet the requirements needed for high precision deformation monitoring. For most of the monitoring applications, the observation stations maintain stationary, which can be provided as a priori constraint information. In this paper, a new PPP algorithm based on a sliding window was proposed to improve the positioning accuracy. Firstly, data from IGS tracking station was processed using both traditional and new PPP algorithm; the results showed that the new algorithm can effectively improve positioning accuracy, especially for the elevation direction. Then, an earthquake simulation platform was used to simulate an earthquake event; the results illustrated that the new algorithm can effectively detect the vibrations change of a reference station during an earthquake. At last, the observed Wenchuan earthquake experimental results showed that the new algorithm was feasible to monitor the real earthquakes and provide early-warning alerts.

Earthquake Triggering in the September 2017 Mexican Earthquake Sequence

NASA Astrophysics Data System (ADS)

Fielding, E. J.; Gombert, B.; Duputel, Z.; Huang, M. H.; Liang, C.; Bekaert, D. P.; Moore, A. W.; Liu, Z.; Ampuero, J. P.

2017-12-01

Southern Mexico was struck by four earthquakes with Mw > 6 and numerous smaller earthquakes in September 2017, starting with the 8 September Mw 8.2 Tehuantepec earthquake beneath the Gulf of Tehuantepec offshore Chiapas and Oaxaca. We study whether this M8.2 earthquake triggered the three subsequent large M>6 quakes in southern Mexico to improve understanding of earthquake interactions and time-dependent risk. All four large earthquakes were extensional despite the the subduction of the Cocos plate. The traditional definition of aftershocks: likely an aftershock if it occurs within two rupture lengths of the main shock soon afterwards. Two Mw 6.1 earthquakes, one half an hour after the M8.2 beneath the Tehuantepec gulf and one on 23 September near Ixtepec in Oaxaca, both fit as traditional aftershocks, within 200 km of the main rupture. The 19 September Mw 7.1 Puebla earthquake was 600 km away from the M8.2 shock, outside the standard aftershock zone. Geodetic measurements from interferometric analysis of synthetic aperture radar (InSAR) and time-series analysis of GPS station data constrain finite fault total slip models for the M8.2, M7.1, and M6.1 Ixtepec earthquakes. The early M6.1 aftershock was too close in time and space to the M8.2 to measure with InSAR or GPS. We analyzed InSAR data from Copernicus Sentinel-1A and -1B satellites and JAXA ALOS-2 satellite. Our preliminary geodetic slip model for the M8.2 quake shows significant slip extended > 150 km NW from the hypocenter, longer than slip in the v1 finite-fault model (FFM) from teleseismic waveforms posted by G. Hayes at USGS NEIC. Our slip model for the M7.1 earthquake is similar to the v2 NEIC FFM. Interferograms for the M6.1 Ixtepec quake confirm the shallow depth in the upper-plate crust and show centroid is about 30 km SW of the NEIC epicenter, a significant NEIC location bias, but consistent with cluster relocations (E. Bergman, pers. comm.) and with Mexican SSN location. Coulomb static stress

CONEDEP: COnvolutional Neural network based Earthquake DEtection and Phase Picking

NASA Astrophysics Data System (ADS)

Zhou, Y.; Huang, Y.; Yue, H.; Zhou, S.; An, S.; Yun, N.

2017-12-01

We developed an automatic local earthquake detection and phase picking algorithm based on Fully Convolutional Neural network (FCN). The FCN algorithm detects and segments certain features (phases) in 3 component seismograms to realize efficient picking. We use STA/LTA algorithm and template matching algorithm to construct the training set from seismograms recorded 1 month before and after the Wenchuan earthquake. Precise P and S phases are identified and labeled to construct the training set. Noise data are produced by combining back-ground noise and artificial synthetic noise to form the equivalent scale of noise set as the signal set. Training is performed on GPUs to achieve efficient convergence. Our algorithm has significantly improved performance in terms of the detection rate and precision in comparison with STA/LTA and template matching algorithms.

Cluster-search based monitoring of local earthquakes in SeisComP3

NASA Astrophysics Data System (ADS)

Roessler, D.; Becker, J.; Ellguth, E.; Herrnkind, S.; Weber, B.; Henneberger, R.; Blanck, H.

2016-12-01

We present a new cluster-search based SeisComP3 module for locating local and regional earthquakes in real time. Real-time earthquake monitoring systems such as SeisComP3 provide the backbones for earthquake early warning (EEW), tsunami early warning (TEW) and the rapid assessment of natural and induced seismicity. For any earthquake monitoring system fast and accurate event locations are fundamental determining the reliability and the impact of further analysis. SeisComP3 in the OpenSource version includes a two-stage detector for picking P waves and a phase associator for locating earthquakes based on P-wave detections. scanloc is a more advanced earthquake location program developed by gempa GmbH with seamless integration into SeisComP3. scanloc performs advanced cluster search to discriminate earthquakes occurring closely in space and time and makes additional use of S-wave detections. It has proven to provide fast and accurate earthquake locations at local and regional distances where it outperforms the base SeisComP3 tools. We demonstrate the performance of scanloc for monitoring induced seismicity as well as local and regional earthquakes in different tectonic regimes including subduction, spreading and intra-plate regions. In particular we present examples and catalogs from real-time monitoring of earthquake in Northern Chile based on data from the IPOC network by GFZ German Research Centre for Geosciences for the recent years. Depending on epicentral distance and data transmission, earthquake locations are available within a few seconds after origin time when using scanloc. The association of automatic S-wave detections provides a better constraint on focal depth.

Analysis of the geophysical data using a posteriori algorithms

NASA Astrophysics Data System (ADS)

Voskoboynikova, Gyulnara; Khairetdinov, Marat

2016-04-01

The problems of monitoring, prediction and prevention of extraordinary natural and technogenic events are priority of modern problems. These events include earthquakes, volcanic eruptions, the lunar-solar tides, landslides, falling celestial bodies, explosions utilized stockpiles of ammunition, numerous quarry explosion in open coal mines, provoking technogenic earthquakes. Monitoring is based on a number of successive stages, which include remote registration of the events responses, measurement of the main parameters as arrival times of seismic waves or the original waveforms. At the final stage the inverse problems associated with determining the geographic location and time of the registration event are solving. Therefore, improving the accuracy of the parameters estimation of the original records in the high noise is an important problem. As is known, the main measurement errors arise due to the influence of external noise, the difference between the real and model structures of the medium, imprecision of the time definition in the events epicenter, the instrumental errors. Therefore, posteriori algorithms more accurate in comparison with known algorithms are proposed and investigated. They are based on a combination of discrete optimization method and fractal approach for joint detection and estimation of the arrival times in the quasi-periodic waveforms sequence in problems of geophysical monitoring with improved accuracy. Existing today, alternative approaches to solving these problems does not provide the given accuracy. The proposed algorithms are considered for the tasks of vibration sounding of the Earth in times of lunar and solar tides, and for the problem of monitoring of the borehole seismic source location in trade drilling.

Mexican Earthquakes and Tsunamis Catalog Reviewed

NASA Astrophysics Data System (ADS)

Ramirez-Herrera, M. T.; Castillo-Aja, R.

2015-12-01

Today the availability of information on the internet makes online catalogs very easy to access by both scholars and the public in general. The catalog in the "Significant Earthquake Database", managed by the National Center for Environmental Information (NCEI formerly NCDC), NOAA, allows access by deploying tabular and cartographic data related to earthquakes and tsunamis contained in the database. The NCEI catalog is the product of compiling previously existing catalogs, historical sources, newspapers, and scientific articles. Because NCEI catalog has a global coverage the information is not homogeneous. Existence of historical information depends on the presence of people in places where the disaster occurred, and that the permanence of the description is preserved in documents and oral tradition. In the case of instrumental data, their availability depends on the distribution and quality of seismic stations. Therefore, the availability of information for the first half of 20th century can be improved by careful analysis of the available information and by searching and resolving inconsistencies. This study shows the advances we made in upgrading and refining data for the earthquake and tsunami catalog of Mexico since 1500 CE until today, presented in the format of table and map. Data analysis allowed us to identify the following sources of error in the location of the epicenters in existing catalogs: • Incorrect coordinate entry • Place name erroneous or mistaken • Too general data that makes difficult to locate the epicenter, mainly for older earthquakes • Inconsistency of earthquakes and the tsunami occurrence: earthquake's epicenter located too far inland reported as tsunamigenic. The process of completing the catalogs directly depends on the availability of information; as new archives are opened for inspection, there are more opportunities to complete the history of large earthquakes and tsunamis in Mexico. Here, we also present new earthquake and

Studies of earthquakes and microearthquakes using near-field seismic and geodetic observations

NASA Astrophysics Data System (ADS)

O'Toole, Thomas Bartholomew

The Centroid-Moment Tensor (CMT) method allows an optimal point-source description of an earthquake to be recovered from a set of seismic observations, and, for over 30 years, has been routinely applied to determine the location and source mechanism of teleseismically recorded earthquakes. The CMT approach is, however, entirely general: any measurements of seismic displacement fields could, in theory, be used within the CMT inversion formulation, so long as the treatment of the earthquake as a point source is valid for that data. We modify the CMT algorithm to enable a variety of near-field seismic observables to be inverted for the source parameters of an earthquake. The first two data types that we implement are provided by Global Positioning System receivers operating at sampling frequencies of 1,Hz and above. When deployed in the seismic near field, these instruments may be used as long-period-strong-motion seismometers, recording displacement time series that include the static offset. We show that both the displacement waveforms, and static displacements alone, can be used to obtain CMT solutions for moderate-magnitude earthquakes, and that performing analyses using these data may be useful for earthquake early warning. We also investigate using waveform recordings - made by conventional seismometers deployed at the surface, or by geophone arrays placed in boreholes - to determine CMT solutions, and their uncertainties, for microearthquakes induced by hydraulic fracturing. A similar waveform inversion approach could be applied in many other settings where induced seismicity and microseismicity occurs..

Istanbul Earthquake Early Warning and Rapid Response System

NASA Astrophysics Data System (ADS)

Erdik, M. O.; Fahjan, Y.; Ozel, O.; Alcik, H.; Aydin, M.; Gul, M.

2003-12-01

As part of the preparations for the future earthquake in Istanbul a Rapid Response and Early Warning system in the metropolitan area is in operation. For the Early Warning system ten strong motion stations were installed as close as possible to the fault zone. Continuous on-line data from these stations via digital radio modem provide early warning for potentially disastrous earthquakes. Considering the complexity of fault rupture and the short fault distances involved, a simple and robust Early Warning algorithm, based on the exceedance of specified threshold time domain amplitude levels is implemented. The band-pass filtered accelerations and the cumulative absolute velocity (CAV) are compared with specified threshold levels. When any acceleration or CAV (on any channel) in a given station exceeds specific threshold values it is considered a vote. Whenever we have 2 station votes within selectable time interval, after the first vote, the first alarm is declared. In order to specify the appropriate threshold levels a data set of near field strong ground motions records form Turkey and the world has been analyzed. Correlations among these thresholds in terms of the epicenter distance the magnitude of the earthquake have been studied. The encrypted early warning signals will be communicated to the respective end users by UHF systems through a "service provider" company. The users of the early warning signal will be power and gas companies, nuclear research facilities, critical chemical factories, subway system and several high-rise buildings. Depending on the location of the earthquake (initiation of fault rupture) and the recipient facility the alarm time can be as high as about 8s. For the rapid response system one hundred 18 bit-resolution strong motion accelerometers were placed in quasi-free field locations (basement of small buildings) in the populated areas of the city, within an area of approximately 50x30km, to constitute a network that will enable early

Earthquake in Hindu Kush Region, Afghanistan

NASA Image and Video Library

2015-10-27

On Oct. 26, 2015, NASA Terra spacecraft acquired this image of northeastern Afghanistan where a magnitude 7.5 earthquake struck the Hindu Kush region. The earthquake's epicenter was at a depth of 130 miles (210 kilometers), on a probable shallowly dipping thrust fault. At this location, the Indian subcontinent moves northward and collides with Eurasia, subducting under the Asian continent, and raising the highest mountains in the world. This type of earthquake is common in the area: a similar earthquake occurred 13 years ago about 12 miles (20 kilometers) away. This perspective image from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra spacecraft, looking southwest, shows the hypocenter with a star. The image was acquired July 8, 2015, and is located near 36.4 degrees north, 70.7 degrees east. http://photojournal.jpl.nasa.gov/catalog/PIA20035

Seismotectonic framework of the 2010 February 27 Mw 8.8 Maule, Chile earthquake sequence

USGS Publications Warehouse

Hayes, Gavin P.; Bergman, Eric; Johnson, Kendra J.; Benz, Harley M.; Brown, Lucy; Meltzer, Anne S.

2013-01-01

After the 2010 Mw 8.8 Maule earthquake, an international collaboration involving teams and instruments from Chile, the US, the UK, France and Germany established the International Maule Aftershock Deployment temporary network over the source region of the event to facilitate detailed, open-access studies of the aftershock sequence. Using data from the first 9-months of this deployment, we have analyzed the detailed spatial distribution of over 2500 well-recorded aftershocks. All earthquakes have been relocated using a hypocentral decomposition algorithm to study the details of and uncertainties in both their relative and absolute locations. We have computed regional moment tensor solutions for the largest of these events to produce a catalogue of 465 mechanisms, and have used all of these data to study the spatial distribution of the aftershock sequence with respect to the Chilean megathrust. We refine models of co-seismic slip distribution of the Maule earthquake, and show how small changes in fault geometries assumed in teleseismic finite fault modelling significantly improve fits to regional GPS data, implying that the accuracy of rapid teleseismic fault models can be substantially improved by consideration of existing fault geometry model databases. We interpret all of these data in an integrated seismotectonic framework for the Maule earthquake rupture and its aftershock sequence, and discuss the relationships between co-seismic rupture and aftershock distributions. While the majority of aftershocks are interplate thrust events located away from regions of maximum co-seismic slip, interesting clusters of aftershocks are identified in the lower plate at both ends of the main shock rupture, implying internal deformation of the slab in response to large slip on the plate boundary interface. We also perform Coulomb stress transfer calculations to compare aftershock locations and mechanisms to static stress changes following the Maule rupture. Without the

A Decision Processing Algorithm for CDC Location Under Minimum Cost SCM Network

NASA Astrophysics Data System (ADS)

Park, N. K.; Kim, J. Y.; Choi, W. Y.; Tian, Z. M.; Kim, D. J.

Location of CDC in the matter of network on Supply Chain is becoming on the high concern these days. Present status of methods on CDC has been mainly based on the calculation manually by the spread sheet to achieve the goal of minimum logistics cost. This study is focused on the development of new processing algorithm to overcome the limit of present methods, and examination of the propriety of this algorithm by case study. The algorithm suggested by this study is based on the principle of optimization on the directive GRAPH of SCM model and suggest the algorithm utilizing the traditionally introduced MST, shortest paths finding methods, etc. By the aftermath of this study, it helps to assess suitability of the present on-going SCM network and could be the criterion on the decision-making process for the optimal SCM network building-up for the demand prospect in the future.

Earthquake locations determined by the Southern Alaska seismograph network for October 1971 through May 1989

USGS Publications Warehouse

Fogleman, Kent A.; Lahr, John C.; Stephens, Christopher D.; Page, Robert A.

1993-01-01

This report describes the instrumentation and evolution of the U.S. Geological Survey’s regional seismograph network in southern Alaska, provides phase and hypocenter data for seismic events from October 1971 through May 1989, reviews the location methods used, and discusses the completeness of the catalog and the accuracy of the computed hypocenters. Included are arrival time data for explosions detonated under the Trans-Alaska Crustal Transect (TACT) in 1984 and 1985.The U.S. Geological Survey (USGS) operated a regional network of seismographs in southern Alaska from 1971 to the mid 1990s. The principal purpose of this network was to record seismic data to be used to precisely locate earthquakes in the seismic zones of southern Alaska, delineate seismically active faults, assess seismic risks, document potential premonitory earthquake phenomena, investigate current tectonic deformation, and study the structure and physical properties of the crust and upper mantle. A task fundamental to all of these goals was the routine cataloging of parameters for earthquakes located within and adjacent to the seismograph network.The initial network of 10 stations, 7 around Cook Inlet and 3 near Valdez, was installed in 1971. In subsequent summers additions or modifications to the network were made. By the fall of 1973, 26 stations extended from western Cook Inlet to eastern Prince William Sound, and 4 stations were located to the east between Cordova and Yakutat. A year later 20 additional stations were installed. Thirteen of these were placed along the eastern Gulf of Alaska with support from the National Oceanic and Atmospheric Administration (NOAA) under the Outer Continental Shelf Environmental Assessment Program to investigate the seismicity of the outer continental shelf, a region of interest for oil exploration. Since then the region covered by the network remained relatively fixed while efforts were made to make the stations more reliable through improved electronic

Accounts of damage from historical earthquakes in the northeastern Caribbean to aid in the determination of their location and intensity magnitudes

USGS Publications Warehouse

Flores, Claudia H.; ten Brink, Uri S.; Bakun, William H.

2012-01-01

Documentation of an event in the past depended on the population and political trends of the island, and the availability of historical documents is limited by the physical resource digitization schedule and by the copyright laws of each archive. Examples of documents accessed are governors' letters, newspapers, and other circulars published within the Caribbean, North America, and Western Europe. Key words were used to search for publications that contain eyewitness accounts of various large earthquakes. Finally, this catalog provides descriptions of damage to buildings used in previous studies for the estimation of moment intensity (MI) and location of significantly damaging or felt earthquakes in Hispaniola and in the northeastern Caribbean, all of which have been described in other studies.

Global Instrumental Seismic Catalog: earthquake relocations for 1900-present

NASA Astrophysics Data System (ADS)

Villasenor, A.; Engdahl, E.; Storchak, D. A.; Bondar, I.

2010-12-01

We present the current status of our efforts to produce a set of homogeneous earthquake locations and improved focal depths towards the compilation of a Global Catalog of instrumentally recorded earthquakes that will be complete down to the lowest magnitude threshold possible on a global scale and for the time period considered. This project is currently being carried out under the auspices of GEM (Global Earthquake Model). The resulting earthquake catalog will be a fundamental dataset not only for earthquake risk modeling and assessment on a global scale, but also for a large number of studies such as global and regional seismotectonics; the rupture zones and return time of large, damaging earthquakes; the spatial-temporal pattern of moment release along seismic zones and faults etc. Our current goal is to re-locate all earthquakes with available station arrival data using the following magnitude thresholds: M5.5 for 1964-present, M6.25 for 1918-1963, M7.5 (complemented with significant events in continental regions) for 1900-1917. Phase arrival time data for earthquakes after 1963 are available in digital form from the International Seismological Centre (ISC). For earthquakes in the time period 1918-1963, phase data is obtained by scanning the printed International Seismological Summary (ISS) bulletins and applying optical character recognition routines. For earlier earthquakes we will collect phase data from individual station bulletins. We will illustrate some of the most significant results of this relocation effort, including aftershock distributions for large earthquakes, systematic differences in epicenter and depth with respect to previous location, examples of grossly mislocated events, etc.

Comparison of four moderate-size earthquakes in southern California using seismology and InSAR

USGS Publications Warehouse

Mellors, R.J.; Magistrale, H.; Earle, P.; Cogbill, A.H.

2004-01-01

Source parameters determined from interferometric synthetic aperture radar (InSAR) measurements and from seismic data are compared from four moderate-size (less than M 6) earthquakes in southern California. The goal is to verify approximate detection capabilities of InSAR, assess differences in the results, and test how the two results can be reconciled. First, we calculated the expected surface deformation from all earthquakes greater than magnitude 4 in areas with available InSAR data (347 events). A search for deformation from the events in the interferograms yielded four possible events with magnitudes less than 6. The search for deformation was based on a visual inspection as well as cross-correlation in two dimensions between the measured signal and the expected signal. A grid-search algorithm was then used to estimate focal mechanism and depth from the InSAR data. The results were compared with locations and focal mechanisms from published catalogs. An independent relocation using seismic data was also performed. The seismic locations fell within the area of the expected rupture zone for the three events that show clear surface deformation. Therefore, the technique shows the capability to resolve locations with high accuracy and is applicable worldwide. The depths determined by InSAR agree with well-constrained seismic locations determined in a 3D velocity model. Depth control for well-imaged shallow events using InSAR data is good, and better than the seismic constraints in some cases. A major difficulty for InSAR analysis is the poor temporal coverage of InSAR data, which may make it impossible to distinguish deformation due to different earthquakes at the same location.

Multisclae heterogeneity of the 2011 Tohoku-oki earthquake by inversion

NASA Astrophysics Data System (ADS)

Aochi, H.; Ulrich, T.; Cornier, G.

2012-12-01

Earthquake fault heterogeneity is often studied on a set of subfaults in kinematic inversion, while it is sometimes described with spatially localized geometry. Aochi and Ide (EPS, 2011) and Ide and Aochi (submitted to Pageoph and AGU, 2012) apply a concept of multi-scale heterogeneity to simulate the dynamic rupture process of the 2011 Tohoku-oki earthquake, introducing circular patches of different dimension in fault fracture energy distribution. Previously the patches are given by the past moderate earthquakes in this region, and this seems to be consistent with the evolution process of this mega earthquake, although a few patches, in particular, the largest patch, had not been known previously. In this study, we try to identify patches by inversion. As demonstrated in several earthquakes including the 2010 Maule (M8.8) earthquake, it is possible to indentify two asperities of ellipse kinematically or dynamically (e.g. Ruiz and Madariaga, 2011, and so on). In the successful examples, different asperities are rather visible, separated in space. However the Tohoku-oki earthquake has hierarchical structure of heterogeneity. We apply the Genetic Algorithm to inverse the model parameters from the ground motions (K-net and Kik-net from NIED) and the high sampling GPS (GSI). Starting from low frequency ranges (> 50 seconds), we obtain an ellipse corresponding to M9 event located around the hypocenter, coherent with the previous result by Madariaga et al. (pers. comm.). However it is difficult to identify the second smaller with few constraints. This is mainly because the largest covers the entire rupture area and any smaller patch improves the fitting only for the closer stations. Again, this needs to introduce the multi-scale concept in inversion procedure. Instead of finding the largest one at first, we have to start to extract rather smaller moderate patches from the beginning of the record, following the rupture process.

2016 update on induced earthquakes in the United States

USGS Publications Warehouse

Petersen, Mark D.

2016-01-01

During the past decade people living in numerous locations across the central U.S. experienced many more small to moderate sized earthquakes than ever before. This earthquake activity began increasing about 2009 and peaked during 2015 and into early 2016. For example, prior to 2009 Oklahoma typically experienced 1 or 2 small earthquakes per year with magnitude greater than 3.0 but by 2015 this number rose to over 900 earthquakes per year of that size and over 30 earthquakes greater than 4.0. These earthquakes can cause damage. In 2011 a magnitude 5.6 earthquake struck near the town of Prague, Oklahoma on a preexisting fault and caused severe damage to several houses and school buildings. During the past 6 years more than 1500 reports of damaging shaking levels were reported in areas of induced seismicity. This rapid increase and the potential for damaging ground shaking from induced earthquakes caused alarm to about 8 million people living nearby and officials responsible for public safety. They wanted to understand why earthquakes were increasing and the potential threats to society and buildings located nearby.

A consistent and uniform research earthquake catalog for the AlpArray region: preliminary results.

NASA Astrophysics Data System (ADS)

Molinari, I.; Bagagli, M.; Kissling, E. H.; Diehl, T.; Clinton, J. F.; Giardini, D.; Wiemer, S.

2017-12-01

The AlpArray initiative (www.alparray.ethz.ch) is a large-scale European collaboration ( 50 institutes involved) to study the entire Alpine orogen at high resolution with a variety of geoscientific methods. AlpArray provides unprecedentedly uniform station coverage for the region with more than 650 broadband seismic stations, 300 of which are temporary. The AlpArray Seismic Network (AASN) is a joint effort of 25 institutes from 10 nations, operates since January 2016 and is expected to continue until the end of 2018. In this study, we establish a uniform earthquake catalogue for the Greater Alpine region during the operation period of the AASN with a aimed completeness of M2.5. The catalog has two main goals: 1) calculation of consistent and precise hypocenter locations 2) provide preliminary but uniform magnitude calculations across the region. The procedure is based on automatic high-quality P- and S-wave pickers, providing consistent phase arrival times in combination with a picking quality assessment. First, we detect all events in the region in 2016/2017 using an STA/LTA based detector. Among the detected events, we select 50 geographically homogeneously distributed events with magnitudes ≥2.5 representative for the entire catalog. We manually pick the selected events to establish a consistent P- and S-phase reference data set, including arrival-time time uncertainties. The reference data, are used to adjust the automatic pickers and to assess their performance. In a first iteration, a simple P-picker algorithm is applied to the entire dataset, providing initial picks for the advanced MannekenPix (MPX) algorithm. In a second iteration, the MPX picker provides consistent and reliable automatic first arrival P picks together with a pick-quality estimate. The derived automatic P picks are then used as initial values for a multi-component S-phase picking algorithm. Subsequently, automatic picks of all well-locatable earthquakes will be considered to calculate

Seismicity and seismic hazard in Sabah, East Malaysia from earthquake and geodetic data

NASA Astrophysics Data System (ADS)

Gilligan, A.; Rawlinson, N.; Tongkul, F.; Stephenson, R.

2017-12-01

While the levels of seismicity are low in most of Malaysia, the state of Sabah in northern Borneo has moderate levels of seismicity. Notable earthquakes in the region include the 1976 M6.2 Lahad Datu earthquake and the 2015 M6 Ranau earthquake. The recent Ranau earthquake resulted in the deaths of 18 people on Mt Kinabalu, an estimated 100 million RM ( US$23 million) damage to buildings, roads, and infrastructure from shaking, and flooding, reduced water quality, and damage to farms from landslides. Over the last 40 years the population of Sabah has increased to over four times what it was in 1976, yet seismic hazard in Sabah remains poorly understood. Using seismic and geodetic data we hope to better quantify the hazards posed by earthquakes in Sabah, and thus help to minimize risk. In order to do this we need to know about the locations of earthquakes, types of earthquakes that occur, and faults that are generating them. We use data from 15 MetMalaysia seismic stations currently operating in Sabah to develop a region-specific velocity model from receiver functions and a pre-existing surface wave model. We use this new velocity model to (re)locate earthquakes that occurred in Sabah from 2005-2016, including a large number of aftershocks from the 2015 Ranau earthquake. We use a probabilistic nonlinear earthquake location program to locate the earthquakes and then refine their relative locations using a double difference method. The recorded waveforms are further used to obtain moment tensor solutions for these earthquakes. Earthquake locations and moment tensor solutions are then compared with the locations of faults throughout Sabah. Faults are identified from high-resolution IFSAR images and subsequent fieldwork, with a particular focus on the Lahad Datau and Ranau areas. Used together, these seismic and geodetic data can help us to develop a new seismic hazard model for Sabah, as well as aiding in the delivery of outreach activities regarding seismic hazard

Surface-Wave Relocation of Remote Continental Earthquakes

NASA Astrophysics Data System (ADS)

Kintner, J. A.; Ammon, C. J.; Cleveland, M.

2017-12-01

Accurate hypocenter locations are essential for seismic event analysis. Single-event location estimation methods provide relatively imprecise results in remote regions with few nearby seismic stations. Previous work has demonstrated that improved relative epicentroid precision in oceanic environments is obtainable using surface-wave cross correlation measurements. We use intermediate-period regional and teleseismic Rayleigh and Love waves to estimate relative epicentroid locations of moderately-sized seismic events in regions around Iran. Variations in faulting geometry, depth, and intermediate-period dispersion make surface-wave based event relocation challenging across this broad continental region. We compare and integrate surface-wave based relative locations with InSAR centroid location estimates. However, mapping an earthquake sequence mainshock to an InSAR fault deformation model centroid is not always a simple process, since the InSAR observations are sensitive to post-seismic deformation. We explore these ideas using earthquake sequences in western Iran. We also apply surface-wave relocation to smaller magnitude earthquakes (3.5 < M < 5.0). Inclusion of smaller-magnitude seismic events in a relocation effort requires a shift in bandwidth to shorter periods, which increases the sensitivity of relocations to surface-wave dispersion. Frequency-domain inter-event phase observations are used to understand the time-domain cross-correlation information, and to choose the appropriate band for applications using shorter periods. Over short inter-event distances, the changing group velocity does not strongly degrade the relative locations. For small-magnitude seismic events in continental regions, surface-wave relocation does not appear simple enough to allow broad routine application, but using this method to analyze individual earthquake sequences can provide valuable insight into earthquake and faulting processes.

Earthquakes in the Central United States, 1699-2010

USGS Publications Warehouse

Dart, Richard L.; Volpi, Christina M.

2010-01-01

This publication is an update of an earlier report, U.S. Geological Survey (USGS) Geologic Investigation I-2812 by Wheeler and others (2003), titled ?Earthquakes in the Central United States-1699-2002.? Like the original poster, the center of the updated poster is a map showing the pattern of earthquake locations in the most seismically active part of the central United States. Arrayed around the map are short explanatory texts and graphics, which describe the distribution of historical earthquakes and the effects of the most notable of them. The updated poster contains additional, post 2002, earthquake data. These are 38 earthquakes covering the time interval from January 2003 to June 2010, including the Mount Carmel, Illinois, earthquake of 2008. The USGS Preliminary Determination of Epicenters (PDE) was the source of these additional data. Like the I-2812 poster, this poster was prepared for a nontechnical audience and designed to inform the general public as to the widespread occurrence of felt and damaging earthquakes in the Central United States. Accordingly, the poster should not be used to assess earthquake hazard in small areas or at individual locations.

Applying time-reverse-imaging techniques to locate individual low-frequency earthquakes on the San Andreas fault near Cholame, California

NASA Astrophysics Data System (ADS)

Horstmann, T.; Harrington, R. M.; Cochran, E.; Shelly, D. R.

2013-12-01

Observations of non-volcanic tremor have become ubiquitous in recent years. In spite of the abundance of observations, locating tremor remains a difficult task because of the lack of distinctive phase arrivals. Here we use time-reverse-imaging techniques that do not require identifying phase arrivals to locate individual low-frequency-earthquakes (LFEs) within tremor episodes on the San Andreas fault near Cholame, California. Time windows of 1.5-second duration containing LFEs are selected from continuously recorded waveforms of the local seismic network filtered between 1-5 Hz. We propagate the time-reversed seismic signal back through the subsurface using a staggered-grid finite-difference code. Assuming all rebroadcasted waveforms result from similar wave fields at the source origin, we search for wave field coherence in time and space to obtain the source location and origin time where the constructive interference is a maximum. We use an interpolated velocity model with a grid spacing of 100 m and a 5 ms time step to calculate the relative curl field energy amplitudes for each rebroadcasted seismogram every 50 ms for each grid point in the model. Finally, we perform a grid search for coherency in the curl field using a sliding time window, and taking the absolute value of the correlation coefficient to account for differences in radiation pattern. The highest median cross-correlation coefficient value over at a given grid point indicates the source location for the rebroadcasted event. Horizontal location errors based on the spatial extent of the highest 10% cross-correlation coefficient are on the order of 4 km, and vertical errors on the order of 3 km. Furthermore, a test of the method using earthquake data shows that the method produces an identical hypocentral location (within errors) as that obtained by standard ray-tracing methods. We also compare the event locations to a LFE catalog that locates the LFEs from stacked waveforms of repeated LFEs

Earthquake triggering at alaskan volcanoes following the 3 November 2002 denali fault earthquake

USGS Publications Warehouse

Moran, S.C.; Power, J.A.; Stihler, S.D.; Sanchez, J.J.; Caplan-Auerbach, J.

2004-01-01

The 3 November 2002 Mw 7.9 Denali fault earthquake provided an excellent opportunity to investigate triggered earthquakes at Alaskan volcanoes. The Alaska Volcano Observatory operates short-period seismic networks on 24 historically active volcanoes in Alaska, 247-2159 km distant from the mainshock epicenter. We searched for evidence of triggered seismicity by examining the unfiltered waveforms for all stations in each volcano network for ???1 hr after the Mw 7.9 arrival time at each network and for significant increases in located earthquakes in the hours after the mainshock. We found compelling evidence for triggering only at the Katmai volcanic cluster (KVC, 720-755 km southwest of the epicenter), where small earthquakes with distinct P and 5 arrivals appeared within the mainshock coda at one station and a small increase in located earthquakes occurred for several hours after the mainshock. Peak dynamic stresses of ???0.1 MPa at Augustine Volcano (560 km southwest of the epicenter) are significantly lower than those recorded in Yellowstone and Utah (>3000 km southeast of the epicenter), suggesting that strong directivity effects were at least partly responsible for the lack of triggering at Alaskan volcanoes. We describe other incidents of earthquake-induced triggering in the KVC, and outline a qualitative magnitude/distance-dependent triggering threshold. We argue that triggering results from the perturbation of magmatic-hydrothermal systems in the KVC and suggest that the comparative lack of triggering at other Alaskan volcanoes could be a result of differences in the nature of magmatic-hydrothermal systems.

The 1868 Hayward Earthquake Alliance: A Case Study - Using an Earthquake Anniversary to Promote Earthquake Preparedness

NASA Astrophysics Data System (ADS)

Brocher, T. M.; Garcia, S.; Aagaard, B. T.; Boatwright, J. J.; Dawson, T.; Hellweg, M.; Knudsen, K. L.; Perkins, J.; Schwartz, D. P.; Stoffer, P. W.; Zoback, M.

2008-12-01

simulations of a Hayward Fault earthquake, (5) a new USGS Fact Sheet about the earthquake and the Hayward Fault, (6) a virtual tour of the 1868 earthquake, and (7) a new online field trip guide to the Hayward Fault using locations accessible by car and public transit. Finally, the California Geological Survey and many other Alliance members sponsored the Third Conference on Earthquake Hazards in the East Bay at CSU East Bay in Hayward for the three days following the 140th anniversary. The 1868 Alliance hopes to commemorate the anniversary of the 1868 Hayward Earthquake every year to maintain and increase public awareness of this fault, the hazards it and other East Bay Faults pose, and the ongoing need for earthquake preparedness and mitigation.

Association of earthquakes and faults in the San Francisco Bay area using Bayesian inference

USGS Publications Warehouse

Wesson, R.L.; Bakun, W.H.; Perkins, D.M.

2003-01-01

Bayesian inference provides a method to use seismic intensity data or instrumental locations, together with geologic and seismologic data, to make quantitative estimates of the probabilities that specific past earthquakes are associated with specific faults. Probability density functions are constructed for the location of each earthquake, and these are combined with prior probabilities through Bayes' theorem to estimate the probability that an earthquake is associated with a specific fault. Results using this method are presented here for large, preinstrumental, historical earthquakes and for recent earthquakes with instrumental locations in the San Francisco Bay region. The probabilities for individual earthquakes can be summed to construct a probabilistic frequency-magnitude relationship for a fault segment. Other applications of the technique include the estimation of the probability of background earthquakes, that is, earthquakes not associated with known or considered faults, and the estimation of the fraction of the total seismic moment associated with earthquakes less than the characteristic magnitude. Results for the San Francisco Bay region suggest that potentially damaging earthquakes with magnitudes less than the characteristic magnitudes should be expected. Comparisons of earthquake locations and the surface traces of active faults as determined from geologic data show significant disparities, indicating that a complete understanding of the relationship between earthquakes and faults remains elusive.

Risk and return: evaluating Reverse Tracing of Precursors earthquake predictions

NASA Astrophysics Data System (ADS)

Zechar, J. Douglas; Zhuang, Jiancang

2010-09-01

In 2003, the Reverse Tracing of Precursors (RTP) algorithm attracted the attention of seismologists and international news agencies when researchers claimed two successful predictions of large earthquakes. These researchers had begun applying RTP to seismicity in Japan, California, the eastern Mediterranean and Italy; they have since applied it to seismicity in the northern Pacific, Oregon and Nevada. RTP is a pattern recognition algorithm that uses earthquake catalogue data to declare alarms, and these alarms indicate that RTP expects a moderate to large earthquake in the following months. The spatial extent of alarms is highly variable and each alarm typically lasts 9 months, although the algorithm may extend alarms in time and space. We examined the record of alarms and outcomes since the prospective application of RTP began, and in this paper we report on the performance of RTP to date. To analyse these predictions, we used a recently developed approach based on a gambling score, and we used a simple reference model to estimate the prior probability of target earthquakes for each alarm. Formally, we believe that RTP investigators did not rigorously specify the first two `successful' predictions in advance of the relevant earthquakes; because this issue is contentious, we consider analyses with and without these alarms. When we included contentious alarms, RTP predictions demonstrate statistically significant skill. Under a stricter interpretation, the predictions are marginally unsuccessful.

Geophysical Anomalies and Earthquake Prediction

NASA Astrophysics Data System (ADS)

Jackson, D. D.

2008-12-01

Finding anomalies is easy. Predicting earthquakes convincingly from such anomalies is far from easy. Why? Why have so many beautiful geophysical abnormalities not led to successful prediction strategies? What is earthquake prediction? By my definition it is convincing information that an earthquake of specified size is temporarily much more likely than usual in a specific region for a specified time interval. We know a lot about normal earthquake behavior, including locations where earthquake rates are higher than elsewhere, with estimable rates and size distributions. We know that earthquakes have power law size distributions over large areas, that they cluster in time and space, and that aftershocks follow with power-law dependence on time. These relationships justify prudent protective measures and scientific investigation. Earthquake prediction would justify exceptional temporary measures well beyond those normal prudent actions. Convincing earthquake prediction would result from methods that have demonstrated many successes with few false alarms. Predicting earthquakes convincingly is difficult for several profound reasons. First, earthquakes start in tiny volumes at inaccessible depth. The power law size dependence means that tiny unobservable ones are frequent almost everywhere and occasionally grow to larger size. Thus prediction of important earthquakes is not about nucleation, but about identifying the conditions for growth. Second, earthquakes are complex. They derive their energy from stress, which is perniciously hard to estimate or model because it is nearly singular at the margins of cracks and faults. Physical properties vary from place to place, so the preparatory processes certainly vary as well. Thus establishing the needed track record for validation is very difficult, especially for large events with immense interval times in any one location. Third, the anomalies are generally complex as well. Electromagnetic anomalies in particular require

Historical and recent large megathrust earthquakes in Chile

NASA Astrophysics Data System (ADS)

Ruiz, S.; Madariaga, R.

2018-05-01

Recent earthquakes in Chile, 2014, Mw 8.2 Iquique, 2015, Mw 8.3 Illapel and 2016, Mw 7.6 Chiloé have put in evidence some problems with the straightforward application of ideas about seismic gaps, earthquake periodicity and the general forecast of large megathrust earthquakes. In northern Chile, before the 2014 Iquique earthquake 4 large earthquakes were reported in written chronicles, 1877, 1786, 1615 and 1543; in North-Central Chile, before the 2015 Illapel event, 3 large earthquakes 1943, 1880, 1730 were reported; and the 2016 Chiloé earthquake occurred in the southern zone of the 1960 Valdivia megathrust rupture, where other large earthquakes occurred in 1575, 1737 and 1837. The periodicity of these events has been proposed as a good long-term forecasting. However, the seismological aspects of historical Chilean earthquakes were inferred mainly from old chronicles written before subduction in Chile was discovered. Here we use the original description of earthquakes to re-analyze the historical archives. Our interpretation shows that a-priori ideas, like seismic gaps and characteristic earthquakes, influenced the estimation of magnitude, location and rupture area of the older Chilean events. On the other hand, the advance in the characterization of the rheological aspects that controlled the contact between Nazca and South-American plate and the study of tsunami effects provide better estimations of the location of historical earthquakes along the seismogenic plate interface. Our re-interpretation of historical earthquakes shows a large diversity of earthquakes types; there is a major difference between giant earthquakes that break the entire plate interface and those of Mw 8.0 that only break a portion of it.

The January 2014 Northern Cuba Earthquake Sequence - Unusual Location and Unexpected Source Mechanism Variability

NASA Astrophysics Data System (ADS)

Braunmiller, J.; Thompson, G.; McNutt, S. R.

2017-12-01

On 9 January 2014, a magnitude Mw=5.1 earthquake occurred along the Bahamas-Cuba suture at the northern coast of Cuba revealing a surprising seismic hazard source for both Cuba and southern Florida where it was widely felt. Due to its location, the event and its aftershocks (M>3.5) were recorded only at far distances (300+ km) resulting in high-detection thresholds, low location accuracy, and limited source parameter resolution. We use three-component regional seismic data to study the sequence. High-pass filtered seismograms at the closest site in southern Florida are similar in character suggesting a relatively tight event cluster and revealing additional, smaller aftershocks not included in the ANSS or ISC catalogs. Aligning on the P arrival and low-pass filtering (T>10 s) uncovers a surprise polarity flip of the large amplitude surface waves on vertical seismograms for some aftershocks relative to the main shock. We performed regional moment tensor inversions of the main shock and its largest aftershocks using complete three-component seismograms from stations distributed throughout the region to confirm the mechanism changes. Consistent with the GCMT solution, we find an E-W trending normal faulting mechanism for the main event and for one immediate aftershock. Two aftershocks indicate E-W trending reverse faulting with essentially flipped P- and T-axes relative to the normal faulting events (and the same B-axes). Within uncertainties, depths of the two event families are indistinguishable and indicate shallow faulting (<10 km). One intriguing possible interpretation is that both families ruptured the same fault with reverse mechanisms compensating for overshooting. However, activity could also be spatially separated either vertically (with reverse mechanisms possibly below extension) or laterally. The shallow source depth and the 200-km long uplifted chain of islands indicate that larger, shallow and thus potentially tsunamigenic earthquakes could occur just

An Isometric Mapping Based Co-Location Decision Tree Algorithm

NASA Astrophysics Data System (ADS)

Zhou, G.; Wei, J.; Zhou, X.; Zhang, R.; Huang, W.; Sha, H.; Chen, J.

2018-05-01

Decision tree (DT) induction has been widely used in different pattern classification. However, most traditional DTs have the disadvantage that they consider only non-spatial attributes (ie, spectral information) as a result of classifying pixels, which can result in objects being misclassified. Therefore, some researchers have proposed a co-location decision tree (Cl-DT) method, which combines co-location and decision tree to solve the above the above-mentioned traditional decision tree problems. Cl-DT overcomes the shortcomings of the existing DT algorithms, which create a node for each value of a given attribute, which has a higher accuracy than the existing decision tree approach. However, for non-linearly distributed data instances, the euclidean distance between instances does not reflect the true positional relationship between them. In order to overcome these shortcomings, this paper proposes an isometric mapping method based on Cl-DT (called, (Isomap-based Cl-DT), which is a method that combines heterogeneous and Cl-DT together. Because isometric mapping methods use geodetic distances instead of Euclidean distances between non-linearly distributed instances, the true distance between instances can be reflected. The experimental results and several comparative analyzes show that: (1) The extraction method of exposed carbonate rocks is of high accuracy. (2) The proposed method has many advantages, because the total number of nodes, the number of leaf nodes and the number of nodes are greatly reduced compared to Cl-DT. Therefore, the Isomap -based Cl-DT algorithm can construct a more accurate and faster decision tree.

The Pocatello Valley, Idaho, earthquake

USGS Publications Warehouse

Rogers, A. M.; Langer, C.J.; Bucknam, R.C.

1975-01-01

A Richter magnitude 6.3 earthquake occurred at 8:31 p.m mountain daylight time on March 27, 1975, near the Utah-Idaho border in Pocatello Valley. The epicenter of the main shock was located at 42.094° N, 112.478° W, and had a focal depth of 5.5 km. This earthquake was the largest in the continental United States since the destructive San Fernando earthquake of February 1971. The main shock was preceded by a magnitude 4.5 foreshock on March 26. 

High-resolution earthquake relocation in the Fort Worth and Permian Basins using regional seismic stations

NASA Astrophysics Data System (ADS)

Ogwari, P.; DeShon, H. R.; Hornbach, M.

2017-12-01

Post-2008 earthquake rate increases in the Central United States have been associated with large-scale subsurface disposal of waste-fluids from oil and gas operations. The beginning of various earthquake sequences in Fort Worth and Permian basins have occurred in the absence of seismic stations at local distances to record and accurately locate hypocenters. Most typically, the initial earthquakes have been located using regional seismic network stations (>100km epicentral distance) and using global 1D velocity models, which usually results in large location uncertainty, especially in depth, does not resolve magnitude <2.5 events, and does not constrain the geometry of the activated fault(s). Here, we present a method to better resolve earthquake occurrence and location using matched filters and regional relative location when local data becomes available. We use the local distance data for high-resolution earthquake location, identifying earthquake templates and accurate source-station raypath velocities for the Pg and Lg phases at regional stations. A matched-filter analysis is then applied to seismograms recorded at US network stations and at adopted TA stations that record the earthquakes before and during the local network deployment period. Positive detections are declared based on manual review of associated with P and S arrivals on local stations. We apply hierarchical clustering to distinguish earthquakes that are both spatially clustered and spatially separated. Finally, we conduct relative earthquake and earthquake cluster location using regional station differential times. Initial analysis applied to the 2008-2009 DFW airport sequence in north Texas results in time continuous imaging of epicenters extending into 2014. Seventeen earthquakes in the USGS earthquake catalog scattered across a 10km2 area near DFW airport are relocated onto a single fault using these approaches. These techniques will also be applied toward imaging recent earthquakes in the

A smoothed stochastic earthquake rate model considering seismicity and fault moment release for Europe

NASA Astrophysics Data System (ADS)

Hiemer, S.; Woessner, J.; Basili, R.; Danciu, L.; Giardini, D.; Wiemer, S.

2014-08-01

We present a time-independent gridded earthquake rate forecast for the European region including Turkey. The spatial component of our model is based on kernel density estimation techniques, which we applied to both past earthquake locations and fault moment release on mapped crustal faults and subduction zone interfaces with assigned slip rates. Our forecast relies on the assumption that the locations of past seismicity is a good guide to future seismicity, and that future large-magnitude events occur more likely in the vicinity of known faults. We show that the optimal weighted sum of the corresponding two spatial densities depends on the magnitude range considered. The kernel bandwidths and density weighting function are optimized using retrospective likelihood-based forecast experiments. We computed earthquake activity rates (a- and b-value) of the truncated Gutenberg-Richter distribution separately for crustal and subduction seismicity based on a maximum likelihood approach that considers the spatial and temporal completeness history of the catalogue. The final annual rate of our forecast is purely driven by the maximum likelihood fit of activity rates to the catalogue data, whereas its spatial component incorporates contributions from both earthquake and fault moment-rate densities. Our model constitutes one branch of the earthquake source model logic tree of the 2013 European seismic hazard model released by the EU-FP7 project `Seismic HAzard haRmonization in Europe' (SHARE) and contributes to the assessment of epistemic uncertainties in earthquake activity rates. We performed retrospective and pseudo-prospective likelihood consistency tests to underline the reliability of our model and SHARE's area source model (ASM) using the testing algorithms applied in the collaboratory for the study of earthquake predictability (CSEP). We comparatively tested our model's forecasting skill against the ASM and find a statistically significant better performance for

Catalog of earthquake hypocenters at Alaskan volcanoes: January 1 through December 31, 2011

USGS Publications Warehouse

Dixon, James P.; Stihler, Scott D.; Power, John A.; Searcy, Cheryl K.

2012-01-01

Between January 1 and December 31, 2011, the Alaska Volcano Observatory (AVO) located 4,364 earthquakes, of which 3,651 occurred within 20 kilometers of the 33 volcanoes with seismograph subnetworks. There was no significant seismic activity above background levels in 2011 at these instrumented volcanic centers. This catalog includes locations, magnitudes, and statistics of the earthquakes located in 2011 with the station parameters, velocity models, and other files used to locate these earthquakes.

Plenty of Deep Long-Period Earthquakes Beneath Cascade Volcanoes

NASA Astrophysics Data System (ADS)

Nichols, M. L.; Malone, S. D.; Moran, S. C.; Thelen, W. A.; Vidale, J. E.

2009-12-01

The Pacific Northwest Seismic Network (PNSN) records and locates earthquakes within Washington and Oregon, including those occurring at 10 Cascade volcanic centers. In an earlier study (Malone and Moran, EOS 1997), a total of 11 deep long-period (DLP) earthquakes were reported beneath 3 Washington volcanoes. They are characterized by emergent P- and S- arrivals, long and ringing codas, and contain most of their energy below 5 Hz. DLP earthquakes are significant because they have been observed to occur prior to or in association with eruptions at several volcanoes, and as a result are inferred to represent movement of deep-seated magma and associated fluids in the mid-to-lower crust. To more thoroughly characterize DLP occurrence in Washington and Oregon, we employed a two-step algorithm to systematically search the PNSN’s earthquake catalogue for DLP events occurring between 1980 and 2008. In the first step we applied a spectral ratio test to the demeaned and tapered triggered event waveforms to distinguish long-period events from the more common higher frequency volcano-tectonic and regional tectonic earthquakes. In the second step we visually analyzed waveforms of the flagged long-period events to distinguish DLP earthquakes from long-period rockfalls, explosions, shallow low-frequency events, and glacier quakes. We identified 56 DLP earthquakes beneath 7 Cascade volcanic centers. Of these, 31 occurred at Mount Baker, where the background flux of magmatic gases is greater than at the other volcanoes in our study. The other 6 volcanoes with DLPs (counts in parentheses) are Glacier Peak (5), Mount Rainier (9), Mount St. Helens (9), Mount Hood (1), Three Sisters (1), and Crater Lake (1). No DLP events were identified beneath Mount Adams, Mount Jefferson, or Newberry Volcano. The events are 10-40 km deep and have an average magnitude of around 1.5 (Mc), with both the largest and deepest DLPs occurring beneath Mount Baker. Cascade DLP earthquakes occur mostly as

Coupling of Sentinel-1, Sentinel-2 and ALOS-2 to assess coseismic deformation and earthquake-induced landslides following 26 June, 2016 earthquake in Kyrgyzstan

NASA Astrophysics Data System (ADS)

Vajedian, Sanaz; Motagh, Mahdi; Wetzel, Hans-Ulrich; Teshebaeva, Kanayim

2017-04-01

The active deformation in Kyrgyzstan results from the collision between Indian and Asia tectonic plates at a rate of 29 ± 1 mm/yr. This collision is accommodated by deformation on prominent faults, which can be ruptured coseismically and trigger other hazards like landslides. Many earthquake and earthquake-induced landslides in Kyrgyzstan occur in mountainous areas, where limited accessibility makes ground-based measurements for the assessment of their impact a challenging task. In this context, remote sensing measurements are extraordinary useful as they improve our knowledge about coseismic rupture process and provide information on other types of hazards that are triggered during and/or after the earthquakes. This investigation aims to use L-band ALOS/PALSAR, C-band Sentinel-1, Sentinel-2 data to evaluate fault slip model and coseismic-induced landslides related to 26 June 2016 Sary-Tash earthquake, southwest Kyrgyzstan. First we implement three methods to measure coseismic surface motion using radar data including Interferometric SAR (InSAR) analysis, SAR tracking technique and multiple aperture InSAR (MAI), followed by using Genetic Algorithm (GA) to invert the final displacement field to infer combination of orientation, location and slip on rectangular uniform slip fault plane. Slip distribution analysis is done by applying Tikhonov regularization to solve the constrained least-square method with Laplacian smoothing approach. The estimated coseismic slip model suggests a nearly W-E thrusting fault ruptured during the earthquake event in which the main rupture occurred at a depth between 11 and 14 km. Second, the local phase shifts related to landslides are inferred by detailed analysis pre-seismic, coseismic and postseismic C-band and L-band interferograms and the results are compared with the interpretations derived from Sentinel-2 data acquired before and after the earthquake.

Real-time earthquake monitoring using a search engine method.

PubMed

Zhang, Jie; Zhang, Haijiang; Chen, Enhong; Zheng, Yi; Kuang, Wenhuan; Zhang, Xiong

2014-12-04

When an earthquake occurs, seismologists want to use recorded seismograms to infer its location, magnitude and source-focal mechanism as quickly as possible. If such information could be determined immediately, timely evacuations and emergency actions could be undertaken to mitigate earthquake damage. Current advanced methods can report the initial location and magnitude of an earthquake within a few seconds, but estimating the source-focal mechanism may require minutes to hours. Here we present an earthquake search engine, similar to a web search engine, that we developed by applying a computer fast search method to a large seismogram database to find waveforms that best fit the input data. Our method is several thousand times faster than an exact search. For an Mw 5.9 earthquake on 8 March 2012 in Xinjiang, China, the search engine can infer the earthquake's parameters in <1 s after receiving the long-period surface wave data.

Exploring Earthquakes in Real-Time

NASA Astrophysics Data System (ADS)

Bravo, T. K.; Kafka, A. L.; Coleman, B.; Taber, J. J.

2013-12-01

Earthquakes capture the attention of students and inspire them to explore the Earth. Adding the ability to view and explore recordings of significant and newsworthy earthquakes in real-time makes the subject even more compelling. To address this opportunity, the Incorporated Research Institutions for Seismology (IRIS), in collaboration with Moravian College, developed ';jAmaSeis', a cross-platform application that enables students to access real-time earthquake waveform data. Students can watch as the seismic waves are recorded on their computer, and can be among the first to analyze the data from an earthquake. jAmaSeis facilitates student centered investigations of seismological concepts using either a low-cost educational seismograph or streamed data from other educational seismographs or from any seismic station that sends data to the IRIS Data Management System. After an earthquake, students can analyze the seismograms to determine characteristics of earthquakes such as time of occurrence, distance from the epicenter to the station, magnitude, and location. The software has been designed to provide graphical clues to guide students in the analysis and assist in their interpretations. Since jAmaSeis can simultaneously record up to three stations from anywhere on the planet, there are numerous opportunities for student driven investigations. For example, students can explore differences in the seismograms from different distances from an earthquake and compare waveforms from different azimuthal directions. Students can simultaneously monitor seismicity at a tectonic plate boundary and in the middle of the plate regardless of their school location. This can help students discover for themselves the ideas underlying seismic wave propagation, regional earthquake hazards, magnitude-frequency relationships, and the details of plate tectonics. The real-time nature of the data keeps the investigations dynamic, and offers students countless opportunities to explore.

Rupture geometry and slip distribution of the 2016 January 21st Ms6.4 Menyuan, China earthquake

NASA Astrophysics Data System (ADS)

Zhou, Y.

2017-12-01

On 21 January 2016, an Ms6.4 earthquake stroke Menyuan country, Qinghai Province, China. The epicenter of the main shock and locations of its aftershocks indicate that the Menyuan earthquake occurred near the left-lateral Lenglongling fault. However, the focal mechanism suggests that the earthquake should take place on a thrust fault. In addition, field investigation indicates that the earthquake did not rupture the ground surface. Therefore, the rupture geometry is unclear as well as coseismic slip distribution. We processed two pairs of InSAR images acquired by the ESA Sentinel-1A satellite with the ISCE software, and both ascending and descending orbits were included. After subsampling the coseismic InSAR images into about 800 pixels, coseismic displacement data along LOS direction are inverted for earthquake source parameters. We employ an improved mixed linear-nonlinear Bayesian inversion method to infer fault geometric parameters, slip distribution, and the Laplacian smoothing factor simultaneously. This method incorporates a hybrid differential evolution algorithm, which is an efficient global optimization algorithm. The inversion results show that the Menyuan earthquake ruptured a blind thrust fault with a strike of 124°and a dip angle of 41°. This blind fault was never investigated before and intersects with the left-lateral Lenglongling fault, but the strikes of them are nearly parallel. The slip sense is almost pure thrusting, and there is no significant slip within 4km depth. The max slip value is up to 0.3m, and the estimated moment magnitude is Mw5.93, in agreement with the seismic inversion result. The standard error of residuals between InSAR data and model prediction is as small as 0.5cm, verifying the correctness of the inversion results.

Earthquake Fingerprints: Representing Earthquake Waveforms for Similarity-Based Detection

NASA Astrophysics Data System (ADS)

Bergen, K.; Beroza, G. C.

2016-12-01

New earthquake detection methods, such as Fingerprint and Similarity Thresholding (FAST), use fast approximate similarity search to identify similar waveforms in long-duration data without templates (Yoon et al. 2015). These methods have two key components: fingerprint extraction and an efficient search algorithm. Fingerprint extraction converts waveforms into fingerprints, compact signatures that represent short-duration waveforms for identification and search. Earthquakes are detected using an efficient indexing and search scheme, such as locality-sensitive hashing, that identifies similar waveforms in a fingerprint database. The quality of the search results, and thus the earthquake detection results, is strongly dependent on the fingerprinting scheme. Fingerprint extraction should map similar earthquake waveforms to similar waveform fingerprints to ensure a high detection rate, even under additive noise and small distortions. Additionally, fingerprints corresponding to noise intervals should have mutually dissimilar fingerprints to minimize false detections. In this work, we compare the performance of multiple fingerprint extraction approaches for the earthquake waveform similarity search problem. We apply existing audio fingerprinting (used in content-based audio identification systems) and time series indexing techniques and present modified versions that are specifically adapted for seismic data. We also explore data-driven fingerprinting approaches that can take advantage of labeled or unlabeled waveform data. For each fingerprinting approach we measure its ability to identify similar waveforms in a low signal-to-noise setting, and quantify the trade-off between true and false detection rates in the presence of persistent noise sources. We compare the performance using known event waveforms from eight independent stations in the Northern California Seismic Network.

Determination of the fault plane and rupture size of the 2013 Santa Cruz earthquake, Bolivia, 5.2 Mw, by relative location of the aftershocks

NASA Astrophysics Data System (ADS)

Rivadeneyra-Vera, C.; Assumpção, M.; Minaya, E.; Aliaga, P.; Avila, G.

2016-11-01

The Central Andes of southern Bolivia is a highly seismic region with many active faults, that could generate earthquakes up to 8.9 Mw. In 2013, an earthquake of 5.2 Mw occurred in Santa Cruz de la Sierra, in the sub-Andean belt, close to the Mandeyapecua fault, one of the most important reverse faults in Bolivia. Five larger aftershocks were reported by the International Seismological Centre (ISC) and 33 smaller aftershocks were recorded by the San Calixto Observatory (OSC) in the two months after the mainshock. Distances between epicenters of the events were up to 36 km, which is larger than expected for an earthquake of this magnitude. Using data from South American regional stations and the relative location technique with Rayleigh waves, the epicenters of the five larger aftershocks of the Santa Cruz series were determined in relation to the mainshock. This method enabled to achieve epicentral locations with uncertainties smaller than 1 km. Additionally, using data of three Bolivian stations (MOC, SIV and LPAZ) eight smaller aftershocks, recorded by the OSC, were relocated through correlation of P and S waves. The results show a NNW-SSE trend of epicenters and suggest an E dipping plane. The maximum distance between the aftershocks is 14 km, which is not consistent with the expected subsurface rupture length, in accordance with the magnitude of the mainshock. The events are located away from the Mandeyapecua fault and show an opposite dip, demonstrating that these events were generated by another fault in the area, that had not been well studied yet.

Security Implications of Induced Earthquakes

NASA Astrophysics Data System (ADS)

Jha, B.; Rao, A.

2016-12-01

The increase in earthquakes induced or triggered by human activities motivates us to research how a malicious entity could weaponize earthquakes to cause damage. Specifically, we explore the feasibility of controlling the location, timing and magnitude of an earthquake by activating a fault via injection and production of fluids into the subsurface. Here, we investigate the relationship between the magnitude and trigger time of an induced earthquake to the well-to-fault distance. The relationship between magnitude and distance is important to determine the farthest striking distance from which one could intentionally activate a fault to cause certain level of damage. We use our novel computational framework to model the coupled multi-physics processes of fluid flow and fault poromechanics. We use synthetic models representative of the New Madrid Seismic Zone and the San Andreas Fault Zone to assess the risk in the continental US. We fix injection and production flow rates of the wells and vary their locations. We simulate injection-induced Coulomb destabilization of faults and evolution of fault slip under quasi-static deformation. We find that the effect of distance on the magnitude and trigger time is monotonic, nonlinear, and time-dependent. Evolution of the maximum Coulomb stress on the fault provides insights into the effect of the distance on rupture nucleation and propagation. The damage potential of induced earthquakes can be maintained even at longer distances because of the balance between pressure diffusion and poroelastic stress transfer mechanisms. We conclude that computational modeling of induced earthquakes allows us to measure feasibility of weaponzing earthquakes and developing effective defense mechanisms against such attacks.

Glacier quakes mimicking volcanic earthquakes: The challenge of monitoring ice-clad volcanoes and some solutions

NASA Astrophysics Data System (ADS)

Allstadt, K.; Carmichael, J. D.; Malone, S. D.; Bodin, P.; Vidale, J. E.; Moran, S. C.

2012-12-01

Swarms of repeating earthquakes at volcanoes are often a sign of volcanic unrest. However, glaciers also can generate repeating seismic signals, so detecting unrest at glacier-covered volcanoes can be a challenge. We have found that multi-day swarms of shallow, low-frequency, repeating earthquakes occur regularly at Mount Rainier, a heavily glaciated stratovolcano in Washington, but that most swarms had escaped recognition until recently. Typically such earthquakes were too small to be routinely detected by the seismic network and were often buried in the noise on visual records, making the few swarms that had been detected seem more unusual and significant at the time they were identified. Our comprehensive search for repeating earthquakes through the past 10 years of continuous seismic data uncovered more than 30 distinct swarms of low-frequency earthquakes at Rainier, each consisting of hundreds to thousands of events. We found that these swarms locate high on the glacier-covered edifice, occur almost exclusively between late fall and early spring, and that their onset coincides with heavy snowfalls. We interpret the correlation with snowfall to indicate a seismically observable glacial response to snow loading. Efforts are underway to confirm this by monitoring glacier motion before and after a major snowfall event using ground based radar interferometry. Clearly, if the earthquakes in these swarms reflect a glacial source, then they are not directly related to volcanic activity. However, from an operational perspective they make volcano monitoring difficult because they closely resemble earthquakes that often precede and accompany volcanic eruptions. Because we now have a better sense of the background level of such swarms and know that their occurrence is seasonal and correlated with snowfall, it will now be easier to recognize if future swarms at Rainier are unusual and possibly related to volcanic activity. To methodically monitor for such unusual activity

Earthquake Analysis (EA) Software for The Earthquake Observatories

NASA Astrophysics Data System (ADS)

Yanik, K.; Tezel, T.

2009-04-01

There are many software that can used for observe the seismic signals and locate the earthquakes, but some of them commercial and has technical support. For this reason, many seismological observatories developed and use their own seismological software packets which are convenient with their seismological network. In this study, we introduce our software which has some capabilities that it can read seismic signals and process and locate the earthquakes. This software is used by the General Directorate of Disaster Affairs Earthquake Research Department Seismology Division (here after ERD) and will improve according to the new requirements. ERD network consist of 87 seismic stations that 63 of them were equipped with 24 bite digital Guralp CMG-3T, 16 of them with analogue short period S-13-Geometrics and 8 of them 24 bite digital short period S-13j-DR-24 Geometrics seismometers. Data is transmitted with satellite from broadband stations, whereas leased line used from short period stations. Daily data archive capacity is 4 GB. In big networks, it is very important that observe the seismic signals and locate the earthquakes as soon as possible. This is possible, if they use software which was developed considering their network properties. When we started to develop a software for big networks as our, we recognized some realities that all known seismic format data should be read without any convert process, observing of the only selected stations and do this on the map directly, add seismic files with import command, establishing relation between P and S phase readings and location solutions, store in database and entering to the program with user name and password. In this way, we can prevent data disorder and repeated phase readings. There are many advantages, when data store on the database proxies. These advantages are easy access to data from anywhere using ethernet, publish the bulletin and catalogues using website, easily sending of short message (sms) and e

Station Correction Uncertainty in Multiple Event Location Algorithms and the Effect on Error Ellipses

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

Erickson, Jason P.; Carlson, Deborah K.; Ortiz, Anne

Accurate location of seismic events is crucial for nuclear explosion monitoring. There are several sources of error in seismic location that must be taken into account to obtain high confidence results. Most location techniques account for uncertainties in the phase arrival times (measurement error) and the bias of the velocity model (model error), but they do not account for the uncertainty of the velocity model bias. By determining and incorporating this uncertainty in the location algorithm we seek to improve the accuracy of the calculated locations and uncertainty ellipses. In order to correct for deficiencies in the velocity model, itmore » is necessary to apply station specific corrections to the predicted arrival times. Both master event and multiple event location techniques assume that the station corrections are known perfectly, when in reality there is an uncertainty associated with these corrections. For multiple event location algorithms that calculate station corrections as part of the inversion, it is possible to determine the variance of the corrections. The variance can then be used to weight the arrivals associated with each station, thereby giving more influence to stations with consistent corrections. We have modified an existing multiple event location program (based on PMEL, Pavlis and Booker, 1983). We are exploring weighting arrivals with the inverse of the station correction standard deviation as well using the conditional probability of the calculated station corrections. This is in addition to the weighting already given to the measurement and modeling error terms. We re-locate a group of mining explosions that occurred at Black Thunder, Wyoming, and compare the results to those generated without accounting for station correction uncertainty.« less

Identification tibia and fibula bone fracture location using scanline algorithm

NASA Astrophysics Data System (ADS)

Muchtar, M. A.; Simanjuntak, S. E.; Rahmat, R. F.; Mawengkang, H.; Zarlis, M.; Sitompul, O. S.; Winanto, I. D.; Andayani, U.; Syahputra, M. F.; Siregar, I.; Nasution, T. H.

2018-03-01

Fracture is a condition that there is a damage in the continuity of the bone, usually caused by stress, trauma or weak bones. The tibia and fibula are two separated-long bones in the lower leg, closely linked at the knee and ankle. Tibia/fibula fracture often happen when there is too much force applied to the bone that it can withstand. One of the way to identify the location of tibia/fibula fracture is to read X-ray image manually. Visual examination requires more time and allows for errors in identification due to the noise in image. In addition, reading X-ray needs highlighting background to make the objects in X-ray image appear more clearly. Therefore, a method is required to help radiologist to identify the location of tibia/fibula fracture. We propose some image-processing techniques for processing cruris image and Scan line algorithm for the identification of fracture location. The result shows that our proposed method is able to identify it and reach up to 87.5% of accuracy.

3D Buried Utility Location Using A Marching-Cross-Section Algorithm for Multi-Sensor Data Fusion

PubMed Central

Dou, Qingxu; Wei, Lijun; Magee, Derek R.; Atkins, Phil R.; Chapman, David N.; Curioni, Giulio; Goddard, Kevin F.; Hayati, Farzad; Jenks, Hugo; Metje, Nicole; Muggleton, Jennifer; Pennock, Steve R.; Rustighi, Emiliano; Swingler, Steven G.; Rogers, Christopher D. F.; Cohn, Anthony G.

2016-01-01

We address the problem of accurately locating buried utility segments by fusing data from multiple sensors using a novel Marching-Cross-Section (MCS) algorithm. Five types of sensors are used in this work: Ground Penetrating Radar (GPR), Passive Magnetic Fields (PMF), Magnetic Gradiometer (MG), Low Frequency Electromagnetic Fields (LFEM) and Vibro-Acoustics (VA). As part of the MCS algorithm, a novel formulation of the extended Kalman Filter (EKF) is proposed for marching existing utility tracks from a scan cross-section (scs) to the next one; novel rules for initializing utilities based on hypothesized detections on the first scs and for associating predicted utility tracks with hypothesized detections in the following scss are introduced. Algorithms are proposed for generating virtual scan lines based on given hypothesized detections when different sensors do not share common scan lines, or when only the coordinates of the hypothesized detections are provided without any information of the actual survey scan lines. The performance of the proposed system is evaluated with both synthetic data and real data. The experimental results in this work demonstrate that the proposed MCS algorithm can locate multiple buried utility segments simultaneously, including both straight and curved utilities, and can separate intersecting segments. By using the probabilities of a hypothesized detection being a pipe or a cable together with its 3D coordinates, the MCS algorithm is able to discriminate a pipe and a cable close to each other. The MCS algorithm can be used for both post- and on-site processing. When it is used on site, the detected tracks on the current scs can help to determine the location and direction of the next scan line. The proposed “multi-utility multi-sensor” system has no limit to the number of buried utilities or the number of sensors, and the more sensor data used, the more buried utility segments can be detected with more accurate location and

3D Buried Utility Location Using A Marching-Cross-Section Algorithm for Multi-Sensor Data Fusion.

PubMed

Dou, Qingxu; Wei, Lijun; Magee, Derek R; Atkins, Phil R; Chapman, David N; Curioni, Giulio; Goddard, Kevin F; Hayati, Farzad; Jenks, Hugo; Metje, Nicole; Muggleton, Jennifer; Pennock, Steve R; Rustighi, Emiliano; Swingler, Steven G; Rogers, Christopher D F; Cohn, Anthony G

2016-11-02

We address the problem of accurately locating buried utility segments by fusing data from multiple sensors using a novel Marching-Cross-Section (MCS) algorithm. Five types of sensors are used in this work: Ground Penetrating Radar (GPR), Passive Magnetic Fields (PMF), Magnetic Gradiometer (MG), Low Frequency Electromagnetic Fields (LFEM) and Vibro-Acoustics (VA). As part of the MCS algorithm, a novel formulation of the extended Kalman Filter (EKF) is proposed for marching existing utility tracks from a scan cross-section (scs) to the next one; novel rules for initializing utilities based on hypothesized detections on the first scs and for associating predicted utility tracks with hypothesized detections in the following scss are introduced. Algorithms are proposed for generating virtual scan lines based on given hypothesized detections when different sensors do not share common scan lines, or when only the coordinates of the hypothesized detections are provided without any information of the actual survey scan lines. The performance of the proposed system is evaluated with both synthetic data and real data. The experimental results in this work demonstrate that the proposed MCS algorithm can locate multiple buried utility segments simultaneously, including both straight and curved utilities, and can separate intersecting segments. By using the probabilities of a hypothesized detection being a pipe or a cable together with its 3D coordinates, the MCS algorithm is able to discriminate a pipe and a cable close to each other. The MCS algorithm can be used for both post- and on-site processing. When it is used on site, the detected tracks on the current scs can help to determine the location and direction of the next scan line. The proposed "multi-utility multi-sensor" system has no limit to the number of buried utilities or the number of sensors, and the more sensor data used, the more buried utility segments can be detected with more accurate location and orientation.

Visible Earthquakes: a web-based tool for visualizing and modeling InSAR earthquake data

NASA Astrophysics Data System (ADS)

Funning, G. J.; Cockett, R.

2012-12-01

InSAR (Interferometric Synthetic Aperture Radar) is a technique for measuring the deformation of the ground using satellite radar data. One of the principal applications of this method is in the study of earthquakes; in the past 20 years over 70 earthquakes have been studied in this way, and forthcoming satellite missions promise to enable the routine and timely study of events in the future. Despite the utility of the technique and its widespread adoption by the research community, InSAR does not feature in the teaching curricula of most university geoscience departments. This is, we believe, due to a lack of accessibility to software and data. Existing tools for the visualization and modeling of interferograms are often research-oriented, command line-based and/or prohibitively expensive. Here we present a new web-based interactive tool for comparing real InSAR data with simple elastic models. The overall design of this tool was focused on ease of access and use. This tool should allow interested nonspecialists to gain a feel for the use of such data and greatly facilitate integration of InSAR into upper division geoscience courses, giving students practice in comparing actual data to modeled results. The tool, provisionally named 'Visible Earthquakes', uses web-based technologies to instantly render the displacement field that would be observable using InSAR for a given fault location, geometry, orientation, and slip. The user can adjust these 'source parameters' using a simple, clickable interface, and see how these affect the resulting model interferogram. By visually matching the model interferogram to a real earthquake interferogram (processed separately and included in the web tool) a user can produce their own estimates of the earthquake's source parameters. Once satisfied with the fit of their models, users can submit their results and see how they compare with the distribution of all other contributed earthquake models, as well as the mean and median

Remote Imaging of Earthquake Characteristics Along Oceanic Transforms

NASA Astrophysics Data System (ADS)

Cleveland, M.; Ammon, C. J.

2014-12-01

Compared with subduction and continental transform systems, many characteristics of oceanic transform faults (OTF) are better defined (first-order structure and composition, thermal properties, etc.). Still, many aspects of earthquake behavior along OTFs remain poorly understood as a result of their relative remoteness. But the substantial aseismic deformation (averaging roughly 85%) that occurs along OTFs and the implied interaction of aseismic with seismic deformation is an opportunity to explore fundamental earthquake nucleation and rupture processes. However, the study of OTF earthquake properties is not easy because these faults are often located in remote regions, lacking nearby seismic networks. Thus, many standard network-based seismic approaches are infeasible, but some can be adapted to the effort. For example, double-difference methods applied to cross-correlation measured Rayleigh wave time shifts is an effective tool to provide greatly improved relative epicentroid locations, origin-time shifts, and relative event magnitudes for earthquakes in remote regions. The same comparative waveform measurements can provide insight into rupture directivity of the larger OTF events. In this study, we calculate improved relative earthquake locations and magnitudes of earthquakes along the Blanco Fracture Zone in the northeast Pacific Ocean and compare and contrast that work with a study of the more remote Menard Transform Fault (MTF), located in the southeast Pacific Ocean. For the Blanco, we work exclusively with Rayleigh (R1) observations exploiting the dense networks in the northern hemisphere. For the MTF, we combine R1 with Love (G1) observations to map and to analyze the distribution of strong asperities along this remote, 200-km-long fault. Specifically, we attempt to better define the relationship between observed near-transform normal and vertical strike-slip earthquakes in the vicinity of the MTF. We test our ability to use distant observations (the

Combining Real-Time Seismic and GPS Data for Earthquake Early Warning (Invited)

NASA Astrophysics Data System (ADS)

Boese, M.; Heaton, T. H.; Hudnut, K. W.

2013-12-01

Scientists at Caltech, UC Berkeley, the Univ. of SoCal, the Univ. of Washington, the US Geological Survey, and ETH Zurich have developed an earthquake early warning (EEW) demonstration system for California and the Pacific Northwest. To quickly determine the earthquake magnitude and location, 'ShakeAlert' currently processes and interprets real-time data-streams from ~400 seismic broadband and strong-motion stations within the California Integrated Seismic Network (CISN). Based on these parameters, the 'UserDisplay' software predicts and displays the arrival and intensity of shaking at a given user site. Real-time ShakeAlert feeds are currently shared with around 160 individuals, companies, and emergency response organizations to educate potential users about EEW and to identify needs and applications of EEW in a future operational warning system. Recently, scientists at the contributing institutions have started to develop algorithms for ShakeAlert that make use of high-rate real-time GPS data to improve the magnitude estimates for large earthquakes (M>6.5) and to determine slip distributions. Knowing the fault slip in (near) real-time is crucial for users relying on or operating distributed systems, such as for power, water or transportation, especially if these networks run close to or across large faults. As shown in an earlier study, slip information is also useful to predict (in a probabilistic sense) how far a fault rupture will propagate, thus enabling more robust probabilistic ground-motion predictions at distant locations. Finally, fault slip information is needed for tsunami warning, such as in the Cascadia subduction-zone. To handle extended fault-ruptures of large earthquakes in real-time, Caltech and USGS Pasadena are currently developing and testing a two-step procedure that combines seismic and geodetic data; in the first step, high-frequency strong-motion amplitudes are used to rapidly classify near-and far-source stations. Then, the location and

Revision of an automated microseismic location algorithm for DAS - 3C geophone hybrid array

NASA Astrophysics Data System (ADS)

Mizuno, T.; LeCalvez, J.; Raymer, D.

2017-12-01

Application of distributed acoustic sensing (DAS) has been studied in several areas in seismology. One of the areas is microseismic reservoir monitoring (e.g., Molteni et al., 2017, First Break). Considering the present limitations of DAS, which include relatively low signal-to-noise ratio (SNR) and no 3C polarization measurements, a DAS - 3C geophone hybrid array is a practical option when using a single monitoring well. Considering the large volume of data from distributed sensing, microseismic event detection and location using a source scanning type algorithm is a reasonable choice, especially for real-time monitoring. The algorithm must handle both strain rate along the borehole axis for DAS and particle velocity for 3C geophones. Only a small quantity of large SNR events will be detected throughout a large aperture encompassing the hybrid array; therefore, the aperture is to be optimized dynamically to eliminate noisy channels for a majority of events. For such hybrid array, coalescence microseismic mapping (CMM) (Drew et al., 2005, SPE) was revised. CMM forms a likelihood function of location of event and its origin time. At each receiver, a time function of event arrival likelihood is inferred using an SNR function, and it is migrated to time and space to determine hypocenter and origin time likelihood. This algorithm was revised to dynamically optimize such a hybrid array by identifying receivers where a microseismic signal is possibly detected and using only those receivers to compute the likelihood function. Currently, peak SNR is used to select receivers. To prevent false results due to small aperture, a minimum aperture threshold is employed. The algorithm refines location likelihood using 3C geophone polarization. We tested this algorithm using a ray-based synthetic dataset. Leaney (2014, PhD thesis, UBC) is used to compute particle velocity at receivers. Strain rate along the borehole axis is computed from particle velocity as DAS microseismic

Seismogeodesy and Rapid Earthquake and Tsunami Source Assessment

NASA Astrophysics Data System (ADS)

Melgar Moctezuma, Diego

This dissertation presents an optimal combination algorithm for strong motion seismograms and regional high rate GPS recordings. This seismogeodetic solution produces estimates of ground motion that recover the whole seismic spectrum, from the permanent deformation to the Nyquist frequency of the accelerometer. This algorithm will be demonstrated and evaluated through outdoor shake table tests and recordings of large earthquakes, notably the 2010 Mw 7.2 El Mayor-Cucapah earthquake and the 2011 Mw 9.0 Tohoku-oki events. This dissertations will also show that strong motion velocity and displacement data obtained from the seismogeodetic solution can be instrumental to quickly determine basic parameters of the earthquake source. We will show how GPS and seismogeodetic data can produce rapid estimates of centroid moment tensors, static slip inversions, and most importantly, kinematic slip inversions. Throughout the dissertation special emphasis will be placed on how to compute these source models with minimal interaction from a network operator. Finally we will show that the incorporation of off-shore data such as ocean-bottom pressure and RTK-GPS buoys can better-constrain the shallow slip of large subduction events. We will demonstrate through numerical simulations of tsunami propagation that the earthquake sources derived from the seismogeodetic and ocean-based sensors is detailed enough to provide a timely and accurate assessment of expected tsunami intensity immediately following a large earthquake.

A new statistical PCA-ICA algorithm for location of R-peaks in ECG.

PubMed

Chawla, M P S; Verma, H K; Kumar, Vinod

2008-09-16

The success of ICA to separate the independent components from the mixture depends on the properties of the electrocardiogram (ECG) recordings. This paper discusses some of the conditions of independent component analysis (ICA) that could affect the reliability of the separation and evaluation of issues related to the properties of the signals and number of sources. Principal component analysis (PCA) scatter plots are plotted to indicate the diagnostic features in the presence and absence of base-line wander in interpreting the ECG signals. In this analysis, a newly developed statistical algorithm by authors, based on the use of combined PCA-ICA for two correlated channels of 12-channel ECG data is proposed. ICA technique has been successfully implemented in identifying and removal of noise and artifacts from ECG signals. Cleaned ECG signals are obtained using statistical measures like kurtosis and variance of variance after ICA processing. This analysis also paper deals with the detection of QRS complexes in electrocardiograms using combined PCA-ICA algorithm. The efficacy of the combined PCA-ICA algorithm lies in the fact that the location of the R-peaks is bounded from above and below by the location of the cross-over points, hence none of the peaks are ignored or missed.

Detecting and Locating Seismic Events Without Phase Picks or Velocity Models

NASA Astrophysics Data System (ADS)

Arrowsmith, S.; Young, C. J.; Ballard, S.; Slinkard, M.

2015-12-01

The standard paradigm for seismic event monitoring is to scan waveforms from a network of stations and identify the arrival time of various seismic phases. A signal association algorithm then groups the picks to form events, which are subsequently located by minimizing residuals between measured travel times and travel times predicted by an Earth model. Many of these steps are prone to significant errors which can lead to erroneous arrival associations and event locations. Here, we revisit a concept for event detection that does not require phase picks or travel time curves and fuses detection, association and location into a single algorithm. Our pickless event detector exploits existing catalog and waveform data to build an empirical stack of the full regional seismic wavefield, which is subsequently used to detect and locate events at a network level using correlation techniques. Because the technique uses more of the information content of the original waveforms, the concept is particularly powerful for detecting weak events that would be missed by conventional methods. We apply our detector to seismic data from the University of Utah Seismograph Stations network and compare our results with the earthquake catalog published by the University of Utah. We demonstrate that the pickless detector can detect and locate significant numbers of events previously missed by standard data processing techniques.

Earthquakes in and near the northeastern United States, 1638-1998

USGS Publications Warehouse

Wheeler, R.L.; Trevor, N.K.; Tarr, A.C.; Crone, A.J.

2000-01-01

The data are those used to make a large-format, colored map of earthquakes in the northeastern United States and adjacent parts of Canada and the Atlantic Ocean (Wheeler, 2000; Wheeler and others, 2001; references in Data_Quality_Information, Lineage). The map shows the locations of 1,069 known earthquakes of magnitude 3.0 or larger, and is designed for a non-technical audience. Colored circles represent earthquake locations, colored and sized by magnitude. Short descriptions, colonial-era woodcuts, newspaper headlines, and photographs summarize the dates, times of day, damage, and other effects of notable earthquakes. The base map shows color-coded elevation, shaded to emphasize relief.

Evidence for Ancient Mesoamerican Earthquakes

NASA Astrophysics Data System (ADS)

Kovach, R. L.; Garcia, B.

2001-12-01

Evidence for past earthquake damage at Mesoamerican ruins is often overlooked because of the invasive effects of tropical vegetation and is usually not considered as a casual factor when restoration and reconstruction of many archaeological sites are undertaken. Yet the proximity of many ruins to zones of seismic activity would argue otherwise. Clues as to the types of damage which should be soughtwere offered in September 1999 when the M = 7.5 Oaxaca earthquake struck the ruins of Monte Alban, Mexico, where archaeological renovations were underway. More than 20 structures were damaged, 5 of them seriously. Damage features noted were walls out of plumb, fractures in walls, floors, basal platforms and tableros, toppling of columns, and deformation, settling and tumbling of walls. A Modified Mercalli Intensity of VII (ground accelerations 18-34 %b) occurred at the site. Within the diffuse landward extension of the Caribbean plate boundary zone M = 7+ earthquakes occur with repeat times of hundreds of years arguing that many Maya sites were subjected to earthquakes. Damage to re-erected and reinforced stelae, walls, and buildings were witnessed at Quirigua, Guatemala, during an expedition underway when then 1976 M = 7.5 Guatemala earthquake on the Motagua fault struck. Excavations also revealed evidence (domestic pttery vessels and skeleton of a child crushed under fallen walls) of an ancient earthquake occurring about the teim of the demise and abandonment of Quirigua in the late 9th century. Striking evidence for sudden earthquake building collapse at the end of the Mayan Classic Period ~A.D. 889 was found at Benque Viejo (Xunantunich), Belize, located 210 north of Quirigua. It is argued that a M = 7.5 to 7.9 earthquake at the end of the Maya Classic period centered in the vicinity of the Chixoy-Polochic and Motagua fault zones cound have produced the contemporaneous earthquake damage to the above sites. As a consequences this earthquake may have accelerated the

Spatial distribution of earthquake hypocenters in the Crimea—Black Sea region

NASA Astrophysics Data System (ADS)

Burmin, V. Yu; Shumlianska, L. O.

2018-03-01

Some aspects of the seismicity the Crime—Black Sea region are considered on the basis of the catalogued data on earthquakes that have occurred between 1970 and 2012. The complete list of the Crimean earthquakes for this period contains about 2140 events with magnitude ranging from -1.5 to 5.5. Bulletins contain information about compressional and shear waves arrival times regarding nearly 2000 earthquakes. A new approach to the definition of the coordinates of all of the events was applied to re-establish the hypocenters of the catalogued earthquakes. The obtained results indicate that the bulk of the earthquakes' foci in the region are located in the crust. However, some 2.5% of the foci are located at the depths ranging from 50 to 250 km. The new distribution of foci of earthquakes shows the concentration of foci in the form of two inclined branches, the center of which is located under the Yalto-Alushta seismic focal zone. The whole distribution of foci in depth corresponds to the relief of the lithosphere.

The threat of silent earthquakes

USGS Publications Warehouse

Cervelli, Peter

2004-01-01

Not all earthquakes shake the ground. The so-called silent types are forcing scientists to rethink their understanding of the way quake-prone faults behave. In rare instances, silent earthquakes that occur along the flakes of seaside volcanoes may cascade into monstrous landslides that crash into the sea and trigger towering tsunamis. Silent earthquakes that take place within fault zones created by one tectonic plate diving under another may increase the chance of ground-shaking shocks. In other locations, however, silent slip may decrease the likelihood of destructive quakes, because they release stress along faults that might otherwise seem ready to snap.

A flatfile of ground motion intensity measurements from induced earthquakes in Oklahoma and Kansas

USGS Publications Warehouse

Rennolet, Steven B.; Moschetti, Morgan P.; Thompson, Eric M.; Yeck, William

2018-01-01

We have produced a uniformly processed database of orientation-independent (RotD50, RotD100) ground motion intensity measurements containing peak horizontal ground motions (accelerations and velocities) and 5-percent-damped pseudospectral accelerations (0.1–10 s) from more than 3,800 M ≥ 3 earthquakes in Oklahoma and Kansas that occurred between January 2009 and December 2016. Ground motion time series were collected from regional, national, and temporary seismic arrays out to 500 km. We relocated the majority of the earthquake hypocenters using a multiple-event relocation algorithm to produce a set of near-uniformly processed hypocentral locations. Ground motion processing followed standard methods, with the primary objective of reducing the effects of noise on the measurements. Regional wave-propagation features and the high seismicity rate required careful selection of signal windows to ensure that we captured the entire ground motion record and that contaminating signals from extraneous earthquakes did not contribute to the database. Processing was carried out with an automated scheme and resulted in a database comprising more than 174,000 records (https://dx.doi.org/10.5066/F73B5X8N). We anticipate that these results will be useful for improved understanding of earthquake ground motions and for seismic hazard applications.

The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2)

USGS Publications Warehouse

,

2008-01-01

California?s 35 million people live among some of the most active earthquake faults in the United States. Public safety demands credible assessments of the earthquake hazard to maintain appropriate building codes for safe construction and earthquake insurance for loss protection. Seismic hazard analysis begins with an earthquake rupture forecast?a model of probabilities that earthquakes of specified magnitudes, locations, and faulting types will occur during a specified time interval. This report describes a new earthquake rupture forecast for California developed by the 2007 Working Group on California Earthquake Probabilities (WGCEP 2007).

The May 20 (MW 6.1) and 29 (MW 6.0), 2012, Emilia (Po Plain, northern Italy) earthquakes: New seismotectonic implications from subsurface geology and high-quality hypocenter location

NASA Astrophysics Data System (ADS)

Carannante, Simona; Argnani, Andrea; Massa, Marco; D'Alema, Ezio; Lovati, Sara; Moretti, Milena; Cattaneo, Marco; Augliera, Paolo

2015-08-01

This study presents new geological and seismological data that are used to assess the seismic hazard of a sector of the Po Plain (northern Italy), a large alluvial basin hit by two strong earthquakes on May 20 (MW 6.1) and May 29 (MW 6.0), 2012. The proposed interpretation is based on high-quality relocation of 5369 earthquakes ('Emilia sequence') and a dense grid of seismic profiles and exploration wells. The analyzed seismicity was recorded by 44 seismic stations, and initially used to calibrate new one-dimensional and three-dimensional local Vp and Vs velocity models for the area. Considering these new models, the initial sparse hypocenters were then relocated in absolute mode and adjusted using the double-difference relative location algorithm. These data define a seismicity that is elongated in the W-NW to E-SE directions. The aftershocks of the May 20 mainshock appear to be distributed on a rupture surface that dips ~ 45° SSW, and the surface projection indicates an area ~ 10 km wide and 23 km long. The aftershocks of the May 29 mainshock followed a steep rupture surface that is well constrained within the investigated volume, whereby the surface projection of the blind source indicates an area ~ 6 km wide and 33 km long. Multichannel seismic profiles highlight the presence of relevant lateral variations in the structural style of the Ferrara folds that developed during the Pliocene and Pleistocene. There is also evidence of a Mesozoic extensional fault system in the Ferrara arc, with faults that in places have been seismically reactivated. These geological and seismological observations suggest that the 2012 Emilia earthquakes were related to ruptures along blind fault surfaces that are not part of the Pliocene-Pleistocene structural system, but are instead related to a deeper system that is itself closely related to re-activation of a Mesozoic extensional fault system.

User's guide to HYPOINVERSE-2000, a Fortran program to solve for earthquake locations and magnitudes

USGS Publications Warehouse

Klein, Fred W.

2002-01-01

Hypoinverse is a computer program that processes files of seismic station data for an earthquake (like p wave arrival times and seismogram amplitudes and durations) into earthquake locations and magnitudes. It is one of a long line of similar USGS programs including HYPOLAYR (Eaton, 1969), HYPO71 (Lee and Lahr, 1972), and HYPOELLIPSE (Lahr, 1980). If you are new to Hypoinverse, you may want to start by glancing at the section “SOME SIMPLE COMMAND SEQUENCES” to get a feel of some simpler sessions. This document is essentially an advanced user’s guide, and reading it sequentially will probably plow the reader into more detail than he/she needs. Every user must have a crust model, station list and phase data input files, and glancing at these sections is a good place to begin. The program has many options because it has grown over the years to meet the needs of one the largest seismic networks in the world, but small networks with just a few stations do use the program and can ignore most of the options and commands. History and availability. Hypoinverse was originally written for the Eclipse minicomputer in 1978 (Klein, 1978). A revised version for VAX and Pro-350 computers (Klein, 1985) was later expanded to include multiple crustal models and other capabilities (Klein, 1989). This current report documents the expanded Y2000 version and it supercedes the earlier documents. It serves as a detailed user's guide to the current version running on unix and VAX-alpha computers, and to the version supplied with the Earthworm earthquake digitizing system. Fortran-77 source code (Sun and VAX compatible) and copies of this documentation is available via anonymous ftp from computers in Menlo Park. At present, the computer is swave.wr.usgs.gov and the directory is /ftp/pub/outgoing/klein/hyp2000. If you are running Hypoinverse on one of the Menlo Park EHZ or NCSN unix computers, the executable currently is ~klein/hyp2000/hyp2000. New features. The Y2000 version of

The initial subevent of the 1994 Northridge, California, earthquake: Is earthquake size predictable?

USGS Publications Warehouse

Kilb, Debi; Gomberg, J.

1999-01-01

We examine the initial subevent (ISE) of the M?? 6.7, 1994 Northridge, California, earthquake in order to discriminate between two end-member rupture initiation models: the 'preslip' and 'cascade' models. Final earthquake size may be predictable from an ISE's seismic signature in the preslip model but not in the cascade model. In the cascade model ISEs are simply small earthquakes that can be described as purely dynamic ruptures. In this model a large earthquake is triggered by smaller earthquakes; there is no size scaling between triggering and triggered events and a variety of stress transfer mechanisms are possible. Alternatively, in the preslip model, a large earthquake nucleates as an aseismically slipping patch in which the patch dimension grows and scales with the earthquake's ultimate size; the byproduct of this loading process is the ISE. In this model, the duration of the ISE signal scales with the ultimate size of the earthquake, suggesting that nucleation and earthquake size are determined by a more predictable, measurable, and organized process. To distinguish between these two end-member models we use short period seismograms recorded by the Southern California Seismic Network. We address questions regarding the similarity in hypocenter locations and focal mechanisms of the ISE and the mainshock. We also compare the ISE's waveform characteristics to those of small earthquakes and to the beginnings of earthquakes with a range of magnitudes. We find that the focal mechanisms of the ISE and mainshock are indistinguishable, and both events may have nucleated on and ruptured the same fault plane. These results satisfy the requirements for both models and thus do not discriminate between them. However, further tests show the ISE's waveform characteristics are similar to those of typical small earthquakes in the vicinity and more importantly, do not scale with the mainshock magnitude. These results are more consistent with the cascade model.

A hybrid flower pollination algorithm based modified randomized location for multi-threshold medical image segmentation.

PubMed

Wang, Rui; Zhou, Yongquan; Zhao, Chengyan; Wu, Haizhou

2015-01-01

Multi-threshold image segmentation is a powerful image processing technique that is used for the preprocessing of pattern recognition and computer vision. However, traditional multilevel thresholding methods are computationally expensive because they involve exhaustively searching the optimal thresholds to optimize the objective functions. To overcome this drawback, this paper proposes a flower pollination algorithm with a randomized location modification. The proposed algorithm is used to find optimal threshold values for maximizing Otsu's objective functions with regard to eight medical grayscale images. When benchmarked against other state-of-the-art evolutionary algorithms, the new algorithm proves itself to be robust and effective through numerical experimental results including Otsu's objective values and standard deviations.

An Optimal Algorithm towards Successive Location Privacy in Sensor Networks with Dynamic Programming

NASA Astrophysics Data System (ADS)

Zhao, Baokang; Wang, Dan; Shao, Zili; Cao, Jiannong; Chan, Keith C. C.; Su, Jinshu

In wireless sensor networks, preserving location privacy under successive inference attacks is extremely critical. Although this problem is NP-complete in general cases, we propose a dynamic programming based algorithm and prove it is optimal in special cases where the correlation only exists between p immediate adjacent observations.

Purposes and methods of scoring earthquake forecasts

NASA Astrophysics Data System (ADS)

Zhuang, J.

2010-12-01

There are two kinds of purposes in the studies on earthquake prediction or forecasts: one is to give a systematic estimation of earthquake risks in some particular region and period in order to give advice to governments and enterprises for the use of reducing disasters, the other one is to search for reliable precursors that can be used to improve earthquake prediction or forecasts. For the first case, a complete score is necessary, while for the latter case, a partial score, which can be used to evaluate whether the forecasts or predictions have some advantages than a well know model, is necessary. This study reviews different scoring methods for evaluating the performance of earthquake prediction and forecasts. Especially, the gambling scoring method, which is developed recently, shows its capacity in finding good points in an earthquake prediction algorithm or model that are not in a reference model, even if its overall performance is no better than the reference model.

Dynamic 3D simulations of earthquakes on en echelon faults

USGS Publications Warehouse

Harris, R.A.; Day, S.M.

1999-01-01

One of the mysteries of earthquake mechanics is why earthquakes stop. This process determines the difference between small and devastating ruptures. One possibility is that fault geometry controls earthquake size. We test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three-dimensional medium and apply our knowledge to two California fault zones. We find that the size difference between the 1934 and 1966 Parkfield, California, earthquakes may be the product of a stepover at the southern end of the 1934 earthquake and show how the 1992 Landers, California, earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event. If there are no linking structures, such as transfer faults, then strike-slip earthquakes are unlikely to propagate through stepovers >5 km wide. Copyright 1999 by the American Geophysical Union.

Object-based classification of earthquake damage from high-resolution optical imagery using machine learning

NASA Astrophysics Data System (ADS)

Bialas, James; Oommen, Thomas; Rebbapragada, Umaa; Levin, Eugene

2016-07-01

Object-based approaches in the segmentation and classification of remotely sensed images yield more promising results compared to pixel-based approaches. However, the development of an object-based approach presents challenges in terms of algorithm selection and parameter tuning. Subjective methods are often used, but yield less than optimal results. Objective methods are warranted, especially for rapid deployment in time-sensitive applications, such as earthquake damage assessment. Herein, we used a systematic approach in evaluating object-based image segmentation and machine learning algorithms for the classification of earthquake damage in remotely sensed imagery. We tested a variety of algorithms and parameters on post-event aerial imagery for the 2011 earthquake in Christchurch, New Zealand. Results were compared against manually selected test cases representing different classes. In doing so, we can evaluate the effectiveness of the segmentation and classification of different classes and compare different levels of multistep image segmentations. Our classifier is compared against recent pixel-based and object-based classification studies for postevent imagery of earthquake damage. Our results show an improvement against both pixel-based and object-based methods for classifying earthquake damage in high resolution, post-event imagery.

Variable anelastic attenuation and site effect in estimating source parameters of various major earthquakes including M w 7.8 Nepal and M w 7.5 Hindu kush earthquake by using far-field strong-motion data

NASA Astrophysics Data System (ADS)

Kumar, Naresh; Kumar, Parveen; Chauhan, Vishal; Hazarika, Devajit

2017-10-01

Strong-motion records of recent Gorkha Nepal earthquake ( M w 7.8), its strong aftershocks and seismic events of Hindu kush region have been analysed for estimation of source parameters. The M w 7.8 Gorkha Nepal earthquake of 25 April 2015 and its six aftershocks of magnitude range 5.3-7.3 are recorded at Multi-Parametric Geophysical Observatory, Ghuttu, Garhwal Himalaya (India) >600 km west from the epicentre of main shock of Gorkha earthquake. The acceleration data of eight earthquakes occurred in the Hindu kush region also recorded at this observatory which is located >1000 km east from the epicentre of M w 7.5 Hindu kush earthquake on 26 October 2015. The shear wave spectra of acceleration record are corrected for the possible effects of anelastic attenuation at both source and recording site as well as for site amplification. The strong-motion data of six local earthquakes are used to estimate the site amplification and the shear wave quality factor ( Q β) at recording site. The frequency-dependent Q β( f) = 124 f 0.98 is computed at Ghuttu station by using inversion technique. The corrected spectrum is compared with theoretical spectrum obtained from Brune's circular model for the horizontal components using grid search algorithm. Computed seismic moment, stress drop and source radius of the earthquakes used in this work range 8.20 × 1016-5.72 × 1020 Nm, 7.1-50.6 bars and 3.55-36.70 km, respectively. The results match with the available values obtained by other agencies.

Brady's Geothermal Field DAS Earthquake Data

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

Kurt Feigl

The submitted data correspond to the vibration caused by a 3.4 M earthquake and captured by the DAS horizontal and vertical arrays during the PoroTomo Experiment. Earthquake information : M 4.3 - 23km ESE of Hawthorne, Nevada Time: 2016-03-21 07:37:10 (UTC) Location: 38.479 N 118.366 W Depth: 9.9 km

Design of isolated buildings with S-FBI system subjected to near-fault earthquakes using NSGA-II algorithm

NASA Astrophysics Data System (ADS)

Ozbulut, O. E.; Silwal, B.

2014-04-01

This study investigates the optimum design parameters of a superelastic friction base isolator (S-FBI) system through a multi-objective genetic algorithm and performance-based evaluation approach. The S-FBI system consists of a flat steel- PTFE sliding bearing and a superelastic NiTi shape memory alloy (SMA) device. Sliding bearing limits the transfer of shear across the isolation interface and provides damping from sliding friction. SMA device provides restoring force capability to the isolation system together with additional damping characteristics. A three-story building is modeled with S-FBI isolation system. Multiple-objective numerical optimization that simultaneously minimizes isolation-level displacements and superstructure response is carried out with a genetic algorithm (GA) in order to optimize S-FBI system. Nonlinear time history analyses of the building with S-FBI system are performed. A set of 20 near-field ground motion records are used in numerical simulations. Results show that S-FBI system successfully control response of the buildings against near-fault earthquakes without sacrificing in isolation efficacy and producing large isolation-level deformations.

Sun, Moon and Earthquakes

NASA Astrophysics Data System (ADS)

Kolvankar, V. G.

2013-12-01

During a study conducted to find the effect of Earth tides on the occurrence of earthquakes, for small areas [typically 1000km X1000km] of high-seismicity regions, it was noticed that the Sun's position in terms of universal time [GMT] shows links to the sum of EMD [longitude of earthquake location - longitude of Moon's foot print on earth] and SEM [Sun-Earth-Moon angle]. This paper provides the details of this relationship after studying earthquake data for over forty high-seismicity regions of the world. It was found that over 98% of the earthquakes for these different regions, examined for the period 1973-2008, show a direct relationship between the Sun's position [GMT] and [EMD+SEM]. As the time changes from 00-24 hours, the factor [EMD+SEM] changes through 360 degree, and plotting these two variables for earthquakes from different small regions reveals a simple 45 degree straight-line relationship between them. This relationship was tested for all earthquakes and earthquake sequences for magnitude 2.0 and above. This study conclusively proves how Sun and the Moon govern all earthquakes. Fig. 12 [A+B]. The left-hand figure provides a 24-hour plot for forty consecutive days including the main event (00:58:23 on 26.12.2004, Lat.+3.30, Long+95.980, Mb 9.0, EQ count 376). The right-hand figure provides an earthquake plot for (EMD+SEM) vs GMT timings for the same data. All the 376 events including the main event faithfully follow the straight-line curve.

Large earthquakes and creeping faults

USGS Publications Warehouse

Harris, Ruth A.

2017-01-01

Faults are ubiquitous throughout the Earth's crust. The majority are silent for decades to centuries, until they suddenly rupture and produce earthquakes. With a focus on shallow continental active-tectonic regions, this paper reviews a subset of faults that have a different behavior. These unusual faults slowly creep for long periods of time and produce many small earthquakes. The presence of fault creep and the related microseismicity helps illuminate faults that might not otherwise be located in fine detail, but there is also the question of how creeping faults contribute to seismic hazard. It appears that well-recorded creeping fault earthquakes of up to magnitude 6.6 that have occurred in shallow continental regions produce similar fault-surface rupture areas and similar peak ground shaking as their locked fault counterparts of the same earthquake magnitude. The behavior of much larger earthquakes on shallow creeping continental faults is less well known, because there is a dearth of comprehensive observations. Computational simulations provide an opportunity to fill the gaps in our understanding, particularly of the dynamic processes that occur during large earthquake rupture and arrest.

Unexpected earthquake of June 25th, 2015 in Madiun, East Java

NASA Astrophysics Data System (ADS)

Nugraha, Andri Dian; Supendi, Pepen; Shiddiqi, Hasbi Ash; Widiyantoro, Sri

2016-05-01

An earthquake with magnitude 4.2 struck Madiun and its vicinity on June 25, 2015. According to Indonesian Meteorology, Climatology, and Geophysics Agency (BMKG), the earthquake occurred at 10:35:29 GMT+7 and was located in 7.73° S, 111.69 ° E, with a depth of 10 km. At least 57 houses suffered from light to medium damages. We reprocessed earthquake waveform data to obtain an accurate hypocenter location. We manually picked P- and S-waves arrival times from 12 seismic stations in the eastern part of Java. Earthquake location was determined by using Hypoellipse code that employs a single event determination method. Our inversion is able to resolve the fix-depth and shows that the earthquake occurred at 10:35:27.6 GMT+7 and was located in 7.6305° S, 111.7529 ° E with 14.81 km focus depth. Our location depicts a smaller travel time residual compared to that based on the BMKG result. Focal mechanism of the earthquake was determined by using HASH code. We used first arrival polarity of 9 seismic records with azimuthal gap less than 90°, and estimated take-off angles by using assumption of homogenous medium. Our focal mechanism solution shows a strike-slip mechanism with strike direction of 163o, which may be related to a strike-fault in Klangon, an area to the east of Madiun.

Synthetic earthquake catalogs simulating seismic activity in the Corinth Gulf, Greece, fault system

NASA Astrophysics Data System (ADS)

Console, Rodolfo; Carluccio, Roberto; Papadimitriou, Eleftheria; Karakostas, Vassilis

2015-01-01

The characteristic earthquake hypothesis is the basis of time-dependent modeling of earthquake recurrence on major faults. However, the characteristic earthquake hypothesis is not strongly supported by observational data. Few fault segments have long historical or paleoseismic records of individually dated ruptures, and when data and parameter uncertainties are allowed for, the form of the recurrence distribution is difficult to establish. This is the case, for instance, of the Corinth Gulf Fault System (CGFS), for which documents about strong earthquakes exist for at least 2000 years, although they can be considered complete for M ≥ 6.0 only for the latest 300 years, during which only few characteristic earthquakes are reported for individual fault segments. The use of a physics-based earthquake simulator has allowed the production of catalogs lasting 100,000 years and containing more than 500,000 events of magnitudes ≥ 4.0. The main features of our simulation algorithm are (1) an average slip rate released by earthquakes for every single segment in the investigated fault system, (2) heuristic procedures for rupture growth and stop, leading to a self-organized earthquake magnitude distribution, (3) the interaction between earthquake sources, and (4) the effect of minor earthquakes in redistributing stress. The application of our simulation algorithm to the CGFS has shown realistic features in time, space, and magnitude behavior of the seismicity. These features include long-term periodicity of strong earthquakes, short-term clustering of both strong and smaller events, and a realistic earthquake magnitude distribution departing from the Gutenberg-Richter distribution in the higher-magnitude range.

Significant earthquakes on the Enriquillo fault system, Hispaniola, 1500-2010: Implications for seismic hazard

USGS Publications Warehouse

Bakun, William H.; Flores, Claudia H.; ten Brink, Uri S.

2012-01-01

Historical records indicate frequent seismic activity along the north-east Caribbean plate boundary over the past 500 years, particularly on the island of Hispaniola. We use accounts of historical earthquakes to assign intensities and the intensity assignments for the 2010 Haiti earthquakes to derive an intensity attenuation relation for Hispaniola. The intensity assignments and the attenuation relation are used in a grid search to find source locations and magnitudes that best fit the intensity assignments. Here we describe a sequence of devastating earthquakes on the Enriquillo fault system in the eighteenth century. An intensity magnitude MI 6.6 earthquake in 1701 occurred near the location of the 2010 Haiti earthquake, and the accounts of the shaking in the 1701 earthquake are similar to those of the 2010 earthquake. A series of large earthquakes migrating from east to west started with the 18 October 1751 MI 7.4–7.5 earthquake, probably located near the eastern end of the fault in the Dominican Republic, followed by the 21 November 1751 MI 6.6 earthquake near Port-au-Prince, Haiti, and the 3 June 1770 MI 7.5 earthquake west of the 2010 earthquake rupture. The 2010 Haiti earthquake may mark the beginning of a new cycle of large earthquakes on the Enriquillo fault system after 240 years of seismic quiescence. The entire Enriquillo fault system appears to be seismically active; Haiti and the Dominican Republic should prepare for future devastating earthquakes.

Earthquakes: Recurrence and Interoccurrence Times

NASA Astrophysics Data System (ADS)

Abaimov, S. G.; Turcotte, D. L.; Shcherbakov, R.; Rundle, J. B.; Yakovlev, G.; Goltz, C.; Newman, W. I.

2008-04-01

The purpose of this paper is to discuss the statistical distributions of recurrence times of earthquakes. Recurrence times are the time intervals between successive earthquakes at a specified location on a specified fault. Although a number of statistical distributions have been proposed for recurrence times, we argue in favor of the Weibull distribution. The Weibull distribution is the only distribution that has a scale-invariant hazard function. We consider three sets of characteristic earthquakes on the San Andreas fault: (1) The Parkfield earthquakes, (2) the sequence of earthquakes identified by paleoseismic studies at the Wrightwood site, and (3) an example of a sequence of micro-repeating earthquakes at a site near San Juan Bautista. In each case we make a comparison with the applicable Weibull distribution. The number of earthquakes in each of these sequences is too small to make definitive conclusions. To overcome this difficulty we consider a sequence of earthquakes obtained from a one million year “Virtual California” simulation of San Andreas earthquakes. Very good agreement with a Weibull distribution is found. We also obtain recurrence statistics for two other model studies. The first is a modified forest-fire model and the second is a slider-block model. In both cases good agreements with Weibull distributions are obtained. Our conclusion is that the Weibull distribution is the preferred distribution for estimating the risk of future earthquakes on the San Andreas fault and elsewhere.

Some facts about aftershocks to large earthquakes in California

USGS Publications Warehouse

Jones, Lucile M.; Reasenberg, Paul A.

1996-01-01

Earthquakes occur in clusters. After one earthquake happens, we usually see others at nearby (or identical) locations. To talk about this phenomenon, seismologists coined three terms foreshock , mainshock , and aftershock. In any cluster of earthquakes, the one with the largest magnitude is called the mainshock; earthquakes that occur before the mainshock are called foreshocks while those that occur after the mainshock are called aftershocks. A mainshock will be redefined as a foreshock if a subsequent event in the cluster has a larger magnitude. Aftershock sequences follow predictable patterns. That is, a sequence of aftershocks follows certain global patterns as a group, but the individual earthquakes comprising the group are random and unpredictable. This relationship between the pattern of a group and the randomness (stochastic nature) of the individuals has a close parallel in actuarial statistics. We can describe the pattern that aftershock sequences tend to follow with well-constrained equations. However, we must keep in mind that the actual aftershocks are only probabilistically described by these equations. Once the parameters in these equations have been estimated, we can determine the probability of aftershocks occurring in various space, time and magnitude ranges as described below. Clustering of earthquakes usually occurs near the location of the mainshock. The stress on the mainshock's fault changes drastically during the mainshock and that fault produces most of the aftershocks. This causes a change in the regional stress, the size of which decreases rapidly with distance from the mainshock. Sometimes the change in stress caused by the mainshock is great enough to trigger aftershocks on other, nearby faults. While there is no hard "cutoff" distance beyond which an earthquake is totally incapable of triggering an aftershock, the vast majority of aftershocks are located close to the mainshock. As a rule of thumb, we consider earthquakes to be

Catalog of significant historical earthquakes in the Central United States

USGS Publications Warehouse

Bakun, W.H.; Hopper, M.G.

2004-01-01

We use Modified Mercalli intensity assignments to estimate source locations and moment magnitude M for eighteen 19th-century and twenty early- 20th-century earthquakes in the central United States (CUS) for which estimates of M are otherwise not available. We use these estimates, and locations and M estimated elsewhere, to compile a catelog of significant historical earthquakes in the CUS. The 1811-1812 New Madrid earthquakes apparently dominated CUS seismicity in the first two decades of the 19th century. M5-6 earthquakes occurred in the New Madrid Seismic Zone in 1843 and 1878, but none have occurred since 1878. There has been persistent seismic activity in the Illinois Basin in southern Illinois and Indiana, with M > 5.0 earthquakes in 1895, 1909, 1917, 1968, and 1987. Four other M > 5.0 CUS historical earthquakes have occurred: in Kansas in 1867, in Nebraska in 1877, in Oklahoma in 1882, and in Kentucky in 1980.

Induced Earthquakes Are Not All Alike: Examples from Texas Since 2008 (Invited)

NASA Astrophysics Data System (ADS)

Frohlich, C.

2013-12-01

The EarthScope Transportable Array passed through Texas between 2008 and 2011, providing an opportunity to identify and accurately locate earthquakes near and/or within oil/gas fields and injection waste disposal operations. In five widely separated geographical locations, the results suggest seismic activity may be induced/triggered. However, the different regions exhibit different relationships between injection/production operations and seismic activity: In the Barnett Shale of northeast Texas, small earthquakes occurred only near higher-volume (volume rate > 150,000 BWPM) injection disposal wells. These included widely reported earthquakes occurring near Dallas-Fort Worth and Cleburne in 2008 and 2009. Near Alice in south Texas, M3.9 earthquakes occurred in 1997 and 2010 on the boundary of the Stratton Field, which had been highly productive for both oil and gas since the 1950's. Both earthquakes occurred during an era of net declining production, but their focal depths and location at the field boundary suggest an association with production activity. In the Eagle Ford of south central Texas, earthquakes occurred near wells following significant increases in extraction (water+produced oil) volumes as well as injection. The largest earthquake, the M4.8 Fashing earthquake of 20 October 2011, occurred after significant increases in extraction. In the Cogdell Field near Snyder (west Texas), a sequence of earthquakes beginning in 2006 followed significant increases in the injection of CO2 at nearby wells. The largest with M4.4 occurred on 11 September 2011. This is the largest known earthquake possibly attributable to CO2 injection. Near Timpson in east Texas a sequence of earthquakes beginning in 2008, including an M4.8 earthquake on 17 May 2012, occurred within three km of two high-volume injection disposal wells that had begun operation in 2007. These were the first known earthquakes at this location. In summary, the observations find possible induced

Fault Branching and Long-Term Earthquake Rupture Scenario for Strike-Slip Earthquake

NASA Astrophysics Data System (ADS)

Klinger, Y.; CHOI, J. H.; Vallage, A.

2017-12-01

Careful examination of surface rupture for large continental strike-slip earthquakes reveals that for the majority of earthquakes, at least one major branch is involved in the rupture pattern. Often, branching might be either related to the location of the epicenter or located toward the end of the rupture, and possibly related to the stopping of the rupture. In this work, we examine large continental earthquakes that show significant branches at different scales and for which ground surface rupture has been mapped in great details. In each case, rupture conditions are described, including dynamic parameters, past earthquakes history, and regional stress orientation, to see if the dynamic stress field would a priori favor branching. In one case we show that rupture propagation and branching are directly impacted by preexisting geological structures. These structures serve as pathways for the rupture attempting to propagate out of its shear plane. At larger scale, we show that in some cases, rupturing a branch might be systematic, hampering possibilities for the development of a larger seismic rupture. Long-term geomorphology hints at the existence of a strong asperity in the zone where the rupture branched off the main fault. There, no evidence of throughgoing rupture could be seen along the main fault, while the branch is well connected to the main fault. This set of observations suggests that for specific configurations, some rupture scenarios involving systematic branching are more likely than others.

The Dallas-Fort Worth Airport Earthquake Sequence: Seismicity Beyond Injection Period

NASA Astrophysics Data System (ADS)

Ogwari, Paul O.; DeShon, Heather R.; Hornbach, Matthew J.

2018-01-01

The 2008 Dallas-Fort Worth Airport earthquakes mark the beginning of seismicity rate changes linked to oil and gas operations in the central United States. We assess the spatial and temporal evolution of the sequence through December 2015 using template-based waveform correlation and relative location methods. We locate 400 earthquakes spanning 2008-2015 along a basement fault mapped as the Airport fault. The sequence exhibits temporally variable b values, and small-magnitude (m < 3.4) earthquakes spread northeast along strike over time. Pore pressure diffusion models indicate that the high-volume brine injection well located within 1 km of the 2008 earthquakes, although only operating from September 2008 to August 2009, contributes most significantly to long-term pressure perturbations, and hence stress changes, along the fault; a second long-operating, low-volume injector located 10 km north causes insufficient pressure changes. High-volume injection for a short time period near a critically stressed fault can induce long-lasting seismicity.

Earthquakes of Loihi submarine volcano and the Hawaiian hot spot.

USGS Publications Warehouse

Klein, F.W.

1982-01-01

Loihi is an active submarine volcano located 35km S of the island of Hawaii and may eventually grow to be the next and S most island in the Hawaiian chain. The Hawaiian Volcano Observatory recorded two major earthquake swarms located there in 1971-1972 and 1975 which were probably associated with submarine eruptions or intrusions. The swarms were located very close to Loihi's bathymetric summit, except for earthquakes during the second stage of the 1971-1972 swarm, which occurred well onto Loihi's SW flank. The flank earthquakes appear to have been triggered by the preceding activity and possible rifting along Loihi's long axis, similar to the rift-flank relationship at Kilauea volcano. Other changes accompanied the shift in locations from Loihi's summit to its flank, including a shift from burst to continuous seismicity, a rise in maximum magnitude, a change from small earthquake clusters to a larger elongated zone, a drop in b value, and a presumed shift from concentrated volcanic stresses to a more diffuse tectonic stress on Loihi's flank. - Author

Safety and survival in an earthquake

USGS Publications Warehouse

,

1969-01-01

Many earth scientists in this country and abroad are focusing their studies on the search for means of predicting impending earthquakes, but, as yet, an accurate prediction of the time and place of such an event cannot be made. From past experience, however, one can assume that earthquakes will continue to harass mankind and that they will occur most frequently in the areas where they have been relatively common in the past. In the United States, earthquakes can be expected to occur most frequently in the western states, particularly in Alaska, California, Washington, Oregon, Nevada, Utah, and Montana. The danger, however, is not confined to any one part of the country; major earthquakes have occurred at widely scattered locations.

Revised Earthquake Catalog and Relocated Hypocenters Near Fluid Injection Wells and the Waste Isolation Pilot Plant (WIPP) in Southeastern New Mexico

NASA Astrophysics Data System (ADS)

Edel, S.; Bilek, S. L.; Garcia, K.

2014-12-01

Induced seismicity is a class of crustal earthquakes resulting from human activities such as surface and underground mining, impoundment of reservoirs, withdrawal of fluids and gas from the subsurface, and injection of fluids into underground cavities. Within the Permian basin in southeastern New Mexico lies an active area of oil and gas production, as well as the Waste Isolation Pilot Plant (WIPP), a geologic nuclear waste repository located just east of Carlsbad, NM. Small magnitude earthquakes have been recognized in the area for many years, recorded by a network of short period vertical component seismometers operated by New Mexico Tech. However, for robust comparisons between the seismicity patterns and the injection well locations and rates, improved locations and a more complete catalog over time are necessary. We present results of earthquake relocations for this area by using data from the 3-component broadband EarthScope Flexible Array SIEDCAR experiment that operated in the area between 2008-2011. Relocated event locations tighten into a small cluster of ~38 km2, approximately 10 km from the nearest injection wells. The majority of events occurred at 10-12 km depth, given depth residuals of 1.7-3.6 km. We also present a newly developed more complete catalog of events from this area by using a waveform cross-correlation algorithm and the relocated events as templates. This allows us to detect smaller magnitude events that were previously undetected with the short period network data. The updated earthquake catalog is compared with geologic maps and cross sections to identify possible fault locations. The catalog is also compared with available well data on fluid injection and production. Our preliminary results suggest no obvious connection between seismic moment release, fluid injection, or production given the available monthly industry data. We do see evidence in the geologic and well data of previously unidentified faults in the area.

Catalog of earthquake hypocenters at Alaskan volcanoes: January 1 through December 31, 2002

USGS Publications Warehouse

Dixon, James P.; Stihler, Scott D.; Power, John A.; Tytgat, Guy; Moran, Seth C.; Sánchez, John; Estes, Steve; McNutt, Stephen R.; Paskievitch, John

2003-01-01

an EARTHWORM detection system. AVO located 7430 earthquakes during 2002 in the vicinity of the monitored volcanoes. This catalog includes: (1) a description of instruments deployed in the field and their locations; (2) a description of earthquake detection, recording, analysis, and data archival systems; (3) a description of velocity models used for earthquake locations; (4) a summary of earthquakes located in 2002; and (5) an accompanying UNIX tar-file with a summary of earthquake origin times, hypocenters, magnitudes, and location quality statistics; daily station usage statistics; and all HYPOELLIPSE files used to determine the earthquake locations in 2002.The AVO seismic network was used to monitor twenty-four volcanoes in real time in 2002. These include Mount Wrangell, Mount Spurr, Redoubt Volcano, Iliamna Volcano, Augustine Volcano, Katmai Volcanic Group (Snowy Mountain, Mount Griggs, Mount Katmai, Novarupta, Trident Volcano, Mount Mageik, Mount Martin), Aniakchak Crater, Mount Veniaminof, Pavlof Volcano, Mount Dutton, Isanotski Peaks, Shishaldin Volcano, Fisher Caldera, Westdahl Peak, Akutan Peak, Makushin Volcano, Great Sitkin Volcano, and Kanaga Volcano (Figure 1). Monitoring highlights in 2002 include an earthquake swarm at Great Sitkin Volcano in May-June; an earthquake swarm near Snowy Mountain in July-September; low frequency (1-3 Hz) tremor and long-period events at Mount Veniaminof in September-October and in December; and continuing volcanogenic seismic swarms at Shishaldin Volcano throughout the year. Instrumentation and data acquisition highlights in 2002 were the installation of a subnetwork on Okmok Volcano, the establishment of telemetry for the Mount Veniaminof subnetwork, and the change in the data acquisition system to an EARTHWORM detection system. AVO located 7430 earthquakes during 2002 in the vicinity of the monitored volcanoes.This catalog includes: (1) a description of instruments deployed in the field and their locations; (2) a

Location-Aware Mobile Learning of Spatial Algorithms

ERIC Educational Resources Information Center

Karavirta, Ville

2013-01-01

Learning an algorithm--a systematic sequence of operations for solving a problem with given input--is often difficult for students due to the abstract nature of the algorithms and the data they process. To help students understand the behavior of algorithms, a subfield in computing education research has focused on algorithm…

Real Time Earthquake Information System in Japan

NASA Astrophysics Data System (ADS)

Doi, K.; Kato, T.

2003-12-01

An early earthquake notification system in Japan had been developed by the Japan Meteorological Agency (JMA) as a governmental organization responsible for issuing earthquake information and tsunami forecasts. The system was primarily developed for prompt provision of a tsunami forecast to the public with locating an earthquake and estimating its magnitude as quickly as possible. Years after, a system for a prompt provision of seismic intensity information as indices of degrees of disasters caused by strong ground motion was also developed so that concerned governmental organizations can decide whether it was necessary for them to launch emergency response or not. At present, JMA issues the following kinds of information successively when a large earthquake occurs. 1) Prompt report of occurrence of a large earthquake and major seismic intensities caused by the earthquake in about two minutes after the earthquake occurrence. 2) Tsunami forecast in around three minutes. 3) Information on expected arrival times and maximum heights of tsunami waves in around five minutes. 4) Information on a hypocenter and a magnitude of the earthquake, the seismic intensity at each observation station, the times of high tides in addition to the expected tsunami arrival times in 5-7 minutes. To issue information above, JMA has established; - An advanced nationwide seismic network with about 180 stations for seismic wave observation and about 3,400 stations for instrumental seismic intensity observation including about 2,800 seismic intensity stations maintained by local governments, - Data telemetry networks via landlines and partly via a satellite communication link, - Real-time data processing techniques, for example, the automatic calculation of earthquake location and magnitude, the database driven method for quantitative tsunami estimation, and - Dissemination networks, via computer-to-computer communications and facsimile through dedicated telephone lines. JMA operationally

Determining Hypocentral Parameters for Local Earthquakes in 1-D Using a Genetic Algorithm and Two-point ray tracing

NASA Astrophysics Data System (ADS)

Kim, W.; Hahm, I.; Ahn, S. J.; Lim, D. H.

2005-12-01

This paper introduces a powerful method for determining hypocentral parameters for local earthquakes in 1-D using a genetic algorithm (GA) and two-point ray tracing. Using existing algorithms to determine hypocentral parameters is difficult, because these parameters can vary based on initial velocity models. We developed a new method to solve this problem by applying a GA to an existing algorithm, HYPO-71 (Lee and Larh, 1975). The original HYPO-71 algorithm was modified by applying two-point ray tracing and a weighting factor with respect to the takeoff angle at the source to reduce errors from the ray path and hypocenter depth. Artificial data, without error, were generated by computer using two-point ray tracing in a true model, in which velocity structure and hypocentral parameters were known. The accuracy of the calculated results was easily determined by comparing calculated and actual values. We examined the accuracy of this method for several cases by changing the true and modeled layer numbers and thicknesses. The computational results show that this method determines nearly exact hypocentral parameters without depending on initial velocity models. Furthermore, accurate and nearly unique hypocentral parameters were obtained, although the number of modeled layers and thicknesses differed from those in the true model. Therefore, this method can be a useful tool for determining hypocentral parameters in regions where reliable local velocity values are unknown. This method also provides the basic a priori information for 3-D studies. KEY -WORDS: hypocentral parameters, genetic algorithm (GA), two-point ray tracing

Ground Motion Response to a ML 4.3 Earthquake Using Co-Located Distributed Acoustic Sensing and Seismometer Arrays

DOE PAGES

Wang, Herbert F.; Zeng, Xiangfang; Miller, Douglas E.; ...

2018-03-17

The PoroTomo research team deployed two arrays of seismic sensors in a natural laboratory at Brady Hot Springs, Nevada in March 2016. The 1500 m (length) by 500 m (width) by 400 m (depth) volume of the laboratory overlies a geothermal reservoir. The surface Distributed Acoustic Sensing (DAS) array consisted of 8700 m of fiber-optic cable in a shallow trench, including 340 m in a well. The conventional seismometer array consisted of 238 three- component geophones. The DAS cable was laid out in three parallel zig-zag lines with line segments approximately 100 meters in length and geophones were spaced atmore » approximately 60- meter intervals. Both DAS and conventional geophones recorded continuously over 15 days during which a moderate-sized earthquake with a local magnitude of 4.3 was recorded on March 21, 2016. Its epicenter was approximately 150-km south-southeast of the laboratory. Several DAS line segments with co-located geophone stations were used to compare signal-to-noise (SNR) ratios in both time and frequency domains and to test relationships between DAS and geophone data. The ratios were typically within a factor of five of each other with DAS SNR often greater for P-wave but smaller for S-wave relative to geophone SNR. The SNRs measured for an earthquake can be better than for active sources, because the earthquake signal contains more low frequency energy and the noise level is also lower at those lower frequencies. Amplitudes of the sum of several DAS strain-rate waveforms matched the finite difference of two geophone waveforms reasonably well, as did the amplitudes of DAS strain waveforms with particle-velocity waveforms recorded by geophones. Similar agreement was found between DAS and geophone observations and synthetic strain seismograms. In conclusion, the combination of good SNR in the seismic frequency band, high-spatial density, large N, and highly accurate time control among individual sensors suggests that DAS arrays have potential to

Ground Motion Response to a ML 4.3 Earthquake Using Co-Located Distributed Acoustic Sensing and Seismometer Arrays

NASA Astrophysics Data System (ADS)

Wang, Herbert F.; Zeng, Xiangfang; Miller, Douglas E.; Fratta, Dante; Feigl, Kurt L.; Thurber, Clifford H.; Mellors, Robert J.

2018-03-01

The PoroTomo research team deployed two arrays of seismic sensors in a natural laboratory at Brady Hot Springs, Nevada in March 2016. The 1500 m (length) by 500 m (width) by 400 m (depth) volume of the laboratory overlies a geothermal reservoir. The surface Distributed Acoustic Sensing (DAS) array consisted of 8700 m of fiber-optic cable in a shallow trench, including 340 m in a well. The conventional seismometer array consisted of 238 three-component geophones. 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 60-m intervals. Both DAS and conventional geophones recorded continuously over 15 days during which a moderate-sized earthquake with a local magnitude of 4.3 was recorded on March 21, 2016. Its epicenter was approximately 150-km south-southeast of the laboratory. Several DAS line segments with co-located geophone stations were used to compare signal-to-noise (SNR) ratios in both time and frequency domains and to test relationships between DAS and geophone data. The ratios were typically within a factor of five of each other with DAS SNR often greater for P-wave but smaller for S-wave relative to geophone SNR. The SNRs measured for an earthquake can be better than for active sources, because the earthquake signal contains more low frequency energy and the noise level is also lower at those lower frequencies. Amplitudes of the sum of several DAS strain-rate waveforms matched the finite difference of two geophone waveforms reasonably well, as did the amplitudes of DAS strain waveforms with particle-velocity waveforms recorded by geophones. Similar agreement was found between DAS and geophone observations and synthetic strain seismograms. The combination of good SNR in the seismic frequency band, high-spatial density, large N, and highly accurate time control among individual sensors suggests that DAS arrays have potential to assume a role in earthquake

Ground Motion Response to a ML 4.3 Earthquake Using Co-Located Distributed Acoustic Sensing and Seismometer Arrays

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

Wang, Herbert F.; Zeng, Xiangfang; Miller, Douglas E.

The PoroTomo research team deployed two arrays of seismic sensors in a natural laboratory at Brady Hot Springs, Nevada in March 2016. The 1500 m (length) by 500 m (width) by 400 m (depth) volume of the laboratory overlies a geothermal reservoir. The surface Distributed Acoustic Sensing (DAS) array consisted of 8700 m of fiber-optic cable in a shallow trench, including 340 m in a well. The conventional seismometer array consisted of 238 three- component geophones. The DAS cable was laid out in three parallel zig-zag lines with line segments approximately 100 meters in length and geophones were spaced atmore » approximately 60- meter intervals. Both DAS and conventional geophones recorded continuously over 15 days during which a moderate-sized earthquake with a local magnitude of 4.3 was recorded on March 21, 2016. Its epicenter was approximately 150-km south-southeast of the laboratory. Several DAS line segments with co-located geophone stations were used to compare signal-to-noise (SNR) ratios in both time and frequency domains and to test relationships between DAS and geophone data. The ratios were typically within a factor of five of each other with DAS SNR often greater for P-wave but smaller for S-wave relative to geophone SNR. The SNRs measured for an earthquake can be better than for active sources, because the earthquake signal contains more low frequency energy and the noise level is also lower at those lower frequencies. Amplitudes of the sum of several DAS strain-rate waveforms matched the finite difference of two geophone waveforms reasonably well, as did the amplitudes of DAS strain waveforms with particle-velocity waveforms recorded by geophones. Similar agreement was found between DAS and geophone observations and synthetic strain seismograms. In conclusion, the combination of good SNR in the seismic frequency band, high-spatial density, large N, and highly accurate time control among individual sensors suggests that DAS arrays have potential to

Ground motion response to an ML 4.3 earthquake using co-located distributed acoustic sensing and seismometer arrays

NASA Astrophysics Data System (ADS)

Wang, Herbert F.; Zeng, Xiangfang; Miller, Douglas E.; Fratta, Dante; Feigl, Kurt L.; Thurber, Clifford H.; Mellors, Robert J.

2018-06-01

The PoroTomo research team deployed two arrays of seismic sensors in a natural laboratory at Brady Hot Springs, Nevada in March 2016. The 1500 m (length) × 500 m (width) × 400 m (depth) volume of the laboratory overlies a geothermal reservoir. The distributed acoustic sensing (DAS) array consisted of about 8400 m of fiber-optic cable in a shallow trench and 360 m in a well. The conventional seismometer array consisted of 238 shallowly buried three-component geophones. The DAS cable was laid out in three parallel zig-zag lines with line segments approximately 100 m in length and geophones were spaced at approximately 60 m intervals. Both DAS and conventional geophones recorded continuously over 15 d during which a moderate-sized earthquake with a local magnitude of 4.3 was recorded on 2016 March 21. Its epicentre was approximately 150 km south-southeast of the laboratory. Several DAS line segments with co-located geophone stations were used to compare signal-to-noise ratios (SNRs) in both time and frequency domains and to test relationships between DAS and geophone data. The ratios were typically within a factor of five of each other with DAS SNR often greater for P-wave but smaller for S-wave relative to geophone SNR. The SNRs measured for an earthquake can be better than for active sources because the earthquake signal contains more low-frequency energy and the noise level is also lower at those lower frequencies. Amplitudes of the sum of several DAS strain-rate waveforms matched the finite difference of two geophone waveforms reasonably well, as did the amplitudes of DAS strain waveforms with particle-velocity waveforms recorded by geophones. Similar agreement was found between DAS and geophone observations and synthetic strain seismograms. The combination of good SNR in the seismic frequency band, high-spatial density, large N and highly accurate time control among individual sensors suggests that DAS arrays have potential to assume a role in earthquake

Real-time earthquake monitoring using a search engine method

PubMed Central

Zhang, Jie; Zhang, Haijiang; Chen, Enhong; Zheng, Yi; Kuang, Wenhuan; Zhang, Xiong

2014-01-01

When an earthquake occurs, seismologists want to use recorded seismograms to infer its location, magnitude and source-focal mechanism as quickly as possible. If such information could be determined immediately, timely evacuations and emergency actions could be undertaken to mitigate earthquake damage. Current advanced methods can report the initial location and magnitude of an earthquake within a few seconds, but estimating the source-focal mechanism may require minutes to hours. Here we present an earthquake search engine, similar to a web search engine, that we developed by applying a computer fast search method to a large seismogram database to find waveforms that best fit the input data. Our method is several thousand times faster than an exact search. For an Mw 5.9 earthquake on 8 March 2012 in Xinjiang, China, the search engine can infer the earthquake’s parameters in <1 s after receiving the long-period surface wave data. PMID:25472861

Earthquakes triggered by silent slip events on Kīlauea volcano, Hawaii

USGS Publications Warehouse

Segall, Paul; Desmarais, Emily K.; Shelly, David; Miklius, Asta; Cervelli, Peter F.

2006-01-01

Slow-slip events, or ‘silent earthquakes’, have recently been discovered in a number of subduction zones including the Nankai trough1, 2, 3 in Japan, Cascadia4, 5, and Guerrero6 in Mexico, but the depths of these events have been difficult to determine from surface deformation measurements. Although it is assumed that these silent earthquakes are located along the plate megathrust, this has not been proved. Slow slip in some subduction zones is associated with non-volcanic tremor7, 8, but tremor is difficult to locate and may be distributed over a broad depth range9. Except for some events on the San Andreas fault10, slow-slip events have not yet been associated with high-frequency earthquakes, which are easily located. Here we report on swarms of high-frequency earthquakes that accompany otherwise silent slips on Kīlauea volcano, Hawaii. For the most energetic event, in January 2005, the slow slip began before the increase in seismicity. The temporal evolution of earthquakes is well explained by increased stressing caused by slow slip, implying that the earthquakes are triggered. The earthquakes, located at depths of 7–8 km, constrain the slow slip to be at comparable depths, because they must fall in zones of positive Coulomb stress change. Triggered earthquakes accompanying slow-slip events elsewhere might go undetected if background seismicity rates are low. Detection of such events would help constrain the depth of slow slip, and could lead to a method for quantifying the increased hazard during slow-slip events, because triggered events have the potential to grow into destructive earthquakes.

Toward real-time regional earthquake simulation of Taiwan earthquakes

NASA Astrophysics Data System (ADS)

Lee, S.; Liu, Q.; Tromp, J.; Komatitsch, D.; Liang, W.; Huang, B.

2013-12-01

We developed a Real-time Online earthquake Simulation system (ROS) to simulate regional earthquakes in Taiwan. The ROS uses a centroid moment tensor solution of seismic events from a Real-time Moment Tensor monitoring system (RMT), which provides all the point source parameters including the event origin time, hypocentral location, moment magnitude and focal mechanism within 2 minutes after the occurrence of an earthquake. Then, all of the source parameters are automatically forwarded to the ROS to perform an earthquake simulation, which is based on a spectral-element method (SEM). We have improved SEM mesh quality by introducing a thin high-resolution mesh layer near the surface to accommodate steep and rapidly varying topography. The mesh for the shallow sedimentary basin is adjusted to reflect its complex geometry and sharp lateral velocity contrasts. The grid resolution at the surface is about 545 m, which is sufficient to resolve topography and tomography data for simulations accurate up to 1.0 Hz. The ROS is also an infrastructural service, making online earthquake simulation feasible. Users can conduct their own earthquake simulation by providing a set of source parameters through the ROS webpage. For visualization, a ShakeMovie and ShakeMap are produced during the simulation. The time needed for one event is roughly 3 minutes for a 70 sec ground motion simulation. The ROS is operated online at the Institute of Earth Sciences, Academia Sinica (http://ros.earth.sinica.edu.tw/). Our long-term goal for the ROS system is to contribute to public earth science outreach and to realize seismic ground motion prediction in real-time.

Pre-earthquake magnetic pulses

NASA Astrophysics Data System (ADS)

Scoville, J.; Heraud, J.; Freund, F.

2015-08-01

A semiconductor model of rocks is shown to describe unipolar magnetic pulses, a phenomenon that has been observed prior to earthquakes. These pulses are suspected to be generated deep in the Earth's crust, in and around the hypocentral volume, days or even weeks before earthquakes. Their extremely long wavelength allows them to pass through kilometers of rock. Interestingly, when the sources of these pulses are triangulated, the locations coincide with the epicenters of future earthquakes. We couple a drift-diffusion semiconductor model to a magnetic field in order to describe the electromagnetic effects associated with electrical currents flowing within rocks. The resulting system of equations is solved numerically and it is seen that a volume of rock may act as a diode that produces transient currents when it switches bias. These unidirectional currents are expected to produce transient unipolar magnetic pulses similar in form, amplitude, and duration to those observed before earthquakes, and this suggests that the pulses could be the result of geophysical semiconductor processes.

Earthquake Early Warning: User Education and Designing Effective Messages

NASA Astrophysics Data System (ADS)

Burkett, E. R.; Sellnow, D. D.; Jones, L.; Sellnow, T. L.

2014-12-01

The U.S. Geological Survey (USGS) and partners are transitioning from test-user trials of a demonstration earthquake early warning system (ShakeAlert) to deciding and preparing how to implement the release of earthquake early warning information, alert messages, and products to the public and other stakeholders. An earthquake early warning system uses seismic station networks to rapidly gather information about an occurring earthquake and send notifications to user devices ahead of the arrival of potentially damaging ground shaking at their locations. Earthquake early warning alerts can thereby allow time for actions to protect lives and property before arrival of damaging shaking, if users are properly educated on how to use and react to such notifications. A collaboration team of risk communications researchers and earth scientists is researching the effectiveness of a chosen subset of potential earthquake early warning interface designs and messages, which could be displayed on a device such as a smartphone. Preliminary results indicate, for instance, that users prefer alerts that include 1) a map to relate their location to the earthquake and 2) instructions for what to do in response to the expected level of shaking. A number of important factors must be considered to design a message that will promote appropriate self-protective behavior. While users prefer to see a map, how much information can be processed in limited time? Are graphical representations of wavefronts helpful or confusing? The most important factor to promote a helpful response is the predicted earthquake intensity, or how strong the expected shaking will be at the user's location. Unlike Japanese users of early warning, few Californians are familiar with the earthquake intensity scale, so we are exploring how differentiating instructions between intensity levels (e.g., "Be aware" for lower shaking levels and "Drop, cover, hold on" at high levels) can be paired with self-directed supplemental

Turkish Compulsory Earthquake Insurance (TCIP)

NASA Astrophysics Data System (ADS)

Erdik, M.; Durukal, E.; Sesetyan, K.

2009-04-01

Through a World Bank project a government-sponsored Turkish Catastrophic Insurance Pool (TCIP) is created in 2000 with the essential aim of transferring the government's financial burden of replacing earthquake-damaged housing to international reinsurance and capital markets. Providing coverage to about 2.9 Million homeowners TCIP is the largest insurance program in the country with about 0.5 Billion USD in its own reserves and about 2.3 Billion USD in total claims paying capacity. The total payment for earthquake damage since 2000 (mostly small, 226 earthquakes) amounts to about 13 Million USD. The country-wide penetration rate is about 22%, highest in the Marmara region (30%) and lowest in the south-east Turkey (9%). TCIP is the sole-source provider of earthquake loss coverage up to 90,000 USD per house. The annual premium, categorized on the basis of earthquake zones type of structure, is about US90 for a 100 square meter reinforced concrete building in the most hazardous zone with 2% deductible. The earthquake engineering related shortcomings of the TCIP is exemplified by fact that the average rate of 0.13% (for reinforced concrete buildings) with only 2% deductible is rather low compared to countries with similar earthquake exposure. From an earthquake engineering point of view the risk underwriting (Typification of housing units to be insured, earthquake intensity zonation and the sum insured) of the TCIP needs to be overhauled. Especially for large cities, models can be developed where its expected earthquake performance (and consequently the insurance premium) can be can be assessed on the basis of the location of the unit (microzoned earthquake hazard) and basic structural attributes (earthquake vulnerability relationships). With such an approach, in the future the TCIP can contribute to the control of construction through differentiation of premia on the basis of earthquake vulnerability.

Linking giant earthquakes with the subduction of oceanic fracture zones

NASA Astrophysics Data System (ADS)

Landgrebe, T. C.; Müller, R. D.; EathByte Group

2011-12-01

Giant subduction earthquakes are known to occur in areas not previously identified as prone to high seismic risk. This highlights the need to better identify subduction zone segments potentially dominated by relatively long (up to 1000 years and more) recurrence times of giant earthquakes. Global digital data sets represent a promising source of information for a multi-dimensional earthquake hazard analysis. We combine the NGDC global Significant Earthquakes database with a global strain rate map, gridded ages of the ocean floor, and a recently produced digital data set for oceanic fracture zones, major aseismic ridges and volcanic chains to investigate the association of earthquakes as a function of magnitude with age of the downgoing slab and convergence rates. We use a so-called Top-N recommendation method, a technology originally developed to search, sort, classify, and filter very large and often statistically skewed data sets on the internet, to analyse the association of subduction earthquakes sorted by magnitude with key parameters. The Top-N analysis is used to progressively assess how strongly particular "tectonic niche" locations (e.g. locations along subduction zones intersected with aseismic ridges or volcanic chains) are associated with sets of earthquakes in sorted order in a given magnitude range. As the total number N of sorted earthquakes is increased, by progressively including smaller-magnitude events, the so-called recall is computed, defined as the number of Top-N earthquakes associated with particular target areas divided by N. The resultant statistical measure represents an intuitive description of the effectiveness of a given set of parameters to account for the location of significant earthquakes on record. We use this method to show that the occurrence of great (magnitude ≥ 8) earthquakes on overriding plate segments is strongly biased towards intersections of oceanic fracture zones with subduction zones. These intersection regions are

Limiting the effects of earthquakes on gravitational-wave interferometers

USGS Publications Warehouse

Coughlin, Michael; Earle, Paul; Harms, Jan; Biscans, Sebastien; Buchanan, Christopher; Coughlin, Eric; Donovan, Fred; Fee, Jeremy; Gabbard, Hunter; Guy, Michelle; Mukund, Nikhil; Perry, Matthew

2017-01-01

Ground-based gravitational wave interferometers such as the Laser Interferometer Gravitational-wave Observatory (LIGO) are susceptible to ground shaking from high-magnitude teleseismic events, which can interrupt their operation in science mode and significantly reduce their duty cycle. It can take several hours for a detector to stabilize enough to return to its nominal state for scientific observations. The down time can be reduced if advance warning of impending shaking is received and the impact is suppressed in the isolation system with the goal of maintaining stable operation even at the expense of increased instrumental noise. Here, we describe an early warning system for modern gravitational-wave observatories. The system relies on near real-time earthquake alerts provided by the U.S. Geological Survey (USGS) and the National Oceanic and Atmospheric Administration (NOAA). Preliminary low latency hypocenter and magnitude information is generally available in 5 to 20 min of a significant earthquake depending on its magnitude and location. The alerts are used to estimate arrival times and ground velocities at the gravitational-wave detectors. In general, 90% of the predictions for ground-motion amplitude are within a factor of 5 of measured values. The error in both arrival time and ground-motion prediction introduced by using preliminary, rather than final, hypocenter and magnitude information is minimal. By using a machine learning algorithm, we develop a prediction model that calculates the probability that a given earthquake will prevent a detector from taking data. Our initial results indicate that by using detector control configuration changes, we could prevent interruption of operation from 40 to 100 earthquake events in a 6-month time-period.

Limiting the effects of earthquakes on gravitational-wave interferometers

NASA Astrophysics Data System (ADS)

Coughlin, Michael; Earle, Paul; Harms, Jan; Biscans, Sebastien; Buchanan, Christopher; Coughlin, Eric; Donovan, Fred; Fee, Jeremy; Gabbard, Hunter; Guy, Michelle; Mukund, Nikhil; Perry, Matthew

2017-02-01

Ground-based gravitational wave interferometers such as the Laser Interferometer Gravitational-wave Observatory (LIGO) are susceptible to ground shaking from high-magnitude teleseismic events, which can interrupt their operation in science mode and significantly reduce their duty cycle. It can take several hours for a detector to stabilize enough to return to its nominal state for scientific observations. The down time can be reduced if advance warning of impending shaking is received and the impact is suppressed in the isolation system with the goal of maintaining stable operation even at the expense of increased instrumental noise. Here, we describe an early warning system for modern gravitational-wave observatories. The system relies on near real-time earthquake alerts provided by the U.S. Geological Survey (USGS) and the National Oceanic and Atmospheric Administration (NOAA). Preliminary low latency hypocenter and magnitude information is generally available in 5 to 20 min of a significant earthquake depending on its magnitude and location. The alerts are used to estimate arrival times and ground velocities at the gravitational-wave detectors. In general, 90% of the predictions for ground-motion amplitude are within a factor of 5 of measured values. The error in both arrival time and ground-motion prediction introduced by using preliminary, rather than final, hypocenter and magnitude information is minimal. By using a machine learning algorithm, we develop a prediction model that calculates the probability that a given earthquake will prevent a detector from taking data. Our initial results indicate that by using detector control configuration changes, we could prevent interruption of operation from 40 to 100 earthquake events in a 6-month time-period.

Geometry and earthquake potential of the shoreline fault, central California

USGS Publications Warehouse

Hardebeck, Jeanne L.

2013-01-01

The Shoreline fault is a vertical strike‐slip fault running along the coastline near San Luis Obispo, California. Much is unknown about the Shoreline fault, including its slip rate and the details of its geometry. Here, I study the geometry of the Shoreline fault at seismogenic depth, as well as the adjacent section of the offshore Hosgri fault, using seismicity relocations and earthquake focal mechanisms. The Optimal Anisotropic Dynamic Clustering (OADC) algorithm (Ouillon et al., 2008) is used to objectively identify the simplest planar fault geometry that fits all of the earthquakes to within their location uncertainty. The OADC results show that the Shoreline fault is a single continuous structure that connects to the Hosgri fault. Discontinuities smaller than about 1 km may be undetected, but would be too small to be barriers to earthquake rupture. The Hosgri fault dips steeply to the east, while the Shoreline fault is essentially vertical, so the Hosgri fault dips towards and under the Shoreline fault as the two faults approach their intersection. The focal mechanisms generally agree with pure right‐lateral strike‐slip on the OADC planes, but suggest a non‐planar Hosgri fault or another structure underlying the northern Shoreline fault. The Shoreline fault most likely transfers strike‐slip motion between the Hosgri fault and other faults of the Pacific–North America plate boundary system to the east. A hypothetical earthquake rupturing the entire known length of the Shoreline fault would have a moment magnitude of 6.4–6.8. A hypothetical earthquake rupturing the Shoreline fault and the section of the Hosgri fault north of the Hosgri–Shoreline junction would have a moment magnitude of 7.2–7.5.

Aftershocks and triggered events of the Great 1906 California earthquake

USGS Publications Warehouse

Meltzner, A.J.; Wald, D.J.

2003-01-01

The San Andreas fault is the longest fault in California and one of the longest strike-slip faults in the world, yet little is known about the aftershocks following the most recent great event on the San Andreas, the Mw 7.8 San Francisco earthquake on 18 April 1906. We conducted a study to locate and to estimate magnitudes for the largest aftershocks and triggered events of this earthquake. We examined existing catalogs and historical documents for the period April 1906 to December 1907, compiling data on the first 20 months of the aftershock sequence. We grouped felt reports temporally and assigned modified Mercalli intensities for the larger events based on the descriptions judged to be the most reliable. For onshore and near-shore events, a grid-search algorithm (derived from empirical analysis of modern earthquakes) was used to find the epicentral location and magnitude most consistent with the assigned intensities. For one event identified as far offshore, the event's intensity distribution was compared with those of modern events, in order to contrain the event's location and magnitude. The largest aftershock within the study period, an M ???6.7 event, occurred ???100 km west of Eureka on 23 April 1906. Although not within our study period, another M ???6.7 aftershock occurred near Cape Mendocino on 28 October 1909. Other significant aftershocks included an M ???5.6 event near San Juan Bautista on 17 May 1906 and an M ???6.3 event near Shelter Cove on 11 August 1907. An M ???4.9 aftershock occurred on the creeping segment of the San Andreas fault (southeast of the mainshock rupture) on 6 July 1906. The 1906 San Francisco earthquake also triggered events in southern California (including separate events in or near the Imperial Valley, the Pomona Valley, and Santa Monica Bay), in western Nevada, in southern central Oregon, and in western Arizona, all within 2 days of the mainshock. Of these trigerred events, the largest were an M ???6.1 earthquake near Brawley

Space technologies for short-term earthquake warning

NASA Astrophysics Data System (ADS)

Pulinets, S.

Recent theoretical and experimental studies explicitly demonstrated the ability of space technologies to identify and monitor the specific variations at near-earth space plasma, atmosphere and ground surface associated with approaching severe earthquakes (named as earthquake precursors) appearing several days (from 1 to 5) before the seismic shock over the seismically active areas. Several countries and private companies are in the stage of preparation (or already launched) the dedicated spacecrafts for monitoring of the earthquake precursors from space and for short-term earthquake prediction. The present paper intends to outline the optimal algorithm for creation of the space-borne system for the earthquake precursors monitoring and for short-term earthquake prediction. It takes into account the following considerations: Selection of the precursors in the terms of priority, taking into account their statistical and physical parameters Configuration of the spacecraft payload Configuration of the satellite constellation (orbit selection, satellite distribution, operation schedule) Proposal of different options (cheap microsatellite or comprehensive multisatellite constellation) Taking into account that the most promising are the ionospheric precursors of earthquakes, the special attention will be devoted to the radiophysical techniques of the ionosphere monitoring. The advantages and disadvantages of such technologies as vertical sounding, in-situ probes, ionosphere tomography, GPS TEC and GPS MET technologies will be considered.

Space technologies for short-term earthquake warning

NASA Astrophysics Data System (ADS)

Pulinets, S. A.

Recent theoretical and experimental studies explicitly demonstrated the ability of space technologies to identify and monitor the specific variations at near-earth space plasma, atmosphere and ground surface associated with approaching severe earthquakes (named as earthquake precursors) which appear several days (from 1 to 5) before the seismic shock over the seismically active areas. Several countries and private companies are in the stage of preparation (or already launched) the dedicated spacecrafts for monitoring of the earthquake precursors from space and for short-term earthquake prediction. The present paper intends to outline the optimal algorithm for creation of the space-borne system for the earthquake precursors monitoring and for short-term earthquake prediction. It takes into account the following: Selection of the precursors in the terms of priority, considering their statistical and physical parameters.Configuration of the spacecraft payload.Configuration of the satellite constellation (orbit selection, satellite distribution, operation schedule).Different options of the satellite systems (cheap microsatellite or comprehensive multisatellite constellation). Taking into account that the most promising are the ionospheric precursors of earthquakes, the special attention is devoted to the radiophysical techniques of the ionosphere monitoring. The advantages and disadvantages of such technologies as vertical sounding, in-situ probes, ionosphere tomography, GPS TEC and GPS MET technologies are considered.

Pre-Earthquake Unipolar Electromagnetic Pulses

NASA Astrophysics Data System (ADS)

Scoville, J.; Freund, F.

2013-12-01

Transient ultralow frequency (ULF) electromagnetic (EM) emissions have been reported to occur before earthquakes [1,2]. They suggest powerful transient electric currents flowing deep in the crust [3,4]. Prior to the M=5.4 Alum Rock earthquake of Oct. 21, 2007 in California a QuakeFinder triaxial search-coil magnetometer located about 2 km from the epicenter recorded unusual unipolar pulses with the approximate shape of a half-cycle of a sine wave, reaching amplitudes up to 30 nT. The number of these unipolar pulses increased as the day of the earthquake approached. These pulses clearly originated around the hypocenter. The same pulses have since been recorded prior to several medium to moderate earthquakes in Peru, where they have been used to triangulate the location of the impending earthquakes [5]. To understand the mechanism of the unipolar pulses, we first have to address the question how single current pulses can be generated deep in the Earth's crust. Key to this question appears to be the break-up of peroxy defects in the rocks in the hypocenter as a result of the increase in tectonic stresses prior to an earthquake. We investigate the mechanism of the unipolar pulses by coupling the drift-diffusion model of semiconductor theory to Maxwell's equations, thereby producing a model describing the rock volume that generates the pulses in terms of electromagnetism and semiconductor physics. The system of equations is then solved numerically to explore the electromagnetic radiation associated with drift-diffusion currents of electron-hole pairs. [1] Sharma, A. K., P. A. V., and R. N. Haridas (2011), Investigation of ULF magnetic anomaly before moderate earthquakes, Exploration Geophysics 43, 36-46. [2] Hayakawa, M., Y. Hobara, K. Ohta, and K. Hattori (2011), The ultra-low-frequency magnetic disturbances associated with earthquakes, Earthquake Science, 24, 523-534. [3] Bortnik, J., T. E. Bleier, C. Dunson, and F. Freund (2010), Estimating the seismotelluric current

The persistence of directivity in small earthquakes

USGS Publications Warehouse

Boatwright, J.

2007-01-01

We derive a simple inversion of peak ground acceleration (PGA) or peak ground velocity (PGV) for rupture direction and rupture velocity and then test this inversion on the peak motions obtained from seven 3.5 ??? M ??? 4.1 earthquakes that occurred in two clusters in November 2002 and February 2003 near San Ramon, California. These clusters were located on two orthogonal strike-slip faults so that the events share the same approximate focal mechanism but not the same fault plane. Three earthquakes exhibit strong directivity, but the other four earthquakes exhibit relatively weak directivity. We use the residual PGAs and PGVs from the other six events to determine station corrections for each earthquake. The inferred rupture directions unambiguously identify the fault plane for the three earthquakes with strong directivity and for three of the four earthquakes with weak directivity. The events with strong directivity have fast rupture velocities (0.63????? v ??? 0.87??); the events with weak directivity either rupture more slowly (0.17????? v ???0.35??) or bilaterally. The simple unilateral inversion cannot distinguish between slow and bilateral ruptures: adding a bilateral rupture component degrades the fit of the rupture directions to the fault planes. By comparing PGAs from the events with strong and weak directivity, we show how an up-dip rupture in small events can distort the attenuation of peak ground motion with distance. When we compare the rupture directions of the earthquakes to the location of aftershocks in the two clusters, we find than almost all the aftershocks of the three earthquakes with strong directivity occur within 70?? of the direction of rupture.

Application of τc*Pd for identifying damaging earthquakes for earthquake early warning

NASA Astrophysics Data System (ADS)

Huang, P. L.; Lin, T. L.; Wu, Y. M.

2014-12-01

Earthquake Early Warning System (EEWS) is an effective approach to mitigate earthquake damage. In this study, we used the seismic record by the Kiban Kyoshin network (KiK-net), because it has dense station coverage and co-located borehole strong-motion seismometers along with the free-surface strong-motion seismometers. We used inland earthquakes with moment magnitude (Mw) from 5.0 to 7.3 between 1998 and 2012. We choose 135 events and 10950 strong ground accelerograms recorded by the 696 strong ground accelerographs. Both the free-surface and the borehole data are used to calculate τc and Pd, respectively. The results show that τc*Pd has a good correlation with PGV and is a robust parameter for assessing the potential of damaging earthquake. We propose the value of τc*Pd determined from seconds after the arrival of P wave could be a threshold for the on-site type of EEW.

The pathway to earthquake early warning in the US

NASA Astrophysics Data System (ADS)

Allen, R. M.; Given, D. D.; Heaton, T. H.; Vidale, J. E.; West Coast Earthquake Early Warning Development Team

2013-05-01

The development of earthquake early warning capabilities in the United States is now accelerating and expanding as the technical capability to provide warning is demonstrated and additional funding resources are making it possible to expand the current testing region to the entire west coast (California, Oregon and Washington). Over the course of the next two years we plan to build a prototype system that will provide a blueprint for a full public system in the US. California currently has a demonstrations warning system, ShakeAlert, that provides alerts to a group of test users from the public and private sector. These include biotech companies, technology companies, the entertainment industry, the transportation sector, and the emergency planning and response community. Most groups are currently in an evaluation mode, receiving the alerts and developing protocols for future response. The Bay Area Rapid Transit (BART) system is the one group who has now implemented an automated response to the warning system. BART now stops trains when an earthquake of sufficient size is detected. Research and development also continues to develop improved early warning algorithms to better predict the distribution of shaking in large earthquakes when the finiteness of the source becomes important. The algorithms under development include the use of both seismic and GPS instrumentation and integration with existing point source algorithms. At the same time, initial testing and development of algorithms in and for the Pacific Northwest is underway. In this presentation we will review the current status of the systems, highlight the new research developments, and lay out a pathway to a full public system for the US west coast. The research and development described is ongoing at Caltech, UC Berkeley, University of Washington, ETH Zurich, Southern California Earthquake Center, and the US Geological Survey, and is funded by the Gordon and Betty Moore Foundation and the US Geological

A mobile agent-based moving objects indexing algorithm in location based service

NASA Astrophysics Data System (ADS)

Fang, Zhixiang; Li, Qingquan; Xu, Hong

2006-10-01

This paper will extends the advantages of location based service, specifically using their ability to management and indexing the positions of moving object, Moreover with this objective in mind, a mobile agent-based moving objects indexing algorithm is proposed in this paper to efficiently process indexing request and acclimatize itself to limitation of location based service environment. The prominent feature of this structure is viewing moving object's behavior as the mobile agent's span, the unique mapping between the geographical position of moving objects and span point of mobile agent is built to maintain the close relationship of them, and is significant clue for mobile agent-based moving objects indexing to tracking moving objects.

Earthquake damage orientation to infer seismic parameters in archaeological sites and historical earthquakes

NASA Astrophysics Data System (ADS)

Martín-González, Fidel

2018-01-01

Studies to provide information concerning seismic parameters and seismic sources of historical and archaeological seismic events are used to better evaluate the seismic hazard of a region. This is of especial interest when no surface rupture is recorded or the seismogenic fault cannot be identified. The orientation pattern of the earthquake damage (ED) (e.g., fallen columns, dropped key stones) that affected architectonic elements of cities after earthquakes has been traditionally used in historical and archaeoseismological studies to infer seismic parameters. However, in the literature depending on the authors, the parameters that can be obtained are contradictory (it has been proposed: the epicenter location, the orientation of the P-waves, the orientation of the compressional strain and the fault kinematics) and authors even question these relations with the earthquake damage. The earthquakes of Lorca in 2011, Christchurch in 2011 and Emilia Romagna in 2012 present an opportunity to measure systematically a large number and wide variety of earthquake damage in historical buildings (the same structures that are used in historical and archaeological studies). The damage pattern orientation has been compared with modern instrumental data, which is not possible in historical and archaeoseismological studies. From measurements and quantification of the orientation patterns in the studied earthquakes, it is observed that there is a systematic pattern of the earthquake damage orientation (EDO) in the proximity of the seismic source (fault trace) (<10 km). The EDO in these earthquakes is normal to the fault trend (±15°). This orientation can be generated by a pulse of motion that in the near fault region has a distinguishable acceleration normal to the fault due to the polarization of the S-waves. Therefore, the earthquake damage orientation could be used to estimate the seismogenic fault trend of historical earthquakes studies where no instrumental data are available.

An artificial bee colony algorithm for locating the critical slip surface in slope stability analysis

NASA Astrophysics Data System (ADS)

Kang, Fei; Li, Junjie; Ma, Zhenyue

2013-02-01

Determination of the critical slip surface with the minimum factor of safety of a slope is a difficult constrained global optimization problem. In this article, an artificial bee colony algorithm with a multi-slice adjustment method is proposed for locating the critical slip surfaces of soil slopes, and the Spencer method is employed to calculate the factor of safety. Six benchmark examples are presented to illustrate the reliability and efficiency of the proposed technique, and it is also compared with some well-known or recent algorithms for the problem. The results show that the new algorithm is promising in terms of accuracy and efficiency.

Data mining of atmospheric parameters associated with coastal earthquakes

NASA Astrophysics Data System (ADS)

Cervone, Guido

Earthquakes are natural hazards that pose a serious threat to society and the environment. A single earthquake can claim thousands of lives, cause damages for billions of dollars, destroy natural landmarks and render large territories uninhabitable. Studying earthquakes and the processes that govern their occurrence, is of fundamental importance to protect lives, properties and the environment. Recent studies have shown that anomalous changes in land, ocean and atmospheric parameters occur prior to earthquakes. The present dissertation introduces an innovative methodology and its implementation to identify anomalous changes in atmospheric parameters associated with large coastal earthquakes. Possible geophysical mechanisms are discussed in view of the close interaction between the lithosphere, the hydrosphere and the atmosphere. The proposed methodology is a multi strategy data mining approach which combines wavelet transformations, evolutionary algorithms, and statistical analysis of atmospheric data to analyze possible precursory signals. One dimensional wavelet transformations and statistical tests are employed to identify significant singularities in the data, which may correspond to anomalous peaks due to the earthquake preparatory processes. Evolutionary algorithms and other localized search strategies are used to analyze the spatial and temporal continuity of the anomalies detected over a large area (about 2000 km2), to discriminate signals that are most likely associated with earthquakes from those due to other, mostly atmospheric, phenomena. Only statistically significant singularities occurring within a very short time of each other, and which tract a rigorous geometrical path related to the geological properties of the epicentral area, are considered to be associated with a seismic event. A program called CQuake was developed to implement and validate the proposed methodology. CQuake is a fully automated, real time semi-operational system, developed to

Combining historical and geomorphological information to investigate earthquake induced landslides

NASA Astrophysics Data System (ADS)

Cardinali, M.; Ferrari, G.; Galli, M.; Guidoboni, E.; Guzzetti, F.

2003-04-01

Landslides are caused by many different triggers, including earthquakes. In Italy, a detailed new generation catalogue of information on historical earthquakes for the period 461 B.C to 1997 is available (Catalogue of Strong Italian Earthquakes from 461 B.C. to 1997, ING-SGA 2000). The catalogue lists 548 earthquakes and provides information on a total of about 450 mass-movements triggered by 118 seismic events. The information on earthquake-induced landslides listed in the catalogue was obtained through the careful scrutiny of historical documents and chronicles, but was rarely checked in the field. We report on an attempt to combine the available historical information on landslides caused by earthquakes with standard geomorphological techniques, including the interpretation of aerial photographs and field surveys, to better determine the location, type and distribution of seismically induced historical slope failures. We present four examples in the Central Apennines. The first example describes a rock slide triggered by the 1279 April 30 Umbria-Marche Apennines earthquake (Io = IX) at Serravalle, along the Chienti River (Central Italy). The landslide is the oldest known earthquake-induced slope failure in Italy. The second example describes the location of 2 large landslides triggered by the 1584 September 10 earthquake (Io = IX) at San Piero in Bagno, along the Savio River (Northern Italy). The landslides were subsequently largely modified by mass movements occurred on 1855 making the recognition of the original seismically induced failures difficult, if not impossible. In the third example we present the geographical distribution of the available information on landslide events triggered by 8 earthquakes in Central Valnerina, in the period 1703 to 1979. A comparison with the location of landslides triggered by the September-October 1997 Umbria-Marche earthquake sequence is presented. The fourth example describes the geographical distribution of the available

Induced earthquake during the 2016 Kumamoto earthquake (Mw7.0): Importance of real-time shake monitoring for Earthquake Early Warning

NASA Astrophysics Data System (ADS)

Hoshiba, M.; Ogiso, M.

2016-12-01

hypocenter location and magnitude. Because we want to predict ground shaking in EEW, we should more focus on monitoring of ground shaking. Experience of the induced earthquake also indicates the importance of the real-time monitor of ground shaking for making EEW more rapid and precise.

Migrating swarms of brittle-failure earthquakes in the lower crust beneath Mammoth Mountain, California

USGS Publications Warehouse

Shelly, D.R.; Hill, D.P.

2011-01-01

Brittle-failure earthquakes in the lower crust, where high pressures and temperatures would typically promote ductile deformation, are relatively rare but occasionally observed beneath active volcanic centers. Where they occur, these earthquakes provide a rare opportunity to observe volcanic processes in the lower crust, such as fluid injection and migration, which may induce brittle faulting under these conditions. Here, we examine recent short-duration earthquake swarms deep beneath the southwestern margin of Long Valley Caldera, near Mammoth Mountain. We focus in particular on a swarm that occurred September 29-30, 2009. To maximally illuminate the spatial-temporal progression, we supplement catalog events by detecting additional small events with similar waveforms in the continuous data, achieving up to a 10-fold increase in the number of locatable events. We then relocate all events, using cross-correlation and a double-difference algorithm. We find that the 2009 swarm exhibits systematically decelerating upward migration, with hypocenters shallowing from 21 to 19 km depth over approximately 12 hours. This relatively high migration rate, combined with a modest maximum magnitude of 1.4 in this swarm, suggests the trigger might be ascending CO2 released from underlying magma.

Investigation of earthquake factor for optimum tuned mass dampers

NASA Astrophysics Data System (ADS)

Nigdeli, Sinan Melih; Bekdaş, Gebrail

2012-09-01

In this study the optimum parameters of tuned mass dampers (TMD) are investigated under earthquake excitations. An optimization strategy was carried out by using the Harmony Search (HS) algorithm. HS is a metaheuristic method which is inspired from the nature of musical performances. In addition to the HS algorithm, the results of the optimization objective are compared with the results of the other documented method and the corresponding results are eliminated. In that case, the best optimum results are obtained. During the optimization, the optimum TMD parameters were searched for single degree of freedom (SDOF) structure models with different periods. The optimization was done for different earthquakes separately and the results were compared.

Fault parameter constraints using relocated earthquakes: A validation of first-motion focal-mechanism data

USGS Publications Warehouse

Kilb, Debi; Hardebeck, J.L.

2006-01-01

We estimate the strike and dip of three California fault segments (Calaveras, Sargent, and a portion of the San Andreas near San Jaun Bautistia) based on principle component analysis of accurately located microearthquakes. We compare these fault orientations with two different first-motion focal mechanism catalogs: the Northern California Earthquake Data Center (NCEDC) catalog, calculated using the FPFIT algorithm (Reasenberg and Oppenheimer, 1985), and a catalog created using the HASH algorithm that tests mechanism stability relative to seismic velocity model variations and earthquake location (Hardebeck and Shearer, 2002). We assume any disagreement (misfit >30° in strike, dip, or rake) indicates inaccurate focal mechanisms in the catalogs. With this assumption, we can quantify the parameters that identify the most optimally constrained focal mechanisms. For the NCEDC/FPFIT catalogs, we find that the best quantitative discriminator of quality focal mechanisms is the station distribution ratio (STDR) parameter, an indicator of how the stations are distributed about the focal sphere. Requiring STDR > 0.65 increases the acceptable mechanisms from 34%–37% to 63%–68%. This suggests stations should be uniformly distributed surrounding, rather than aligning, known fault traces. For the HASH catalogs, the fault plane uncertainty (FPU) parameter is the best discriminator, increasing the percent of acceptable mechanisms from 63%–78% to 81%–83% when FPU ≤ 35°. The overall higher percentage of acceptable mechanisms and the usefulness of the formal uncertainty in identifying quality mechanisms validate the HASH approach of testing for mechanism stability.

Statistical earthquake focal mechanism forecasts

NASA Astrophysics Data System (ADS)

Kagan, Yan Y.; Jackson, David D.

2014-04-01

Forecasts of the focal mechanisms of future shallow (depth 0-70 km) earthquakes are important for seismic hazard estimates and Coulomb stress, and other models of earthquake occurrence. Here we report on a high-resolution global forecast of earthquake rate density as a function of location, magnitude and focal mechanism. In previous publications we reported forecasts of 0.5° spatial resolution, covering the latitude range from -75° to +75°, based on the Global Central Moment Tensor earthquake catalogue. In the new forecasts we have improved the spatial resolution to 0.1° and the latitude range from pole to pole. Our focal mechanism estimates require distance-weighted combinations of observed focal mechanisms within 1000 km of each gridpoint. Simultaneously, we calculate an average rotation angle between the forecasted mechanism and all the surrounding mechanisms, using the method of Kagan & Jackson proposed in 1994. This average angle reveals the level of tectonic complexity of a region and indicates the accuracy of the prediction. The procedure becomes problematical where longitude lines are not approximately parallel, and where shallow earthquakes are so sparse that an adequate sample spans very large distances. North or south of 75°, the azimuths of points 1000 km away may vary by about 35°. We solved this problem by calculating focal mechanisms on a plane tangent to the Earth's surface at each forecast point, correcting for the rotation of the longitude lines at the locations of earthquakes included in the averaging. The corrections are negligible between -30° and +30° latitude, but outside that band uncorrected rotations can be significantly off. Improved forecasts at 0.5° and 0.1° resolution are posted at http://eq.ess.ucla.edu/kagan/glob_gcmt_index.html.

Implementing a C++ Version of the Joint Seismic-Geodetic Algorithm for Finite-Fault Detection and Slip Inversion for Earthquake Early Warning

NASA Astrophysics Data System (ADS)

Smith, D. E.; Felizardo, C.; Minson, S. E.; Boese, M.; Langbein, J. O.; Guillemot, C.; Murray, J. R.

2015-12-01

The earthquake early warning (EEW) systems in California and elsewhere can greatly benefit from algorithms that generate estimates of finite-fault parameters. These estimates could significantly improve real-time shaking calculations and yield important information for immediate disaster response. Minson et al. (2015) determined that combining FinDer's seismic-based algorithm (Böse et al., 2012) with BEFORES' geodetic-based algorithm (Minson et al., 2014) yields a more robust and informative joint solution than using either algorithm alone. FinDer examines the distribution of peak ground accelerations from seismic stations and determines the best finite-fault extent and strike from template matching. BEFORES employs a Bayesian framework to search for the best slip inversion over all possible fault geometries in terms of strike and dip. Using FinDer and BEFORES together generates estimates of finite-fault extent, strike, dip, preferred slip, and magnitude. To yield the quickest, most flexible, and open-source version of the joint algorithm, we translated BEFORES and FinDer from Matlab into C++. We are now developing a C++ Application Protocol Interface for these two algorithms to be connected to the seismic and geodetic data flowing from the EEW system. The interface that is being developed will also enable communication between the two algorithms to generate the joint solution of finite-fault parameters. Once this interface is developed and implemented, the next step will be to run test seismic and geodetic data through the system via the Earthworm module, Tank Player. This will allow us to examine algorithm performance on simulated data and past real events.

Seismicity Pattern Changes before the M = 4.8 Aeolian Archipelago (Italy) Earthquake of August 16, 2010

PubMed Central

2014-01-01

We investigated the seismicity patterns associated with an M = 4.8 earthquake recorded in the Aeolian Archipelago on 16, August, 2010, by means of the region-time-length (RTL) algorithm. This earthquake triggered landslides at Lipari; a rock fall on the flanks of the Vulcano, Lipari, and Salina islands, and some damages to the village of Lipari. The RTL algorithm is widely used for investigating precursory seismicity changes before large and moderate earthquakes. We examined both the spatial and temporal characteristics of seismicity changes in the Aeolian Archipelago region before the M = 4.8 earthquake. The results obtained reveal 6-7 months of seismic quiescence which started about 15 months before the earthquake. The spatial distribution shows an extensive area characterized by seismic quiescence that suggests a relationship between quiescence and the Aeolian Archipelago regional tectonics. PMID:24511288

Hiding earthquakes from scrupulous monitoring eyes of dense local seismic networks

NASA Astrophysics Data System (ADS)

Bogiatzis, P.; Ishii, M.; Kiser, E.

2012-12-01

Accurate and complete cataloguing of aftershocks is essential for a variety of purposes, including the estimation of the mainshock rupture area, the identification of seismic gaps, and seismic hazard assessment. However, immediately following large earthquakes, the seismograms recorded by local networks are noisy, with energy arriving from hundreds of aftershocks, in addition to different seismic phases interfering with one another. This causes deterioration in the performance of detection and location of earthquakes using conventional methods such as the S-P approach. This is demonstrated by results of back-projection analysis of teleseismic data showing that a significant number of events are undetected by the Japan Meteorological Agency, within the first twenty-four hours after the Mw9.0 Tohoku-oki, Japan earthquake. The spatial distribution of the hidden events is not arbitrary. Most of these earthquakes are located close to the trench, while some are located at the outer rise. Furthermore, there is a relatively sharp trench-parallel boundary separating the detected and undetected events. We investigate the cause of these hidden earthquakes using forward modeling. The calculation of raypaths for various source locations and takeoff angles with the "shooting" method suggests that this phenomenon is a consequence of the complexities associated with subducting slab. Laterally varying velocity structure defocuses the seismic energy from shallow earthquakes located near the trench and makes the observation of P and S arrivals difficult at stations situated on mainland Japan. Full waveform simulations confirm these results. Our forward calculations also show that the probability of detection is sensitive to the depth of the event. Shallower events near the trench are more difficult to detect than deeper earthquakes that are located inside the subducting plate for which the shadow-zone effect diminishes. The modeling effort is expanded to include three

Borehole strain observations of very low frequency earthquakes

NASA Astrophysics Data System (ADS)

Hawthorne, J. C.; Ghosh, A.; Hutchinson, A. A.

2016-12-01

We examine the signals of very low frequency earthquakes (VLFEs) in PBO borehole strain data in central Cascadia. These MW 3.3 - 4.1 earthquakes are best observed in seismograms at periods of 20 to 50 seconds. We look for the strain they produce on timescales from about 1 to 30 minutes. First, we stack the strain produced by 13 VLFEs identified by a grid search moment tensor inversion algorithm by Ghosh et. al. (2015) and Hutchinson and Ghosh (2016), as well as several thousand VLFEs detected through template matching these events. The VLFEs are located beneath southernmost Vancouver Island and the eastern Olympic Peninsula, and are best recorded at co-located stations B005 and B007. However, even at these stations, the signal to noise in the stack is often low, and the records are difficult to interpret. Therefore we also combine data from multiple stations and VLFE locations, and simply look for increases in the strain rate at the VLFE times, as increases in strain rate would suggest an increase in the moment rate. We compare the background strain rate in the 12 hours centered on the VLFEs with the strain rate in the 10 minutes centered on the VLFEs. The 10-minute duration is chosen as a compromise that averages out some instrumental noise without introducing too much longer-period random walk noise. Our results suggest a factor of 2 increase in strain rate--and thus moment rate--during the 10-minute VLFE intervals. The increase gives an average VLFE magnitude around M 3.5, within the range of magnitudes obtained with seismology. Further analyses are currently being carried out to better understand the evolution of moment release before, during, and after the VLFEs.

Long aftershock sequences within continents and implications for earthquake hazard assessment.

PubMed

Stein, Seth; Liu, Mian

2009-11-05

One of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries. Plate tectonics gives no insight, however, into where and when earthquakes will occur within plates, because the interiors of ideal plates should not deform. As a result, within plate interiors, assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes. Here, however, we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago. We present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded. Aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries. These predictions are in accord with observations. So the common practice of treating continental earthquakes as steady-state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere.

Composite Earthquake Catalog of the Yellow Sea for Seismic Hazard Studies

NASA Astrophysics Data System (ADS)

Kang, S. Y.; Kim, K. H.; LI, Z.; Hao, T.

2017-12-01

The Yellow Sea (a.k.a West Sea in Korea) is an epicontinental and semi-closed sea located between Korea and China. Recent earthquakes in the Yellow Sea including, but not limited to, the Seogyuckryulbi-do (1 April 2014, magnitude 5.1), Heuksan-do (21 April 2013, magnitude 4.9), Baekryung-do (18 May 2013, magnitude 4.9) earthquakes, and the earthquake swarm in the Boryung offshore region in 2013, remind us of the seismic hazards affecting east Asia. This series of earthquakes in the Yellow Sea raised numerous questions. Unfortunately, both governments have trouble in monitoring seismicity in the Yellow Sea because earthquakes occur beyond their seismic networks. For example, the epicenters of the magnitude 5.1 earthquake in the Seogyuckryulbi-do region in 2014 reported by the Korea Meteorological Administration and China Earthquake Administration differed by approximately 20 km. This illustrates the difficulty with seismic monitoring and locating earthquakes in the region, despite the huge effort made by both governments. Joint effort is required not only to overcome the limits posed by political boundaries and geographical location but also to study seismicity and the underground structures responsible. Although the well-established and developing seismic networks in Korea and China have provided unprecedented amount and quality of seismic data, high quality catalog is limited to the recent 10s of years, which is far from major earthquake cycle. It is also noticed the earthquake catalog from either country is biased to its own and cannot provide complete picture of seismicity in the Yellow Sea. In order to understand seismic hazard and tectonics in the Yellow Sea, a composite earthquake catalog has been developed. We gathered earthquake information during last 5,000 years from various sources. There are good reasons to believe that some listings account for same earthquake, but in different source parameters. We established criteria in order to provide consistent

A Smartphone Indoor Localization Algorithm Based on WLAN Location Fingerprinting with Feature Extraction and Clustering.

PubMed

Luo, Junhai; Fu, Liang

2017-06-09

With the development of communication technology, the demand for location-based services is growing rapidly. This paper presents an algorithm for indoor localization based on Received Signal Strength (RSS), which is collected from Access Points (APs). The proposed localization algorithm contains the offline information acquisition phase and online positioning phase. Firstly, the AP selection algorithm is reviewed and improved based on the stability of signals to remove useless AP; secondly, Kernel Principal Component Analysis (KPCA) is analyzed and used to remove the data redundancy and maintain useful characteristics for nonlinear feature extraction; thirdly, the Affinity Propagation Clustering (APC) algorithm utilizes RSS values to classify data samples and narrow the positioning range. In the online positioning phase, the classified data will be matched with the testing data to determine the position area, and the Maximum Likelihood (ML) estimate will be employed for precise positioning. Eventually, the proposed algorithm is implemented in a real-world environment for performance evaluation. Experimental results demonstrate that the proposed algorithm improves the accuracy and computational complexity.

Toward real-time regional earthquake simulation II: Real-time Online earthquake Simulation (ROS) of Taiwan earthquakes

NASA Astrophysics Data System (ADS)

Lee, Shiann-Jong; Liu, Qinya; Tromp, Jeroen; Komatitsch, Dimitri; Liang, Wen-Tzong; Huang, Bor-Shouh

2014-06-01

We developed a Real-time Online earthquake Simulation system (ROS) to simulate regional earthquakes in Taiwan. The ROS uses a centroid moment tensor solution of seismic events from a Real-time Moment Tensor monitoring system (RMT), which provides all the point source parameters including the event origin time, hypocentral location, moment magnitude and focal mechanism within 2 min after the occurrence of an earthquake. Then, all of the source parameters are automatically forwarded to the ROS to perform an earthquake simulation, which is based on a spectral-element method (SEM). A new island-wide, high resolution SEM mesh model is developed for the whole Taiwan in this study. We have improved SEM mesh quality by introducing a thin high-resolution mesh layer near the surface to accommodate steep and rapidly varying topography. The mesh for the shallow sedimentary basin is adjusted to reflect its complex geometry and sharp lateral velocity contrasts. The grid resolution at the surface is about 545 m, which is sufficient to resolve topography and tomography data for simulations accurate up to 1.0 Hz. The ROS is also an infrastructural service, making online earthquake simulation feasible. Users can conduct their own earthquake simulation by providing a set of source parameters through the ROS webpage. For visualization, a ShakeMovie and ShakeMap are produced during the simulation. The time needed for one event is roughly 3 min for a 70 s ground motion simulation. The ROS is operated online at the Institute of Earth Sciences, Academia Sinica (http://ros.earth.sinica.edu.tw/). Our long-term goal for the ROS system is to contribute to public earth science outreach and to realize seismic ground motion prediction in real-time.

Bi-directional volcano-earthquake interaction at Mauna Loa Volcano, Hawaii

NASA Astrophysics Data System (ADS)

Walter, T. R.; Amelung, F.

2004-12-01

At Mauna Loa volcano, Hawaii, large-magnitude earthquakes occur mostly at the west flank (Kona area), at the southeast flank (Hilea area), and at the east flank (Kaoiki area). Eruptions at Mauna Loa occur mostly at the summit region and along fissures at the southwest rift zone (SWRZ), or at the northeast rift zone (NERZ). Although historic earthquakes and eruptions at these zones appear to correlate in space and time, the mechanisms and implications of an eruption-earthquake interaction was not cleared. Our analysis of available factual data reveals the highly statistical significance of eruption-earthquake pairs, with a random probability of 5-to-15 percent. We clarify this correlation with the help of elastic stress-field models, where (i) we simulate earthquakes and calculate the resulting normal stress change at volcanic active zones of Mauna Loa, and (ii) we simulate intrusions in Mauna Loa and calculate the Coulomb stress change at the active fault zones. Our models suggest that Hilea earthquakes encourage dike intrusion in the SWRZ, Kona earthquakes encourage dike intrusion at the summit and in the SWRZ, and Kaoiki earthquakes encourage dike intrusion in the NERZ. Moreover, a dike in the SWRZ encourages earthquakes in the Hilea and Kona areas. A dike in the NERZ may encourage and discourage earthquakes in the Hilea and Kaoiki areas. The modeled stress change patterns coincide remarkably with the patterns of several historic eruption-earthquake pairs, clarifying the mechanisms of bi-directional volcano-earthquake interaction for Mauna Loa. The results imply that at Mauna Loa volcanic activity influences the timing and location of earthquakes, and that earthquakes influence the timing, location and the volume of eruptions. In combination with near real-time geodetic and seismic monitoring, these findings may improve volcano-tectonic risk assessment.

Tsunamigenic earthquake simulations using experimentally derived friction laws

NASA Astrophysics Data System (ADS)

Murphy, S.; Di Toro, G.; Romano, F.; Scala, A.; Lorito, S.; Spagnuolo, E.; Aretusini, S.; Festa, G.; Piatanesi, A.; Nielsen, S.

2018-03-01

Seismological, tsunami and geodetic observations have shown that subduction zones are complex systems where the properties of earthquake rupture vary with depth as a result of different pre-stress and frictional conditions. A wealth of earthquakes of different sizes and different source features (e.g. rupture duration) can be generated in subduction zones, including tsunami earthquakes, some of which can produce extreme tsunamigenic events. Here, we offer a geological perspective principally accounting for depth-dependent frictional conditions, while adopting a simplified distribution of on-fault tectonic pre-stress. We combine a lithology-controlled, depth-dependent experimental friction law with 2D elastodynamic rupture simulations for a Tohoku-like subduction zone cross-section. Subduction zone fault rocks are dominantly incohesive and clay-rich near the surface, transitioning to cohesive and more crystalline at depth. By randomly shifting along fault dip the location of the high shear stress regions ("asperities"), moderate to great thrust earthquakes and tsunami earthquakes are produced that are quite consistent with seismological, geodetic, and tsunami observations. As an effect of depth-dependent friction in our model, slip is confined to the high stress asperity at depth; near the surface rupture is impeded by the rock-clay transition constraining slip to the clay-rich layer. However, when the high stress asperity is located in the clay-to-crystalline rock transition, great thrust earthquakes can be generated similar to the Mw 9 Tohoku (2011) earthquake.

A pipeline leakage locating method based on the gradient descent algorithm

NASA Astrophysics Data System (ADS)

Li, Yulong; Yang, Fan; Ni, Na

2018-04-01

A pipeline leakage locating method based on the gradient descent algorithm is proposed in this paper. The method has low computing complexity, which is suitable for practical application. We have built experimental environment in real underground pipeline network. A lot of real data has been gathered in the past three months. Every leak point has been certificated by excavation. Results show that positioning error is within 0.4 meter. Rate of false alarm and missing alarm are both under 20%. The calculating time is not above 5 seconds.

Foreshocks and aftershocks of Pisagua 2014 earthquake: time and space evolution of megathrust event.

NASA Astrophysics Data System (ADS)

Fuenzalida Velasco, Amaya; Rietbrock, Andreas; Wollam, Jack; Thomas, Reece; de Lima Neto, Oscar; Tavera, Hernando; Garth, Thomas; Ruiz, Sergio

2016-04-01

The 2014 Pisagua earthquake of magnitude 8.2 is the first case in Chile where a foreshock sequence was clearly recorded by a local network, as well all the complete sequence including the mainshock and its aftershocks. The seismicity of the last year before the mainshock include numerous clusters close to the epicentral zone (Ruiz et al; 2014) but it was on 16th March that this activity became stronger with the Mw 6.7 precursory event taking place in front of Iquique coast at 12 km depth. The Pisagua earthquake arrived on 1st April 2015 breaking almost 120 km N-S and two days after a 7.6 aftershock occurred in the south of the rupture, enlarging the zone affected by this sequence. In this work, we analyse the foreshocks and aftershock sequence of Pisagua earthquake, from the spatial and time evolution for a total of 15.764 events that were recorded from the 1st March to 31th May 2015. This event catalogue was obtained from the automatic analyse of seismic raw data of more than 50 stations installed in the north of Chile and the south of Peru. We used the STA/LTA algorithm for the detection of P and S arrival times on the vertical components and then a method of back propagation in a 1D velocity model for the event association and preliminary location of its hypocenters following the algorithm outlined by Rietbrock et al. (2012). These results were then improved by locating with NonLinLoc software using a regional velocity model. We selected the larger events to analyse its moment tensor solution by a full waveform inversion using ISOLA software. In order to understand the process of nucleation and propagation of the Pisagua earthquake, we also analysed the evolution in time of the seismicity of the three months of data. The zone where the precursory events took place was strongly activated two weeks before the mainshock and remained very active until the end of the analysed period with an important quantity of the seismicity located in the upper plate and having

An Algorithm to Identify and Localize Suitable Dock Locations from 3-D LiDAR Scans

DTIC Science & Technology

2013-05-10

Locations from 3-D LiDAR Scans 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Graves, Mitchell Robert 5d. PROJECT NUMBER...Ranging ( LiDAR ) scans. A LiDAR sensor is a sensor that collects range images from a rotating array of vertically aligned lasers. Our solution leverages...Algorithm, Dock, Locations, Point Clouds, LiDAR , Identify 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a

a Collaborative Cyberinfrastructure for Earthquake Seismology

NASA Astrophysics Data System (ADS)

Bossu, R.; Roussel, F.; Mazet-Roux, G.; Lefebvre, S.; Steed, R.

2013-12-01

One of the challenges in real time seismology is the prediction of earthquake's impact. It is particularly true for moderate earthquake (around magnitude 6) located close to urbanised areas, where the slightest uncertainty in event location, depth, magnitude estimates, and/or misevaluation of propagation characteristics, site effects and buildings vulnerability can dramatically change impact scenario. The Euro-Med Seismological Centre (EMSC) has developed a cyberinfrastructure to collect observations from eyewitnesses in order to provide in-situ constraints on actual damages. This cyberinfrastructure takes benefit of the natural convergence of earthquake's eyewitnesses on EMSC website (www.emsc-csem.org), the second global earthquake information website within tens of seconds of the occurrence of a felt event. It includes classical crowdsourcing tools such as online questionnaires available in 39 languages, and tools to collect geolocated pics. It also comprises information derived from the real time analysis of the traffic on EMSC website, a method named flashsourcing; In case of a felt earthquake, eyewitnesses reach EMSC website within tens of seconds to find out the cause of the shaking they have just been through. By analysing their geographical origin through their IP address, we automatically detect felt earthquakes and in some cases map the damaged areas through the loss of Internet visitors. We recently implemented a Quake Catcher Network (QCN) server in collaboration with Stanford University and the USGS, to collect ground motion records performed by volunteers and are also involved in a project to detect earthquakes from ground motions sensors from smartphones. Strategies have been developed for several social media (Facebook, Twitter...) not only to distribute earthquake information, but also to engage with the Citizens and optimise data collection. A smartphone application is currently under development. We will present an overview of this

Earthquake Warning Performance in Vallejo for the South Napa Earthquake

NASA Astrophysics Data System (ADS)

Wurman, G.; Price, M.

2014-12-01

In 2002 and 2003, Seismic Warning Systems, Inc. installed first-generation QuakeGuardTM earthquake warning devices at all eight fire stations in Vallejo, CA. These devices are designed to detect the P-wave of an earthquake and initiate predetermined protective actions if the impending shaking is estimated at approximately Modifed Mercalli Intensity V or greater. At the Vallejo fire stations the devices were set up to sound an audio alert over the public address system and to command the equipment bay doors to open. In August 2014, after more than 11 years of operating in the fire stations with no false alarms, the five units that were still in use triggered correctly on the MW 6.0 South Napa earthquake, less than 16 km away. The audio alert sounded in all five stations, providing fire fighters with 1.5 to 2.5 seconds of warning before the arrival of the S-wave, and the equipment bay doors opened in three of the stations. In one station the doors were disconnected from the QuakeGuard device, and another station lost power before the doors opened completely. These problems highlight just a small portion of the complexity associated with realizing actionable earthquake warnings. The issues experienced in this earthquake have already been addressed in subsequent QuakeGuard product generations, with downstream connection monitoring and backup power for critical systems. The fact that the fire fighters in Vallejo were afforded even two seconds of warning at these epicentral distances results from the design of the QuakeGuard devices, which focuses on rapid false positive rejection and ground motion estimates. We discuss the performance of the ground motion estimation algorithms, with an emphasis on the accuracy and timeliness of the estimates at close epicentral distances.

Infrasound Signal Characteristics from Small Earthquakes

DTIC Science & Technology

2011-09-01

INFRASOUND SIGNAL CHARACTERISTICS FROM SMALL EARTHQUAKES Stephen J. Arrowsmith1, J. Mark Hale2, Relu Burlacu2, Kristine L. Pankow2, Brian W. Stump3...ABSTRACT Physical insight into source properties that contribute to the generation of infrasound signals is critical to understanding the...m, with one element being co-located with a seismic station. One of the goals of this project is the recording of infrasound from earthquakes of

Constructing new seismograms from old earthquakes: Retrospective seismology at multiple length scales

NASA Astrophysics Data System (ADS)

Entwistle, Elizabeth; Curtis, Andrew; Galetti, Erica; Baptie, Brian; Meles, Giovanni

2015-04-01

If energy emitted by a seismic source such as an earthquake is recorded on a suitable backbone array of seismometers, source-receiver interferometry (SRI) is a method that allows those recordings to be projected to the location of another target seismometer, providing an estimate of the seismogram that would have been recorded at that location. Since the other seismometer may not have been deployed at the time the source occurred, this renders possible the concept of 'retrospective seismology' whereby the installation of a sensor at one period of time allows the construction of virtual seismograms as though that sensor had been active before or after its period of installation. Using the benefit of hindsight of earthquake location or magnitude estimates, SRI can establish new measurement capabilities closer to earthquake epicenters, thus potentially improving earthquake location estimates. Recently we showed that virtual SRI seismograms can be constructed on target sensors in both industrial seismic and earthquake seismology settings, using both active seismic sources and ambient seismic noise to construct SRI propagators, and on length scales ranging over 5 orders of magnitude from ~40 m to ~2500 km[1]. Here we present the results from earthquake seismology by comparing virtual earthquake seismograms constructed at target sensors by SRI to those actually recorded on the same sensors. We show that spatial integrations required by interferometric theory can be calculated over irregular receiver arrays by embedding these arrays within 2D spatial Voronoi cells, thus improving spatial interpolation and interferometric results. The results of SRI are significantly improved by restricting the backbone receiver array to include approximately those receivers that provide a stationary phase contribution to the interferometric integrals. We apply both correlation-correlation and correlation-convolution SRI, and show that the latter constructs virtual seismograms with fewer

Shallow moonquakes - How they compare with earthquakes

NASA Technical Reports Server (NTRS)

Nakamura, Y.

1980-01-01

Of three types of moonquakes strong enough to be detectable at large distances - deep moonquakes, meteoroid impacts and shallow moonquakes - only shallow moonquakes are similar in nature to earthquakes. A comparison of various characteristics of moonquakes with those of earthquakes indeed shows a remarkable similarity between shallow moonquakes and intraplate earthquakes: (1) their occurrences are not controlled by tides; (2) they appear to occur in locations where there is evidence of structural weaknesses; (3) the relative abundances of small and large quakes (b-values) are similar, suggesting similar mechanisms; and (4) even the levels of activity may be close. The shallow moonquakes may be quite comparable in nature to intraplate earthquakes, and they may be of similar origin.

An autocorrelation method to detect low frequency earthquakes within tremor

USGS Publications Warehouse

Brown, J.R.; Beroza, G.C.; Shelly, D.R.

2008-01-01

Recent studies have shown that deep tremor in the Nankai Trough under western Shikoku consists of a swarm of low frequency earthquakes (LFEs) that occur as slow shear slip on the down-dip extension of the primary seismogenic zone of the plate interface. The similarity of tremor in other locations suggests a similar mechanism, but the absence of cataloged low frequency earthquakes prevents a similar analysis. In this study, we develop a method for identifying LFEs within tremor. The method employs a matched-filter algorithm, similar to the technique used to infer that tremor in parts of Shikoku is comprised of LFEs; however, in this case we do not assume the origin times or locations of any LFEs a priori. We search for LFEs using the running autocorrelation of tremor waveforms for 6 Hi-Net stations in the vicinity of the tremor source. Time lags showing strong similarity in the autocorrelation represent either repeats, or near repeats, of LFEs within the tremor. We test the method on an hour of Hi-Net recordings of tremor and demonstrates that it extracts both known and previously unidentified LFEs. Once identified, we cross correlate waveforms to measure relative arrival times and locate the LFEs. The results are able to explain most of the tremor as a swarm of LFEs and the locations of newly identified events appear to fill a gap in the spatial distribution of known LFEs. This method should allow us to extend the analysis of Shelly et al. (2007a) to parts of the Nankai Trough in Shikoku that have sparse LFE coverage, and may also allow us to extend our analysis to other regions that experience deep tremor, but where LFEs have not yet been identified. Copyright 2008 by the American Geophysical Union.

Localizing Submarine Earthquakes by Listening to the Water Reverberations

NASA Astrophysics Data System (ADS)

Castillo, J.; Zhan, Z.; Wu, W.

2017-12-01

Mid-Ocean Ridge (MOR) earthquakes generally occur far from any land based station and are of moderate magnitude, making it complicated to detect and in most cases, locate accurately. This limits our understanding of how MOR normal and transform faults move and the manner in which they slip. Different from continental events, seismic records from earthquakes occurring beneath the ocean floor show complex reverberations caused by P-wave energy trapped in the water column that are highly dependent of the source location and the efficiency to which energy propagated to the near-source surface. These later arrivals are commonly considered to be only a nuisance as they might sometimes interfere with the primary arrivals. However, in this study, we take advantage of the wavefield's high sensitivity to small changes in the seafloor topography and the present-day availability of worldwide multi-beam bathymetry to relocate submarine earthquakes by modeling these water column reverberations in teleseismic signals. Using a three-dimensional hybrid method for modeling body wave arrivals, we demonstrate that an accurate hypocentral location of a submarine earthquake (<5 km) can be achieved if the structural complexities near the source region are appropriately accounted for. This presents a novel way of studying earthquake source properties and will serve as a means to explore the influence of physical fault structure on the seismic behavior of transform faults.

Seismicity map tools for earthquake studies

NASA Astrophysics Data System (ADS)

Boucouvalas, Anthony; Kaskebes, Athanasios; Tselikas, Nikos

2014-05-01

We report on the development of new and online set of tools for use within Google Maps, for earthquake research. We demonstrate this server based and online platform (developped with PHP, Javascript, MySQL) with the new tools using a database system with earthquake data. The platform allows us to carry out statistical and deterministic analysis on earthquake data use of Google Maps and plot various seismicity graphs. The tool box has been extended to draw on the map line segments, multiple straight lines horizontally and vertically as well as multiple circles, including geodesic lines. The application is demonstrated using localized seismic data from the geographic region of Greece as well as other global earthquake data. The application also offers regional segmentation (NxN) which allows the studying earthquake clustering, and earthquake cluster shift within the segments in space. The platform offers many filters such for plotting selected magnitude ranges or time periods. The plotting facility allows statistically based plots such as cumulative earthquake magnitude plots and earthquake magnitude histograms, calculation of 'b' etc. What is novel for the platform is the additional deterministic tools. Using the newly developed horizontal and vertical line and circle tools we have studied the spatial distribution trends of many earthquakes and we here show for the first time the link between Fibonacci Numbers and spatiotemporal location of some earthquakes. The new tools are valuable for examining visualizing trends in earthquake research as it allows calculation of statistics as well as deterministic precursors. We plan to show many new results based on our newly developed platform.

A seismoacoustic study of the 2011 January 3 Circleville earthquake

NASA Astrophysics Data System (ADS)

Arrowsmith, Stephen J.; Burlacu, Relu; Pankow, Kristine; Stump, Brian; Stead, Richard; Whitaker, Rod; Hayward, Chris

2012-05-01

We report on a unique set of infrasound observations from a single earthquake, the 2011 January 3 Circleville earthquake (Mw 4.7, depth of 8 km), which was recorded by nine infrasound arrays in Utah. Based on an analysis of the signal arrival times and backazimuths at each array, we find that the infrasound arrivals at six arrays can be associated to the same source and that the source location is consistent with the earthquake epicentre. Results of propagation modelling indicate that the lack of associated arrivals at the remaining three arrays is due to path effects. Based on these findings we form the working hypothesis that the infrasound is generated by body waves causing the epicentral region to pump the atmosphere, akin to a baffled piston. To test this hypothesis, we have developed a numerical seismoacoustic model to simulate the generation of epicentral infrasound from earthquakes. We model the generation of seismic waves using a 3-D finite difference algorithm that accounts for the earthquake moment tensor, source time function, depth and local geology. The resultant acceleration-time histories on a 2-D grid at the surface then provide the initial conditions for modelling the near-field infrasonic pressure wave using the Rayleigh integral. Finally, we propagate the near-field source pressure through the Ground-to-Space atmospheric model using a time-domain Parabolic Equation technique. By comparing the resultant predictions with the six epicentral infrasound observations from the 2011 January 3, Circleville earthquake, we show that the observations agree well with our predictions. The predicted and observed amplitudes are within a factor of 2 (on average, the synthetic amplitudes are a factor of 1.6 larger than the observed amplitudes). In addition, arrivals are predicted at all six arrays where signals are observed, and importantly not predicted at the remaining three arrays. Durations are typically predicted to within a factor of 2, and in some cases

Volcano-earthquake interaction at Mauna Loa volcano, Hawaii

NASA Astrophysics Data System (ADS)

Walter, Thomas R.; Amelung, Falk

2006-05-01

The activity at Mauna Loa volcano, Hawaii, is characterized by eruptive fissures that propagate into the Southwest Rift Zone (SWRZ) or into the Northeast Rift Zone (NERZ) and by large earthquakes at the basal decollement fault. In this paper we examine the historic eruption and earthquake catalogues, and we test the hypothesis that the events are interconnected in time and space. Earthquakes in the Kaoiki area occur in sequence with eruptions from the NERZ, and earthquakes in the Kona and Hilea areas occur in sequence with eruptions from the SWRZ. Using three-dimensional numerical models, we demonstrate that elastic stress transfer can explain the observed volcano-earthquake interaction. We examine stress changes due to typical intrusions and earthquakes. We find that intrusions change the Coulomb failure stress along the decollement fault so that NERZ intrusions encourage Kaoiki earthquakes and SWRZ intrusions encourage Kona and Hilea earthquakes. On the other hand, earthquakes decompress the magma chamber and unclamp part of the Mauna Loa rift zone, i.e., Kaoiki earthquakes encourage NERZ intrusions, whereas Kona and Hilea earthquakes encourage SWRZ intrusions. We discuss how changes of the static stress field affect the occurrence of earthquakes as well as the occurrence, location, and volume of dikes and of associated eruptions and also the lava composition and fumarolic activity.

Earthquake prediction evaluation standards applied to the VAN Method

NASA Astrophysics Data System (ADS)

Jackson, David D.

Earthquake prediction research must meet certain standards before it can be suitably evaluated for potential application in decision making. For methods that result in a binary (on or off) alarm condition, requirements include (1) a quantitative description of observables that trigger an alarm, (2) a quantitative description, including ranges of time, location, and magnitude, of the predicted earthquakes, (3) documented evidence of all previous alarms, (4) a complete list of predicted earthquakes, (5) a complete list of unpredicted earthquakes. The VAN technique [Varotsos and Lazaridou, 1991; Varotsos et al., 1996] has not yet been stated as a testable hypothesis. It fails criteria (1) and (2) so it is not ready to be evaluated properly. Although telegrams were transmitted in advance of claimed successes, these telegrams did not fully specify the predicted events, and all of the published statistical evaluations involve many subjective ex post facto decisions. Lacking a statistically demonstrated relationship to earthquakes, a candidate prediction technique should satisfy several plausibility criteria, including: (1) a reasonable relationship between the location of the candidate precursor and that of the predicted earthquake, (2) some demonstration that the candidate precursory observations are related to stress, strain, or other quantities related to earthquakes, and (3) the existence of co-seismic as well as pre-seismic variations of the candidate precursor. The VAN technique meets none of these criteria.

Investigation of an Unusually Shallow Earthquake Sequence in Mogul, NV from a Discrimination Perspective (Postprint): Annual Report 1

DTIC Science & Technology

2012-05-09

the ML>1.0 Mogul, Nevada earthquakes located by the Nevada Seismological Laboratory; mining explosions (ML>2.0) and crustal earthquakes (ML>2.5) in...1.0 Mogul, Nevada earthquakes located by the Nevada Seismological Laboratory; mining explosions (ML>2.0) and crustal earthquakes (ML>2.5) in the in...distinguish between very shallow crustal earthquakes and underground nuclear explosions are not well developed, significantly because such well-instrumented

Did you feel it? : citizens contribute to earthquake science

USGS Publications Warehouse

Wald, David J.; Dewey, James W.

2005-01-01

Since the early 1990s, the magnitude and location of an earthquake have been available within minutes on the Internet. Now, as a result of work by the U.S. Geological Survey and with the cooperation of various regional seismic networks, people who experience an earthquake can go online and share information about its effects to help create a map of shaking intensities and damage. Such “Community Internet Intensity Maps” (CIIMs) contribute greatly toward the quick assessment of the scope of an earthquake emergency and provide valuable data for earthquake research.

Extending the ISC-GEM Global Earthquake Instrumental Catalogue

NASA Astrophysics Data System (ADS)

Di Giacomo, Domenico; Engdhal, Bob; Storchak, Dmitry; Villaseñor, Antonio; Harris, James

2015-04-01

After a 27-month project funded by the GEM Foundation (www.globalquakemodel.org), in January 2013 we released the ISC-GEM Global Instrumental Earthquake Catalogue (1900 2009) (www.isc.ac.uk/iscgem/index.php) as a special product to use for seismic hazard studies. The new catalogue was necessary as improved seismic hazard studies necessitate that earthquake catalogues are homogeneous (to the largest extent possible) over time in their fundamental parameters, such as location and magnitude. Due to time and resource limitation, the ISC-GEM catalogue (1900-2009) included earthquakes selected according to the following time-variable cut-off magnitudes: Ms=7.5 for earthquakes occurring before 1918; Ms=6.25 between 1918 and 1963; and Ms=5.5 from 1964 onwards. Because of the importance of having a reliable seismic input for seismic hazard studies, funding from GEM and two commercial companies in the US and UK allowed us to start working on the extension of the ISC-GEM catalogue both for earthquakes that occurred beyond 2009 and for earthquakes listed in the International Seismological Summary (ISS) which fell below the cut-off magnitude of 6.25. This extension is part of a four-year program that aims at including in the ISC-GEM catalogue large global earthquakes that occurred before the beginning of the ISC Bulletin in 1964. In this contribution we present the updated ISC GEM catalogue, which will include over 1000 more earthquakes that occurred in 2010 2011 and several hundreds more between 1950 and 1959. The catalogue extension between 1935 and 1949 is currently underway. The extension of the ISC-GEM catalogue will also be helpful for regional cross border seismic hazard studies as the ISC-GEM catalogue should be used as basis for cross-checking the consistency in location and magnitude of those earthquakes listed both in the ISC GEM global catalogue and regional catalogues.

Using meta-information of a posteriori Bayesian solutions of the hypocentre location task for improving accuracy of location error estimation

NASA Astrophysics Data System (ADS)

Debski, Wojciech

2015-06-01

The spatial location of sources of seismic waves is one of the first tasks when transient waves from natural (uncontrolled) sources are analysed in many branches of physics, including seismology, oceanology, to name a few. Source activity and its spatial variability in time, the geometry of recording network, the complexity and heterogeneity of wave velocity distribution are all factors influencing the performance of location algorithms and accuracy of the achieved results. Although estimating of the earthquake foci location is relatively simple, a quantitative estimation of the location accuracy is really a challenging task even if the probabilistic inverse method is used because it requires knowledge of statistics of observational, modelling and a priori uncertainties. In this paper, we addressed this task when statistics of observational and/or modelling errors are unknown. This common situation requires introduction of a priori constraints on the likelihood (misfit) function which significantly influence the estimated errors. Based on the results of an analysis of 120 seismic events from the Rudna copper mine operating in southwestern Poland, we propose an approach based on an analysis of Shanon's entropy calculated for the a posteriori distribution. We show that this meta-characteristic of the a posteriori distribution carries some information on uncertainties of the solution found.

Earthquake technology fights crime

USGS Publications Warehouse

Lahr, John C.; Ward, Peter L.; Stauffer, Peter H.; Hendley, James W.

1996-01-01

Scientists with the U.S. Geological Survey have adapted their methods for quickly finding the exact source of an earthquake to the problem of locating gunshots. On the basis of this work, a private company is now testing an automated gunshot-locating system in a San Francisco Bay area community. This system allows police to rapidly pinpoint and respond to illegal gunfire, helping to reduce crime in our neighborhoods.

Using Earthquake Location and Coda Attenuation Analysis to Explore Shallow Structures Above the Socorro Magma Body, New Mexico

NASA Astrophysics Data System (ADS)

Schmidt, J. P.; Bilek, S. L.; Worthington, L. L.; Schmandt, B.; Aster, R. C.

2017-12-01

The Socorro Magma Body (SMB) is a thin, sill-like intrusion with a top at 19 km depth covering approximately 3400 km2 within the Rio Grande Rift. InSAR studies show crustal uplift patterns linked to SMB inflation with deformation rates of 2.5 mm/yr in the area of maximum uplift with some peripheral subsidence. Our understanding of the emplacement history and shallow structure above the SMB is limited. We use a large seismic deployment to explore seismicity and crustal attenuation in the SMB region, focusing on the area of highest observed uplift to investigate the possible existence of fluid/magma in the upper crust. We would expect to see shallower earthquakes and/or higher attenuation if high heat flow, fluid or magma is present in the upper crust. Over 800 short period vertical component geophones situated above the northern portion of the SMB were deployed for two weeks in 2015. This data is combined with other broadband and short period seismic stations to detect and locate earthquakes as well as to estimate seismic attenuation. We use phase arrivals from the full dataset to relocate a set of 33 local/regional earthquakes recorded during the deployment. We also measure amplitude decay after the S-wave arrival to estimate coda attenuation caused by scattering of seismic waves and anelastic processes. Coda attenuation is estimated using the single backscatter method described by Aki and Chouet (1975), filtering the seismograms at 6, 9 and 12 Hz center frequencies. Earthquakes occurred at 2-13 km depth during the deployment, but no spatial patterns linked with the high uplift region were observed over this short duration. Attenuation results for this deployment suggest Q ranging in values of 130 to 2000, averaging around Q of 290, comparable to Q estimates of other studies of the western US. With our dense station coverage, we explore attenuation over smaller scales, and find higher attenuation for stations in the area of maximum uplift relative to stations

Assessing the Applicability of Earthquake Early Warning in Nicaragua.

NASA Astrophysics Data System (ADS)

Massin, F.; Clinton, J. F.; Behr, Y.; Strauch, W.; Cauzzi, C.; Boese, M.; Talavera, E.; Tenorio, V.; Ramirez, J.

2016-12-01

Nicaragua, like much of Central America, suffers from frequent damaging earthquakes (6 M7+ earthquakes occurred in the last 100 years). Thrust events occur at the Middle America Trench where the Cocos plate subducts by 72-81 mm/yr eastward beneath the Caribbean plate. Shallow crustal events occur on-shore, with potential extensive damage as demonstrated in 1972 by a M6.2 earthquake, 5 km beneath Managua. This seismotectonic setting is challenging for Earthquake Early Warning (EEW) because the target events derive from both the offshore seismicity, with potentially large lead times but uncertain locations, and shallow seismicity in close proximity to densely urbanized areas, where an early warning would be short if available at all. Nevertheless, EEW could reduce Nicaragua's earthquake exposure. The Swiss Development and Cooperation Fund and the Nicaraguan Government have funded a collaboration between the Swiss Seismological Service (SED) at ETH Zurich and the Nicaraguan Geosciences Institute (INETER) in Managua to investigate and build a prototype EEW system for Nicaragua and the wider region. In this contribution, we present the potential of EEW to effectively alert Nicaragua and the neighbouring regions. We model alert time delays using all available seismic stations (existing and planned) in the region, as well as communication and processing delays (observed and optimal) to estimate current and potential performances of EEW alerts. Theoretical results are verified with the output from the Virtual Seismologist in SeisComP3 (VS(SC3)). VS(SC3) is implemented in the INETER SeisComP3 system for real-time operation and as an offline instance, that simulates real-time operation, to record processing delays of playback events. We compare our results with similar studies for Europe, California and New Zealand. We further highlight current capabilities and challenges for providing EEW alerts in Nicaragua. We also discuss how combining different algorithms, like e.g. VS

Modified-Fibonacci-Dual-Lucas method for earthquake prediction

NASA Astrophysics Data System (ADS)

Boucouvalas, A. C.; Gkasios, M.; Tselikas, N. T.; Drakatos, G.

2015-06-01

The FDL method makes use of Fibonacci, Dual and Lucas numbers and has shown considerable success in predicting earthquake events locally as well as globally. Predicting the location of the epicenter of an earthquake is one difficult challenge the other being the timing and magnitude. One technique for predicting the onset of earthquakes is the use of cycles, and the discovery of periodicity. Part of this category is the reported FDL method. The basis of the reported FDL method is the creation of FDL future dates based on the onset date of significant earthquakes. The assumption being that each occurred earthquake discontinuity can be thought of as a generating source of FDL time series The connection between past earthquakes and future earthquakes based on FDL numbers has also been reported with sample earthquakes since 1900. Using clustering methods it has been shown that significant earthquakes (<6.5R) can be predicted with very good accuracy window (+-1 day). In this contribution we present an improvement modification to the FDL method, the MFDL method, which performs better than the FDL. We use the FDL numbers to develop possible earthquakes dates but with the important difference that the starting seed date is a trigger planetary aspect prior to the earthquake. Typical planetary aspects are Moon conjunct Sun, Moon opposite Sun, Moon conjunct or opposite North or South Modes. In order to test improvement of the method we used all +8R earthquakes recorded since 1900, (86 earthquakes from USGS data). We have developed the FDL numbers for each of those seeds, and examined the earthquake hit rates (for a window of 3, i.e. +-1 day of target date) and for <6.5R. The successes are counted for each one of the 86 earthquake seeds and we compare the MFDL method with the FDL method. In every case we find improvement when the starting seed date is on the planetary trigger date prior to the earthquake. We observe no improvement only when a planetary trigger coincided with

Comparison of hypocentre parameters of earthquakes in the Aegean region

NASA Astrophysics Data System (ADS)

Özel, Nurcan M.; Shapira, Avi; Harris, James

2007-06-01

The Aegean Sea is one of the more seismically active areas in the Euro-Mediterranean region. The seismic activity in the Aegean Sea is monitored by a number of local agencies that contribute their data to the International Seismological Centre (ISC). Consequently, the ISC Bulletin may serve as a reliable reference for assessing the capabilities of local agencies to monitor moderate and low magnitude earthquakes. We have compared bulletins of the Kandilli Observatory and Earthquake Research Institute (KOERI) and the ISC, for the period 1976-2003 that comprises the most complete data sets for both KOERI and ISC. The selected study area is the East Aegean Sea and West Turkey, bounded by latitude 35-41°N and by longitude 24-29°E. The total number of events known to occur in this area, during 1976-2003 is about 41,638. Seventy-two percent of those earthquakes were located by ISC and 75% were located by KOERI. As expected, epicentre location discrepancy between ISC and KOERI solutions are larger as we move away from the KOERI seismic network. Out of the 22,066 earthquakes located by both ISC and KOERI, only 4% show a difference of 50 km or more. About 140 earthquakes show a discrepancy of more than 100 km. Focal Depth determinations differ mainly in the subduction zone along the Hellenic arc. Less than 2% of the events differ in their focal depth by more than 25 km. Yet, the location solutions of about 30 events differ by more than 100 km. Almost a quarter of the events listed in the ISC Bulletin are missed by KOERI, most of them occurring off the coast of Turkey, in the East Aegean. Based on the frequency-magnitude distributions, the KOERI Bulletin is complete for earthquakes with duration magnitudes Md > 2.7 (both located and assigned magnitudes) where as the threshold magnitude for events with location and magnitude determinations by ISC is mb > 4.0. KOERI magnitudes seem to be poorly correlated with ISC magnitudes suggesting relatively high uncertainty in the

Fault Identification by Unsupervised Learning Algorithm

NASA Astrophysics Data System (ADS)

Nandan, S.; Mannu, U.

2012-12-01

Contemporary fault identification techniques predominantly rely on the surface expression of the fault. This biased observation is inadequate to yield detailed fault structures in areas with surface cover like cities deserts vegetation etc and the changes in fault patterns with depth. Furthermore it is difficult to estimate faults structure which do not generate any surface rupture. Many disastrous events have been attributed to these blind faults. Faults and earthquakes are very closely related as earthquakes occur on faults and faults grow by accumulation of coseismic rupture. For a better seismic risk evaluation it is imperative to recognize and map these faults. We implement a novel approach to identify seismically active fault planes from three dimensional hypocenter distribution by making use of unsupervised learning algorithms. We employ K-means clustering algorithm and Expectation Maximization (EM) algorithm modified to identify planar structures in spatial distribution of hypocenter after filtering out isolated events. We examine difference in the faults reconstructed by deterministic assignment in K- means and probabilistic assignment in EM algorithm. The method is conceptually identical to methodologies developed by Ouillion et al (2008, 2010) and has been extensively tested on synthetic data. We determined the sensitivity of the methodology to uncertainties in hypocenter location, density of clustering and cross cutting fault structures. The method has been applied to datasets from two contrasting regions. While Kumaon Himalaya is a convergent plate boundary, Koyna-Warna lies in middle of the Indian Plate but has a history of triggered seismicity. The reconstructed faults were validated by examining the fault orientation of mapped faults and the focal mechanism of these events determined through waveform inversion. The reconstructed faults could be used to solve the fault plane ambiguity in focal mechanism determination and constrain the fault

Source properties of earthquakes near the Salton Sea triggered by the 16 October 1999 M 7.1 Hector Mine, California, earthquake

USGS Publications Warehouse

Hough, S.E.; Kanamori, H.

2002-01-01

We analyze the source properties of a sequence of triggered earthquakes that occurred near the Salton Sea in southern California in the immediate aftermath of the M 7.1 Hector Mine earthquake of 16 October 1999. The sequence produced a number of early events that were not initially located by the regional network, including two moderate earthquakes: the first within 30 sec of the P-wave arrival and a second approximately 10 minutes after the mainshock. We use available amplitude and waveform data from these events to estimate magnitudes to be approximately 4.7 and 4.4, respectively, and to obtain crude estimates of their locations. The sequence of small events following the initial M 4.7 earthquake is clustered and suggestive of a local aftershock sequence. Using both broadband TriNet data and analog data from the Southern California Seismic Network (SCSN), we also investigate the spectral characteristics of the M 4.4 event and other triggered earthquakes using empirical Green's function (EGF) analysis. We find that the source spectra of the events are consistent with expectations for tectonic (brittle shear failure) earthquakes, and infer stress drop values of 0.1 to 6 MPa for six M 2.1 to M 4.4 events. The estimated stress drop values are within the range observed for tectonic earthquakes elsewhere. They are relatively low compared to typically observed stress drop values, which is consistent with expectations for faulting in an extensional, high heat flow regime. The results therefore suggest that, at least in this case, triggered earthquakes are associated with a brittle shear failure mechanism. This further suggests that triggered earthquakes may tend to occur in geothermal-volcanic regions because shear failure occurs at, and can be triggered by, relatively low stresses in extensional regimes.

The 2008 Wells, Nevada Earthquake Sequence: Application of Subspace Detection and Multiple Event Relocation Techniques

NASA Astrophysics Data System (ADS)

Nealy, J. L.; Benz, H.; Hayes, G. P.; Bergman, E.; Barnhart, W. D.

2016-12-01

On February 21, 2008 at 14:16:02 (UTC), Wells, Nevada experienced a Mw 6.0 earthquake, the largest earthquake in the state within the past 50 years. Here, we re-analyze in detail the spatiotemporal variations of the foreshock and aftershock sequence and compare the distribution of seismicity to a recent slip model based on inversion of InSAR observations. A catalog of earthquakes for the time period of February 1, 2008 through August 31, 2008 was derived from a combination of arrival time picks using a kurtosis detector (primarily P arrival times), subspace detector (primarily S arrival times), associating the combined pick dataset, and applying multiple event relocation techniques using the 19 closest USArray Transportable Array stations, permanent regional seismic monitoring stations in Nevada and Utah, and temporary stations deployed for an aftershock study. We were able to detect several thousand earthquakes in the months following the mainshock as well as several foreshocks in the days leading up to the event. We reviewed the picks for the largest 986 earthquakes and relocated them using the Hypocentroidal Decomposition (HD) method. The HD technique provides both relative locations for the individual earthquakes and an absolute location for the earthquake cluster, resulting in absolute locations of the events in the cluster having minimal bias from unknown Earth structure. A subset of these "calibrated" earthquake locations that spanned the duration of the sequence and had small uncertainties in location were used as prior constraints within a second relocation effort using the entire dataset and the Bayesloc approach. Accurate locations (to within 2 km) were obtained using Bayesloc for 1,952 of the 2,157 events associated over the seven-month period of the study. The final catalog of earthquake hypocenters indicates that the aftershocks extend for about 20 km along the strike of the ruptured fault. The aftershocks occur primarily updip and along the

Monochromatic body waves excited by great subduction zone earthquakes

NASA Astrophysics Data System (ADS)

Ihmlé, Pierre F.; Madariaga, Raúl

Large quasi-monochromatic body waves were excited by the 1995 Chile Mw=8.1 and by the 1994 Kurile Mw=8.3 events. They are observed on vertical/radial component seismograms following the direct P and Pdiff arrivals, at all azimuths. We devise a slant stack algorithm to characterize the source of the oscillations. This technique aims at locating near-source isotropic scatterers using broadband data from global networks. For both events, we find that the oscillations emanate from the trench. We show that these monochromatic waves are due to localized oscillations of the water column. Their period corresponds to the gravest ID mode of a water layer for vertically traveling compressional waves. We suggest that these monochromatic body waves may yield additional constraints on the source process of great subduction zone earthquakes.

Updated earthquake catalogue for seismic hazard analysis in Pakistan