Limiting the Effects of Earthquake Shaking on Gravitational-Wave Interferometers

NASA Astrophysics Data System (ADS)

Perry, M. R.; Earle, P. S.; Guy, M. R.; Harms, J.; Coughlin, M.; Biscans, S.; Buchanan, C.; Coughlin, E.; Fee, J.; Mukund, N.

2016-12-01

Second-generation ground-based gravitational wave interferometers such as the Laser Interferometer Gravitational-wave Observatory (LIGO) are susceptible to high-amplitude waves from teleseismic events, which can cause astronomical detectors to fall out of mechanical lock (lockloss). This causes the data to be useless for gravitational wave detection around the time of the seismic arrivals and for several hours thereafter while the detector stabilizes enough to return to the locked state. 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 lock 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). Hypocenter and magnitude information is typically available within 5 to 20 minutes of the origin time of significant earthquakes, generally before the arrival of high-amplitude waves from these teleseisms at LIGO. These alerts are used to estimate arrival times and ground velocities at the gravitational wave detectors. In general, 94% 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 with about 90% of the events falling within a factor of 2 of the final predicted value. By using a Machine Learning Algorithm, we develop a lockloss 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 save lockloss from 40-100 earthquake events in a 6-month time-period.

ARRIVAL TIME DIFFERENCES BETWEEN GRAVITATIONAL WAVES AND ELECTROMAGNETIC SIGNALS DUE TO GRAVITATIONAL LENSING

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

Takahashi, Ryuichi

In this study we demonstrate that general relativity predicts arrival time differences between gravitational wave (GW) and electromagnetic (EM) signals caused by the wave effects in gravitational lensing. The GW signals can arrive earlier than the EM signals in some cases if the GW/EM signals have passed through a lens, even if both signals were emitted simultaneously by a source. GW wavelengths are much larger than EM wavelengths; therefore, the propagation of the GWs does not follow the laws of geometrical optics, including the Shapiro time delay, if the lens mass is less than approximately 10{sup 5} M {sub ⊙}(more » f /Hz){sup −1}, where f is the GW frequency. The arrival time difference can reach ∼0.1 s ( f /Hz){sup −1} if the signals have passed by a lens of mass ∼8000 M {sub ⊙}( f /Hz){sup −1} with the impact parameter smaller than the Einstein radius; therefore, it is more prominent for lower GW frequencies. For example, when a distant supermassive black hole binary (SMBHB) in a galactic center is lensed by an intervening galaxy, the time lag becomes of the order of 10 days. Future pulsar timing arrays including the Square Kilometre Array and X-ray detectors may detect several time lags by measuring the orbital phase differences between the GW/EM signals in the SMBHBs. Gravitational lensing imprints a characteristic modulation on a chirp waveform; therefore, we can deduce whether a measured arrival time lag arises from intrinsic source properties or gravitational lensing. Determination of arrival time differences would be extremely useful in multimessenger observations and tests of general relativity.« less

Examining P-Wave Arrivals of Low-Frequency Earthquakes for Evidence of Attenuation and its Effects on Moment-Duration Scaling

NASA Astrophysics Data System (ADS)

Gerzina, J.; Rubin, A. M.

2017-12-01

Bostock et. al. (2015) found that low-frequency earthquake (LFE) duration is nearly independent of moment, a result that is surprising enough to warrant investigating whether it might be an artifact of attenuation. Bostock et. al. (2017) found that bulk crustal attenuation could not be the culprit, but suggested that near-source attenuation might cause pronounced depletion of high frequency S-waves. Despite their lower signal-to noise ratio, looking at the P-waves might be enlightening because they aren't expected to attenuate as much as S-waves in the high Vp/Vs region near the tremor source. We have examined P-wave arrivals of LFEs that occurred during episodic tremor in the Cascadia subduction zone with the goal of refining the relationship between LFE magnitude and duration.Bostock et. al's duration measurements were made on stacked templates rather than individual arrivals. Because members of Bostock's LFE families vary in location, and therefore in P-S delay time, aligning the stacks primarily on the S arrival may artificially widen the P pulse. To circumvent this, we used cross-station cross correlations on Bostock's detections to identify and stack events with similar locations and therefore similar P-S delay times, until P arrivals became visible. We then stacked these stacks based on cross-correlating the optimal P component in a small window surrounding the P arrival. Although this procedure narrowed both the P and S pulse widths, it did not dramatically narrow P in relation to S, nor did we observe different P pulse widths for small and large events.We also compared the frequency spectra of small windows around the expected P and S arrivals for each amplitude bin. Although there is more high-frequency content in P-waves than S-waves, we have not yet been able to resolve a difference in P-wave corner frequency for different event sizes. Thus our preliminary results support the notion that LFEs are intrinsically low frequency.

Pulsar Timing and Its Application for Navigation and Gravitational Wave Detection

NASA Astrophysics Data System (ADS)

Becker, Werner; Kramer, Michael; Sesana, Alberto

2018-02-01

Pulsars are natural cosmic clocks. On long timescales they rival the precision of terrestrial atomic clocks. Using a technique called pulsar timing, the exact measurement of pulse arrival times allows a number of applications, ranging from testing theories of gravity to detecting gravitational waves. Also an external reference system suitable for autonomous space navigation can be defined by pulsars, using them as natural navigation beacons, not unlike the use of GPS satellites for navigation on Earth. By comparing pulse arrival times measured on-board a spacecraft with predicted pulse arrivals at a reference location (e.g. the solar system barycenter), the spacecraft position can be determined autonomously and with high accuracy everywhere in the solar system and beyond. We describe the unique properties of pulsars that suggest that such a navigation system will certainly have its application in future astronautics. We also describe the on-going experiments to use the clock-like nature of pulsars to "construct" a galactic-sized gravitational wave detector for low-frequency (f_{GW}˜ 10^{-9} - 10^{-7} Hz) gravitational waves. We present the current status and provide an outlook for the future.

Incorporating fault zone head wave and direct wave secondary arrival times into seismic tomography: Application at Parkfield, California

NASA Astrophysics Data System (ADS)

Bennington, Ninfa L.; Thurber, Clifford; Peng, Zhigang; Zhang, Haijiang; Zhao, Peng

2013-03-01

We present a three-dimensional (3D) P wave velocity (Vp) model of the Parkfield region that utilizes existing P wave arrival time data, including fault zone head waves (FZHWs), and data from direct wave secondary arrivals (DWSAs). The first-arrival and DWSA travel times are obtained as the global- and local-minimum travel time paths, respectively. The inclusion of FZHWs and DWSAs results in as much as a 5% and a 10% increase in the across-fault velocity contrast, respectively, for the Vp model at Parkfield relative to that of Thurber et al. [2006]. Viewed along strike, three pronounced velocity contrast regions are observed: a pair of strong positive velocity contrasts (SW fast), one NW of the 1966 Parkfield earthquake hypocenter and the other SE of the 2004 Parkfield earthquake hypocenter, and a strong negative velocity contrast (NE fast) between the two hypocenters. The negative velocity contrast partially to entirely encompasses peak coseismic slip estimated in several slip models for the 2004 earthquake, suggesting that the negative velocity contrast played a part in defining the rupture patch of the 2004 Parkfield earthquake. Following Ampuero and Ben-Zion (2008), the pattern of velocity contrasts is consistent with the observed bilateral rupture propagation for the 2004 Parkfield earthquake. Although the velocity contrasts also suggest bilateral rupture propagation for the 1966 Parkfield earthquake, the fault is creeping to the NW here, i.e., exhibiting velocity-strengthening behavior. Thus, it is not surprising that rupture propagated only SE during this event.

Fiber optic sensor employing successively destroyed coupled points or reflectors for detecting shock wave speed and damage location

DOEpatents

Weiss, Jonathan D.

1995-01-01

A shock velocity and damage location sensor providing a means of measuring shock speed and damage location. The sensor consists of a long series of time-of-arrival "points" constructed with fiber optics. The fiber optic sensor apparatus measures shock velocity as the fiber sensor is progressively crushed as a shock wave proceeds in a direction along the fiber. The light received by a receiving means changes as time-of-arrival points are destroyed as the sensor is disturbed by the shock. The sensor may comprise a transmitting fiber bent into a series of loops and fused to a receiving fiber at various places, time-of-arrival points, along the receiving fibers length. At the "points" of contact, where a portion of the light leaves the transmitting fiber and enters the receiving fiber, the loops would be required to allow the light to travel backwards through the receiving fiber toward a receiving means. The sensor may also comprise a single optical fiber wherein the time-of-arrival points are comprised of reflection planes distributed along the fibers length. In this configuration, as the shock front proceeds along the fiber it destroys one reflector after another. The output received by a receiving means from this sensor may be a series of downward steps produced as the shock wave destroys one time-of-arrival point after another, or a nonsequential pattern of steps in the event time-of-arrival points are destroyed at any point along the sensor.

Fiber optic sensor employing successively destroyed coupled points or reflectors for detecting shock wave speed and damage location

DOEpatents

Weiss, J.D.

1995-08-29

A shock velocity and damage location sensor providing a means of measuring shock speed and damage location is disclosed. The sensor consists of a long series of time-of-arrival ``points`` constructed with fiber optics. The fiber optic sensor apparatus measures shock velocity as the fiber sensor is progressively crushed as a shock wave proceeds in a direction along the fiber. The light received by a receiving means changes as time-of-arrival points are destroyed as the sensor is disturbed by the shock. The sensor may comprise a transmitting fiber bent into a series of loops and fused to a receiving fiber at various places, time-of-arrival points, along the receiving fibers length. At the ``points`` of contact, where a portion of the light leaves the transmitting fiber and enters the receiving fiber, the loops would be required to allow the light to travel backwards through the receiving fiber toward a receiving means. The sensor may also comprise a single optical fiber wherein the time-of-arrival points are comprised of reflection planes distributed along the fibers length. In this configuration, as the shock front proceeds along the fiber it destroys one reflector after another. The output received by a receiving means from this sensor may be a series of downward steps produced as the shock wave destroys one time-of-arrival point after another, or a nonsequential pattern of steps in the event time-of-arrival points are destroyed at any point along the sensor. 6 figs.

Shear wave speed recovery using moving interference patterns obtained in sonoelastography experiments.

PubMed

McLaughlin, Joyce; Renzi, Daniel; Parker, Kevin; Wu, Zhe

2007-04-01

Two new experiments were created to characterize the elasticity of soft tissue using sonoelastography. In both experiments the spectral variance image displayed on a GE LOGIC 700 ultrasound machine shows a moving interference pattern that travels at a very small fraction of the shear wave speed. The goal of this paper is to devise and test algorithms to calculate the speed of the moving interference pattern using the arrival times of these same patterns. A geometric optics expansion is used to obtain Eikonal equations relating the moving interference pattern arrival times to the moving interference pattern speed and then to the shear wave speed. A cross-correlation procedure is employed to find the arrival times; and an inverse Eikonal solver called the level curve method computes the speed of the interference pattern. The algorithm is tested on data from a phantom experiment performed at the University of Rochester Center for Biomedical Ultrasound.

Localization of Gunfire from Multiple Shooters (ARO Research Topic 5.2, Information Processing and Fusion; STIR Program)

DTIC Science & Technology

2016-03-03

for each shot, as well as "raw" data that includes time-of-arrival (TOA) and direction-of-arrival (DOA) of the muzzle blast (MB) produced by the weapon...angle of arrival, muzzle blast, shock wave, bullet deceleration, fusion REPORT DOCUMENTATION PAGE 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 10. SPONSOR...of the muzzle blast (MB) produced by the weapon and the shock wave (SW) produced by the supersonic bullet. The localization accuracy is improved

Nonlinear Localized Dissipative Structures for Long-Time Solution of Wave Equation

DTIC Science & Technology

2009-07-01

are described in this chapter. These details are required to compute interference. WC can be used to generate constant arrival time ( Eikonal phase...complicated using Eikonal schemes. Some recent developments in Eikonal methods [2] can treat multiple arrival times but, these methods require extra

Variations in population vulnerability to tectonic and landslide-related tsunami hazards in Alaska

USGS Publications Warehouse

Wood, Nathan J.; Peters, Jeff

2015-01-01

Effective tsunami risk reduction requires an understanding of how at-risk populations are specifically vulnerable to tsunami threats. Vulnerability assessments primarily have been based on single hazard zones, even though a coastal community may be threatened by multiple tsunami sources that vary locally in terms of inundation extents and wave arrival times. We use the Alaskan coastal communities of Cordova, Kodiak, Seward, Valdez, and Whittier (USA), as a case study to explore population vulnerability to multiple tsunami threats. We use anisotropic pedestrian evacuation models to assess variations in population exposure as a function of travel time out of hazard zones associated with tectonic and landslide-related tsunamis (based on scenarios similar to the 1964 M w9.2 Good Friday earthquake and tsunami disaster). Results demonstrate that there are thousands of residents, employees, and business customers in tsunami hazard zones associated with tectonically generated waves, but that at-risk individuals will likely have sufficient time to evacuate to high ground before waves are estimated to arrive 30–60 min after generation. Tsunami hazard zones associated with submarine landslides initiated by a subduction zone earthquake are smaller and contain fewer people, but many at-risk individuals may not have enough time to evacuate as waves are estimated to arrive in 1–2 min and evacuations may need to occur during earthquake ground shaking. For all hazard zones, employees and customers at businesses far outnumber residents at their homes and evacuation travel times are highest on docks and along waterfronts. Results suggest that population vulnerability studies related to tsunami hazards should recognize non-residential populations and differences in wave arrival times if emergency managers are to develop realistic preparedness and outreach efforts.

Improved Location of Microseismic Events in Borehole Monitoring by Inclusion of Particle Motion Analysis: a Case Study at a CBM Field in Indonesia

NASA Astrophysics Data System (ADS)

Verdhora Ry, Rexha; Septyana, T.; Widiyantoro, S.; Nugraha, A. D.; Ardjuna, A.

2017-04-01

Microseismic monitoring and constraining its hypocenters in and around hydrocarbon reservoirs provides insight into induced deformation related to hydraulic fracturing. In this study, we used data from a single vertical array of sensors in a borehole, providing measures of arrival times and polarizations. Microseismic events are located using 1-D velocity models and arrival times of P- and S-waves. However, in the case of all the sensors being deployed in a near-vertical borehole, there is a high ambiguity in the source location. Herein, we applied a procedure using azimuth of P-wave particle motion to constrain and improve the source location. We used a dataset acquired during 1-day of fracture stimulation at a CBM field in Indonesia. We applied five steps of location procedure to investigate microseismic events induced by these hydraulic fracturing activities. First, arrival times for 1584 candidate events were manually picked. Then we refined the arrival times using energy ratio method to obtain high consistency picking. Using these arrival times, we estimated back-azimuth using P-wave polarization analysis. We also added the combination of polarities analysis to remove 180° ambiguity. In the end, we determined hypocenter locations using grid-search method that guided in the back-azimuth trace area to minimize the misfit function of arrival times. We have successfully removed the ambiguity and produced a good solution for hypocenter locations as indicated statistically by small RMS. Most of the events clusters highlight coherent structures around the treatment well site and revealed faults. The same procedure can be applied to various other cases such as microseismic monitoring in the field of geothermal and shale gas/oil exploration, also CCS (Carbon Capture and Storage) development.

An automatic P‐Phase arrival‐time picker

USGS Publications Warehouse

Kalkan, Erol

2016-01-01

Presented is a new approach for picking P‐phase arrival time in single‐component acceleration or broadband velocity records without requiring detection interval or threshold settings. The algorithm PPHASEPICKER transforms the signal into a response domain of a single‐degree‐of‐freedom (SDOF) oscillator with viscous damping and then tracks the rate of change of dissipated damping energy to pick P‐wave phases. The SDOF oscillator has a short natural period and a correspondingly high resonant frequency, which is higher than most frequencies in a seismic wave. It also has a high damping ratio (60% of critical). At this damping level, the frequency response approaches the Butterworth maximally flat magnitude filter, and phase angles are preserved. The relative input energy imparted to the oscillator by the input signal is converted to elastic strain energy and then dissipated by the damping element as damping energy. The damping energy yields a smooth envelope over time; it is zero in the beginning of the signal, zero or near zero before theP‐phase arrival, and builds up rapidly with the P wave. Because the damping energy function changes considerably at the onset of the P wave, it is used as a metric to track and pick the P‐phase arrival time. The PPHASEPICKER detects P‐phase onset using the histogram method. Its performance is compared with picking techniques using short‐term‐average to long‐term‐average ratio, and a picking method that finds the first P‐phase arrival time using the Akaike information criterion. A large set of records with various intensities and signal‐to‐noise ratios is used for testing the PPHASEPICKER, and it is demonstrated thatPPHASEPICKER is able to more accurately pick the onset of genuine signals against the background noise and to correctly distinguish between whether the first arrival is a P wave (emergent or impulsive) or whether the signal is from a faulty sensor.

Pipe wall damage detection by electromagnetic acoustic transducer generated guided waves in absence of defect signals.

PubMed

Vasiljevic, Milos; Kundu, Tribikram; Grill, Wolfgang; Twerdowski, Evgeny

2008-05-01

Most investigators emphasize the importance of detecting the reflected signal from the defect to determine if the pipe wall has any damage and to predict the damage location. However, often the small signal from the defect is hidden behind the other arriving wave modes and signal noise. To overcome the difficulties associated with the identification of the small defect signal in the time history plots, in this paper the time history is analyzed well after the arrival of the first defect signal, and after different wave modes have propagated multiple times through the pipe. It is shown that the defective pipe can be clearly identified by analyzing these late arriving diffuse ultrasonic signals. Multiple reflections and scattering of the propagating wave modes by the defect and pipe ends do not hamper the defect detection capability; on the contrary, it apparently stabilizes the signal and makes it easier to distinguish the defective pipe from the defect-free pipe. This paper also highlights difficulties associated with the interpretation of the recorded time histories due to mode conversion by the defect. The design of electro-magnetic acoustic transducers used to generate and receive the guided waves in the pipe is briefly described in the paper.

ZERO-TIME INDICATOR

DOEpatents

Sander, H.H.

1960-08-30

The travel time of a nuclear shock wave from its point of origin to a location can be determined accurately by an apparatus for noting and comparably recording both zerotime, as indicated by the electromagnetic transient associated with the nuclear detonation, and shock wave arrival time.

AIMBAT: A Python/Matplotlib Tool for Measuring Teleseismic Arrival Times

NASA Astrophysics Data System (ADS)

Lou, X.; van der Lee, S.; Lloyd, S.

2013-12-01

Python is an open-source, platform-independent, and object-oriented scripting language. It became more popular in the seismologist community since the appearance of ObsPy (Beyreuther et al. 2010, Megies et al. 2011), which provides a powerful framework for seismic data access and processing. This study introduces a new Python-based tool named AIMBAT (Automated and Interactive Measurement of Body-wave Arrival Times) for measuring teleseismic body-wave arrival times on large-scale seismic event data (Lou et al. 2013). Compared to ObsPy, AIMBAT is a lighter tool that is more focused on a particular aspect of seismic data processing. It originates from the widely used MCCC (Multi-Channel Cross-Correlation) method developed by VanDecar and Crosson (1990). On top of the original MCCC procedure, AIMBAT is automated in initial phase picking and is interactive in quality control. The core cross-correlation function is implemented in Fortran to boost up performance in addition to Python. The GUI (graphical user interface) of AIMBAT depends on Matplotlib's GUI-neutral widgets and event-handling API. A number of sorting and (de)selecting options are designed to facilitate the quality control of seismograms. By using AIMBAT, both relative and absolute teleseismic body-wave arrival times are measured. AIMBAT significantly improves efficiency and quality of the measurements. User interaction is needed only to pick the target phase arrival and to set a time window on the array stack. The package is easy to install and use, open-source, and is publicly available. Graphical user interface of AIMBAT.

Optical fiber repeatered transmission systems utilizing SAW filters

NASA Astrophysics Data System (ADS)

Rosenberg, R. L.; Ross, D. G.; Trischitta, P. R.; Fishman, D. A.; Armitage, C. B.

1983-05-01

Baseband digital transmission-line systems capable of signaling rates of several hundred to several thousand Mbit/s are presently being developed around the world. The pulse regeneration process is gated by a timing wave which is synchronous with the symbol rate of the arriving pulse stream. Synchronization is achieved by extracting a timing wave from the arriving pulse stream, itself. To date, surface acoustic-wave (SAW) filters have been widely adopted for timing recovery in the in-line regenerators of high-bit-rate systems. The present investigation has the objective to acquaint the SAW community in general, and SAW filter suppliers in particular, with the requirements for timing recovery filters in repeatered digital transmission systems. Attention is given to the system structure, the timing loop function, the system requirements affecting the timing-recovery filter, the decision process, timing jitter accumulation, the filter 'ringing' requirement, and aspects of reliability.

Assessing Multiple Methods for Determining Active Source Travel Times in a Dense Array

NASA Astrophysics Data System (ADS)

Parker, L.; Zeng, X.; Thurber, C. H.; Team, P.

2016-12-01

238 three-component nodal seismometers were deployed at the Brady Hot Springs geothermal field in Nevada to characterize changes in the subsurface as a result of changes in pumping conditions. The array consisted of a 500 meter by 1600 meter irregular grid with 50 meter spacing centered in an approximately rectangular 1200 meter by 1600 meter grid with 200 meter spacing. A large vibroseis truck (T-Rex) was deployed as an active seismic source at 216 locations. Over the course of 15 days, the truck occupied each location up to four times. At each location a swept-frequency source between 5 and 80 Hz over 20 seconds was produced using three vibration modes: longitudinal S-wave, transverse S-wave, and P-wave. Seismic wave arrivals were identified using three methods: cross-correlation, deconvolution, and Wigner-Ville distribution (WVD) plus the Hough Transform (HT). Surface wave arrivals were clear for all three modes of vibration using all three methods. Preliminary tomographic models will be presented, using the arrivals of the identified phases. This analysis is part of the PoroTomo project: Poroelastic Tomography by Adjoint Inverse Modeling of Data from Seismology, Geodesy, and Hydrology; http://geoscience.wisc.edu/feigl/porotomo.

Detecting P and S-wave of Mt. Rinjani seismic based on a locally stationary autoregressive (LSAR) model

NASA Astrophysics Data System (ADS)

Nurhaida, Subanar, Abdurakhman, Abadi, Agus Maman

2017-08-01

Seismic data is usually modelled using autoregressive processes. The aim of this paper is to find the arrival times of the seismic waves of Mt. Rinjani in Indonesia. Kitagawa algorithm's is used to detect the seismic P and S-wave. Householder transformation used in the algorithm made it effectively finding the number of change points and parameters of the autoregressive models. The results show that the use of Box-Cox transformation on the variable selection level makes the algorithm works well in detecting the change points. Furthermore, when the basic span of the subinterval is set 200 seconds and the maximum AR order is 20, there are 8 change points which occur at 1601, 2001, 7401, 7601,7801, 8001, 8201 and 9601. Finally, The P and S-wave arrival times are detected at time 1671 and 2045 respectively using a precise detection algorithm.

Impacts of short-time scale water column variability on broadband high-frequency acoustic wave propagation

NASA Astrophysics Data System (ADS)

Eickmeier, Justin

Acoustical oceanography is one way to study the ocean, its internal layers, boundaries and all processes occurring within using underwater acoustics. Acoustical sensing techniques allows for the measurement of ocean processes from within that logistically or financially preclude traditional in-situ measurements. Acoustic signals propagate as pressure wavefronts from a source to a receiver through an ocean medium with variable physical parameters. The water column physical parameters that change acoustic wave propagation in the ocean include temperature, salinity, current, surface roughness, seafloor bathymetry, and vertical stratification over variable time scales. The impacts of short-time scale water column variability on acoustic wave propagation include coherent and incoherent surface reflections, wavefront arrival time delay, focusing or defocusing of the intensity of acoustic beams and refraction of acoustic rays. This study focuses on high-frequency broadband acoustic waves, and examines the influence of short-time scale water column variability on broadband high-frequency acoustics, wavefronts, from 7 to 28 kHz, in shallow water. Short-time scale variability is on the order of seconds to hours and the short-spatial scale variability is on the order of few centimeters. Experimental results were collected during an acoustic experiment along 100 m isobaths and data analysis was conducted using available acoustic wave propagation models. Three main topics are studied to show that acoustic waves are viable as a remote sensing tool to measure oceanographic parameters in shallow water. First, coherent surface reflections forming striation patterns, from multipath receptions, through rough surface interaction of broadband acoustic signals with the dynamic sea surface are analyzed. Matched filtered results of received acoustic waves are compared with a ray tracing numerical model using a sea surface boundary generated from measured water wave spectra at the time of signal propagation. It is determined that on a time scale of seconds, corresponding to typical periods of surface water waves, the arrival time of reflected acoustic signals from surface waves appear as striation patterns in measured data and can be accurately modelled by ray tracing. Second, changes in acoustic beam arrival angle and acoustic ray path influenced by isotherm depth oscillations are analyzed using an 8-element delay-sum beamformer. The results are compared with outputs from a two-dimensional (2-D) parabolic equation (PE) model using measured sound speed profiles (SSPs) in the water column. Using the method of beamforming on the received signal, the arrival time and angle of an acoustic beam was obtained for measured acoustic signals. It is determined that the acoustic ray path, acoustic beam intensity and angular spread are a function of vertical isotherm oscillations on a time scale of minutes and can be modeled accurately by a 2-D PE model. Third, a forward problem is introduced which uses acoustic wavefronts received on a vertical line array, 1.48 km from the source, in the lower part of the water column to infer range dependence or independence in the SSP. The matched filtering results of received acoustic wavefronts at all hydrophone depths are compared with a ray tracing routine augmented to calculate only direct path and bottom reflected signals. It is determined that the SSP range dependence can be inferred on a time scale of hours using an array of hydrophones spanning the water column. Sound speed profiles in the acoustic field were found to be range independent for 11 of the 23 hours in the measurements. A SSP cumulative reconstruction process, conducted from the seafloor to the sea surface, layer-by-layer, identifies critical segments in the SSP that define the ray path, arrival time and boundary interactions. Data-model comparison between matched filtered arrival time spread and arrival time output from the ray tracing was robust when the SSP measured at the receiver was input to the model. When the SSP measured nearest the source (at the same instant in time) was input to the ray tracing model, the data-model comparison was poor. It was determined that the cumulative sound speed change in the SSP near the source was 1.041 m/s greater than that of the SSP at the receiver and resulted in the poor data-model comparison. In this study, the influences on broadband acoustic wave propagation in the frequency range of 7 to 28 kHz of spatial and temporal changes in the oceanography of shallow water regions are addressed. Acoustic waves can be used as remote sensing tools to measure oceanographic parameters in shallow water and data-model comparison results show a direct relationship between the oceanographic variations and acoustic wave propagations.

Multimode seismoelectric phenomena generated using explosive and vibroseis sources

NASA Astrophysics Data System (ADS)

Butler, Karl E.; Kulessa, Bernd; Pugin, André J.-M.

2018-05-01

A field trial of seismoelectric surveying was carried out at a site underlain by 20 m of water-saturated clayey Champlain Sea sediments, renowned for their amenability to high resolution imaging by seismic reflection surveys. Seismically induced electrokinetic effects were recorded using an array of 26 grounded dipole electric field antennas, and two different seismic sources including an eight-gauge shotgun, and a moderate power (10 000 lb Minivib) vibrator. Despite the high electrical conductivity of the sediments, shot records show evidence of possible interfacial seismoelectric conversions caused by the arrival of P-waves at the base of the clay/top of bedrock and at the top of a layer of elevated porosity and conductivity within the clay at 7 m depth. However, the data are more remarkable for the fact that P-wave, S-wave, and PS/SP converted wave reflections evident in the seismic records all give rise to electrical arrivals exhibiting very similar moveout patterns in the seismoelectric records. Superficially, these electrical responses could be misinterpreted as simple coseismic seismoelectric effects associated with the arrival of reflected seismic waves at each dipole antenna on surface. However, their broader bandwidth, superior coherency and earlier arrival times compared to their corresponding seismic arrivals indicate that the electrical effects are generated by the arrival of seismic reflections below each dipole at the shallow intraclay interface 7 m below surface. Such quasi-coseismic arrivals have recently been predicted by full-waveform seismoelectric modelling and characterized as evanescent electromagnetic (EM) waves. In retrospect, they were also observed in earlier seismoelectric field trials, but not measured as clearly nor recognized as a distinct seismoelectric mode intermediate between interfacial and coseismic effects. We propose that the observed quasi-coseismic effect can be understood physically as a fringing field emanating from the travelling charge separation associated with a P-wave (direct or mode-converted) crossing a subsurface interface at an oblique angle. Such effects may be nearly indistinguishable from coseismic effects if the interface depth is small compared to the seismic wavelength, but recognition of the phenomenon contributes to an improved understanding of the seismoelectric wavefield, and will lead to improved interpretations. From a practical standpoint, the results of this field trial suggest that using electric field receivers to supplement geophones on surface could yield significantly higher resolution seismic reflection images in those areas where suitable near-surface layers exist for the generation of quasi-coseismic effects. The results also reinforce the importance of using multichannel recording to allow interfacial seismoelectric conversions originating at depth to be distinguished from stronger coseismic and quasi-coseismic arrivals originating in the near-surface by measurement of their arrival time versus offset (moveout) and amplitude versus offset behaviours.

Time operators in stroboscopic wave-packet basis and the time scales in tunneling

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

Bokes, P.

2011-03-15

We demonstrate that the time operator that measures the time of arrival of a quantum particle into a chosen state can be defined as a self-adjoint quantum-mechanical operator using periodic boundary conditions and applied to wave functions in energy representation. The time becomes quantized into discrete eigenvalues; and the eigenstates of the time operator, i.e., the stroboscopic wave packets introduced recently [Phys. Rev. Lett. 101, 046402 (2008)], form an orthogonal system of states. The formalism provides simple physical interpretation of the time-measurement process and direct construction of normalized, positive definite probability distribution for the quantized values of the arrival time.more » The average value of the time is equal to the phase time but in general depends on the choice of zero time eigenstate, whereas the uncertainty of the average is related to the traversal time and is independent of this choice. The general formalism is applied to a particle tunneling through a resonant tunneling barrier in one dimension.« less

Incorporating fault zone head wave and direct wave secondary arrival times into seismic tomography: Application at Parkfield, California

NASA Astrophysics Data System (ADS)

Bennington, N. L.; Thurber, C. H.; Zhang, H.; Peng, Z.; Zhao, P.

2011-12-01

Large crustal faults such as the San Andreas fault (SAF) often juxtapose rocks of significantly different elastic properties, resulting in well-defined bimaterial interfaces. A sharp material contrast across the fault interface is expected to generate fault zone head waves (FZHW's) that spend a large portion of their propagation paths refracting along the bimaterial interface (Ben-Zion 1989, 1990; Ben-Zion & Aki 1990). Because of this FZHW's provide a high-resolution tool for imaging the velocity contrast across the fault. Recently, Zhao et al. (2010) systematically analyzed large data sets of near-fault waveforms recorded by several permanent and temporary seismic networks along the Parkfield section of the SAF. The local-scale tomography study of Zhang et al. (2009) for a roughly 10 km3 volume centered on SAFOD and the more regional-scale study of Thurber et al. (2006) for a 130 km x 120 km x 20 km volume centered on the 2004 Parkfield earthquake rupture provide what are probably the best 3D images of the seismic velocity structure of the area. The former shows a low velocity zone associated with the SAF extending to significant depth, and both image the well-known velocity contrast across the fault. Seismic tomography generally uses just first P and/or S arrivals because of the relative simplicity of phase picking and ray tracing. Adding secondary arrivals such as FZHW's, however, can enhance the resolution of structure and strengthen constraints on earthquake locations and focal mechanisms. We present a model of 3D velocity structure for the Parkfield region that utilizes a combination of arrival times for FZHW's and the associated direct-wave secondary arrivals as well as existing P-wave arrival time data. The resulting image provides a higher-resolution model of the SAF at depth than previously published models. In addition, we plan to measure polarizations of the direct P and S waves and FZHW's and incorporate the data into our updated velocity tomography/relocation inversion. Through these efforts, we hope to refine the 3D tomographic image of seismic velocity structure and the complex geometry of the active fault strands near SAFOD and along the Parkfield rupture zone.

Seismic tomography of northeastern Tibetan Plateau from body wave arrival times and surface wave dispersion data

NASA Astrophysics Data System (ADS)

Fang, H.; Yao, H.; Zhang, H.

2017-12-01

Reliable crustal and upper mantle structure is important to understand expansion of material from the Tibetan plateau to its northeastern margin. Previous studies have used either ambient noise tomography or body wave traveltime tomography to obtain the crustal velocity models in northeastern Tibetan Plateau. However, clear differences appear in these models obtained using different datasets. Here we propose to jointly invert local and teleseismic body wave arrival times and surface wave dispersion data from ambient noise cross correlation to obtain a unified P and S wavespeed model of the crust and upper mantle in NE Tibetan Plateau. Following Fang et al. (2016), we adopt the direct inversion strategy for surface wave data (Fang et al., 2015), which eliminates the need to construct the phase/group velocity maps and allows the straightforward incorporation of surface wave dispersion data into the body wave inversion framework. For body wave data including both local and teleseismic arrival times, we use the fast marching method (Rawlinson et al., 2004) in order to trace multiple seismic phases simultaneously. The joint inversion method takes advantage of the complementary strengths of different data types, with local body wave data constraining more on the P than S wavespeed in the crust, surface wave data most sensitive to S wavespeed in the crust and upper mantle, teleseismic body wave data resolving the upper mantle structure. A series of synthetic tests will be used to show the robustness and superiority of the joint inversion method. Besides, the inverted model will be validated by waveform simulation and comparison with other studies, like receiver function imaging. The resultant P and S wavespeed models, as well as the derived Vp/Vs model, will be essential to understand the regional tectonics of the northeastern Tibetan Plateau, and to address the related geodynamic questions of the Tibetan Plateau formation and expansion.

The large tsunami of 26 December 2004: Field observations and eyewitnesses accounts from Sri Lanka, Maldives Is. and Thailand

NASA Astrophysics Data System (ADS)

Papadopoulos, Gerassimos A.; Caputo, Riccardo; McAdoo, Brian; Pavlides, Spyros; Karastathis, Vassilios; Fokaefs, Anna; Orfanogiannaki, Katerina; Valkaniotis, Sotiris

2006-02-01

Post-event field surveys were conducted and measurements were taken in Sri Lanka and Maldives about two weeks after the catastrophic Indian Ocean tsunami of 26 December 2004. The measurements taken were cross-checked after interviewing with local people. In the southwest, south and east coastal zones of Sri Lanka maximum water levels ranging from h = 3 m to h = 11 m a.m.s.l. were estimated. The highest values observed were in the south of the island: Galle h ˜ 10 m, Hambantota h ˜ 11m. Maximum inundation of d ˜ 2 km was observed in Hambantota. The heavy destruction and thousands of victims caused in coastal communities, buildings and infrastructure, like railways and bridges, is attributed not only to physical parameters, like the strength of the tsunami hydrodynamic flow, coastal geomorphology and the wave erosional action in soil, but also to anthropogenic factors including the increased vulnerability of the non-RC buildings and the high population density. Local people usually described the tsunami as a series of three main waves. The leading wave phase was only a silent sea level rise of h ≤ 1.5 m and d ≤ 150 m, while the second wave was the strongest one. The first two waves occurred between 09:00 and 09:30 local time, depending on the locality. It is well documented that near Galle, southern part, the strong wave arrived at 09:25:30. In the west coast the third wave was a late arrival which possibly represents reflection phases. In Maldives, three waves were also reported to arrive between 09:00 and 09:30 local time. Maximum water level was only h ˜ 3 m in Laamu Atoll, which is interpreted by the wave amplitude damping by the coral reef to the east of the island complex as well as to that the tsunami did not arrived at high tide time. Damage was observed in several islands of Maldives but this was minimal as compared to the heavy destruction observed in Sri Lanka. About 25 Greek eyewitnesses, who happened to experience the tsunami attack in Padong and Blue Lagoon Port of Phuket island as well as in Maya Bay, Phi-Phi islands, Thailand, were interviewed on the basis of a standard questionnaire. The first sea motion was a retreat of at least 100 m. Then, two main waves arrived, the first being the strong one occurring at about 09:55-10:05 local time, with h ˜ 6m in Padong causing significant destruction and human victims. The collected information clearly indicates that the tsunami propagated as the leading crest wave to the west side, e.g. in Sri Lanka and Maldives, and as the leading trough wave to the east, e.g. in Thailand.

A Nonparametric Approach to Automated S-Wave Picking

NASA Astrophysics Data System (ADS)

Rawles, C.; Thurber, C. H.

2014-12-01

Although a number of very effective P-wave automatic pickers have been developed over the years, automatic picking of S waves has remained more challenging. Most automatic pickers take a parametric approach, whereby some characteristic function (CF), e.g. polarization or kurtosis, is determined from the data and the pick is estimated from the CF. We have adopted a nonparametric approach, estimating the pick directly from the waveforms. For a particular waveform to be auto-picked, the method uses a combination of similarity to a set of seismograms with known S-wave arrivals and dissimilarity to a set of seismograms that do not contain S-wave arrivals. Significant effort has been made towards dealing with the problem of S-to-P conversions. We have evaluated the effectiveness of our method by testing it on multiple sets of microearthquake seismograms with well-determined S-wave arrivals for several areas around the world, including fault zones and volcanic regions. In general, we find that the results from our auto-picker are consistent with reviewed analyst picks 90% of the time at the 0.2 s level and 80% of the time at the 0.1 s level, or better. For most of the large datasets we have analyzed, our auto-picker also makes far more S-wave picks than were made previously by analysts. We are using these enlarged sets of high-quality S-wave picks to refine tomographic inversions for these areas, resulting in substantial improvement in the quality of the S-wave images. We will show examples from New Zealand, Hawaii, and California.

Ultrafast propagation of Schroedinger waves in absorbing media

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

Delgado, F.; Muga, J.G.; Ruschhaupt, A.

2004-02-01

We show that the temporal peak of a quantum wave may arrive at different locations simultaneously in an absorbing medium. The arrival occurs at the lifetime of the particle in the medium from the instant when a point source with a sharp onset is turned on. We also identify other characteristic times. In particular, the 'traversal' or 'Buettiker-Landauer' time (which grows linearly with the distance to the source) for the Hermitian, non-absorbing case is substituted by several characteristic quantities in the absorbing case. The simultaneous arrival due to absorption, unlike the Hartman effect, occurs for carrier frequencies under or abovemore » the cutoff, and for arbitrarily large distances. It holds also in a relativistic generalization but limited by causality. A possible physical realization is proposed by illuminating a two-level atom with a detuned laser.« less

Opportunities for shear energy scaling in bulk acoustic wave resonators.

PubMed

Jose, Sumy; Hueting, Raymond J E

2014-10-01

An important energy loss contribution in bulk acoustic wave resonators is formed by so-called shear waves, which are transversal waves that propagate vertically through the devices with a horizontal motion. In this work, we report for the first time scaling of the shear-confined spots, i.e., spots containing a high concentration of shear wave displacement, controlled by the frame region width at the edge of the resonator. We also demonstrate a novel methodology to arrive at an optimum frame region width for spurious mode suppression and shear wave confinement. This methodology makes use of dispersion curves obtained from finite-element method (FEM) eigenfrequency simulations for arriving at an optimum frame region width. The frame region optimization is demonstrated for solidly mounted resonators employing several shear wave optimized reflector stacks. Finally, the FEM simulation results are compared with measurements for resonators with Ta2O5/ SiO2 stacks showing suppression of the spurious modes.

Identification of the Low-velocity Zone Beneath the Northern Taiwan by the P-wave Delays Analysis

NASA Astrophysics Data System (ADS)

Chang, C. W.; Che-Min, L.

2017-12-01

Taipei City, the capital of Taiwan, located in northern Taiwan is near to the Tatun volcano group and the Shanchiao fault which is an active fault. This region is a complex tectonic environment. The Tatun volcano group is seen as a dormant volcano. Recently, the location of the magma reservoir of the Tatun volcano was discussed again. However, the volume and the location of the magma reservoir are still unclear. There are several seismic networks operated by different institutions around Taipei and Tatun volcano. In this study, we combined the data of these networks to analysis the P-wave arrival times for clarifying the magma reservoir. The events with hypocenters are deeper than 100 km and the local magnitude (ML) are larger than 4.0 were collected to analysis. Our results show that the stations could be separated into three groups by the slope of the P-wave arrival time. They are distributed at the western of the Basin edge, the Jin-Shan Plain areal and the Taipei Basin, respectively. When the epicenter distance of the different stations is the same, the P-wave arrival time of the stations on the west side of the basin edge will be 0.3 0.5 seconds later than that in the Taipei Basin, and the stations on the Jin-Shan Plain will be 0.1 0.4 seconds later than in the Taipei Basin. The slope of the P-wave arrival time in 3 groups is very different, indicating that the low-velocity zone is existed in shallow crustal beneath of these areas. However, the low-velocity zone can be connected to the magma reservoir of the Tatun volcano group or submarine volcano of Keelung Island or not? It can be discussed the correlation between the magma reservoir and the low-velocity zone by more events collected.

Empirical transfer functions: Application to the determination of outermost core velocity structure using teleseismic SmKS phases

NASA Astrophysics Data System (ADS)

Eaton, D. W.; Alexandrakis, C.

2007-05-01

Teleseismic SmKS waves propagate as S-waves in the mantle and compressional (K) waves in the core, with m-1 underside bounce points at the core-mantle boundary. For long-period or broadband recordings at epicentral distances of 115-135°, higher-order SmKS waves (3 ≤ m < ∞) are not often discernible as distinct pulses. Instead, they are typically manifested as a weakly dispersive waveform that lags SKKS by ~ 12-32s. In a ray-theoretical representation of this process, there is a strong geometrical similarity between the coalescence of SmKS turning waves to form a composite arrival and the interference of mantle S waves to form teleseismic Love waves. SmKS waves can thus be viewed as a type of pseudo-interface wave, the dispersive properties of which depend strongly on the fine-scale velocity structure of the outermost core. In order to analyze SmKS arrivals, we have developed an empirical transfer-function (ETF) technique that uses SKKS as a reference phase. An ETF is a wave-shaping filter that transforms the observed SKKS pulse into the observed SmKS pulse. We obtain this filter by windowing the respective pulses and applying frequency- domain Wiener deconvolution. Each ETF contains SmKS-SKKS differential arrival-time, phase-shift and relative-amplitude information; it also implicitly removes the source-time function and instrument response, thus facilitating the merging of results from different stations and events. Here, we apply this approach to global observations of SmKS phases and invert the results to yield a new velocity model for the outermost core region.

6C polarization analysis - seismic direction finding in coherent noise, automated event identification, and wavefield separation

NASA Astrophysics Data System (ADS)

Schmelzbach, C.; Sollberger, D.; Greenhalgh, S.; Van Renterghem, C.; Robertsson, J. O. A.

2017-12-01

Polarization analysis of standard three-component (3C) seismic data is an established tool to determine the propagation directions of seismic waves recorded by a single station. A major limitation of seismic direction finding methods using 3C recordings, however, is that a correct propagation-direction determination is only possible if the wave mode is known. Furthermore, 3C polarization analysis techniques break down in the presence of coherent noise (i.e., when more than one event is present in the analysis time window). Recent advances in sensor technology (e.g., fibre-optical, magnetohydrodynamic angular rate sensors, and ring laser gyroscopes) have made it possible to accurately measure all three components of rotational ground motion exhibited by seismic waves, in addition to the conventionally recorded three components of translational motion. Here, we present an extension of the theory of single station 3C polarization analysis to six-component (6C) recordings of collocated translational and rotational ground motions. We demonstrate that the information contained in rotation measurements can help to overcome some of the main limitations of standard 3C seismic direction finding, such as handling multiple arrivals simultaneously. We show that the 6C polarisation of elastic waves measured at the Earth's free surface does not only depend on the seismic wave type and propagation direction, but also on the local P- and S-wave velocities just beneath the recording station. Using an adaptation of the multiple signal classification algorithm (MUSIC), we demonstrate how seismic events can univocally be identified and characterized in terms of their wave type. Furthermore, we show how the local velocities can be inferred from single-station 6C data, in addition to the direction angles (inclination and azimuth) of seismic arrivals. A major benefit of our proposed 6C method is that it also allows the accurate recovery of the wave type, propagation directions, and phase velocities of multiple, interfering arrivals in one time window. We demonstrate how this property can be exploited to separate the wavefield into its elastic wave-modes and to isolate or suppress waves arriving from specific directions (directional filtering), both in a fully automated fashion.

Spiral-shaped piezoelectric sensors for Lamb waves direction of arrival (DoA) estimation

NASA Astrophysics Data System (ADS)

De Marchi, L.; Testoni, N.; Marzani, A.

2018-04-01

A novel strategy to design piezoelectric sensors suited for direction of arrival (DoA) estimation of incoming Lamb waves is presented in this work. The designed sensor is composed by two piezoelectric patches (P1, P2) bonded on the structure to be inspected. In particular, by exploiting the Radon transform, the proposed procedure computes the shape of P2 given the shape of P1 so that the difference in time of arrival (DToA) of the Lamb waves at the two patches is linearly related to the DoA while being agnostic of the waveguide dispersion curves. With a dedicated processing procedure, the waveforms acquired from the two electrodes and digitized can be used to retrieve the DoA information. Numerical and experimental results show that DoA estimation performed by means of the proposed shaped transducers is extremely robust.

Subduction zone guided waves in Northern Chile

NASA Astrophysics Data System (ADS)

Garth, Thomas; Rietbrock, Andreas

2016-04-01

Guided wave dispersion is observed in subduction zones as high frequency energy is retained and delayed by low velocity structure in the subducting slab, while lower frequency energy is able to travel at the faster velocities associated with the surrounding mantle material. As subduction zone guided waves spend longer interacting with the low velocity structure of the slab than any other seismic phase, they have a unique capability to resolve these low velocity structures. In Northern Chile, guided wave arrivals are clearly observed on two stations in the Chilean fore-arc on permanent stations of the IPOC network. High frequency (> 5 Hz) P-wave arrivals are delayed by approximately 2 seconds compared to the low frequency (< 2 Hz) P-wave arrivals. Full waveform finite difference modelling is used to test the low velocity slab structure that cause this P-wave dispersion. The synthetic waveforms produced by these models are compared to the recorded waveforms. Spectrograms are used to compare the relative arrival times of different frequencies, while the velocity spectra is used to constrain the relative amplitude of the arrivals. Constraining the waveform in these two ways means that the full waveform is also matched, and the low pass filtered observed and synthetic waveforms can be compared. A combined misfit between synthetic and observed waveforms is then calculated following Garth & Rietbrock (2014). Based on this misfit criterion we constrain the velocity model by using a grid search approach. Modelling the guided wave arrivals suggest that the observed dispersion cannot be solely accounted for by a single low velocity layer as suggested by previous guided wave studies. Including dipping low velocity normal fault structures in the synthetic model not only accounts for the observed strong P-wave coda, but also produces a clear first motion dispersion. We therefore propose that the lithospheric mantle of the subducting Nazca plate is highly hydrated at intermediate depths by dipping low velocity normal faults. Additionally, we show that the low velocity oceanic crust persists to depths of up to 200 km, well beyond the depth range where the eclogite transition is expected to have occurred. Our results suggest that young subducting lithosphere also has the potential to carry much larger amounts of water to the mantle than has previously been appreciated.

Velocity Structure Determination Through Seismic Waveform Modeling and Time Deviations

NASA Astrophysics Data System (ADS)

Savage, B.; Zhu, L.; Tan, Y.; Helmberger, D. V.

2001-12-01

Through the use of seismic waveforms recorded by TriNet, a dataset of earthquake focal mechanisms and deviations (time shifts) relative to a standard model facilitates the investigation of the crust and uppermost mantle of southern California. The CAP method of focal mechanism determination, in use by TriNet on a routine basis, provides time shifts for surface waves and Pnl arrivals independently relative to the reference model. These shifts serve as initial data for calibration of local and regional seismic paths. Time shifts from the CAP method are derived by splitting the Pnl section of the waveform, the first arriving Pn to just before the arrival of the S wave, from the much slower surface waves then cross-correlating the data with synthetic waveforms computed from a standard model. Surface waves interact with the entire crust, but the upper crust causes the greatest effect. Whereas, Pnl arrivals sample the deeper crust, upper mantle, and source region. This natural division separates the upper from lower crust for regional calibration and structural modeling and allows 3-D velocity maps to be created using the resulting time shifts. Further examination of Pnl and other arrivals which interact with the Moho illuminate the complex nature of this boundary. Initial attempts at using the first 10 seconds of the Pnl section to determine upper most mantle structure have proven insightful. Two large earthquakes north of southern California in Nevada and Mammoth Lakes, CA allow the creation of record sections from 200 to 600 km. As the paths swing from east to west across southern California, simple 1-D models turn into complex structure, dramatically changing the waveform character. Using finite difference models to explain the structure, we determine that a low velocity zone is present at the base of the crust and extends to 100 km in depth. Velocity variations of 5 percent of the mantle in combination with steeply sloping edges produces complex waveform variations. Characteristics of this complex propagation appear from the southern Sierra Nevada Mountains, in the west, to Death Valley in the east. The structure does not cross the Garlock fault to the south, but we are unsure of the structures northern extent.

Time of arrival in quantum and Bohmian mechanics

NASA Astrophysics Data System (ADS)

Leavens, C. R.

1998-08-01

In a recent paper Grot, Rovelli, and Tate (GRT) [Phys. Rev. A 54, 4676 (1996)] derived an expression for the probability distribution π(TX) of intrinsic arrival times T(X) at position x=X for a quantum particle with initial wave function ψ(x,t=0) freely evolving in one dimension. This was done by quantizing the classical expression for the time of arrival of a free particle at X, assuming a particular choice of operator ordering, and then regulating the resulting time of arrival operator. For the special case of a minimum-uncertainty-product wave packet at t=0 with average wave number and variance Δk they showed that their analytical expression for π(TX) agreed with the probability current density J(x=X,t=T) only to terms of order Δk/. They dismissed the probability current density as a viable candidate for the exact arrival time distribution on the grounds that it can sometimes be negative. This fact is not a problem within Bohmian mechanics where the arrival time distribution for a particle, either free or in the presence of a potential, is rigorously given by \\|J(X,T)\\| (suitably normalized) [W. R. McKinnon and C. R. Leavens, Phys. Rev. A 51, 2748 (1995); C. R. Leavens, Phys. Lett. A 178, 27 (1993); M. Daumer et al., in On Three Levels: The Mathematical Physics of Micro-, Meso-, and Macro-Approaches to Physics, edited by M. Fannes et al. (Plenum, New York, 1994); M. Daumer, in Bohmian Mechanics and Quantum Theory: An Appraisal, edited by J. T. Cushing et al. (Kluwer Academic, Dordrecht, 1996)]. The two theories are compared in this paper and a case presented for which the results could not differ more: According to GRT's theory, every particle in the ensemble reaches a point x=X, where ψ(x,t) and J(x,t) are both zero for all t, while no particle ever reaches X according to the theory based on Bohmian mechanics. Some possible implications are discussed.

THE NANOGRAV NINE-YEAR DATA SET: OBSERVATIONS, ARRIVAL TIME MEASUREMENTS, AND ANALYSIS OF 37 MILLISECOND PULSARS

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

Arzoumanian, Zaven; Brazier, Adam; Chatterjee, Shami

2015-11-01

We present high-precision timing observations spanning up to nine years for 37 millisecond pulsars monitored with the Green Bank and Arecibo radio telescopes as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project. We describe the observational and instrumental setups used to collect the data, and methodology applied for calculating pulse times of arrival; these include novel methods for measuring instrumental offsets and characterizing low signal-to-noise ratio timing results. The time of arrival data are fit to a physical timing model for each source, including terms that characterize time-variable dispersion measure and frequency-dependent pulse shape evolution. Inmore » conjunction with the timing model fit, we have performed a Bayesian analysis of a parameterized timing noise model for each source, and detect evidence for excess low-frequency, or “red,” timing noise in 10 of the pulsars. For 5 of these cases this is likely due to interstellar medium propagation effects rather than intrisic spin variations. Subsequent papers in this series will present further analysis of this data set aimed at detecting or limiting the presence of nanohertz-frequency gravitational wave signals.« less

Rapid Estimation of Building Damage by Conventional Weapons

DTIC Science & Technology

2014-09-01

impulse applied to reflect surface 17 iso = impulse of incident wave t0 = wave duration Lw = wavelength of incident wave ta = arrival time...floor area = 3 x 100 x 90 = 27000 ft2 Tributary area support per column = 27000 /30 = 900 ft2 Therefore, the tributary area supported by a column is

A non-parametric method for automatic determination of P-wave and S-wave arrival times: application to local micro earthquakes

NASA Astrophysics Data System (ADS)

Rawles, Christopher; Thurber, Clifford

2015-08-01

We present a simple, fast, and robust method for automatic detection of P- and S-wave arrivals using a nearest neighbours-based approach. The nearest neighbour algorithm is one of the most popular time-series classification methods in the data mining community and has been applied to time-series problems in many different domains. Specifically, our method is based on the non-parametric time-series classification method developed by Nikolov. Instead of building a model by estimating parameters from the data, the method uses the data itself to define the model. Potential phase arrivals are identified based on their similarity to a set of reference data consisting of positive and negative sets, where the positive set contains examples of analyst identified P- or S-wave onsets and the negative set contains examples that do not contain P waves or S waves. Similarity is defined as the square of the Euclidean distance between vectors representing the scaled absolute values of the amplitudes of the observed signal and a given reference example in time windows of the same length. For both P waves and S waves, a single pass is done through the bandpassed data, producing a score function defined as the ratio of the sum of similarity to positive examples over the sum of similarity to negative examples for each window. A phase arrival is chosen as the centre position of the window that maximizes the score function. The method is tested on two local earthquake data sets, consisting of 98 known events from the Parkfield region in central California and 32 known events from the Alpine Fault region on the South Island of New Zealand. For P-wave picks, using a reference set containing two picks from the Parkfield data set, 98 per cent of Parkfield and 94 per cent of Alpine Fault picks are determined within 0.1 s of the analyst pick. For S-wave picks, 94 per cent and 91 per cent of picks are determined within 0.2 s of the analyst picks for the Parkfield and Alpine Fault data set, respectively. For the Parkfield data set, our method picks 3520 P-wave picks and 3577 S-wave picks out of 4232 station-event pairs. For the Alpine Fault data set, the method picks 282 P-wave picks and 311 S-wave picks out of a total of 344 station-event pairs. For our testing, we note that the vast majority of station-event pairs have analyst picks, although some analyst picks are excluded based on an accuracy assessment. Finally, our tests suggest that the method is portable, allowing the use of a reference set from one region on data from a different region using relatively few reference picks.

Localization of small arms fire using acoustic measurements of muzzle blast and/or ballistic shock wave arrivals.

PubMed

Lo, Kam W; Ferguson, Brian G

2012-11-01

The accurate localization of small arms fire using fixed acoustic sensors is considered. First, the conventional wavefront-curvature passive ranging method, which requires only differential time-of-arrival (DTOA) measurements of the muzzle blast wave to estimate the source position, is modified to account for sensor positions that are not strictly collinear (bowed array). Second, an existing single-sensor-node ballistic model-based localization method, which requires both DTOA and differential angle-of-arrival (DAOA) measurements of the muzzle blast wave and ballistic shock wave, is improved by replacing the basic external ballistics model (which describes the bullet's deceleration along its trajectory) with a more rigorous model and replacing the look-up table ranging procedure with a nonlinear (or polynomial) equation-based ranging procedure. Third, a new multiple-sensor-node ballistic model-based localization method, which requires only DTOA measurements of the ballistic shock wave to localize the point of fire, is formulated. The first method is applicable to situations when only the muzzle blast wave is received, whereas the third method applies when only the ballistic shock wave is received. The effectiveness of each of these methods is verified using an extensive set of real data recorded during a 7 day field experiment.

Ultrasonic guided wave tomography of pipes: A development of new techniques for the nondestructive evaluation of cylindrical geometries and guided wave multi-mode analysis

NASA Astrophysics Data System (ADS)

Leonard, Kevin Raymond

This dissertation concentrates on the development of two new tomographic techniques that enable wide-area inspection of pipe-like structures. By envisioning a pipe as a plate wrapped around upon itself, the previous Lamb Wave Tomography (LWT) techniques are adapted to cylindrical structures. Helical Ultrasound Tomography (HUT) uses Lamb-like guided wave modes transmitted and received by two circumferential arrays in a single crosshole geometry. Meridional Ultrasound Tomography (MUT) creates the same crosshole geometry with a linear array of transducers along the axis of the cylinder. However, even though these new scanning geometries are similar to plates, additional complexities arise because they are cylindrical structures. First, because it is a single crosshole geometry, the wave vector coverage is poorer than in the full LWT system. Second, since waves can travel in both directions around the circumference of the pipe, modes can also constructively and destructively interfere with each other. These complexities necessitate improved signal processing algorithms to produce accurate and unambiguous tomographic reconstructions. Consequently, this work also describes a new algorithm for improving the extraction of multi-mode arrivals from guided wave signals. Previous work has relied solely on the first arriving mode for the time-of-flight measurements. In order to improve the LWT, HUT and MUT systems reconstructions, improved signal processing methods are needed to extract information about the arrival times of the later arriving modes. Because each mode has different through-thickness displacement values, they are sensitive to different types of flaws, and the information gained from the multi-mode analysis improves understanding of the structural integrity of the inspected material. Both tomographic frequency compounding and mode sorting algorithms are introduced. It is also shown that each of these methods improve the reconstructed images both qualitatively and quantitatively.

Strong SH-to-Love wave scattering off the Southern California Continental Borderland

USGS Publications Warehouse

Yu, Chunquan; Zhan, Zhongwen; Hauksson, Egill; Cochran, Elizabeth S.

2017-01-01

Seismic scattering is commonly observed and results from wave propagation in heterogeneous medium. Yet, deterministic characterization of scatterers associated with lateral heterogeneities remains challenging. In this study, we analyze broadband waveforms recorded by the Southern California Seismic Network and observe strongly scattered Love waves following the arrival of teleseismic SH wave. These scattered Love waves travel approximately in the same (azimuthal) direction as the incident SH wave at a dominant period of ~10 s but at an apparent velocity of ~3.6 km/s as compared to the ~11 km/s for the SH wave. Back-projection suggests that this strong scattering is associated with pronounced bathymetric relief in the Southern California Continental Borderland, in particular the Patton Escarpment. Finite-difference simulations using a simplified 2-D bathymetric and crustal model are able to predict the arrival times and amplitudes of major scatterers. The modeling suggests a relatively low shear wave velocity in the Continental Borderland.

Passive characterization of hydrofracture properties using signals from the hydraulic pumps

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

Rector, J.W. III; Dong, Qichen

1995-12-31

In this study we utilize conical shear wave arrivals recorded in geophone observation wells to characterize a hydrofracture performed in the South Belridge Diatomite oil field. The conical wave arrivals are initially created by the hydraulic pumps on the surface, which send tube waves down the treatment borehole. Since the tube wave velocity in the Diatomite is greater than the shear formation velocity (the shear velocity in the diatomite is about 2,200 ft/s) cortical shear waves are radiated into the formation by the tube waves traveling down the treatment borehole. We use the decrease in amplitude of the tube wavemore » as it passes through the fracture zone to image changes in hydraulic conductivity of the fracture. By combining this information with estimates of the fracture height we obtain estimates of fracture width changes over time using the model of Tang and Cheng (1993). We find an excellent qualitative agreement between tube wave attenuation and pump pressure over time. Fracture widths estimated from the Tang and Cheng model appear to be consistent with the volume of injected fluid and the known length of the hydrofracture. Provided a monitor well can be instrumented, this technique holds potential for obtaining a relatively inexpensive real-time characterization of hydrofracs.« less

Hong-Ou-Mandel effect in terms of the temporal biphoton wave function with two arrival-time variables

NASA Astrophysics Data System (ADS)

Fedorov, M. V.; Sysoeva, A. A.; Vintskevich, S. V.; Grigoriev, D. A.

2018-03-01

The well-known Hong-Ou-Mandel effect is revisited. Two physical reasons are discussed for the effect to be less pronounced or even to disappear: differing polarizations of photons coming to the beamsplitter and delay time of photons in one of two channels. For the latter we use the concepts of biphoton frequency and temporal wave functions depending, correspondingly, on two frequency continuous variables of photons and on two time variables t 1 and t 2 interpreted as the arrival times of photons to the beamsplitter. Explicit expressions are found for the probability densities and total probabilities for photon pairs to be split between two channels after the beamsplitter and to be unsplit, when two photons appear together in one of two channels.

Forecasting spring from afar? Timing of migration and predictability of phenology along different migration routes of an avian herbivore.

PubMed

Kölzsch, Andrea; Bauer, Silke; de Boer, Rob; Griffin, Larry; Cabot, David; Exo, Klaus-Michael; van der Jeugd, Henk P; Nolet, Bart A

2015-01-01

Herbivorous birds are hypothesized to migrate in spring along a seasonal gradient of plant profitability towards their breeding grounds (green wave hypothesis). For Arctic breeding species in particular, following highly profitable food is important, so that they can replenish resources along the way and arrive in optimal body condition to start breeding early. We compared the timing of migratory movements of Arctic breeding geese on different flyways to examine whether flyways differed in the predictability of spring conditions at stopovers and whether this was reflected in the degree to which birds were following the green wave. Barnacle geese (Branta leucopsis) were tracked with solar GPS/ARGOS PTTs from their wintering grounds to breeding sites in Greenland (N = 7), Svalbard (N = 21) and the Barents Sea (N = 12). The numerous stopover sites of all birds were combined into a set of 16 general stopover regions. The predictability of climatic conditions along the flyways was calculated as the correlation and slope between onsets of spring at consecutive stopovers. These values differed between sites, mainly because of the presence or absence of ecological barriers. Goose arrival at stopovers was more closely tied to the local onset of spring when predictability was higher and when geese attempted breeding that year. All birds arrived at early stopovers after the onset of spring and arrived at the breeding grounds before the onset of spring, thus overtaking the green wave. This is in accordance with patterns expected for capital breeders: first, they must come into condition; at intermediate stopovers, arrival with the food quality peak is important to stay in condition, and at the breeding grounds, early arrival is favoured so that hatching of young can coincide with the peak of food quality. Our results suggest that a chain of correlations between climatic conditions at subsequent stopovers enables geese to closely track the green wave. However, the birds' precision of migratory timing seems uninfluenced by ecological barriers, indicating partly fixed migration schedules. These might become non-optimal due to climate warming and preclude accurate timing of long-distance migrants in the future. © 2014 The Authors. Journal of Animal Ecology © 2014 British Ecological Society.

Method of Laser Vibration Defect Analysis

DTIC Science & Technology

2010-06-04

415. In one embodiment, the frequencies from the reflected ultrasonic wave 430 are sensed and transformed to an electrical signal by transducer...actuator and sensor patches, respectively. Then, a process module loads sensor signal data to identify wave modes, determine the time of arrival of...conditions. An interrogation system includes at least one wave generator for generating a wave signal and optical fiber sensors applied to a structure

Regional Wave Propagation in Southeastern United States

NASA Astrophysics Data System (ADS)

Jemberie, A. L.; Langston, C. A.

2003-12-01

Broad band seismograms from the April 29, 2003, M4.6 Fort Payne, Alabama earthquake are analyzed to infer mechanisms of crustal wave propagation, crust and upper mantle velocity structure in southeastern United States, and source parameters of the event. In particular, we are interested in producing deterministic models of the distance attenuation of earthquake ground motions through computation of synthetic seismograms. The method first requires constraining the source parameters of an earthquake and then modeling the amplitude and times of broadband arrivals within the waveforms to infer appropriate layered earth models. A first look at seismograms recorded by stations outside the Mississippi Embayment (ME) show clear body phases such P, sP, Pnl, Sn and Lg. The ME signals are qualitatively different from others because they have longer durations and large surface waves. A straightforward interpretation of P wave arrival times shows a typical upper mantle velocity of 8.18 km/s. However, there is evidence of significantly higher P phase velocities at epicentral distances between 400 and 600km, that may be caused by a high velocity upper mantle anomaly; triplication of P-waves is seen in these seismograms. The arrival time differences between regional P and the depth phase sP at different stations are used to constrain the depth of the earthquake. The source depth lies between 9.5 km and 13km which is somewhat more shallow than the network location that was constrained to 15km depth. The Fort Payne earthquake is the largest earthquake to have occurred within the Eastern Tennessee Seismic Zone.

Seismic Observations of the Mid-Pacific Large Low Shear Velocity Province

NASA Astrophysics Data System (ADS)

Chan, A.; Helmberger, D. V.; Sun, D.; Li, D.; Jackson, J. M.

2015-12-01

Seismic data from earthquakes originating in the Fiji-Tonga region exhibits waveform complexity of a number of phases which may be attributed to various structures along ray paths to stations of USArray, including anomalous structures at the core-mantle boundary. The data shows variation in multipathing, that is, the presence of secondary arrivals following the S phase at diffracted distances (Sdiff) which suggests that the waveform complexity is due to structures at the eastern edge of the mid-Pacific Large Low Shear Velocity Province (LLSVP). This study examines data from earthquake events while the Transportable Array portion of USArray was situated in the midwest United States, reinforcing previous studies that indicate late arrivals occurring as long as 26 seconds after the primary arrivals (To et al., 2011). Using earth flattening transformations and finite difference methods, simulations of tapered wedge structures of low velocity material allow for wave energy trapping, producing the observed waveform complexity and delayed arrivals at large distances, with such structures having characteristic properties of, for example, a height of 70 km, in-plane extent more than 1000 km, and shear wave velocity drop of 3% at the top to 15% at the bottom relative to PREM. Differential arrival times for SH and SV components suggest anisotropy and possible wave propagation through downgoing slabs beneath the source region. The arrivals of the SPdKS phase further support the presence of an ultra-low velocity zone (ULVZ) within a two-humped LLSVP. Some systematic delays in arrival times of multiple phases for distances less than 102º are accounted for and attributed to the presence of a mantle slab underneath the continental United States. Comparisons to seismic data from earthquakes originating from other locations further constrain depths of the deep mantle structures. Possible explanations include iron-enrichment of deep mantle phases.

Shear Wave Splitting Inversion in a Complex Crust

NASA Astrophysics Data System (ADS)

Lucas, A.

2015-12-01

Shear wave splitting (SWS) inversion presents a method whereby the upper crust can be interrogated for fracture density. It is caused when a shear wave traverses an area of anisotropy, splits in two, with each wave experiencing a different velocity resulting in an observable separation in arrival times. A SWS observation consists of the first arrival polarization direction and the time delay. Given the large amount of data common in SWS studies, manual inspection for polarization and time delay is considered prohibitively time intensive. All automated techniques used can produce high amounts of observations falsely interpreted as SWS. Thus introducing error into the interpretation. The technique often used for removing these false observations is to manually inspect all SWS observations defined as high quality by the automated routine, and remove false identifications. We investigate the nature of events falsely identified compared to those correctly identified. Once this identification is complete we conduct a inversion for crack density from SWS time delay. The current body of work on linear SWS inversion utilizes an equation that defines the time delay between arriving shear waves with respect to fracture density. This equation makes the assumption that no fluid flow occurs as a result of the passing shear wave, a situation called squirt flow. We show that the assumption is not applicable in all geological situations. When it is not true, its use in an inversion produces a result which is negatively affected by the assumptions. This is shown to be the case at the test case of 6894 SWS observations gathered in a small area at Puna geothermal field, Hawaii. To rectify this situation, a series of new time delay formulae, applicable to linear inversion, are derived from velocity equations presented in literature. The new formula use a 'fluid influence parameter' which indicates the degree to which squirt flow is influencing the SWS. It is found that accounting for squirt flow better fits the data and is more applicable. The fluid influence factor that best describes the data can be identified prior to solving the inversion. Implementing this formula in a linear inversion has a significantly improved fit to the time delay observations than that of the current methods.

Acoustic and Electrical Property Changes Due to Microbial Growth and Biofilm Formation in Porous Media

EPA Science Inventory

A laboratory study was conducted to investigate the effect of microbial growth and biofilm formation on compressional waves, and complex conductivity during stimulated microbial growth. Over the 29 day duration of the experiment, compressional wave amplitudes and arrival times f...

Hypocenter for the 1979 Imperial Valley Earthquake

USGS Publications Warehouse

Archuleta, Ralph J.

1982-01-01

Using P-and S-wave arrival times with the laterally varying P-wave velocity structure derived from analysis of a refraction survey of the Imperial Valley, a hypocenter is ascertained for the October 15, 1979, Imperial Valley earthquake: Latitude 32° 39.50′N, Longitude 115° 19.80′W, Depth 8.0 km, Time 23:16:54.40 GMT.

Infrasound radiated by the Gerdec and Chelopechene explosions: propagation along unexpected paths

NASA Astrophysics Data System (ADS)

Green, David N.; Vergoz, Julien; Gibson, Robert; Le Pichon, Alexis; Ceranna, Lars

2011-05-01

Infrasound propagation paths through the atmosphere are controlled by the temporally and spatially varying sound speed and wind speed amplitudes. Because of the complexity of atmospheric acoustic propagation it is often difficult to reconcile observed infrasonic arrivals with the sound speed profiles predicted by meteorological specifications. This paper provides analyses of unexpected arrivals recorded in Europe and north Africa from two series of accidental munitions dump explosions, recorded at ranges greater than 1000 km: two explosions at Gerdec, Albania, on 2008 March 15 and four explosions at Chelopechene, Bulgaria, on 2008 July 3. The recorded signal characteristics include multiple pulsed arrivals, celerities between 0.24 and 0.34 km s-1 and some signal frequency content above 1 Hz. Often such characteristics are associated with waves that have propagated within a ground-to-stratosphere waveguide, although the observed celerities extend both above and below the conventional range for stratospheric arrivals. However, state-of-the-art meteorological specifications indicate that either weak, or no, ground-to-stratosphere waveguides are present along the source-to-receiver paths. By incorporating realistic gravity-wave induced horizontal velocity fluctuations into time-domain Parabolic Equation models the pulsed nature of the signals is simulated, and arrival times are predicted to within 30 s of the observed values (<1 per cent of the source-to-receiver transit time). Modelling amplitudes is highly dependent upon estimates of the unknown acoustic source strength (or equivalent chemical explosive yield). Current empirical explosive yield relationships, derived from infrasonic amplitude measurements from point-source chemical explosions, suggest that the equivalent chemical yield of the largest Gerdec explosion was of the order of 1 kt and the largest Chelopechene explosion was of the order of 100 t. When incorporating these assumed yields, the Parabolic Equation simulations predict peak signal amplitudes to within an order of magnitude of the observed values. As gravity wave velocity perturbations can significantly influence both infrasonic arrival times and signal amplitudes they need to be accounted for in source location and yield estimation routines, both of which are important for explosion monitoring, especially in the context of the Comprehensive Nuclear-Test-Ban Treaty.

Tunneling dynamics in relativistic and nonrelativistic wave equations

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

Delgado, F.; Muga, J. G.; Ruschhaupt, A.

2003-09-01

We obtain the solution of a relativistic wave equation and compare it with the solution of the Schroedinger equation for a source with a sharp onset and excitation frequencies below cutoff. A scaling of position and time reduces to a single case all the (below cutoff) nonrelativistic solutions, but no such simplification holds for the relativistic equation, so that qualitatively different ''shallow'' and ''deep'' tunneling regimes may be identified relativistically. The nonrelativistic forerunner at a position beyond the penetration length of the asymptotic stationary wave does not tunnel; nevertheless, it arrives at the traversal (semiclassical or Buettiker-Landauer) time {tau}. Themore » corresponding relativistic forerunner is more complex: it oscillates due to the interference between two saddle-point contributions and may be characterized by two times for the arrival of the maxima of lower and upper envelopes. There is in addition an earlier relativistic forerunner, right after the causal front, which does tunnel. Within the penetration length, tunneling is more robust for the precursors of the relativistic equation.« less

THE NANOGRAV NINE-YEAR DATA SET: EXCESS NOISE IN MILLISECOND PULSAR ARRIVAL TIMES

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

Lam, M. T.; Jones, M. L.; McLaughlin, M. A.

Gravitational wave (GW) astronomy using a pulsar timing array requires high-quality millisecond pulsars (MSPs), correctable interstellar propagation delays, and high-precision measurements of pulse times of arrival. Here we identify noise in timing residuals that exceeds that predicted for arrival time estimation for MSPs observed by the North American Nanohertz Observatory for Gravitational Waves. We characterize the excess noise using variance and structure function analyses. We find that 26 out of 37 pulsars show inconsistencies with a white-noise-only model based on the short timescale analysis of each pulsar, and we demonstrate that the excess noise has a red power spectrum formore » 15 pulsars. We also decompose the excess noise into chromatic (radio-frequency-dependent) and achromatic components. Associating the achromatic red-noise component with spin noise and including additional power-spectrum-based estimates from the literature, we estimate a scaling law in terms of spin parameters (frequency and frequency derivative) and data-span length and compare it to the scaling law of Shannon and Cordes. We briefly discuss our results in terms of detection of GWs at nanohertz frequencies.« less

Wavelet-based group and phase velocity measurements: Method

NASA Astrophysics Data System (ADS)

Yang, H. Y.; Wang, W. W.; Hung, S. H.

2016-12-01

Measurements of group and phase velocities of surface waves are often carried out by applying a series of narrow bandpass or stationary Gaussian filters localized at specific frequencies to wave packets and estimating the corresponding arrival times at the peak envelopes and phases of the Fourier spectra. However, it's known that seismic waves are inherently nonstationary and not well represented by a sum of sinusoids. Alternatively, a continuous wavelet transform (CWT) which decomposes a time series into a family of wavelets, translated and scaled copies of a generally fast oscillating and decaying function known as the mother wavelet, is capable of retaining localization in both the time and frequency domain and well-suited for the time-frequency analysis of nonstationary signals. Here we develop a wavelet-based method to measure frequency-dependent group and phase velocities, an essential dataset used in crust and mantle tomography. For a given time series, we employ the complex morlet wavelet to obtain the scalogram of amplitude modulus |Wg| and phase φ on the time-frequency plane. The instantaneous frequency (IF) is then calculated by taking the derivative of phase with respect to time, i.e., (1/2π)dφ(f, t)/dt. Time windows comprising strong energy arrivals to be measured can be identified by those IFs close to the frequencies with the maximum modulus and varying smoothly and monotonically with time. The respective IFs in each selected time window are further interpolated to yield a smooth branch of ridge points or representative IFs at which the arrival time, tridge(f), and phase, φridge(f), after unwrapping and correcting cycle skipping based on a priori knowledge of the possible velocity range, are determined for group and phase velocity estimation. We will demonstrate our measurement method using both ambient noise cross correlation functions and multi-mode surface waves from earthquakes. The obtained dispersion curves will be compared with those by a conventional narrow bandpass method.

Fast first arrival picking algorithm for noisy microseismic data

NASA Astrophysics Data System (ADS)

Kim, Dowan; Byun, Joongmoo; Lee, Minho; Choi, Jihoon; Kim, Myungsun

2017-01-01

Most microseismic events occur during hydraulic fracturing. Thus microseismic monitoring, by recording seismic waves from microseismic events, is one of the best methods for locating the positions of hydraulic fractures. However, since microseismic events have very low energy, the data often have a low signal-to-noise ratio (S/N ratio) and it is not easy to pick the first arrival time. In this study, we suggest a new fast picking method optimised for noisy data using cross-correlation and stacking. In this method, a reference trace is selected and the time differences between the first arrivals of the reference trace and those of the other traces are computed by cross-correlation. Then, all traces are aligned with the reference trace by time shifting, and the aligned traces are summed together to produce a stacked reference trace that has a considerably improved S/N ratio. After the first arrival time of the stacked reference trace is picked, the first arrival time of each trace is calculated automatically using the time differences obtained in the cross-correlation process. In experiments with noisy synthetic data and field data, this method produces more reliable results than the traditional method, which picks the first arrival time of each noisy trace separately. In addition, the computation time is dramatically reduced.

A new algorithm for three-dimensional joint inversion of body wave and surface wave data and its application to the Southern California plate boundary region

NASA Astrophysics Data System (ADS)

Fang, Hongjian; Zhang, Haijiang; Yao, Huajian; Allam, Amir; Zigone, Dimitri; Ben-Zion, Yehuda; Thurber, Clifford; van der Hilst, Robert D.

2016-05-01

We introduce a new algorithm for joint inversion of body wave and surface wave data to get better 3-D P wave (Vp) and S wave (Vs) velocity models by taking advantage of the complementary strengths of each data set. Our joint inversion algorithm uses a one-step inversion of surface wave traveltime measurements at different periods for 3-D Vs and Vp models without constructing the intermediate phase or group velocity maps. This allows a more straightforward modeling of surface wave traveltime data with the body wave arrival times. We take into consideration the sensitivity of surface wave data with respect to Vp in addition to its large sensitivity to Vs, which means both models are constrained by two different data types. The method is applied to determine 3-D crustal Vp and Vs models using body wave and Rayleigh wave data in the Southern California plate boundary region, which has previously been studied with both double-difference tomography method using body wave arrival times and ambient noise tomography method with Rayleigh and Love wave group velocity dispersion measurements. Our approach creates self-consistent and unique models with no prominent gaps, with Rayleigh wave data resolving shallow and large-scale features and body wave data constraining relatively deeper structures where their ray coverage is good. The velocity model from the joint inversion is consistent with local geological structures and produces better fits to observed seismic waveforms than the current Southern California Earthquake Center (SCEC) model.

Wave-equation migration velocity inversion using passive seismic sources

NASA Astrophysics Data System (ADS)

Witten, B.; Shragge, J. C.

2015-12-01

Seismic monitoring at injection sites (e.g., CO2 sequestration, waste water disposal, hydraulic fracturing) has become an increasingly important tool for hazard identification and avoidance. The information obtained from this data is often limited to seismic event properties (e.g., location, approximate time, moment tensor), the accuracy of which greatly depends on the estimated elastic velocity models. However, creating accurate velocity models from passive array data remains a challenging problem. Common techniques rely on picking arrivals or matching waveforms requiring high signal-to-noise data that is often not available for the magnitude earthquakes observed over injection sites. We present a new method for obtaining elastic velocity information from earthquakes though full-wavefield wave-equation imaging and adjoint-state tomography. The technique exploits the fact that the P- and S-wave arrivals originate at the same time and location in the subsurface. We generate image volumes by back-propagating P- and S-wave data through initial Earth models and then applying a correlation-based extended-imaging condition. Energy focusing away from zero lag in the extended image volume is used as a (penalized) residual in an adjoint-state tomography scheme to update the P- and S-wave velocity models. We use an acousto-elastic approximation to greatly reduce the computational cost. Because the method requires neither an initial source location or origin time estimate nor picking of arrivals, it is suitable for low signal-to-noise datasets, such as microseismic data. Synthetic results show that with a realistic distribution of microseismic sources, P- and S-velocity perturbations can be recovered. Although demonstrated at an oil and gas reservoir scale, the technique can be applied to problems of all scales from geologic core samples to global seismology.

Amplification of seismic waves by the Seattle basin, Washington State

USGS Publications Warehouse

Pratt, T.L.; Brocher, T.M.; Weaver, C.S.; Creager, K.C.; Snelson, C.M.; Crosson, R.S.; Miller, K.C.; Trehu, A.M.

2003-01-01

Recordings of the 1999 Mw 7.6 Chi-Chi (Taiwan) earthquake, two local earthquakes, and five blasts show seismic-wave amplification over a large sedimentary basin in the U.S. Pacific Northwest. For weak ground motions from the Chi-Chi earthquake, the Seattle basin amplified 0.2- to 0.8-Hz waves by factors of 8 to 16 relative to bedrock sites west of the basin. The amplification and peak frequency change during the Chi-Chi coda: the initial S-wave arrivals (0-30 sec) had maximum amplifications of 12 at 0.5-0.8 Hz, whereas later arrivals (35-65 sec) reached amplifications of 16 at 0.3-0.5 Hz. Analysis of local events in the 1.0- to 10.0-Hz frequency range show fourfold amplifications for 1.0-Hz weak ground motion over the Seattle basin. Amplifications decrease as frequencies increase above 1.0 Hz, with frequencies above 7 Hz showing lower amplitudes over the basin than at bedrock sites. Modeling shows that resonance in low-impedance deposits forming the upper 550 m of the basin beneath our profile could cause most of the observed amplification, and the larger amplification at later arrival times suggests surface waves also play a substantial role. These results emphasize the importance of shallow deposits in determining ground motions over large basins.

Explosion source strong ground motions in the Mississippi embayment

USGS Publications Warehouse

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

2006-01-01

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

Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

NASA Astrophysics Data System (ADS)

Syracuse, E. M.; Zhang, H.; Maceira, M.

2017-10-01

We present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body wave first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region. Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. Without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.

A previously unreported type of seismic source in the firn layer of the East Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

Lough, Amanda C.; Barcheck, C. Grace; Wiens, Douglas A.; Nyblade, Andrew; Anandakrishnan, Sridhar

2015-11-01

We identify a unique type of seismic source in the uppermost part of the East Antarctic Ice Sheet recorded by temporary broadband seismic arrays in East Antarctica. These sources, termed "firnquakes," are characterized by dispersed surface wave trains with frequencies of 1-10 Hz detectable at distances up to 1000 km. Events show strong dispersed Rayleigh wave trains and an absence of observable body wave arrivals; most events also show weaker Love waves. Initial events were discovered by standard detection schemes; additional events were then detected with a correlation scanner using the initial arrivals as templates. We locate sources by determining the L2 misfit for a grid of potential source locations using Rayleigh wave arrival times and polarization directions. We then perform a multiple-filter analysis to calculate the Rayleigh wave group velocity dispersion and invert the group velocity for shear velocity structure. The resulting velocity structure is used as an input model to calculate synthetic seismograms. Inverting the dispersion curves yields ice velocity structures consistent with a low-velocity firn layer ~100 m thick and show that velocity structure is laterally variable. The absence of observable body wave phases and the relative amplitudes of Rayleigh waves and noise constrain the source depth to be less than 20 m. The presence of Love waves for most events suggests the source is not isotropic. We propose the events are linked to the formation of small crevasses in the firn, and several events correlate with shallow crevasse fields mapped in satellite imagery.

Impulse propagation in the nocturnal boundary layer: analysis of the geometric component.

PubMed

Blom, Philip; Waxler, Roger

2012-05-01

On clear dry nights over flat land, a temperature inversion and stable nocturnal wind jet lead to an acoustic duct in the lowest few hundred meters of the atmosphere. An impulsive signal propagating in such a duct is received at long ranges from the source as an extended wave train consisting of a series of weakly dispersed distinct arrivals followed by a strongly dispersed low-frequency tail. The leading distinct arrivals have been previously shown to be well modeled by geometric acoustics. In this paper, the geometric acoustics approximation for the leading arrivals is investigated. Using the solutions of the eikonal and transport equations, travel times, amplitudes, and caustic structures of the distinct arrivals have been determined. The time delay between and relative amplitudes of the direct-refracted and single ground reflection arrivals have been investigated as parameters for an inversion scheme. A two parameter quadratic approximation to the effective sound speed profile has been fit and found to be in strong agreement with meteorological measurements from the time of propagation.

Close range fault tolerant noncontacting position sensor

DOEpatents

Bingham, D.N.; Anderson, A.A.

1996-02-20

A method and system are disclosed for locating the three dimensional coordinates of a moving or stationary object in real time. The three dimensional coordinates of an object in half space or full space are determined based upon the time of arrival or phase of the wave front measured by a plurality of receiver elements and an established vector magnitudes proportional to the measured time of arrival or phase at each receiver element. The coordinates of the object are calculated by solving a matrix equation or a set of closed form algebraic equations. 3 figs.

Improved modified energy ratio method using a multi-window approach for accurate arrival picking

NASA Astrophysics Data System (ADS)

Lee, Minho; Byun, Joongmoo; Kim, Dowan; Choi, Jihun; Kim, Myungsun

2017-04-01

To identify accurately the location of microseismic events generated during hydraulic fracture stimulation, it is necessary to detect the first break of the P- and S-wave arrival times recorded at multiple receivers. These microseismic data often contain high-amplitude noise, which makes it difficult to identify the P- and S-wave arrival times. The short-term-average to long-term-average (STA/LTA) and modified energy ratio (MER) methods are based on the differences in the energy densities of the noise and signal, and are widely used to identify the P-wave arrival times. The MER method yields more consistent results than the STA/LTA method for data with a low signal-to-noise (S/N) ratio. However, although the MER method shows good results regardless of the delay of the signal wavelet for signals with a high S/N ratio, it may yield poor results if the signal is contaminated by high-amplitude noise and does not have the minimum delay. Here we describe an improved MER (IMER) method, whereby we apply a multiple-windowing approach to overcome the limitations of the MER method. The IMER method contains calculations of an additional MER value using a third window (in addition to the original MER window), as well as the application of a moving average filter to each MER data point to eliminate high-frequency fluctuations in the original MER distributions. The resulting distribution makes it easier to apply thresholding. The proposed IMER method was applied to synthetic and real datasets with various S/N ratios and mixed-delay wavelets. The results show that the IMER method yields a high accuracy rate of around 80% within five sample errors for the synthetic datasets. Likewise, in the case of real datasets, 94.56% of the P-wave picking results obtained by the IMER method had a deviation of less than 0.5 ms (corresponding to 2 samples) from the manual picks.

A Simplified Approach for Simultaneous Measurements of Wavefront Velocity and Curvature in the Heart Using Activation Times.

PubMed

Mazeh, Nachaat; Haines, David E; Kay, Matthew W; Roth, Bradley J

2013-12-01

The velocity and curvature of a wave front are important factors governing the propagation of electrical activity through cardiac tissue, particularly during heart arrhythmias of clinical importance such as fibrillation. Presently, no simple computational model exists to determine these values simultaneously. The proposed model uses the arrival times at four or five sites to determine the wave front speed ( v ), direction (θ), and radius of curvature (ROC) ( r 0 ). If the arrival times are measured, then v , θ, and r 0 can be found from differences in arrival times and the distance between these sites. During isotropic conduction, we found good correlation between measured values of the ROC r 0 and the distance from the unipolar stimulus ( r = 0.9043 and p < 0.0001). The conduction velocity (m/s) was correlated ( r = 0.998, p < 0.0001) using our method (mean = 0.2403, SD = 0.0533) and an empirical method (mean = 0.2352, SD = 0.0560). The model was applied to a condition of anisotropy and a complex case of reentry with a high voltage extra stimulus. Again, results show good correlation between our simplified approach and established methods for multiple wavefront morphologies. In conclusion, insignificant measurement errors were observed between this simplified approach and an approach that was more computationally demanding. Accuracy was maintained when the requirement that ε (ε = b/r 0 , ratio of recording site spacing over wave fronts ROC) was between 0.001 and 0.5. The present simplified model can be applied to a variety of clinical conditions to predict behavior of planar, elliptical, and reentrant wave fronts. It may be used to study the genesis and propagation of rotors in human arrhythmias and could lead to rotor mapping using low density endocardial recording electrodes.

Geometry and velocity structure of the northern Costa Rica seismogenic zone from 3D local earthquake tomography

NASA Astrophysics Data System (ADS)

Deshon, H. R.; Schwartz, S. Y.; Newman, A. V.; Dorman, L. M.; Protti, M.; Gonzalez, V.

2003-12-01

We present results of a 3D local earthquake tomography study of the Middle America Trench seismogenic zone in northern Costa Rica. Local earthquake tomography can provide constraints on the updip, downdip, and lateral variability of seismicity and P- and S-wave velocities; these constraints may in turn provide information on compositional and/or mechanical variability along the seismogenic zone. We use arrival time data recorded by the Nicoya Peninsula seismic array, part of the Costa Rica seismogenic zone experiment (CRSEIZE), a collaborative effort undertaken to better understand seismogenic behavior at the Costa Rica subduction zone using data from land and ocean bottom seismic arrays, oceanic fluid flux meters, and GPS receivers. We invert ˜10,000 P-wave and S-wave arrival times from 475 well-recorded local earthquakes (GAP < 180° , >8 P-wave arrivals) to solve for the best-fitting 1D P- and S-wave velocity models, station corrections, and hypocenters using the algorithm VELEST. These 1D velocity models are used as a starting models for 3D simultaneous inversion using the algorithm SIMULPS14. Preliminary P-wave inversions contain a positive velocity anomaly dipping beneath the Nicoya Peninsula, interpreted as the subducting Cocos Plate. Earthquakes occur in a narrow band along the slab-continent interface and are consistent with the results of Newman et al. (2002). The updip limit of seismicity occurs ˜5 km deeper and 5-10 km landward in the northern vs. the southern Nicoya Peninsula, and this shift spatially correlates to the change from Cocos-Nazca to East Pacific Rise derived oceanic plate. P-wave velocities in the upper 5-10 km of the model are consistent with the geology of the Nicoya Peninsula. We will correlate relocated microseismicity to previously noted variability in oceanic plate morphology, heat flow, fluid flow, and thermal structure and compare the resulting P- and S-wave velocity models to wide-angle refraction models and hypothesized mantle wedge compositions.

African Cenozoic hotpot tectonism: new insights from continent-scale body-wave tomography

NASA Astrophysics Data System (ADS)

Bastow, I. D.; Boyce, A.; Caunt, E.; Guilloud De Courbeville, J.; Desai, S.; Kounoudis, R.; Golos, E. M.; Burdick, S.; van der Hilst, R. D.

2017-12-01

The African plate is an ideal study locale for mantle plumes and Cenozoic hotspot tectonism. On the eastern side of the continent, the uplifted East African and Ethiopian plateaus, and the 30Ma Ethiopian Traps, are widely considered to be the result of the African Superplume: a broad thermochemical anomaly that originates below southern Africa. Precisely where and how the superplume traverses the mantle transition zone is debated however. On the western side of the continent, the Cameroon Volcanic Line is a hotspot track with no age-progression; it is less easily attributed to the effects of a mantle plume. Central to our understanding of these issues is an improved picture of mantle seismic structure. Body-wave studies of African mantle wave-speed structure are typically limited to regional relative arrival-time studies that utilize data from temporary seismograph networks of aperture less than 1000km. The resulting tomographic images are higher resolution than continent-scale surface-wave models, but anomaly amplitudes cannot be compared from region to region using the relative arrival-time approach: the 0% contour in each region refers to the regional, not global mean. The challenge is thus to incorporate the often-noisy body-wave data from temporary seismograph networks into a continent-scale absolute delay-time model. We achieve this using the new Absolute Arrival-time Recovery Method (AARM) method of Boyce et. al., (2017) and the tomographic inversion approach described by Li et. al., (2008). We invert for mantle wavespeed structure using data recorded since 1990 by temporary networks in the Atlas Mountains, Cameroon, South Africa, East African Rift system, Ethiopia and Madagascar. Our model is well resolved to lower mantle depths beneath these temporary networks, and offers the most detailed picture yet of mantle wavespeed structure beneath Africa. The contrast between East African and Cameroon mantle structure suggests multiple development mechanisms for hotspot tectonism across the African continent.

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

NASA Astrophysics Data System (ADS)

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

2016-12-01

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

Constraining the Size and Depth of a Shallow Crustal Magma Body at Newberry Volcano Using P-Wave Tomography and Finite-Difference Waveform Modeling

NASA Astrophysics Data System (ADS)

Beachly, M. W.; Hooft, E. E.; Toomey, D. R.; Waite, G. P.

2011-12-01

Imaging magmatic systems improves our understanding of magma ascent and storage in the crust and contributes to hazard assessment. Seismic tomography reveals crustal magma bodies as regions of low velocity; however the ability of delay-time tomography to detect small, low-velocity bodies is limited by wavefront healing. Alternatively, crustal magma chambers have been identified from secondary phases including P and S wave reflections and conversions. We use a combination of P-wave tomography and finite-difference waveform modeling to characterize a shallow crustal magma body at Newberry Volcano, central Oregon. Newberry's eruptions are silicic within the central caldera and mafic on its periphery suggesting a central silicic magma storage system. The system may still be active with a recent eruption ~1300 years ago and a drill hole temperature of 256° C at only 932 m depth. A low-velocity anomaly previously imaged at 3-5 km beneath the caldera indicates either a magma body or a fractured pluton. With the goal of detecting secondary arrivals from a magma chamber beneath Newberry Volcano, we deployed a line of densely-spaced (~300 m), three-component seismometers that recorded a shot of opportunity from the High Lava Plains Experiment in 2008. The data record a secondary P-wave arrival originating from beneath the caldera. In addition we combine travel-time data from our 2008 experiment with data collected in the 1980's by the USGS for a P-wave tomography inversion to image velocity structure to 6 km depth. The inversion includes 16 active sources, 322 receivers and 1007 P-wave first arrivals. The tomography results reveal a high-velocity, ring-like anomaly beneath the caldera ring faults to 2 km depth that surrounds a shallow low-velocity region. Beneath 2.5 km high-velocity anomalies are concentrated east and west of the caldera. A central low-velocity body lies below 3 km depth. Tomographic inversions of synthetic data suggest that the central low-velocity body beneath 3 km depth is not well resolved and that, for example, an unrealistically large low-velocity body with a volume up to 72 km3 at 40% velocity reduction (representing 30±7% partial melt) could be consistent with the observed travel-times. We use the tomographically derived velocity structure to construct 2D finite difference models and include synthetic low-velocity bodies in these models to test various magma chamber geometries and melt contents. Waveform modeling identifies the observed secondary phase as a transmitted P-wave formed by delaying and focusing P-wave energy through the low-velocity region. We will further constrain the size and shape of the low-velocity region by comparing arrival times and amplitudes of observed and synthetic primary and secondary phases. Secondary arrivals provide compelling evidence for an active crustal magmatic system beneath Newberry volcano and demonstrate the ability of waveform modeling to constrain the nature of magma bodies beyond the limits of seismic tomography.

Migration ecology and stopover population size of Red Knots Calidris canutus rufa at Mingan Archipelago after exiting the breeding grounds

USGS Publications Warehouse

Lyons, James E.; Baker, Allan J.; González, Patricia M.; Aubry, Yves; Buidin, Christophe; Rochepault, Yann

2018-01-01

Populations of migratory birds present unique conservation challenges given the often vast distances separating critical resources throughout the annual cycle. Migration areas close to the breeding grounds represent a link between two key stages of the annual cycle, and understanding migration ecology as birds exit the breeding grounds may be particularly informative for successful conservation. We studied migration phenology and stopover ecology of an endangered subspecies of the Red Knot Calidris canutus rufa at a migration area relatively close to its breeding range. Using mark-recapture/resight data and a Jolly-Seber model for open populations, we described the arrival and departure schedules, stopover duration, and passage population size at the Mingan Archipelago, Quebec, Canada. Red Knots arrived at the study area in two distinct waves of birds separated by approximately 22 days. Nearly 30% of the passage population arrived in the first wave of arrivals during 15–18 July, and approximately 22% arrived in a second wave during 8–11 August. The sex-ratio in the stopover population at the time of the first wave was slightly skewed toward females, whereas the second wave was heavily skewed toward males. Because males remain on the breeding grounds to care for young, this may reflect successfulbreeding in the year of our study. The estimated stopover duration (population mean) was 11 days (95% credible interval: 10.3–11.7 days), but stopover persistence was variable throughout the season. We estimated a passage population size of 9,450 birds (8,355–10,710), a minimum estimate for reasons related to the duration of our sampling. Mingan Archipelago is thus an important migration area for this endangered subspecies and could be a priority in conservation planning. Our results also emphasize the advantages of mark-recapture/resight approaches for estimating migration phenology and stopover persistence.

The NANOGrav Observing Program: High-precision Millisecond Pulsar Timing and the Search for Nanohertz Gravitational Waves

NASA Astrophysics Data System (ADS)

Nice, David; NANOGrav

2018-01-01

The North American Observatory for Nanohertz Gravitational Waves (NANOGrav) collaboration is thirteen years into a program of long-term, high-precision millisecond pulsar timing, undertaken with the goal of detecting and characterization nanohertz gravitational waves (i.e., gravitational waves with periods of many years) by measuring their effect on observed pulse arrival times. Our primary instruments are the Arecibo Observatory, used to observe 37 pulsars with declinations between 0 and 39 degrees; and the Green Bank Telescope, used for 24 pulsars, of which 22 are outside the Arecibo range, and 2 are overlaps with the Arecibo source list. Additional observations are made with the VLA and (soon) CHIME.Most pulsars in our program are observed at intervals of three to four weeks, and seven are observed weekly. Observations of each pulsar are made over a wide range of radio frequencies at each epoch in order to measure and mitigate effects of the ionized interstellar medium on the pulse arrival times. Our targets are pulsars for which we can achieve timing precision of 1 microsecond or better in at each epoch; we achieve precision better than 100 nanoseconds in the best cases. Observing a large number of pulsars will allow for robust measurements of gravitational waves by analyzing correlations in the timing of pairs of pulsars depending on their separation on the sky. Our data are pooled with data from telescopes worldwide via the International Pulsar Timing Array (IPTA) collaboration, further increasing our sensitivity to gravitational waves.We release data at regular intervals. We will describe the NANOGrav 5-, 9- and 11-year data sets and give a status report on the NANOGrav 12.5-year data set.

Head wave correlations in ambient noise.

PubMed

Gebbie, John; Siderius, Martin

2016-07-01

Ambient ocean noise is processed with a vertical line array to reveal coherent time-separated arrivals suggesting the presence of head wave multipath propagation. Head waves, which are critically propagating water waves created by seabed waves traveling parallel to the water-sediment interface, can propagate faster than water-only waves. Such eigenrays are much weaker than water-only eigenrays, and are often completely overshadowed by them. Surface-generated noise is different whereby it amplifies the coherence between head waves and critically propagating water-only waves, which is measured by cross-correlating critically steered beams. This phenomenon is demonstrated both experimentally and with a full wave simulation.

Relationships of the group velocity of the time-reversed Lamb wave with bone properties in cortical bone in vitro.

PubMed

Lee, Kang Il; Yoon, Suk Wang

2017-04-11

The present study aims to investigate the feasibility of using the time-reversed Lamb wave as a new method for noninvasive characterization of long cortical bones. The group velocity of the time-reversed Lamb wave launched by using the modified time reversal method was measured in 15 bovine tibiae, and their correlations with the bone properties of the tibia were examined. The group velocity of the time-reversed Lamb wave showed significant positive correlations with the bone properties (r=0.55-0.81). The best univariate predictor of the group velocity of the time-reversed Lamb wave was the cortical thickness, yielding an adjusted squared correlation coefficient (r 2 ) of 0.64. These results imply that the group velocity of the time-reversed Lamb wave, in addition to the velocities of the first arriving signal and the slow guided wave, could potentially be used as a discriminator for osteoporosis. Copyright © 2017 Elsevier Ltd. All rights reserved.

Tsunami: India

Atmospheric Science Data Center

2013-04-16

... Animation At 00:58:53 UTC (Coordinated Universal Time) on December 26, 2004, a magnitude 9.0 earthquake occurred off the west ... UTC, when the tide gauge indicated the arrival of another series of waves. Because MISR's nine cameras imaged the coast over a time span ...

A compositional origin to ultralow-velocity zones

NASA Astrophysics Data System (ADS)

Brown, Samuel P.; Thorne, Michael S.; Miyagi, Lowell; Rost, Sebastian

2015-02-01

We analyzed vertical component short-period ScP waveforms for 26 earthquakes occurring in the Tonga-Fiji trench recorded at the Alice Springs Array in central Australia. These waveforms show strong precursory and postcursory seismic arrivals consistent with ultralow-velocity zone (ULVZ) layering beneath the Coral Sea. We used the Viterbi sparse spike detection method to measure differential travel times and amplitudes of the postcursor arrival ScSP and the precursor arrival SPcP relative to ScP. We compare our measurements to a database of 340,000 synthetic seismograms finding that these data are best fit by a ULVZ model with an S wave velocity reduction of 24%, a P wave velocity reduction of 23%, a thickness of 8.5 km, and a density increase of 6%. This 1:1 VS:VP velocity decrease is commensurate with a ULVZ compositional origin and is most consistent with highly iron enriched ferropericlase.

Joint inversion of gravity and arrival time data from Parkfield: New constraints on structure and hypocenter locations near the SAFOD drill site

USGS Publications Warehouse

Roecker, S.; Thurber, C.; McPhee, D.

2004-01-01

Taking advantage of large datasets of both gravity and elastic wave arrival time observations available for the Parkfield, California region, we generated an image consistent with both types of data. Among a variety of strategies, the best result was obtained from a simultaneous inversion with a stability requirement that encouraged the perturbed model to remain close to a starting model consisting of a best fit to the arrival time data. The preferred model looks essentially the same as the best-fit arrival time model in areas where ray coverage is dense, with differences being greatest at shallow depths and near the edges of the model where ray paths are few. Earthquake locations change by no more than about 100 m, the general effect being migration of the seismic zone to the northeast, closer to the surface trace of the San Andreas Fault. Copyright 2004 by the American Geophysical Union.

Crustal structure in Nevada and southern Idaho from nuclear explosions

USGS Publications Warehouse

Pakiser, L.C.; Hill, D.P.

1962-01-01

The time of first arrival of seismic waves generated by 4 underground nuclear explosions at the Nevada Test Site (NTS) and recorded along a line extending north into southern Idaho is expressed as T0 = 0. 00 + Δ/3.0 (assumed), T1 = 0 .40 + Δ/6.03, and T2 = 6.15 + Δ/7.84, where time is in seconds and the shot-detector distance (Δ) is in km. Assuming constant velocities and horizontal layers, crustal thickness in the vicinity of NTS was determined to be 28 km. Delays in the traveltime segment T2, which represents Pn, indicate that the crust may thicken to 32 km in northern Nevada. A third phase, expressed as T3 = 14.48 + Δ/7.84, was also recognized and has arrival times appropriate for SPS. Amplitudes of Pn were determined at 7 places from recordings of seismic waves from one underground nuclear explosion (ANTLER).

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 much better. These results suggest that measured infrasound from the Circleville earthquake is consistent with the generation of infrasound from body waves in the epicentral region.

The wavefield of acoustic logging in a cased-hole with a single casing - Part I: a monopole tool

NASA Astrophysics Data System (ADS)

Wang, Hua; Fehler, Michael

2018-01-01

The bonding quality of the seal formed by the cement or collapse material between casing and formation rock is critical for the hydraulic isolation of reservoir layers with shallow aquifers, production and environmental safety, and plug and abandonment issues. Acoustic logging is a very good tool for evaluating the condition of the bond between different interfaces. The understanding of the acoustic logging wavefields in wells with single casing is still incomplete. We use a 3-D finite difference method to simulate wireline monopole wavefields in a single cased borehole with different bonding conditions at two locations: (1) between the cement and casing and (2) between the cement and formation. Pressure snapshots and waveforms for different models are shown, which allow us to better understand the wave propagation. Modal dispersion curves and data processing methods such as velocity-time semblance and dispersion analysis facilitate the identification of propagation modes in the different models. We find that the P wave is submerged in the casing modes and the S wave has poor coherency when the cement is replaced with fluid. The casing modes are strong when cement next to the casing is partially or fully replaced with fluid. The amplitude of these casing modes can be used to determine the bonding condition of the interface between casing and cement. However, the limited variation of the amplitude with fluid thickness means that amplitude measurements may lead to an ambiguous interpretation. When the cement next to the formation is partially replaced with fluid, the modes propagate in the combination of steel casing and cement and the velocities are highly dependent on the cement thickness. However, if the cement thickness is large (more than 2/3 of the annulus between casing and rock), the arrival time of the first arrival approximates that of the formation compressional wave when cement is good. It would highly likely that an analyst could misjudge cement quality because the amplitudes of these modes are very small and their arrival times are very near to the formation P arrival time. It is possible to use the amplitude to estimate the thickness of the cement sheath because the variation of amplitude with thickness is strong. While the Stoneley mode (ST1) propagates in the borehole fluid, a slow Stoneley mode (ST2) appears when there is a fluid column in the annulus between the casing and formation rock. The velocity of ST2 is sensitive to the total thickness of the fluid column in the annulus independent of the location of the fluid in the casing annulus. We propose a full waveform method, which includes the utilization of the amplitude of the first arrival and also the velocity of the ST2 wave, to estimate the bonding condition of multiple interfaces. These two measurements provide more information than the current method that uses only the first arrival to evaluate the bonding interfa next to the casing.

Improved Event Location Uncertainty Estimates

DTIC Science & Technology

2008-06-30

throughout this study . The data set consists of GT0-2 nuclear explosions from the SAIC Nuclear Explosion Database (www.rdss.info, Bahavar et al...errors: Bias and variance In this study SNR dependence of both delay and variance of reading errors of first arriving P waves are analyzed and...ground truth and range of event size. For other datasets we turn to estimates based on double- differences between arrival times of station pairs

Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

DOE PAGES

Syracuse, Ellen Marie; Zhang, Haijiang; Maceira, Monica

2017-07-11

Here, we present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body waves first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region.more » Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. In conclusion, without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.« less

Joint inversion of seismic and gravity data for imaging seismic velocity structure of the crust and upper mantle beneath Utah, United States

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

Syracuse, Ellen Marie; Zhang, Haijiang; Maceira, Monica

Here, we present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body waves first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region.more » Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. In conclusion, without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.« less

Testing model for prediction system of 1-AU arrival times of CME-associated interplanetary shocks

NASA Astrophysics Data System (ADS)

Ogawa, Tomoya; den, Mitsue; Tanaka, Takashi; Sugihara, Kohta; Takei, Toshifumi; Amo, Hiroyoshi; Watari, Shinichi

We test a model to predict arrival times of interplanetary shock waves associated with coronal mass ejections (CMEs) using a three-dimensional adaptive mesh refinement (AMR) code. The model is used for the prediction system we develop, which has a Web-based user interface and aims at people who is not familiar with operation of computers and numerical simulations or is not researcher. We apply the model to interplanetary CME events. We first choose coronal parameters so that property of background solar wind observed by ACE space craft is reproduced. Then we input CME parameters observed by SOHO/LASCO. Finally we compare the predicted arrival times with observed ones. We describe results of the test and discuss tendency of the model.

Electromagnetic plane-wave pulse transmission into a Lorentz half-space.

PubMed

Cartwright, Natalie A

2011-12-01

The propagation of an electromagnetic plane-wave signal obliquely incident upon a Lorentz half-space is studied analytically. Time-domain asymptotic expressions that increase in accuracy with propagation distance are derived by application of uniform saddle point methods on the Fourier-Laplace integral representation of the transmitted field. The results are shown to be continuous in time and comparable with numerical calculations of the field. Arrival times and angles of refraction are given for prominent transient pulse features and the steady-state signal.

Archaeological Graves Revealing By Means of Seismic-electric Effect

NASA Astrophysics Data System (ADS)

Boulytchov, A.

[a4paper,12pt]article english Seismic-electric effect was applied in field to forecast subsurface archaeological cul- tural objects. A source of seismic waves were repeated blows of a heavy hammer or powerful signals of magnetostrictive installation. Main frequency used was 500 Hz. Passed a soil layer and reached a second boundary between upper clayey-sand sedi- ments and archaeological object, the seismic wave caused electromagnetic fields on the both boundaries what in general is due to dipole charge separation owe to an im- balance of streaming currents induced by the seismic wave on opposite sides of a boundary interface. According to theoretical works of Pride the electromagnetic field appears on a boundary between two layers with different physical properties in the time of seismic wave propagation. Electric responses of electromagnetic fields were measured on a surface by pair of grounded dipole antennas or by one pivot and a long wire antenna acting as a capacitive pickup. The arrival times of first series of responses correspond to the time of seismic wave propagation from a source to a boundary between soil and clayey-sand layers. The arrival times of second row of responses correspond to the time of seismic wave way from a source to a boundary of clayey-sand layer with the archaeological object. The method depths successfully investigated were between 0.5-10 m. Similar electromagnetic field on another type of geological structure was also revealed by Mikhailov et al., Massachusetts, but their signals registered from two frontiers were too faint and not evident in comparing with ours ones that occurred to be perfect and clear. Seismic-electric method field experi- ments were successfully provided for the first time on archaeological objects.

Remotely triggered seismicity on the United States west coast following the Mw 7.9 Denali fault earthquake

USGS Publications Warehouse

Prejean, S.G.; Hill, D.P.; Brodsky, E.E.; Hough, S.E.; Johnston, M.J.S.; Malone, S.D.; Oppenheimer, D.H.; Pitt, A.M.; Richards-Dinger, K. B.

2004-01-01

The Mw 7.9 Denali fault earthquake in central Alaska of 3 November 2002 triggered earthquakes across western North America at epicentral distances of up to at least 3660 km. We describe the spatial and temporal development of triggered activity in California and the Pacific Northwest, focusing on Mount Rainier, the Geysers geothermal field, the Long Valley caldera, and the Coso geothermal field.The onset of triggered seismicity at each of these areas began during the Love and Raleigh waves of the Mw 7.9 wave train, which had dominant periods of 15 to 40 sec, indicating that earthquakes were triggered locally by dynamic stress changes due to low-frequency surface wave arrivals. Swarms during the wave train continued for ∼4 min (Mount Rainier) to ∼40 min (the Geysers) after the surface wave arrivals and were characterized by spasmodic bursts of small (M ≤ 2.5) earthquakes. Dynamic stresses within the surface wave train at the time of the first triggered earthquakes ranged from 0.01 MPa (Coso) to 0.09 MPa (Mount Rainier). In addition to the swarms that began during the surface wave arrivals, Long Valley caldera and Mount Rainier experienced unusually large seismic swarms hours to days after the Denali fault earthquake. These swarms seem to represent a delayed response to the Denali fault earthquake. The occurrence of spatially and temporally distinct swarms of triggered seismicity at the same site suggests that earthquakes may be triggered by more than one physical process.

One billion year-old Mid-continent Rift leaves virtually no clues in the mantle

NASA Astrophysics Data System (ADS)

Bollmann, T. A.; Frederiksen, A. W.; van der Lee, S.; Wolin, E.; Revenaugh, J.; Wiens, D.; Darbyshire, F. A.; Aleqabi, G. I.; Wysession, M. E.; Stein, S.; Jurdy, D. M.

2017-12-01

We measured the relative arrival times of more than forty-six thousand teleseismic P waves recorded by seismic stations of Earthscope's Superior Province Rifting Earthscope Experiment (SPREE) and combined them with a similar amount of such measurements from other seismic stations in the larger region. SPREE recorded seismic waves for two and a half years around the prominent, one billion year-old Mid-continent Rift structure. The curvilinear Mid-continent Rift (MR) is distinguished by voluminous one billion year-old lava flows, which produce a prominent gravity high along the MR. As for other seismic waves, these lava flows along with their underplated counterpart, slightly slow down the measured teleseismic P waves, on average, compared to P waves that did not traverse structures beneath the Mid-continent Rift. However, the variance in the P wave arrival times in these two groups is nearly ten times higher than their average difference. In a seismic-tomographic inversion, we mapped all measured arrival times into structures deep beneath the crust, in the Earth's mantle. Beneath the crust we generally find relatively high P velocities, indicating relatively cool and undeformable mantle structures. However, the uppermost mantle beneath the MR shows several patches of slightly decreased P velocities. These patches are coincident with where the gravity anomalies peak, in Iowa and along the northern Minnesota/Wisconsin border. We will report on the likelihood that these anomalies are indeed a remaining mantle-lithospheric signature of the MR or whether these patches indirectly reflect the presence of the lava flows and their underplated counterparts at the crust-mantle interface. Other structures of interest and of varying depth extent in our tomographic image locate at 1) the intersection of the Superior Craton with the Penokean Province and the Marshfield Terrane west of the MR in southern Minnesota, 2) the intersection of the Penokean, Yavapai, and Mazatzal Terranes along the eastern edge of the Michigan arm of the MR, and 3) beneath Lake Nipigon, north of Lake Superior. Our tomographic image also reveals an intricate distribution of deep high-velocity anomalies, including in the lower mantle, potentially related to Mesozoic subduction of the Kula and/or Farallon Plates.

Waveform Tomography Applied to Long Streamer MCS Data from the Scotian Slope

NASA Astrophysics Data System (ADS)

Delescluse, Matthias; Louden, Keith; Nedimovic, Mladen

2010-05-01

Detailed velocity models of the earth subsurface can be obtained through waveform tomography, a method that relies on using information from the full wavefield. Such models can be of significantly higher resolution than the corresponding models formed by more generic traveltime tomography methods, which are constrained only by the wave arrival times. However, to derive the detailed subsurface velocity, the waveform method is sensitive to modelling low-frequency refracted waves that have long paths through target structures. Thus field examples primarily have focused on the analysis of long-offset wide-angle datasets collected using autonomous receivers, in which refractions arrive at earlier times than reflections and there is a significant separation between the two wave arrivals. MCS datasets with shorter offsets typically lack these important features, which result in methodological problems (e.g. Hicks and Pratt, 2001), even though they benefit from a high density of raypaths and uniformity of receiver and shot properties. Modern marine seismic acquisition using long streamers now offers both the ability to record refracted waves at far offsets arriving ahead of the seafloor reflection, and the ability to do this at great density using uniform sources. In this study, we use 2D MCS data acquired with a 9-km-long streamer by ION GX-Technology over the Nova Scotia Slope in water depths of ~1600 m. We show that the refracted arrivals, although restricted to receivers between offsets of 7.5 and 9 km, provide sufficient information to successfully invert for a high-resolution velocity field. Using a frequency domain acoustic code (Pratt, 1999) over frequencies from 8 Hz to 24 Hz on two crossing profiles (45 and 20 km long), we detail how the limited refracted waves can constrain the velocity field above the depth of the turning waves (~1.5 km below seafloor). Several important features are resolved by the waveform velocity model that are not present in the initial travel-time model. In particular, a high velocity layer due to gas hydrates is imaged along the entire profile even where a characteristic BSR is not visible. The velocity increase in the gas hydrate layer is very small (< 100 m/s). In addition, a strong velocity increase of ~ 300 m/s exists below a deeper, gently dipping reflector along which discontinuous low-velocity zones, probably related to gas, are present. Velocity models are consistent at the crossing point between the two profiles. The depth limitation of the detailed MCS waveform tomography imaging could be extended by even longer streamers (e.g. 15 km) or by joint inversion with OBS data.

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

NASA Astrophysics Data System (ADS)

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

2005-05-01

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

Anomalous waveforms observed in laboratory-formed gas hydrate-bearing and ice-bearing sediments

PubMed Central

Lee, Myung W.; Waite, William F.

2011-01-01

Acoustic transmission measurements of compressional, P, and shear, S, wave velocities rely on correctly identifying the P- and S-body wave arrivals in the measured waveform. In cylindrical samples for which the sample is much longer than the acoustic wavelength, these body waves can be obscured by high-amplitude waveform features arriving just after the relatively small-amplitude P-body wave. In this study, a normal mode approach is used to analyze this type of waveform, observed in sediment containing gas hydrate or ice. This analysis extends an existing normal-mode waveform propagation theory by including the effects of the confining medium surrounding the sample, and provides guidelines for estimating S-wave velocities from waveforms containing multiple large-amplitude arrivals. PMID:21476628

Influence of off-great-circle propagation of Rayleigh waves on event-based surface wave tomography in Northeast China

NASA Astrophysics Data System (ADS)

Chen, Haopeng; Ni, Sidao; Chu, Risheng; Chong, Jiajun; Liu, Zhikun; Zhu, Liangbao

2018-05-01

Surface waves are generally assumed to propagate along great-circle paths in most surface-wave tomography. However, when lateral heterogeneity is strong, off-great-circle propagation may occur and deteriorate surface wave tomography results based on the great-circle assumption. In this study, we used teleseismic waveforms recorded by the NECESSArray in Northeast China to study off-great-circle propagation of Rayleigh waves using the beamforming method and evaluated the influence of off-great-circle propagation on event-based surface wave tomography. The results show that arrival angle anomalies generally increase with decreasing period. The arrival angle anomalies at 60 and 50 s periods are smaller than that at 40 and 30 s periods, which indicates that the off-great-circle propagation is relatively weak for longer periods. At 30 s period, the arrival angle anomalies are relatively larger and some of the measurements can exceed 20°, which represents a strong off-great-circle propagation effect. In some areas, the arrival angle anomalies of adjacent events differ significantly, which may be attributed to multipathing propagation of surface waves. To evaluate the influence of off-great-circle propagation on event-based surface wave tomography, we used measured arrival angle anomalies to correct two-station phase velocity measurements, and performed azimuthal anisotropy tomography using dispersion datasets with and without the arrival angle correction. At longer periods, such as 60 s, the influence of off-great-circle propagation on surface wave tomography is weak even though the corrected model has better data fit than the uncorrected model. However, the influence of off-great-circle propagation is non-negligible at short periods. The tomography results at 30 s period show that the differences in phase velocity, the strength of anisotropy and the fast direction can be as large as 1.5 per cent, 1.0 per cent and 30°, respectively. Furthermore, the corrected phase velocity is systematically lower than that without correction. This study illustrates the necessity of studying the off-great-circle propagation of surface waves to improve the accuracy of event-based surface wave tomography, especially for shorter periods.

A practical implementation of wave front construction for 3-D isotropic media

NASA Astrophysics Data System (ADS)

Chambers, K.; Kendall, J.-M.

2008-06-01

Wave front construction (WFC) methods are a useful tool for tracking wave fronts and are a natural extension to standard ray shooting methods. Here we describe and implement a simple WFC method that is used to interpolate wavefield properties throughout a 3-D heterogeneous medium. Our approach differs from previous 3-D WFC procedures primarily in the use of a ray interpolation scheme, based on approximating the wave front as a `locally spherical' surface and a `first arrival mode', which reduces computation times, where only first arrivals are required. Both of these features have previously been included in 2-D WFC algorithms; however, until now they have not been extended to 3-D systems. The wave front interpolation scheme allows for rays to be traced from a nearly arbitrary distribution of take-off angles, and the calculation of derivatives with respect to take-off angles is not required for wave front interpolation. However, in regions of steep velocity gradient, the locally spherical approximation is not valid, and it is necessary to backpropagate rays to a sufficiently homogenous region before interpolation of the new ray. Our WFC technique is illustrated using a realistic velocity model, based on a North Sea oil reservoir. We examine wavefield quantities such as traveltimes, ray angles, source take-off angles and geometrical spreading factors, all of which are interpolated on to a regular grid. We compare geometrical spreading factors calculated using two methods: using the ray Jacobian and by taking the ratio of a triangular area of wave front to the corresponding solid angle at the source. The results show that care must be taken when using ray Jacobians to calculate geometrical spreading factors, as the poles of the source coordinate system produce unreliable values, which can be spread over a large area, as only a few initial rays are traced in WFC. We also show that the use of the first arrival mode can reduce computation time by ~65 per cent, with the accuracy of the interpolated traveltimes, ray angles and source take-off angles largely unchanged. However, the first arrival mode does lead to inaccuracies in interpolated angles near caustic surfaces, as well as small variations in geometrical spreading factors for ray tubes that have passed through caustic surfaces.

Studying the Effects of Transparent vs. Opaque Shallow Thrust Faults Using Synthetic P and SH Seismograms

NASA Astrophysics Data System (ADS)

Smith, D. E.; Aagaard, B. T.; Heaton, T. H.

2001-12-01

It has been hypothesized (Brune, 1996) that teleseismic inversions may underestimate the moment of shallow thrust fault earthquakes if energy becomes trapped in the hanging wall of the fault, i.e. if the fault boundary becomes opaque. We address this by creating and analyzing synthetic P and SH seismograms for a variety of friction models. There are a total of five models: (1) crack model (slip weakening) with instantaneous healing (2) crack model without healing (3) crack model with zero sliding friction (4) pulse model (slip and rate weakening) (5) prescribed model (Haskell-like rupture with the same final slip and peak slip-rate as model 4). Models 1-4 are all dynamic models where fault friction laws determine the rupture history. This allows feedback between the ongoing rupture and waves from the beginning of the rupture that hit the surface and reflect downwards. Hence, models 1-4 can exhibit opaque fault characteristics. Model 5, a prescribed rupture, allows for no interaction between the rupture and reflected waves, therefore, it is a transparent fault. We first produce source time functions for the different friction models by rupturing shallow thrust faults in 3-D dynamic finite-element simulations. The source time functions are used as point dislocations in a teleseismic body-wave code. We examine the P and SH waves for different azimuths and epicentral distances. The peak P and S first arrival displacement amplitudes for the crack, crack with healing and pulse models are all very similar. These dynamic models with opaque faults produce smaller peak P and S first arrivals than the prescribed, transparent fault. For example, a fault with strike = 90 degrees, azimuth = 45 degrees has P arrivals smaller by about 30% and S arrivals smaller by about 15%. The only dynamic model that doesn't fit this pattern is the crack model with zero sliding friction. It oscillates around its equilibrium position; therefore, it overshoots and yields an excessively large peak first arrival. In general, it appears that the dynamic, opaque faults have smaller peak teleseismic displacements that would lead to lower moment estimates by a modest amount.

Beat-the-wave evacuation mapping for tsunami hazards in Seaside, Oregon, USA

USGS Publications Warehouse

Priest, George R.; Stimely, Laura; Wood, Nathan J.; Madin, Ian; Watzig, Rudie

2016-01-01

Previous pedestrian evacuation modeling for tsunamis has not considered variable wave arrival times or critical junctures (e.g., bridges), nor does it effectively communicate multiple evacuee travel speeds. We summarize an approach that identifies evacuation corridors, recognizes variable wave arrival times, and produces a map of minimum pedestrian travel speeds to reach safety, termed a “beat-the-wave” (BTW) evacuation analysis. We demonstrate the improved approach by evaluating difficulty of pedestrian evacuation of Seaside, Oregon, for a local tsunami generated by a Cascadia subduction zone earthquake. We establish evacuation paths by calculating the least cost distance (LCD) to safety for every grid cell in a tsunami-hazard zone using geospatial, anisotropic path distance algorithms. Minimum BTW speed to safety on LCD paths is calculated for every grid cell by dividing surface distance from that cell to safety by the tsunami arrival time at safety. We evaluated three scenarios of evacuation difficulty: (1) all bridges are intact with a 5-minute evacuation delay from the start of earthquake, (2) only retrofitted bridges are considered intact with a 5-minute delay, and (3) only retrofitted bridges are considered intact with a 10-minute delay. BTW maps also take into account critical evacuation points along complex shorelines (e.g., peninsulas, bridges over shore-parallel estuaries) where evacuees could be caught by tsunami waves. The BTW map is able to communicate multiple pedestrian travel speeds, which are typically visualized by multiple maps with current LCD-based mapping practices. Results demonstrate that evacuation of Seaside is problematic seaward of the shore-parallel waterways for those with any limitations on mobility. Tsunami vertical-evacuation refuges or additional pedestrian bridges may be effective ways of reducing loss of life seaward of these waterways.

Non-linear resonant coupling of tsunami edge waves using stochastic earthquake source models

USGS Publications Warehouse

Geist, Eric L.

2016-01-01

Non-linear resonant coupling of edge waves can occur with tsunamis generated by large-magnitude subduction zone earthquakes. Earthquake rupture zones that straddle beneath the coastline of continental margins are particularly efficient at generating tsunami edge waves. Using a stochastic model for earthquake slip, it is shown that a wide range of edge-wave modes and wavenumbers can be excited, depending on the variability of slip. If two modes are present that satisfy resonance conditions, then a third mode can gradually increase in amplitude over time, even if the earthquake did not originally excite that edge-wave mode. These three edge waves form a resonant triad that can cause unexpected variations in tsunami amplitude long after the first arrival. An M ∼ 9, 1100 km-long continental subduction zone earthquake is considered as a test case. For the least-variable slip examined involving a Gaussian random variable, the dominant resonant triad includes a high-amplitude fundamental mode wave with wavenumber associated with the along-strike dimension of rupture. The two other waves that make up this triad include subharmonic waves, one of fundamental mode and the other of mode 2 or 3. For the most variable slip examined involving a Cauchy-distributed random variable, the dominant triads involve higher wavenumbers and modes because subevents, rather than the overall rupture dimension, control the excitation of edge waves. Calculation of the resonant period for energy transfer determines which cases resonant coupling may be instrumentally observed. For low-mode triads, the maximum transfer of energy occurs approximately 20–30 wave periods after the first arrival and thus may be observed prior to the tsunami coda being completely attenuated. Therefore, under certain circumstances the necessary ingredients for resonant coupling of tsunami edge waves exist, indicating that resonant triads may be observable and implicated in late, large-amplitude tsunami arrivals.

Active doublet method for measuring small changes in physical properties

DOEpatents

Roberts, Peter M.; Fehler, Michael C.; Johnson, Paul A.; Phillips, W. Scott

1994-01-01

Small changes in material properties of a work piece are detected by measuring small changes in elastic wave velocity and attenuation within a work piece. Active, repeatable source generate coda wave responses from a work piece, where the coda wave responses are temporally displaced. By analyzing progressive relative phase and amplitude changes between the coda wave responses as a function of elapsed time, accurate determinations of velocity and attenuation changes are made. Thus, a small change in velocity occurring within a sample region during the time periods between excitation origin times (herein called "doublets") will produce a relative delay that changes with elapsed time over some portion of the scattered waves. This trend of changing delay is easier to detect than an isolated delay based on a single arrival and provides a direct measure of elastic wave velocity changes arising from changed material properties of the work piece.

The NANOGrav Eleven-Year Data Set: High-precision timing of 48 Millisecond Pulsars

NASA Astrophysics Data System (ADS)

Nice, David J.; NANOGrav

2017-01-01

Gravitational waves from sources such as supermassive black hole binary systems perturb times-of-flight of signals traveling from pulsars to the Earth. The NANOGrav collaboration aims to measure these perturbations in high precision millisecond pulsar timing data and thus to directly detect gravitational waves and characterize the gravitational wave sources. By observing pulsars over time spans of many years, we are most sensitive to gravitational waves at nanohertz frequencies. This work is complimentary to ground based detectors such as LIGO, which are sensitive to gravitational waves with frequencies 10 orders of magnitude higher.In this presentation we describe the NANOGrav eleven-year data set. This includes pulsar time-of-arrival measurements from 48 millisecond pulsars made with the Arecibo Observatory (for pulsars with declinations between -1 and 39 degrees) and the Green Bank Telescope (for other pulsars, with two pulsars overlapping with Arecibo). The data set consists of more than 300,000 pulse time-of-arrival measurements made in nearly 7000 unique observations (a given pulsar observed with a given telescope receiver on a given day). In the best cases, measurement precision is better than 100 nanoseconds, and in nearly all cases it is better than 1 microsecond.All pulsars in our program are observed at intervals of 3 to 4 weeks. Observations use wideband data acquisition systems and are made at two receivers at widely separated frequencies at each epoch, allowing for characterization and mitigation of the effects of interstellar medium on the signal propagation. Observation of a large number of pulsars allows for searches for correlated perturbations among the pulsar signals, which is crucial for achieving high-significance detection of gravitational waves in the face of uncorrelated noise (from gravitational waves and rotation noise) in the individual pulsars. In addition, seven pulsars are observed at weekly intervals. This increases our sensitivity to individual gravitational wave sources.

Ultrasound shear wave simulation based on nonlinear wave propagation and Wigner-Ville Distribution analysis

NASA Astrophysics Data System (ADS)

Bidari, Pooya Sobhe; Alirezaie, Javad; Tavakkoli, Jahan

2017-03-01

This paper presents a method for modeling and simulation of shear wave generation from a nonlinear Acoustic Radiation Force Impulse (ARFI) that is considered as a distributed force applied at the focal region of a HIFU transducer radiating in nonlinear regime. The shear wave propagation is simulated by solving the Navier's equation from the distributed nonlinear ARFI as the source of the shear wave. Then, the Wigner-Ville Distribution (WVD) as a time-frequency analysis method is used to detect the shear wave at different local points in the region of interest. The WVD results in an estimation of the shear wave time of arrival, its mean frequency and local attenuation which can be utilized to estimate medium's shear modulus and shear viscosity using the Voigt model.

Locating Microseism Sources Using Spurious Arrivals in Intercontinental Noise Correlations

NASA Astrophysics Data System (ADS)

Retailleau, Lise; Boué, Pierre; Stehly, Laurent; Campillo, Michel

2017-10-01

The accuracy of Green's functions retrieved from seismic noise correlations in the microseism frequency band is limited by the uneven distribution of microseism sources at the surface of the Earth. As a result, correlation functions are often biased as compared to the expected Green's functions, and they can include spurious arrivals. These spurious arrivals are seismic arrivals that are visible on the correlation and do not belong to the theoretical impulse response. In this article, we propose to use Rayleigh wave spurious arrivals detected on correlation functions computed between European and United States seismic stations to locate microseism sources in the Atlantic Ocean. We perform a slant stack on a time distance gather of correlations obtained from an array of stations that comprises a regional deployment and a distant station. The arrival times and the apparent slowness of the spurious arrivals lead to the location of their source, which is obtained through a grid search procedure. We discuss improvements in the location through this methodology as compared to classical back projection of microseism energy. This method is interesting because it only requires an array and a distant station on each side of an ocean, conditions that can be met relatively easily.

An explanation for the anomalous wave profiles obtained in composition B-3 impacted by flat nosed steel rods

NASA Astrophysics Data System (ADS)

James, H. R.; Gustavsen, R. L.; Dattelbaum, D. M.

2017-01-01

In previous work involving firing flat nosed steel rods into the 60/40 RDX/TNT explosive Composition B-3, we found an apparently anomalous "hump" in particle velocity wave profiles. The "hump" occurred on the center-line established by the rod, and at relatively late times, > 1 µs, after detonation onset. Several explanations, including that of a late time reaction, were postulated. This report will present evidence that the anomalous late time "hump" is due to the arrival of rarefaction waves from the rod's periphery. Simple analytic calculations and reactive-burn hydro-code calculations will be presented supporting this hypothesis.

Numerical simulation and experimental validation of Lamb wave propagation behavior in composite plates

NASA Astrophysics Data System (ADS)

Kim, Sungwon; Uprety, Bibhisha; Mathews, V. John; Adams, Daniel O.

2015-03-01

Structural Health Monitoring (SHM) based on Acoustic Emission (AE) is dependent on both the sensors to detect an impact event as well as an algorithm to determine the impact location. The propagation of Lamb waves produced by an impact event in thin composite structures is affected by several unique aspects including material anisotropy, ply orientations, and geometric discontinuities within the structure. The development of accurate numerical models of Lamb wave propagation has important benefits towards the development of AE-based SHM systems for impact location estimation. Currently, many impact location algorithms utilize the time of arrival or velocities of Lamb waves. Therefore the numerical prediction of characteristic wave velocities is of great interest. Additionally, the propagation of the initial symmetric (S0) and asymmetric (A0) wave modes is important, as these wave modes are used for time of arrival estimation. In this investigation, finite element analyses were performed to investigate aspects of Lamb wave propagation in composite plates with active signal excitation. A comparative evaluation of two three-dimensional modeling approaches was performed, with emphasis placed on the propagation and velocity of both the S0 and A0 wave modes. Results from numerical simulations are compared to experimental results obtained from active AE testing. Of particular interest is the directional dependence of Lamb waves in quasi-isotropic carbon/epoxy composite plates. Numerical and experimental results suggest that although a quasi-isotropic composite plate may have the same effective elastic modulus in all in-plane directions, the Lamb wave velocity may have some directional dependence. Further numerical analyses were performed to investigate Lamb wave propagation associated with circular cutouts in composite plates.

Acoustic resonances of fluid-immersed elastic cylinders and spheroids: Theory and experiment

NASA Astrophysics Data System (ADS)

Niemiec, Jan; Überall, Herbert; Bao, X. L.

2002-05-01

Frequency resonances in the scattering of acoustic waves from a target object are caused by the phase matching of surface waves repeatedly encircling the object. This is exemplified here by considering elastic finite cylinders and spheroids, and the phase-matching condition provides a means of calculating the complex resonance frequencies of such objects. Tank experiments carried out at Catholic University, or at the University of Le Havre, France by G. Maze and J. Ripoche, have been interpreted using this approach. The experiments employed sound pulses to measure arrival times, which allowed identification of the surface paths taken by the surface waves, thus giving rise to resonances in the scattering amplitude. A calculation of the resonance frequencies using the T-matrix approach showed satisfactory agreement with the experimental resonance frequencies that were either measured directly (as at Le Havre), or that were obtained by the interpretation of measured arrival times (at Catholic University) using calculated surface wave paths, and the extraction of resonance frequencies therefrom, on the basis of the phase-matching condition. Results for hemispherically endcapped, evacuated steel cylinders obtained in a lake experiment carried out by the NSWC were interpreted in the same fashion.

Value of shear wave arrival time contour display in shear wave elastography for breast masses diagnosis.

PubMed

Zhou, Bang-Guo; Wang, Dan; Ren, Wei-Wei; Li, Xiao-Long; He, Ya-Ping; Liu, Bo-Ji; Wang, Qiao; Chen, Shi-Gao; Alizad, Azra; Xu, Hui-Xiong

2017-08-01

To evaluate the diagnostic performance of shear wave arrival time contour (SWATC) display for the diagnosis of breast lesions and to identify factors associated with the quality of shear wave propagation (QSWP) in breast lesions. This study included 277 pathologically confirmed breast lesions. Conventional B-mode ultrasound characteristics and shear wave elastography parameters were computed. Using the SWATC display, the QSWP of each lesion was assigned to a two-point scale: score 1 (low quality) and score 2 (high quality). Binary logistic regression analysis was performed to identify factors associated with QSWP. The area under the receiver operating characteristic curve (AUROC) for QSWP to differentiate benign from malignant lesions was 0.913, with a sensitivity of 91.9%, a specificity of 90.7%, a positive predictive value (PPV) of 74.0%, and a negative predictive value (NPV) of 97.5%. Compared with using the standard deviation of shear wave speed (SWS SD ) alone, SWS SD combined with QSWP increased the sensitivity from 75.8% to 93.5%, but decreased the specificity from 95.8% to 89.3% (P < 0.05). SWS SD was identified to be the strongest factor associated with the QSWP, followed by tumor malignancy and the depth of the lesion. In conclusion, SWATC display may be useful for characterization of breast lesions.

Anomalous waveforms observed in laboratory-formed gas hydrate-bearing and ice-bearing sediments

USGS Publications Warehouse

Lee, M.W.; Waite, W.F.

2011-01-01

Acoustic transmission measurements of compressional, P, and shear, S, wave velocities rely on correctly identifying the P- and S-body wave arrivals in the measured waveform. In cylindrical samples for which the sample is much longer than the acoustic wavelength, these body waves can be obscured by high-amplitude waveform features arriving just after the relatively small-amplitude P-body wave. In this study, a normal mode approach is used to analyze this type of waveform, observed in sediment containing gas hydrate or ice. This analysis extends an existing normal-mode waveform propagation theory by including the effects of the confining medium surrounding the sample, and provides guidelines for estimating S-wave velocities from waveforms containing multiple large-amplitude arrivals. ?? 2011 Acoustical Society of America.

June 13, 2013 U.S. East Coast Meteotsunami: Comparing a Numerical Model With Observations

NASA Astrophysics Data System (ADS)

Wang, D.; Becker, N. C.; Weinstein, S.; Whitmore, P.; Knight, W.; Kim, Y.; Bouchard, R. H.; Grissom, K.

2013-12-01

On June 13, 2013, a tsunami struck the U.S. East Coast and caused several reported injuries. This tsunami occurred after a derecho moved offshore from North America into the Atlantic Ocean. The presence of this storm, the lack of a seismic source, and the fact that tsunami arrival times at tide stations and deep ocean-bottom pressure sensors cannot be attributed to a 'point-source' suggest this tsunami was caused by atmospheric forces, i.e., a meteotsunami. In this study we attempt to reproduce the observed phenomenon using a numerical model with idealized atmospheric pressure forcing resembling the propagation of the observed barometric anomaly. The numerical model was able to capture some observed features of the tsunami at some tide stations, including the time-lag between the time of pressure jump and the time of tsunami arrival. The model also captures the response at a deep ocean-bottom pressure gauge (DART 44402), including the primary wave and the reflected wave. There are two components of the oceanic response to the propagating pressure anomaly, inverted barometer response and dynamic response. We find that the dynamic response over the deep ocean to be much smaller than the inverted barometer response. The time lag between the pressure jump and tsunami arrival at tide stations is due to the dynamic response: waves generated and/or reflected at the shelf-break propagate shoreward and amplify due to the shoaling effect. The evolution of the derecho over the deep ocean (propagation direction and intensity) is not well defined, however, because of the lack of data so the forcing used for this study is somewhat speculative. Better definition of the pressure anomaly through increased observation or high resolution atmospheric models would improve meteotsunami forecast capabilities.

Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles

DOEpatents

Benjamin, R.F.

1983-10-18

An apparatus for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously.

Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles

DOEpatents

Benjamin, Robert F.

1987-01-01

An apparatus for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously.

Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles

DOEpatents

Benjamin, R.F.

1987-03-10

An apparatus is disclosed for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously. 3 figs.

A new prototype system for earthquake early warning in Taiwan

NASA Astrophysics Data System (ADS)

Hsiao, N.; Wu, Y.; Chen, D.; Kuo, K.; Shin, T.

2009-12-01

Earthquake early warning (EEW) system has already been developed and tested in Taiwan for more than ten years. With the implementation of a real-time strong-motion network by the Central Weather Bureau (CWB), a virtual sub-network (VSN) system based on regional early warning approach was utilized at the first attempt. In order to shorten the processing time, seismic waveforms in a 10-sec time window starting from the first P-wave arrival time at the nearest station are used to determine the hypocenter and earthquake magnitude which is dubbed ML10. Since 2001, this EEW system has responded to a total of 255 events with magnitude greater than 4.5 occurred inland or off the coast of Taiwan. The system is capable of issuing an earthquake report within 20 sec of its occurrence with good magnitude estimations for events up to magnitude 6.5. This will provide early warning for metropolitan areas located 70 km away from the epicentre. In the latest development, a new prototype EEW system based on P-wave method was developed. Instead of ML10, we adopt the “Pd magnitude”, MPd, as our magnitude indicator in the new system. Pd is defined as the peak amplitude of the initial P-wave displacement. In the previous studies, by analyzing the Pd attenuation relationship with earthquake magnitudes, Pd was proved to be a good magnitude estimator for EEW purpose. Therefore, we adopt the Pd magnitude in developing our next generation EEW system. The new system is designed and constructed based on the Central Weather Bureau Seismographic Network (CWBSN). The CWBSN is a real-time seismographic network with more than one hundred digital telemetered seismic stations distributed over the entire Taiwan. Currently, there are three types of seismic instruments installed at the stations, either co-site or separately installed, including short-period seismographs, accelerometers, and broadband instruments. For the need of integral data processing, we use the Earthworm system as a common platform to integrate all real-time signals. In the process, strong-motion and broadband signals are used for automatic P-wave arrival time and Pd determination. However, short-period signals are only used for P-wave arrival time picking. This new system is still under development and being improved, with the hope of replacing the current operational EEW system in the future.

Rapid magnitude estimation from time-dependent displacement amplitude measured with seismogeodetic instrumentation

NASA Astrophysics Data System (ADS)

Goldberg, D.; Bock, Y.; Melgar, D.

2017-12-01

Earthquake magnitude is a concise metric that illuminates the destructive potential of a seismic event. Rapid determination of earthquake magnitude is currently the main prerequisite for dissemination of a tsunami early warning, thus timely and automated calculation is of high importance. Seismic instrumentation experiences well-documented complications at long periods, making the accurate measurement of ground displacement in the near field unreliable. As a result, the relation between ground motion measured with seismic instrumentation and magnitude saturates, causing underestimation of the size of very large events. In the case of tsunamigenic earthquakes, magnitude underestimation in turn leads to a flawed tsunami inundation assessment, which limits the effectiveness of an early warning, in particular for local tsunamis. Global Navigation Satellite System (GNSS) instrumentation measures the displacement field directly, leading to more accurate magnitude estimates with near-field data. Unlike seismic-only instrumentation, near-field GNSS has been shown to provide an accurate magnitude estimate using the peak ground displacement (PGD) after just 2 minutes [Melgar et al., 2015]. However, GNSS alone is too noisy to detect the first seismic wave arrivals (P-waves), thus it cannot be as timely as a seismic system on its own. Using collocated seismic and geodetic instrumentation, we refine magnitude scaling relations by incorporating a large dataset of earthquakes in Japan. We demonstrate that consideration of the time-dependence of displacement amplitude with respect to P-wave arrival time reduces the time to convergence of the magnitude estimate. We present findings on the growth of events of large magnitude, and demonstrate time-dependent scaling relations that adapt to the amount of recorded data, starting with the P-wave arrival and continuing through PGD. We illustrate real-time, automated implementation of this method, and consider network improvements to advance rapid characterization of large events. Improvement of initial magnitude estimates through integration of geodetic and seismogeodetic observations is a top priority of an ongoing collaboration with NASA and NOAA's National and Pacific Tsunami Warning Centers (NOAA/NASA GNSS Tsunami Team).

BAROMETRIC AND WATER-SURFACE WAVES PRODUCED BY MIKE SHOT

DTIC Science & Technology

Barometric and water -surface waves generated by Mike shot were studied by means of 25 instruments in 19 locations in the Pacific Basin ranging from...on the tops of two mounts. The first water waves arriving at Eniwetok Island apparently traveled along paths outside the lagoon. At several of the...stations there were two distinct arrivals of water waves, the first apparently being driven by the propagated rise in atmospheric pressure caused by the

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

Hatano, H.; Watanabe, T.

A new system was developed for the reciprocity calibration of acoustic emission transducers in Rayleigh-wave and longitudinal-wave sound fields. In order to reduce interference from spurious waves due to reflections and mode conversions, a large cylindrical block of forged steel was prepared for the transfer medium, and direct and spurious waves were discriminated between on the basis of their arrival times. Frequency characteristics of velocity sensitivity to both the Rayleigh wave and longitudinal wave were determined in the range of 50 kHz{endash}1 MHz by means of electrical measurements without the use of mechanical sound sources or reference transducers. {copyright} {italmore » 1997 Acoustical Society of America.}« less

Detecting stochastic backgrounds of gravitational waves with pulsar timing arrays

NASA Astrophysics Data System (ADS)

Siemens, Xavier

2016-03-01

For the past decade the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has been using the Green Bank Telescope and the Arecibo Observatory to monitor millisecond pulsars. NANOGrav, along with two other international collaborations, the European Pulsar Timing Array and the Parkes Pulsar Timing Array in Australia, form a consortium of consortia: the International Pulsar Timing Array (IPTA). The goal of the IPTA is to directly detect low-frequency gravitational waves which cause small changes to the times of arrival of radio pulses from millisecond pulsars. In this talk I will discuss the work of NANOGrav and the IPTA, as well as our sensitivity to stochastic backgrounds of gravitational waves. I will show that a detection of the background produced by supermassive black hole binaries is possible by the end of the decade. Supported by the NANOGrav Physics Frontiers Center.

A new physics-based modeling approach for tsunami-ionosphere coupling

NASA Astrophysics Data System (ADS)

Meng, X.; Komjathy, A.; Verkhoglyadova, O. P.; Yang, Y.-M.; Deng, Y.; Mannucci, A. J.

2015-06-01

Tsunamis can generate gravity waves propagating upward through the atmosphere, inducing total electron content (TEC) disturbances in the ionosphere. To capture this process, we have implemented tsunami-generated gravity waves into the Global Ionosphere-Thermosphere Model (GITM) to construct a three-dimensional physics-based model WP (Wave Perturbation)-GITM. WP-GITM takes tsunami wave properties, including the wave height, wave period, wavelength, and propagation direction, as inputs and time-dependently characterizes the responses of the upper atmosphere between 100 km and 600 km altitudes. We apply WP-GITM to simulate the ionosphere above the West Coast of the United States around the time when the tsunami associated with the March 2011 Tohuku-Oki earthquke arrived. The simulated TEC perturbations agree with Global Positioning System observations reasonably well. For the first time, a fully self-consistent and physics-based model has reproduced the GPS-observed traveling ionospheric signatures of an actual tsunami event.

Constraints from the time lag between gravitational waves and gamma rays: Implications of GW170817 and GRB 170817A

NASA Astrophysics Data System (ADS)

Shoemaker, Ian M.; Murase, Kohta

2018-04-01

The Laser Interferometer Gravitational-Wave Observatory (LIGO) has recently discovered gravitational waves (GWs) from its first neutron star-neutron star merger at a distance of ˜40 Mpc from the Earth. The associated electromagnetic (EM) detection of the event, including the short gamma-ray burst within Δ t ˜2 s after the GW arrival, can be used to test various aspects of sources physics and GW propagation. Using GW170817 as the first GW-EM example, we show that this event provides a stringent direct test that GWs travel at the speed of light. The gravitational potential of the Milky Way provides a potential source of Shapiro time delay difference between the arrival of photons and GWs, and we demonstrate that the nearly coincident detection of the GW and EM signals can yield strong limits on anomalous gravitational time delay, through updating the previous limits taking into account details of Milky Way's gravitational potential. Finally, we also obtain an intriguing limit on the size of the prompt emission region of GRB 170817A, and discuss implications for the emission mechanism of short gamma-ray bursts.

Sensitivity of Pulsar Timing Arrays

NASA Astrophysics Data System (ADS)

Siemens, Xavier

2015-08-01

For the better part of the last decade, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has been using the Green Bank and Arecibo radio telescopes to monitor millisecond pulsars. NANOGrav, along with similar international collaborations, the European Pulsar Timing Array and the Parkes Pulsar Timing Array in Australia, form a consortium of consortia: the International Pulsar Timing Array (IPTA). The goal of the IPTA is to directly detect low-frequency gravitational waves which cause small changes to the times of arrival of radio pulses from millisecond pulsars. In this talk I will discuss the work of NANOGrav and the IPTA as well as our sensitivity to gravitational waves from astrophysical sources. I will show that a detection is possible by the end of the decade.

Extending RTM Imaging With a Focus on Head Waves

NASA Astrophysics Data System (ADS)

Holicki, Max; Drijkoningen, Guy

2016-04-01

Conventional industry seismic imaging predominantly focuses on pre-critical reflections, muting post-critical arrivals in the process. This standard approach neglects a lot of information present in the recorded wave field. This negligence has been partially remedied with the inclusion of head waves in more advanced imaging techniques, like Full Waveform Inversion (FWI). We would like to see post-critical information leave the realm of labour-intensive travel-time picking and tomographic inversion towards full migration to improve subsurface imaging and parameter estimation. We present a novel seismic imaging approach aimed at exploiting post-critical information, using the constant travel path for head-waves between shots. To this end, we propose to generalize conventional Reverse Time Migration (RTM) to scenarios where the sources for the forward and backward propagated wave-fields are not coinciding. RTM functions on the principle that backward propagated receiver data, due to a source at some locations, must overlap with the forward propagated source wave field, from the same source location, at subsurface scatterers. Where the wave-fields overlap in the subsurface there is a peak at the zero-lag cross-correlation, and this peak is used for the imaging. For the inclusion of head waves, we propose to relax the condition of coincident sources. This means that wave-fields, from non-coincident-sources, will not overlap properly in the subsurface anymore. We can make the wave-fields overlap in the subsurface again, by time shifting either the forward or backward propagated wave-fields until the wave-fields overlap. This is the same as imaging at non-zero cross-correlation lags, where the lag is the travel time difference between the two wave-fields for a given event. This allows us to steer which arrivals we would like to use for imaging. In the simplest case we could use Eikonal travel-times to generate our migration image, or we exclusively image the subsurface with the head wave from the nth-layer. To illustrate the method we apply it to a layered Earth model with five layers and compare it to conventional RTM. We will show that conventional RTM highlights interfaces, while our head-wave based images highlight layers, producing fundamentally different images. We also demonstrate that our proposed imaging scheme is more sensitive to the velocity model than conventional RTM, which is important for improved velocity model building in the future.

Constraints on Born-Infeld gravity from the speed of gravitational waves after GW170817 and GRB 170817A

NASA Astrophysics Data System (ADS)

Jana, Soumya; Chakravarty, Girish Kumar; Mohanty, Subhendra

2018-04-01

The observations of gravitational waves from the binary neutron star merger event GW170817 and the subsequent observation of its electromagnetic counterparts from the gamma-ray burst GRB 170817A provide us a significant opportunity to study theories of gravity beyond general relativity. An important outcome of these observations is that they constrain the difference between the speed of gravity and the speed of light to less than 10-15c . Also, the time delay between the arrivals of gravitational waves at different detectors constrains the speed of gravity at the Earth to be in the range 0.55 c

3D P and S Wave Velocity Structure and Tremor Locations in the Parkfield Region

NASA Astrophysics Data System (ADS)

Zeng, X.; Thurber, C. H.; Shelly, D. R.; Bennington, N. L.; Cochran, E. S.; Harrington, R. M.

2014-12-01

We have assembled a new dataset to refine the 3D seismic velocity model in the Parkfield region. The S arrivals from 184 earthquakes recorded by the Parkfield Experiment to Record MIcroseismicity and Tremor array (PERMIT) during 2010-2011 were picked by a new S wave picker, which is based on machine learning. 74 blasts have been assigned to four quarries, whose locations were identified with Google Earth. About 1000 P and S wave arrivals from these blasts at permanent seismic network were also incorporated. Low frequency earthquakes (LFEs) occurring within non-volcanic tremor (NVT) are valuable for improving the precision of NVT location and the seismic velocity model at greater depths. Based on previous work (Shelley and Hardebeck, 2010), waveforms of hundreds of LFEs in same family were stacked to improve signal qualify. In a previous study (McClement et al., 2013), stacked traces of more than 30 LFE families at the Parkfileld Array Seismic Observatory (PASO) have been picked. We expanded our work to include LFEs recorded by the PERMIT array. The time-frequency Phase Weight Stacking (tf-PWS) method was introduced to improve the stack quality, as direct stacking does not produce clear S-wave arrivals on the PERMIT stations. This technique uses the coherence of the instantaneous phase among the stacked signals to enhance the signal-to-noise ratio (SNR) of the stack. We found that it is extremely effective for picking LFE arrivals (Thurber et al., 2014). More than 500 P and about 1000 S arrivals from 58 LFE families were picked at the PERMIT and PASO arrays. Since the depths of LFEs are much deeper than earthquakes, we are able to extend model resolution to lower crustal depths. Both P and S wave velocity structure have been obtained with the tomoDD method. The result suggests that there is a low velocity zone (LVZ) in the lower crust and the location of the LVZ is consistent with the high conductivity zone beneath the southern segment of the Rinconada fault that was revealed in the 3D magnetotelluric inversion of Tietze and Ritter(2013).

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

Draelos, Timothy J.; Ballard, Sanford; Young, Christopher J.

Given a set of observations within a specified time window, a fitness value is calculated at each grid node by summing station-specific conditional fitness values. Assuming each observation was generated by a refracted P wave, these values are proportional to the conditional probabilities that each observation was generated by a seismic event at the grid node. The node with highest fitness value is accepted as a hypothetical event location, subject to some minimal fitness value, and all arrivals within a longer time window consistent with that event are associated with it. During the association step, a variety of different phasesmore » are considered. In addition, once associated with an event, an arrival is removed from further consideration. While unassociated arrivals remain, the search for other events is repeated until none are identified.« less

Discrete charge diagnostics on Pre-DIRECT COURSE

NASA Astrophysics Data System (ADS)

Guice, R. L.; Bryant, C.

1984-02-01

The Air Force Weapons Laboratory attempted to make 100 time-of-arrival measurements on Pre-DIRECT COURSE. With an 88 percent success rate, the detonation wave propagation within the charge was measured. The top and bottom hemispheres detonated at two different rates. However, the detonation velocities were well within the existing data base for Ammonium-Nitrate Fuel Oil charges. One large jet was observed on the charge but its location should not have caused any problems for ground level measurements. Twenty experimental time-of-arrival crystals were also fielded; however, the results are skeptical due to the grounding system of the support structure.

TIMING OF SHOCK WAVES

DOEpatents

Tuck, J.L.

1955-03-01

This patent relates to means for ascertaining the instant of arrival of a shock wave in an exploslve charge and apparatus utilizing this means to coordinate the timing of two operations involving a short lnterval of time. A pair of spaced electrodes are inserted along the line of an explosive train with a voltage applied there-across which is insufficient to cause discharge. When it is desired to initiate operation of a device at the time the explosive shock wave reaches a particular point on the explosive line, the device having an inherent time delay, the electrodes are located ahead of the point such that the ionization of the area between the electrodes caused by the traveling explosive shock wave sends a signal to initiate operation of the device to cause it to operate at the proper time. The operated device may be photographic equipment consisting of an x-ray illuminating tube.

Intelligent feature selection techniques for pattern classification of Lamb wave signals

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

Hinders, Mark K.; Miller, Corey A.

2014-02-18

Lamb wave interaction with flaws is a complex, three-dimensional phenomenon, which often frustrates signal interpretation schemes based on mode arrival time shifts predicted by dispersion curves. As the flaw severity increases, scattering and mode conversion effects will often dominate the time-domain signals, obscuring available information about flaws because multiple modes may arrive on top of each other. Even for idealized flaw geometries the scattering and mode conversion behavior of Lamb waves is very complex. Here, multi-mode Lamb waves in a metal plate are propagated across a rectangular flat-bottom hole in a sequence of pitch-catch measurements corresponding to the double crossholemore » tomography geometry. The flaw is sequentially deepened, with the Lamb wave measurements repeated at each flaw depth. Lamb wave tomography reconstructions are used to identify which waveforms have interacted with the flaw and thereby carry information about its depth. Multiple features are extracted from each of the Lamb wave signals using wavelets, which are then fed to statistical pattern classification algorithms that identify flaw severity. In order to achieve the highest classification accuracy, an optimal feature space is required but it’s never known a priori which features are going to be best. For structural health monitoring we make use of the fact that physical flaws, such as corrosion, will only increase over time. This allows us to identify feature vectors which are topologically well-behaved by requiring that sequential classes “line up” in feature vector space. An intelligent feature selection routine is illustrated that identifies favorable class distributions in multi-dimensional feature spaces using computational homology theory. Betti numbers and formal classification accuracies are calculated for each feature space subset to establish a correlation between the topology of the class distribution and the corresponding classification accuracy.« less

Improving Interstellar Medium Mitigation in Millisecond PulsarTiming Models for Gravitational Wave Detection Sensitivity

NASA Astrophysics Data System (ADS)

Wilson, Robert C.

2018-01-01

This study aims to increase the sensitivity of pulsar timing arrays (PTAs) used by astronomers ofthe North American Nanohertz Observatory for Gravitational Waves (NANOGrav) to detectgravitational waves (GWs). Millisecond pulsars with many epochs of observations will be used todetermine if dispersive, frequency-dependent pulse time-of-arrival (TOA) delays caused by theinterstellar medium (ISM) can be more accurately predicted over numerous frequency channels.This project will contribute to the ongoing work to detect low-frequency GWs using PTAs. Dataused for this study will be from both the 110m telescope at the Green Bank Observatory in WestVirginia and the 305m telescope at the Arecibo Observatory in Puerto Rico.

Group velocity of discrete-time quantum walks

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

Kempf, A.; Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1; Portugal, R.

2009-05-15

We show that certain types of quantum walks can be modeled as waves that propagate in a medium with phase and group velocities that are explicitly calculable. Since the group and phase velocities indicate how fast wave packets can propagate causally, we propose the use of these wave velocities in our definition for the hitting time of quantum walks. Our definition of hitting time has the advantage that it requires neither the specification of a walker's initial condition nor of an arrival probability threshold. We give full details for the case of quantum walks on the Cayley graphs of Abelianmore » groups. This includes the special cases of quantum walks on the line and on hypercubes.« less

Investigation of Backprojection Uncertainties With M6 Earthquakes

NASA Astrophysics Data System (ADS)

Fan, Wenyuan; Shearer, Peter M.

2017-10-01

We investigate possible biasing effects of inaccurate timing corrections on teleseismic P wave backprojection imaging of large earthquake ruptures. These errors occur because empirically estimated time shifts based on aligning P wave first arrivals are exact only at the hypocenter and provide approximate corrections for other parts of the rupture. Using the Japan subduction zone as a test region, we analyze 46 M6-M7 earthquakes over a 10 year period, including many aftershocks of the 2011 M9 Tohoku earthquake, performing waveform cross correlation of their initial P wave arrivals to obtain hypocenter timing corrections to global seismic stations. We then compare backprojection images for each earthquake using its own timing corrections with those obtained using the time corrections from other earthquakes. This provides a measure of how well subevents can be resolved with backprojection of a large rupture as a function of distance from the hypocenter. Our results show that backprojection is generally very robust and that the median subevent location error is about 25 km across the entire study region (˜700 km). The backprojection coherence loss and location errors do not noticeably converge to zero even when the event pairs are very close (<20 km). This indicates that most of the timing differences are due to 3-D structure close to each of the hypocenter regions, which limits the effectiveness of attempts to refine backprojection images using aftershock calibration, at least in this region.

Considerations of the Use of 3-D Geophysical Models to Predict Test Ban Monitoring Observables

DTIC Science & Technology

2007-09-01

predict first P arrival times. Since this is a 3-D model, the travel times are predicted with a 3-D finite-difference code solving the eikonal equations...for the eikonal wave equation should provide more accurate predictions of travel-time from 3D models. These techniques and others are being

Thermal averages in a quantum point contact with a single coherent wave packet.

PubMed

Heller, E J; Aidala, K E; LeRoy, B J; Bleszynski, A C; Kalben, A; Westervelt, R M; Maranowski, K D; Gossard, A C

2005-07-01

A novel formal equivalence between thermal averages of coherent properties (e.g., conductance) and time averages of a single wave packet arises for Fermi gases and certain geometries. In the case of one open channel in a quantum point contact (QPC), only one wave packet history, with the wave packet width equal to the thermal length, completely determines the thermally averaged conductance. The formal equivalence moreover allows very simple physical interpretations of interference features surviving under thermal averaging. Simply put, pieces of the thermal wave packet returning to the QPC along independent paths must arrive at the same time in order to interfere. Remarkably, one immediate result of this approach is that higher temperature leads to narrower wave packets and therefore better resolution of events in the time domain. In effect, experiments at 4.2 K are performing time-gated experiments at better than a gigahertz. Experiments involving thermally averaged ballistic conductance in 2DEGS are presented as an application of this picture.

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.

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.

Meteotsunamis in the Great Lakes and Investigation into the May 27, 2012 Event on Lake Erie

NASA Astrophysics Data System (ADS)

Anderson, E. J.; Bechle, A.; Wu, C. H.; Schwab, D. J.; Mann, G.

2016-02-01

Meteotsunami events have been documented in several countries around the world in the coastal ocean, semi-enclosed basins, and in the Great Lakes. In particular, investigations in the Great Lakes have raised the issue of dangers posed by enclosed basins due to the reflection and interaction of meteotsunami waves, in which the destructive waves can arrive several hours after the atmospheric disturbance has passed. This disassociation in time and space between the atmospheric disturbance and resultant meteotsunami wave can pose a significant threat to the public. In a recent event on May 27, 2012, atmospheric conditions gave rise to two convective systems that generated a series of waves in the meteotsunami band on Lake Erie. The resulting waves swept three swimmers a half-mile offshore, inundated a marina, and may have led to a capsized boat along the southern shoreline. Examination of the observed conditions shows that these events occurred at a time between the arrivals of these two storm systems when atmospheric conditions were relatively calm but water level displacements were at their greatest. In this work, we attempt to explain the processes that led to these conditions through a combination of atmospheric and hydrodynamic modeling and an analysis of the observed radial velocities associated with the meteotsunami-inducing front. Results from a high-resolution atmospheric model and hydrodynamic model reveal that the formation of these destructive waves resulted from a combination of wave reflection, focusing, and edge waves that impacted the southern shore of Lake Erie. This event illustrates the unique danger posed by temporal lags between the inducing atmospheric conditions and resulting dangerous nearshore wave conditions.

Interaction between shock wave and single inertial bubbles near an elastic boundary.

PubMed

Sankin, G N; Zhong, P

2006-10-01

The interaction of laser-generated single inertial bubbles (collapse time = 121 mus) near a silicon rubber membrane with a shock wave (55 MPa in peak pressure and 1.7 mus in compressive pulse duration) is investigated. The interaction leads to directional, forced asymmetric collapse of the bubble with microjet formation toward the surface. Maximum jet penetration into the membrane is produced during the bubble collapse phase with optimal shock wave arrival time and stand-off distance. Such interaction may provide a unique acoustic means for in vivo microinjection, applicable to targeted delivery of macromolecules and gene vectors to biological tissues.

Tomographic inversion of P-wave velocity and Q structures beneath the Kirishima volcanic complex, Southern Japan, based on finite difference calculations of complex traveltimes

USGS Publications Warehouse

Tomatsu, T.; Kumagai, H.; Dawson, P.B.

2001-01-01

We estimate the P-wave velocity and attenuation structures beneath the Kirishima volcanic complex, southern Japan, by inverting the complex traveltimes (arrival times and pulse widths) of waveform data obtained during an active seismic experiment conducted in 1994. In this experiment, six 200-250 kg shots were recorded at 163 temporary seismic stations deployed on the volcanic complex. We use first-arrival times for the shots, which were hand-measured interactively. The waveform data are Fourier transformed into the frequency domain and analysed using a new method based on autoregressive modelling of complex decaying oscillations in the frequency domain to determine pulse widths for the first-arrival phases. A non-linear inversion method is used to invert 893 first-arrival times and 325 pulse widths to estimate the velocity and attenuation structures of the volcanic complex. Wavefronts for the inversion are calculated with a finite difference method based on the Eikonal equation, which is well suited to estimating the complex traveltimes for the structures of the Kirishima volcano complex, where large structural heterogeneities are expected. The attenuation structure is derived using ray paths derived from the velocity structure. We obtain 3-D velocity and attenuation structures down to 1.5 and 0.5 km below sea level, respectively. High-velocity pipe-like structures with correspondingly low attenuation are found under the summit craters. These pipe-like structures are interpreted as remnant conduits of solidified magma. No evidence of a shallow magma chamber is visible in the tomographic images.

Location of long-period events below Kilauea Volcano using seismic amplitudes and accurate relative relocation

USGS Publications Warehouse

Battaglia, J.; Got, J.-L.; Okubo, P.

2003-01-01

We present methods for improving the location of long-period (LP) events, deep and shallow, recorded below Kilauea Volcano by the permanent seismic network. LP events might be of particular interest to understanding eruptive processes as their source mechanism is assumed to directly involve fluid transport. However, it is usually difficult or impossible to locate their source using traditional arrival time methods because of emergent wave arrivals. At Kilauea, similar LP waveform signatures suggest the existence of LP multiplets. The waveform similarity suggests spatially close sources, while catalog solutions using arrival time estimates are widely scattered beneath Kilauea's summit caldera. In order to improve estimates of absolute LP location, we use the distribution of seismic amplitudes corrected for station site effects. The decay of the amplitude as a function of hypocentral distance is used for inferring LP location. In a second stage, we use the similarity of the events to calculate their relative positions. The analysis of the entire LP seismicity recorded between January 1997 and December 1999 suggests that a very large part of the LP event population, both deep and shallow, is generated by a small number of compact sources. Deep events are systematically composed of a weak high-frequency onset followed by a low-frequency wave train. Aligning the low-frequency wave trains does not lead to aligning the onsets indicating the two parts of the signal are dissociated. This observation favors an interpretation in terms of triggering and resonance of a magmatic conduit. Instead of defining fault planes, the precise relocation of similar LP events, based on the alignment of the high-energy low-frequency wave trains, defines limited size volumes. Copyright 2003 by the American Geophysical Union.

Some Observations of Ben Franklin Related to the Stilling of Waves by Oil

NASA Astrophysics Data System (ADS)

Gugliotti, Marcos

2007-06-01

While studying the calming effect of oil on water, Benjamin Franklin made other interesting observations and arrived at conclusions related to chemical concepts and phenomena unusual for scientists of that time. A careful analysis of Franklin's article on wave damping can lead to discussions on different topics in chemistry, and may be an interesting manner to present chemical concepts in introductory chemistry courses.

Special Data Collection System (SDCS) event report, NTS event 'LEYDEN', 26 November 1975. Technical report

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

Hill, K.J.; Dawkins, M.S.; Baumstark, R.R.

1976-02-24

Short-period signals associated with the NTS Event 'LEYDEN' on 26 November 1975 were recorded at a RK-ON and LASA. Station descriptions, arrival times, magitude of seismic waves, and seismic signatures are included.

Traveltime delay relative to the maximum energy of the wave train for dispersive tsunamis propagating across the Pacific Ocean: the case of 2010 and 2015 Chilean Tsunamis

NASA Astrophysics Data System (ADS)

Poupardin, A.; Heinrich, P.; Hébert, H.; Schindelé, F.; Jamelot, A.; Reymond, D.; Sugioka, H.

2018-05-01

This paper evaluates the importance of frequency dispersion in the propagation of recent trans-Pacific tsunamis. Frequency dispersion induces a time delay for the most energetic waves, which increases for long propagation distances and short source dimensions. To calculate this time delay, propagation of tsunamis is simulated and analyzed from spectrograms of time-series at specific gauges in the Pacific Ocean. One- and two-dimensional simulations are performed by solving either shallow water or Boussinesq equations and by considering realistic seismic sources. One-dimensional sensitivity tests are first performed in a constant-depth channel to study the influence of the source width. Two-dimensional tests are then performed in a simulated Pacific Ocean with a 4000-m constant depth and by considering tectonic sources of 2010 and 2015 Chilean earthquakes. For these sources, both the azimuth and the distance play a major role in the frequency dispersion of tsunamis. Finally, simulations are performed considering the real bathymetry of the Pacific Ocean. Multiple reflections, refractions as well as shoaling of waves result in much more complex time series for which the effects of the frequency dispersion are hardly discernible. The main point of this study is to evaluate frequency dispersion in terms of traveltime delays by calculating spectrograms for a time window of 6 hours after the arrival of the first wave. Results of the spectral analysis show that the wave packets recorded by pressure and tide sensors in the Pacific Ocean seem to be better reproduced by the Boussinesq model than the shallow water model and approximately follow the theoretical dispersion relationship linking wave arrival times and frequencies. Additionally, a traveltime delay is determined above which effects of frequency dispersion are considered to be significant in terms of maximum surface elevations.

Nanohertz gravitational wave searches with interferometric pulsar timing experiments.

PubMed

Tinto, Massimo

2011-05-13

We estimate the sensitivity to nano-Hertz gravitational waves of pulsar timing experiments in which two highly stable millisecond pulsars are tracked simultaneously with two neighboring radio telescopes that are referenced to the same timekeeping subsystem (i.e., "the clock"). By taking the difference of the two time-of-arrival residual data streams we can exactly cancel the clock noise in the combined data set, thereby enhancing the sensitivity to gravitational waves. We estimate that, in the band (10(-9)-10(-8))  Hz, this "interferometric" pulsar timing technique can potentially improve the sensitivity to gravitational radiation by almost 2 orders of magnitude over that of single-telescopes. Interferometric pulsar timing experiments could be performed with neighboring pairs of antennas of the NASA's Deep Space Network and the forthcoming large arraying projects.

Lunar Seismology: the Internal Structure of the Moon. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Goins, N. R.

1978-01-01

The direct P and S wave arrival times are the primary data set that can be measured on the seismograms of natural lunar seismic events. Polarization filtering techniques allow the enhancement of secondary body wave arrivals and record curves to identify the secondary phases and deduce structural information. Finally, shear wave amplitude vs. distance curves yield information on the location and magnitude of seismic velocity gradients in the interior. The results of these analyses show that the moon appears to have a two-layer crust at all four seismic stations: a 20 km upper crust that seems to be constant at all sites and a lower crust that is 40 km thick at stations 12 and 14 (mare), 55 + or - 10 km at station 16 (highland), and tentatively either 40 km or 70 km at station 15. The lower mantle extends from 480 km to at least 1100 km depth which is the maximum depth of penetration of all but a few seismic waves used as data. No definitive evidence for or against a lunar core exists.

A Case Study of Array-based Early Warning System for Tsunami Offshore Ventura, California

NASA Astrophysics Data System (ADS)

Xie, Y.; Meng, L.

2017-12-01

Extreme scenarios of M 7.5+ earthquakes on the Red Mountain and Pitas Point faults can potentially generate significant local tsunamis in southern California. The maximum water elevation could be as large as 10 m in the nearshore region of Oxnard and Santa Barbara. Recent development in seismic array processing enables rapid tsunami prediction and early warning based on the back-projection approach (BP). The idea is to estimate the rupture size by back-tracing the seismic body waves recorded by stations at local and regional distances. A simplified source model of uniform slip is constructed and used as an input for tsunami simulations that predict the tsunami wave height and arrival time. We demonstrate the feasibility of this approach in southern California by implementing it in a simulated real-time environment and applying to a hypothetical M 7.7 Dip-slip earthquake scenario on the Pitas Point fault. Synthetic seismograms are produced using the SCEC broadband platform based on the 3D SoCal community velocity model. We use S-wave instead of P-wave to avoid S-minus-P travel times shorter than rupture duration. Two clusters of strong-motion stations near Bakersfield and Palmdale are selected to determine the back-azimuth of the strongest high-frequency radiations (0.5-1 Hz). The back-azimuths of the two clusters are then intersected to locate the source positions. The rupture area is then approximated by enclosing these BP radiators with an ellipse or a polygon. Our preliminary results show that the extent of 1294 square kilometers rupture area and magnitude of 7.6 obtained by this approach is reasonably close to the 1849 square kilometers and 7.7 of the input model. The average slip of 7.3 m is then estimated according to the scaling relation between slip and rupture area, which is close to the actual average dislocation amount, 8.3 m. Finally, a tsunami simulation is conducted to assess the wave height and arrival time. The errors of -3 to +9 s in arrival time and 0.4 m in wave amplitude are reasonably small for early warning purpose. The blind zone for early warning is the region north of the outcrop of Pitas Point faults and has a scale close to the length of the fault, 43 km. The warning time is above 15 min in the nearshore region west of Cojo Bay Beach and south of Oxnard.

Shear-wave splitting and moonquakes

NASA Astrophysics Data System (ADS)

Dimech, J. L.; Weber, R. C.; Savage, M. K.

2017-12-01

Shear-wave splitting is a powerful tool for measuring anisotropy in the Earth's crust and mantle, and is sensitive to geological features such as fluid filled cracks, thin alternating layers of rock with different elastic properties, and preferred mineral orientations caused by strain. Since a shear wave splitting measurement requires only a single 3-component seismic station, it has potential applications for future single-station planetary seismic missions, such as the InSight geophysical mission to Mars, as well as possible future missions to Europa and the Moon. Here we present a preliminary shear-wave splitting analysis of moonquakes detected by the Apollo Passive Seismic Experiment. Lunar seismic data suffers from several drawbacks compared to modern terrestrial data, including severe seismic scattering, low intrinsic attenuation, 10-bit data resolution, thermal spikes, and timing errors. Despite these drawbacks, we show that it is in principle possible to make a shear wave splitting measurement using the S-phase arrival of a relatively high-quality moonquake, as determined by several agreeing measurement criteria. Encouraged by this finding, we further extend our analysis to clusters of "deep moonquake" events by stacking multiple events from the same cluster together to further enhance the quality of the S-phase arrivals that the measurement is based on.

An Analysis of the Relationship Between the Heat Index and Arrivals in the Emergency Department

PubMed Central

Levy, Matthew; Broccoli, Morgan; Cole, Gai; Jenkins, J Lee; Klein, Eili Y.

2015-01-01

Background: Heatwaves are one of the most deadly weather-related events in the United States and account for more deaths annually than hurricanes, tornadoes, floods, and earthquakes combined. However, there are few statistically rigorous studies of the effect of heatwaves on emergency department (ED) arrivals. A better understanding of this relationship can help hospitals plan better and provide better care for patients during these types of events. Methods: A retrospective review of all ED patient arrivals that occurred from April 15 through August 15 for the years 2008 through 2013 was performed. Daily patient arrival data were combined with weather data (temperature and humidity) to examine the potential relationships between the heat index and ED arrivals as well as the length of time patients spend in the ED using generalized additive models. In particular the effect the 2012 heat wave that swept across the United States, and which was hypothesized to increase arrivals was examined. Results: While there was no relationship found between the heat index and arrivals on a single day, a non-linear relationship was found between the mean three-day heat index and the number of daily arrivals. As the mean three-day heat index initially increased, the number of arrivals significantly declined. However, as the heat index continued to increase, the number of arrivals increased. It was estimated that there was approximately a 2% increase in arrivals when the mean heat index for three days approached 100°F. This relationship was strongest for adults aged 18-64, as well as for patients arriving with lower acuity. Additionally, a positive relationship was noted between the mean three-day heat index and the length of stay (LOS) for patients in the ED, but no relationship was found for the time from which a patient was first seen to when a disposition decision was made. No significant relationship was found for the effect of the 2012 heat wave on ED arrivals, though it did have an effect on patient LOS. Conclusion: A single hot day has only a limited effect on ED arrivals, but continued hot weather has a cumulative effect. When the heat index is high (~90°F) for a number of days in a row, this curtails peoples activities, but if the heat index is very hot (~100°F) this likely results in an exacerbation of underlying conditions as well as heat-related events that drives an increase in ED arrivals. Periods of high heat also affects the length of stay of patients either by complicating care or by making it more difficult to discharge patients. PMID:26579329

A new method for producing automated seismic bulletins: Probabilistic event detection, association, and location

DOE PAGES

Draelos, Timothy J.; Ballard, Sanford; Young, Christopher J.; ...

2015-10-01

Given a set of observations within a specified time window, a fitness value is calculated at each grid node by summing station-specific conditional fitness values. Assuming each observation was generated by a refracted P wave, these values are proportional to the conditional probabilities that each observation was generated by a seismic event at the grid node. The node with highest fitness value is accepted as a hypothetical event location, subject to some minimal fitness value, and all arrivals within a longer time window consistent with that event are associated with it. During the association step, a variety of different phasesmore » are considered. In addition, once associated with an event, an arrival is removed from further consideration. While unassociated arrivals remain, the search for other events is repeated until none are identified.« less

Viterbi sparse spike detection and a compositional origin to ultralow-velocity zones

NASA Astrophysics Data System (ADS)

Brown, Samuel Paul

Accurate interpretation of seismic travel times and amplitudes in both the exploration and global scales is complicated by the band-limited nature of seismic data. We present a stochastic method, Viterbi sparse spike detection (VSSD), to reduce a seismic waveform into a most probable constituent spike train. Model waveforms are constructed from a set of candidate spike trains convolved with a source wavelet estimate. For each model waveform, a profile hidden Markov model (HMM) is constructed to represent the waveform as a stochastic generative model with a linear topology corresponding to a sequence of samples. The Viterbi algorithm is employed to simultaneously find the optimal nonlinear alignment between a model waveform and the seismic data, and to assign a score to each candidate spike train. The most probable travel times and amplitudes are inferred from the alignments of the highest scoring models. Our analyses show that the method can resolve closely spaced arrivals below traditional resolution limits and that travel time estimates are robust in the presence of random noise and source wavelet errors. We applied the VSSD method to constrain the elastic properties of a ultralow- velocity zone (ULVZ) at the core-mantle boundary beneath the Coral Sea. We analyzed vertical component short period ScP waveforms for 16 earthquakes occurring in the Tonga-Fiji trench recorded at the Alice Springs Array (ASAR) in central Australia. These waveforms show strong pre and postcursory seismic arrivals consistent with ULVZ layering. We used the VSSD method to measure differential travel-times and amplitudes of the post-cursor arrival ScSP and the precursor arrival SPcP relative to ScP. We compare our measurements to a database of approximately 340,000 synthetic seismograms finding that these data are best fit by a ULVZ model with an S-wave velocity reduction of 24%, a P-wave velocity reduction of 23%, a thickness of 8.5 km, and a density increase of 6%. We simultaneously constrain both P- and S-wave velocity reductions as a 1:1 ratio inside this ULVZ. This 1:1 ratio is not consistent with a partial melt origin to ULVZs. Rather, we demonstrate that a compositional origin is more likely.

Seismic interferometry of railroad induced ground motions: body and surface wave imaging

NASA Astrophysics Data System (ADS)

Quiros, Diego A.; Brown, Larry D.; Kim, Doyeon

2016-04-01

Seismic interferometry applied to 120 hr of railroad traffic recorded by an array of vertical component seismographs along a railway within the Rio Grande rift has recovered surface and body waves characteristic of the geology beneath the railway. Linear and hyperbolic arrivals are retrieved that agree with surface (Rayleigh), direct and reflected P waves observed by nearby conventional seismic surveys. Train-generated Rayleigh waves span a range of frequencies significantly higher than those recovered from typical ambient noise interferometry studies. Direct P-wave arrivals have apparent velocities appropriate for the shallow geology of the survey area. Significant reflected P-wave energy is also present at relatively large offsets. A common midpoint stack produces a reflection image consistent with nearby conventional reflection data. We suggest that for sources at the free surface (e.g. trains) increasing the aperture of the array to record wide angle reflections, in addition to longer recording intervals, might allow the recovery of deeper geological structure from railroad traffic. Frequency-wavenumber analyses of these recordings indicate that the train source is symmetrical (i.e. approaching and receding) and that deeper refracted energy is present although not evident in the time-offset domain. These results confirm that train-generated vibrations represent a practical source of high-resolution subsurface information, with particular relevance to geotechnical and environmental applications.

Study of 3D P-wave Velocity Structure in Lushan Area of Yunnan Province

NASA Astrophysics Data System (ADS)

Wang, X.

2017-12-01

The double difference seismic tomography method is applied to 50,711 absolute first arrival P wave arrival times and 7,294,691 high quality relative P arrival times of 5,285 events of Lushan seismic sequence to simultaneously determine the detailed crustal 3D P wave velocity structure and the hypocenter parameters in the Lushan seismic area. The results show that the front edge of aftershock in the northeast of mainshock present a spade with a steep dip angle. In the southwest of Lushan mainshock, the front edge of aftershock in low velocity zone slope gently. Our high-resolution tomographic model not only displays the general features contained in the previous models, but also reveals some new features. The Tianquan, Shuangshi and Daguan line lies in the transition zone between high velocity anomalies to the southeast and low velocity anomalies to the northwest at the ground surface. An obvious high-velocity anomaly is visible in Daxing area. With the depth increasing, Baoxing high velocity anomaly extends to Lingguan, while the southeast of the Tianquan, Shuangshi and Daguan line still shows low velocity. The high-velocity anomalies beneath Baoxing and Daxing connect each other in 10km depth, which makes the contrast between high and low velocity anomalies more sharp. Above all, the P wave velocity structure of Lushan seismic area shows obviously lateral heterogeneity. The P wave velocity anomalies represent close relationship with topographic relief and geological structure. In Baoxing area the complex rocks correspond obvious high-velocity anomalies extending down to 15km depth, while the Cenozoic rocks are correlated with low-velocity anomalies. Lushan mainshock locates at the leading edge of a low-velocity anomaly surrounded by the Baoxing and Daxing high-velocity anomalies. The main seismogenic layer dips to northwest. Meanwhile, a recoil seismic belt dips to southeast above the main seismogenic layer exists at the lower boundary of Baoxing high-velocity anomaly. A "y" distribution pattern is shown between two seismic belts.

Simultaneous, Joint Inversion of Seismic Body Wave Travel Times and Satellite Gravity Data for Three-Dimensional Tomographic Imaging of Western Colombia

NASA Astrophysics Data System (ADS)

Dionicio, V.; Rowe, C. A.; Maceira, M.; Zhang, H.; Londoño, J.

2009-12-01

We report on the three-dimensional seismic structure of western Colombia determined through the use of a new, simultaneous, joint inversion tomography algorithm. Using data recorded by the national Seismological Network of Colombia (RSNC), we have selected 3,609 earthquakes recorded at 33 sensors distributed throughout the country, with additional data from stations in neighboring countries. 20,338 P-wave arrivals and 17,041 S-wave arrivals are used to invert for structure within a region extending approximately 72.5 to 77.5 degrees West and 2 to 7.5 degrees North. Our algorithm is a modification of the Maceira and Ammon joint inversion code, in combination with the Zhang and Thurber TomoDD (double-difference tomography) program, with a fast LSQR solver operating on the gridded values jointly. The inversion uses gravity anomalies obtained during the GRACE2 satellite mission, and solves using these values with the seismic travel-times through application of an empirical relationship first proposed by Harkrider, mapping densities to Vp and Vs within earth materials. In previous work, Maceira and Ammon demonstrated that incorporation of gravity data predicts shear wave velocities more accurately than the inversion of surface waves alone, particularly in regions where the crust exhibits abrupt and significant lateral variations in lithology, such as the Tarim Basin. The significant complexity of crustal structure in Colombia, due to its active tectonic environment, makes it a good candidate for the application with gravity and body waves. We present the results of this joint inversion and compare it to results obtained using travel times alone

Local pulse wave velocity estimated from small vibrations measured ultrasonically at multiple points on the arterial wall

NASA Astrophysics Data System (ADS)

Ito, Mika; Arakawa, Mototaka; Kanai, Hiroshi

2018-07-01

Pulse wave velocity (PWV) is used as a diagnostic criterion for arteriosclerosis, a major cause of heart disease and cerebrovascular disease. However, there are several problems with conventional PWV measurement techniques. One is that a pulse wave is assumed to only have an incident component propagating at a constant speed from the heart to the femoral artery, and another is that PWV is only determined from a characteristic time such as the rise time of the blood pressure waveform. In this study, we noninvasively measured the velocity waveform of small vibrations at multiple points on the carotid arterial wall using ultrasound. Local PWV was determined by analyzing the phase component of the velocity waveform by the least squares method. This method allowed measurement of the time change of the PWV at approximately the arrival time of the pulse wave, which discriminates the period when the reflected component is not contaminated.

Damage Detection in Concrete Elements with Surface Wave Measurements

DTIC Science & Technology

1992-01-01

Structures, identified the need for "Better techniques for detection of flaws or defects inside structural members". At the same conference, the...1 6 12 1 7 13 19 13 7 18 12 6 17 11 5 14 8 2 10 8 2 83 Saw cut Sawm cu Saw cut Sawcu SSaw cut Figre4. -I ltie ocaio o Dmae ndSoc- RcieAra 84 4.2...cracking and defects . Some methods used in the past to determine the size and location of cracks are the P-wave arrival time, imaging systems, time

Luminescence from edge fracture in shocked lithium fluoride crystals

DOE PAGES

Turley, W. D.; Stevens, G. D.; Capelle, G. A.; ...

2013-04-03

Light emitted from a [100] lithium fluoride crystal was characterized under shock wave compression to 28 GPa followed by complete stress release at the edges. We examined the light using time-gated optical spectrometry and imaging, time-resolved optical emission measurements, and hydrodynamic modeling. The shock arrival at the circumference of the crystal was delayed relative to the center so that the two regions could be studied at different times. The majority of the light emission originated when the shock waves released at the circumference of the crystal. Unlike previously reported results for shocked lithium fluoride, we found that the light spectrummore » is not strictly broad band, but has spectral lines associated with atomic lithium in addition to a broad band background. Also, the emission spectrum depends strongly on the gas surrounding the sample. Based on our observations, the line emission appears to be related to fracture of the lithium fluoride crystal from the shock wave releasing at the edges. Moreover, experimenters frequently utilize lithium fluoride crystals as transparent windows for observing shock compressed samples. Because of the experimental geometries used, the shock wave in such cases often reaches the circumference of the window at nearly the same moment as when it reaches the center of the sample-window interface. Light generated at the circumference could contaminate the measurement at the interface when this light scatters into the observed region. Finally, this background light may be reduced or avoided using experimental geometries which delay the arrival of the shock wave at the edges of the crystal.« less

Seismoacoustic Coupled Signals From Earthquakes in Central Italy: Epicentral and Secondary Sources of Infrasound

NASA Astrophysics Data System (ADS)

Shani-Kadmiel, Shahar; Assink, Jelle D.; Smets, Pieter S. M.; Evers, Läslo G.

2018-01-01

In this study we analyze infrasound signals from three earthquakes in central Italy. The Mw 6.0 Amatrice, Mw 5.9 Visso, and Mw 6.5 Norcia earthquakes generated significant epicentral ground motions that couple to the atmosphere and produce infrasonic waves. Epicentral seismic and infrasonic signals are detected at I26DE; however, a third type of signal, which arrives after the seismic wave train and before the epicentral infrasound signal, is also detected. This peculiar signal propagates across the array at acoustic wave speeds, but the celerity associated with it is 3 times the speed of sound. Atmosphere-independent backprojections and full 3-D ray tracing using atmospheric conditions of the European Centre for Medium-Range Weather Forecasts are used to demonstrate that this apparently fast-arriving infrasound signal originates from ground motions more than 400 km away from the epicenter. The location of the secondary infrasound patch coincides with the closest bounce point to I26DE as depicted by ray tracing backprojections.

Estimates of velocity structure and source depth using multiple P waves from aftershocks of the 1987 Elmore Ranch and Superstition Hills, California, earthquakes

USGS Publications Warehouse

Mori, J.

1991-01-01

Event record sections, which are constructed by plotting seismograms from many closely spaced earthquakes recorded on a few stations, show multiple free-surface reflections (PP, PPP, PPPP) of the P wave in the Imperial Valley. The relative timing of these arrivals is used to estimate the strength of the P-wave velocity gradient within the upper 5 km of the sediment layer. Consistent with previous studies, a velocity model with a value of 1.8 km/sec at the surface increasing linearly to 5.8 km/sec at a depth of 5.5 km fits the data well. The relative amplitudes of the P and PP arrivals are used to estimate the source depth for the aftershock distributions of the Elmore Ranch and Superstition Hills main shocks. Although the depth determination has large uncertainties, both the Elmore Ranch and Superstition Hills aftershock sequencs appear to have similar depth distribution in the range of 4 to 10 km. -Author

Multiscale 2D Inversions of Active-source First-arrival Times in Taiwan

NASA Astrophysics Data System (ADS)

Lin, Y. P.; Zhao, L.; Hung, S. H.

2015-12-01

In this study, we make use of the active-source records collected by the TAIGER (TAiwan Integrated GEodynamics Research) project in 2008 at nearly 1400 locations on the island of Taiwan and the surrounding ocean bottom. We manually picked the first-arrival times from the waveform records to obtain a set of highly accurate P-wave traveltimes. Among the 1400 receivers, more than 1000 were deployed along four almost linear cross-island profiles with inter-seismometer spacing down to 200 m. This ground-truth dataset provides strong constrains on the structure between the exactly known active sources and densely distributed receivers, which can be used to calibrate the seismic structure in the upper crust in Taiwan. In this study, we use this dataset to image the two-dimensional P-wave structure along the four linear profiles. A wavelet parameterization of the model is adopted to achieve an objective and data-adaptive multiscale resolution to the 2D structures. Rigorous estimations of resolution lengths were also conducted to quantify the spatial resolutions of the tomography inversions. The resulting 2D models yield first-arrival time predictions that are in excellent agreement with the observations. The seismic structures along the 2D profiles display strong lateral variations (up to 80% relative to regional average) with more realistic amplitudes of velocity perturbations and spatial patterns consistent with geological zonations of Taiwan

Rogue wave generation by inelastic quasi-soliton collisions in optical fibres

NASA Astrophysics Data System (ADS)

Eberhard, M.; Savojardo, A.; Maruta, A.; Römer, R. A.

2017-11-01

We demonstrate a simple cascade mechanism that drives the formation and emergence of rogue waves in the generalized non-linear Schr\\"{o}dinger equation with third-order dispersion. This conceptually novel generation mechanism is based on inelastic collisions of quasi-solitons and is well described by a resonant-like scattering behaviour for the energy transfer in pair-wise quasi-soliton collisions. Our results demonstrate a threshold for rogue wave emergence and the existence of a period of reduced amplitudes - a "calm before the storm" - preceding the arrival of a rogue wave event. Comparing with ultra-long time window simulations of $3.865\\times 10^{6}$ps we observe the statistics of rogue waves in optical fibres with an unprecedented level of detail and accuracy, unambiguously establishing the long-ranged character of the rogue wave power-distribution function over seven orders of magnitude.

The influence of the energy emitted by solar flare soft X-ray bursts on the propagation of their associated interplanetary shock waves

NASA Technical Reports Server (NTRS)

Pinter, S.; Dryer, M.

1985-01-01

The relationship between the thermal energy released from 29 solar flares and the propagation features of their associated interplanetary shock waves that were detected at 1 AU is investigated. The 29 interplanetary shock waves were identified unambiguously and their tracking from each solar flare was deduced by tracking their associated interplanetary type-II radio emission. The thermal energy released in the solar flares was estimated from the time-intensity profiles of 1-8 A soft X-ray bursts from each flare. A good relationship is found between the flares' thermal energy with the IP shock-waves' transient velocity and arrival time at the earth - that is, the largest flare energy released is associated with the faster shock waves. Finally, a possible scenario of formation of a shock wave during the early phase of the flare and its propagation features is discussed.

The energy radiated by the 26 December 2004 Sumatra-Andaman earthquake estimated from 10-minute P-wave windows

USGS Publications Warehouse

Choy, G.L.; Boatwright, J.

2007-01-01

The rupture process of the Mw 9.1 Sumatra-Andaman earthquake lasted for approximately 500 sec, nearly twice as long as the teleseismic time windows between the P and PP arrival times generally used to compute radiated energy. In order to measure the P waves radiated by the entire earthquake, we analyze records that extend from the P-wave to the S-wave arrival times from stations at distances ?? >60??. These 8- to 10-min windows contain the PP, PPP, and ScP arrivals, along with other multiply reflected phases. To gauge the effect of including these additional phases, we form the spectral ratio of the source spectrum estimated from extended windows (between TP and TS) to the source spectrum estimated from normal windows (between TP and TPP). The extended windows are analyzed as though they contained only the P-pP-sP wave group. We analyze four smaller earthquakes that occurred in the vicinity of the Mw 9.1 mainshock, with similar depths and focal mechanisms. These smaller events range in magnitude from an Mw 6.0 aftershock of 9 January 2005 to the Mw 8.6 Nias earthquake that occurred to the south of the Sumatra-Andaman earthquake on 28 March 2005. We average the spectral ratios for these four events to obtain a frequency-dependent operator for the extended windows. We then correct the source spectrum estimated from the extended records of the 26 December 2004 mainshock to obtain a complete or corrected source spectrum for the entire rupture process (???600 sec) of the great Sumatra-Andaman earthquake. Our estimate of the total seismic energy radiated by this earthquake is 1.4 ?? 1017 J. When we compare the corrected source spectrum for the entire earthquake to the source spectrum from the first ???250 sec of the rupture process (obtained from normal teleseismic windows), we find that the mainshock radiated much more seismic energy in the first half of the rupture process than in the second half, especially over the period range from 3 sec to 40 sec.

Regional seismic-wave propagation from the M5.8 23 August 2011, Mineral, Virginia, earthquake

USGS Publications Warehouse

Pollitz, Fred; Mooney, Walter D.

2015-01-01

The M5.8 23 August 2011 Mineral, Virginia, earthquake was felt over nearly the entire eastern United States and was recorded by a wide array of seismic broadband instruments. The earthquake occurred ~200 km southeast of the boundary between two distinct geologic belts, the Piedmont and Blue Ridge terranes to the southeast and the Valley and Ridge Province to the northwest. At a dominant period of 3 s, coherent postcritical P-wave (i.e., direct longitudinal waves trapped in the crustal waveguide) arrivals persist to a much greater distance for propagation paths toward the northwest quadrant than toward other directions; this is probably related to the relatively high crustal thickness beneath and west of the Appalachian Mountains. The seismic surface-wave arrivals comprise two distinct classes: those with weakly dispersed Rayleigh waves and those with strongly dispersed Rayleigh waves. We attribute the character of Rayleigh wave arrivals in the first class to wave propagation through a predominantly crystalline crust (Blue Ridge Mountains and Piedmont terranes) with a relatively thin veneer of sedimentary rock, whereas the temporal extent of the Rayleigh wave arrivals in the second class are well explained as the effect of the thick sedimentary cover of the Valley and Ridge Province and adjacent Appalachian Plateau province to its northwest. Broadband surface-wave ground velocity is amplified along both north-northwest and northeast azimuths from the Mineral, Virginia, source. The former may arise from lateral focusing effects arising from locally thick sedimentary cover in the Appalachian Basin, and the latter may result from directivity effects due to a northeast rupture propagation along the finite fault plane.

In Vivo Determination of the Complex Elastic Moduli of Cetacean Head Tissue

DTIC Science & Technology

2009-09-30

remotely generated elastic waves can be detected remotely using a modified version of an ultrasonic Doppler vibration measurement system called NIVMS...developed at Georgia Techiii. Algorithms are being developed to enable the magnitude and phase of vibration to be determined, as well as the range (tissue...depth) along the ultrasonic beam at which the vibration is being measured. By measuring the amplitude and arrival time of the shear wave at two

Estimation of Uncertainties of Full Moment Tensors

DTIC Science & Technology

2017-10-06

Nevada Test Site (tab. 1 of Ford et al., 2009). Figure 1 shows the three regions and the stations used within the moment tensor inversions . For the...and additional bandpass filtering, were applied during the moment tensor inversions . We use high-frequency P waves for the Uturuncu and NTS events...reliable when we align the P waves on the observed P arrival time. 3.2 Methods Seismic moment tensor inversion requires specifying a misfit function

Analyzing the Possibility of Dynamic Earthquake Triggering in Socorro, New Mexico

NASA Astrophysics Data System (ADS)

Morton, E.; Bilek, S. L.

2011-12-01

The release of energy during an earthquake changes the stress state and seismicity both locally and remotely. Far-field stress changes can lead to triggered earthquakes coinciding with the arrival of the surface waves. This dynamic triggering is found to occur in a variety of tectonic settings, but in particular magmatic regions. Here we test whether the Socorro Magma Body region in central New Mexico hosts triggered seismicity. Preliminary inspection of continuous network data in central New Mexico suggested a local triggered event with the passage of surface waves from an MW 6.9 event in 2009. For a more comprehensive view, we examine data from 379 earthquakes MW ≥ 6.0 between January 15, 2008 to March 13, 2010 recorded on the EarthScope USArray Transportable Network stations located within New Mexico and providing more dense coverage for better detectability. Waveforms from twenty EarthScope stations were windowed around the time of the large event, high-pass filtered at 5 Hz to remove low frequency signals and analyzed to detect high frequency triggered local earthquakes. For each possible trigger detected, waveforms from nine short-period stations in the Socorro Seismic Network were added to aid in locating the events. In the time period analyzed, twelve triggered events were detected. Only one of these events, on August 30, 2009, corresponded to the arrival of surface waves, occurring about a minute after their arrival. The majority of the triggered events occur well after the arrival of the surface waves, indicating that they are either independent of the main shock or the result of delayed dynamic triggering. Delayed dynamic triggering can occur hours or days after the passage of surface waves, and are marked by an increase in seismicity relative to background. Only one of the events, on September 18, 2009, occurred within the Socorro Magma Body area. The rest of these events occur spread throughout New Mexico. The widely spread distribution of possibly triggered events and the low ratio of triggers to main shocks indicates that the rifted magmatic region above the Socorro Magma Body is not particularly susceptible to dynamic triggering from remote main shocks. The lack of direct correspondence to a seismic phase can mean that the detected events may be independent (not triggered events), or the result of delayed dynamic triggering. A comparison to randomly chosen waveforms within the time period as background will reveal if the possible events are a result of delayed dynamic triggering or part of the background.

Constraints on a plume in the mid-mantle beneath the Iceland region from seismic array data

USGS Publications Warehouse

Pritchard, M.J.; Foulger, G.R.; Julian, B.R.; Fyen, J.

2000-01-01

Teleseismic P waves passing through low-wave-speed bodies in the mantle are refracted, causing anomalies in their propagation directions that can be measured by seismometer arrays. Waves from earthquakes in the eastern Pacific and western North America arriving at the NORSAR array in Norway and at seismic stations in Scotland pass beneath the Iceland region at depths of ~ 1000-2000 km. Waves arriving at NORSAR have anomalous arrival azimuths consistent with a low-wave-speed body at a depth of ~ 1500 km beneath the Iceland-Faeroe ridge with a maximum diameter of ~ 250 km and a maximum wave-speed contrast of ~ 1.5 per cent. This agrees well with whole-mantle tomography results, which image a low-wave-speed body at this location with a diameter of ~ 500 km and a wave-speed anomaly of ~ 0.5 per cent, bearing in mind that whole-mantle tomography, because of its limited resolution, broadens and weakens small anomalies. The observations cannot resolve the location of the body, and the anomaly could be caused in whole or in part by larger bodies farther away, for example by a body imaged beneath Greenland by whole-mantle tomography.

Testing a New Method for Imaging Crustal Magma Bodies: A Pilot Study at Newberry Volcano, Central OR

NASA Astrophysics Data System (ADS)

Beachly, M. W.; Hooft, E. E.; Toomey, D. R.; Waite, G. P.; Durant, D. T.

2010-12-01

Magmatic systems are often imaged using delay time seismic tomography, though a known limitation is that wavefront healing limits the ability of transmitted waves to detect small, low-velocity regions such as magma chambers. Crustal magma chambers have been successfully identified using secondary arrivals, including both P and S wave reflections and conversions. Such secondary phases are often recorded by marine seismic experiments owing to the density and quality of airgun data, which improves the identification of coherent arrivals. In 2008 we conducted a pilot study at Newberry volcano to test a new method of detecting secondary arrivals in a terrestrial setting. Our experimental geometry used a line of densely spaced (~300 m), three-component seismometers to record a shot-of-opportunity from the High Lave Plains Experiment. An ideal study would record several shots, however, data from this single event proves the concept. As part of our study, we also reanalyze all existing seismic data from Newberry volcano to obtain a tomographic image of the velocity structure to 6 km depth. Newberry is a lone shield volcano in central Oregon, located 40 km east of the Cascade axis. Newberry eruptions are silicic within the central caldera and mafic on its periphery suggesting a central silicic magma storage system, possibly located at upper crustal depths. The system may still be active with a recent eruption ~1300 years ago, and a central drill hole temperature of 256° C at only 932 m depth. A low-velocity anomaly previously imaged at 3-5 km beneath the caldera indicates either a magma body or a fractured pluton. Our tomographic study combines our 2008 seismic data with profile and array data collected in the 1980s by the USGS. In total, the inversion includes 16 active sources and 322 receivers yielding 1007 P-wave first arrivals. Beneath the caldera ring faults we image a high-velocity ring-like anomaly extending to 2 km depth. This anomaly is inferred to be near-vertical ring-dikes, 200-500 m thick, that resulted from caldera formation 5 mya. Low velocities imaged within the ring are attributed to caldera fill. Below 2.5 km depth a pair of high velocity bodies may be solidified intrusive complexes east and west of the caldera. Our results also indicate a low velocity body between 4-6 km depth although it is poorly resolved by delay time data. Tomographic inversions of synthetic data suggest that the observed travel times are consistent with a low-velocity body up to 35 km3 with up to 40% velocity reduction. Using data from our densely instrumented 2008 seismic profile, we identify a secondary P-wave arrival that originates from beneath the caldera. Preliminary finite-difference waveform modeling produces a similar arrival for a model including a low-velocity body with a 2-km-long melt sill at 3 km depth underlain by a partial-melt region to 5 km depth. The secondary arrival provides additional evidence for an active crustal magmatic system beneath Newberry volcano and demonstrates the potential of novel experimental geometries for detecting and locating terrestrial crustal magma bodies.

Mean-square angle-of-arrival difference between two counter-propagating spherical waves in the presence of atmospheric turbulence.

PubMed

Chen, Chunyi; Yang, Huamin; Tong, Shoufeng; Lou, Yan

2015-09-21

The mean-square angle-of-arrival (AOA) difference between two counter-propagating spherical waves in atmospheric turbulence is theoretically formulated. Closed-form expressions for the path weighting functions are obtained. It is found that the diffraction and refraction effects of turbulent cells make negative and positive contributions to the mean-square AOA difference, respectively, and the turbulent cells located at the midpoint of the propagation path have no contributions to the mean-square AOA difference. If the mean-square AOA difference is separated into the refraction and diffraction parts, the refraction part always dominates the diffraction one, and the ratio of the diffraction part to the refraction one is never larger than 0.5 for any turbulence spectrum. Based on the expressions for the mean-square AOA difference, formulae for the correlation coefficient between the angles of arrival of two counter-propagating spherical waves in atmospheric turbulence are derived. Numerical calculations are carried out by considering that the turbulence spectrum has no path dependence. It is shown that the mean-square AOA difference always approximates to the variance of AOA fluctuations. It is found that the correlation coefficient between the angles of arrival in the x or y direction of two counter-propagating spherical waves ranges from 0.46 to 0.5, implying that the instantaneous angles of arrival of two counter-propagating spherical waves in atmospheric turbulence are far from being perfectly correlated even when the turbulence spectrum does not vary along the path.

Imaging Strong Lateral Heterogeneities with USArray using Body-to-Surface Wave Scattering

NASA Astrophysics Data System (ADS)

Yu, C.; Zhan, Z.; Hauksson, E.; Cochran, E. S.

2017-12-01

Seismic scattering is commonly observed and results from wave propagation in heterogeneous medium. Yet, deterministic characterization of scatterers remains challenging. In this study, we analyze broadband waveforms recorded by the USArray across the entire conterminous US. With array analysis, we observe strong scattered surface waves following the arrival of teleseismic body waves over several hundreds of kilometers. We use back-projection to locate the body-to-surface scattering sources, and detect strong scatterers both around and within the conterminous US. For the former, strong scattering is associated with pronounced bathymetric relief, such as the Patton Escarpment in the Southern California Continental Borderland. For the latter, scatterers are consistent with sharp lateral heterogeneities, such as near the Yellowstone hotspot and Southern California fault zones. We further model the body-to-surface wave scattering using finite-difference simulations. As an example, in the Southern California Continental Borderland a simplified 2-D bathymetric and crustal model are able to predict the arrival times and amplitudes of major scatterers. The modeling also suggests a relatively low shear wave velocity in the Continental Borderland. These observation of strong body-to-surface wave scattering and waveform modeling not only helps us image sharp heterogeneities but also are useful for assessing seismic hazard, including the calibration and refinement of seismic velocity models used to locate earthquakes and simulate strong ground motions.

Accurate seismic phase identification and arrival time picking of glacial icequakes

NASA Astrophysics Data System (ADS)

Jones, G. A.; Doyle, S. H.; Dow, C.; Kulessa, B.; Hubbard, A.

2010-12-01

A catastrophic lake drainage event was monitored continuously using an array of 6, 4.5 Hz 3 component geophones in the Russell Glacier catchment, Western Greenland. Many thousands of events and arrival time phases (e.g., P- or S-wave) were recorded, often with events occurring simultaneously but at different locations. In addition, different styles of seismic events were identified from 'classical' tectonic earthquakes to tremors usually observed in volcanic regions. The presence of such a diverse and large dataset provides insight into the complex system of lake drainage. One of the most fundamental steps in seismology is the accurate identification of a seismic event and its associated arrival times. However, the collection of such a large and complex dataset makes the manual identification of a seismic event and picking of the arrival time phases time consuming with variable results. To overcome the issues of consistency and manpower, a number of different methods have been developed including short-term and long-term averages, spectrograms, wavelets, polarisation analyses, higher order statistics and auto-regressive techniques. Here we propose an automated procedure which establishes the phase type and accurately determines the arrival times. The procedure combines a number of different automated methods to achieve this, and is applied to the recently acquired lake drainage data. Accurate identification of events and their arrival time phases are the first steps in gaining a greater understanding of the extent of the deformation and the mechanism of such drainage events. A good knowledge of the propagation pathway of lake drainage meltwater through a glacier will have significant consequences for interpretation of glacial and ice sheet dynamics.

Investigation of Back-Projection Uncertainties with M6 Earthquakes

NASA Astrophysics Data System (ADS)

Fan, W.; Shearer, P. M.

2017-12-01

We investigate possible biasing effects of inaccurate timing corrections on teleseismic P-wave back-projection imaging of large earthquake ruptures. These errors occur because empirically-estimated time shifts based on aligning P-wave first arrivals are exact only at the hypocenter and provide approximate corrections for other parts of the rupture. Using the Japan subduction zone as a test region, we analyze 46 M6-7 earthquakes over a ten-year period, including many aftershocks of the 2011 M9 Tohoku earthquake, performing waveform cross-correlation of their initial P-wave arrivals to obtain hypocenter timing corrections to global seismic stations. We then compare back-projection images for each earthquake using its own timing corrections with those obtained using the time corrections for other earthquakes. This provides a measure of how well sub-events can be resolved with back-projection of a large rupture as a function of distance from the hypocenter. Our results show that back-projection is generally very robust and that sub-event location errors average about 20 km across the entire study region ( 700 km). The back-projection coherence loss and location errors do not noticeably converge to zero even when the event pairs are very close (<20 km). This indicates that most of the timing differences are due to 3D structure close to each of the hypocenter regions, which limits the effectiveness of attempts to refine back-projection images using aftershock calibration, at least in this region.

Initial observations from seismometers frozen into a borehole through the McMurdo Ice Shelf.

NASA Astrophysics Data System (ADS)

Prior, David; Eccles, Jennifer; Cooper, Joanna; Craw, Lisa; van Haastrecht, Laurine; Hamish Bowman, M.; Stevens, Craig; Gamble Rosevear, Madi; Hulbe, Christina; Gorman, Andrew; Horgan, Huw; Pyne, Alex

2017-04-01

A seismometer cable with two, three-component seismometers was frozen into a hot water borehole through the McMurdo Ice Shelf at Windless Bight in late December 2016. The seismometers are at 39m and 189m depth. The upper seismometer lies just below the firn-ice transition ( 37m) and very close to sea level ( 38m). The lower seismometer is positioned 30m above the base of the ice shelf ( 222m). The seismometers froze in within 40 (upper) to 60 (lower) hours of the last reaming operation. The temperature evolution during freezing is complicated, particularly for the lower seismometer. The complications are interpreted as the result of brine expulsion and brine pocket migration. We conducted an active source experiment using the frozen-in seismometers together with a surface seismometer and four lines of geophones radiating from the borehole, at 45-degree angles, to a distance of 240m. Sources included a traditional hammer and surface plate, two types of hammer activated surface shear wave sources (for hard and soft surfaces) and a hammer activated borehole source. The frozen-in seismometers show excellent separation of P - wave and S - wave arrivals for all sources, particularly on the lower seismometer. The surface shear sources give clearer separation of arrivals on the vertical and horizontal components. For some source to receiver geometries the surface shear sources give no P - wave arrival on the horizontal seismometer components and a very strong S - wave arrival that is partitioned between the horizontal components in correspondence with the source orientation. The borehole source (at 3 to 10m in the firn) also gives clearer separation of P - wave and S - wave arrivals compared to a surface hammer and plate. The frozen-in seismometers were also used to listen for natural events in the ice. Comparing the same events recorded at the surface and at depth, the latter are much less noisy than the former, leading to more clear interpretation. As in the active source experiments, P-wave and S-wave arrivals are clear and the partitioning onto different components (vertical and horizontal) is very clear. Using seismology to interpret the physical properties of ice masses is dependent on quality data. The patterns of anisotropy related to ice crystallographic preferred orientations (CPOs) are particularly rich for S - waves and the ability to measure S - wave velocities and shear wave splitting is of particular importance in using seismology to constrain CPOs. Our initial observations suggest that seismometers frozen-in at depth, together with artificial sources with controlled shear wave kinematics have great potential to help us constrain ice CPOs and resultant plastic anisotropy through seismic data.

Quantum mechanics of neutrino oscillations - hand waving for pedestrians.

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

Lipkin, H. J.

1998-12-22

Why Hand Waving? All calculations in books describe oscillations in time. But real experiments don't measure time. Hand waving is used to convert the results of a ''gedanken time experiment'' to the result of a real experiment measuring oscillations in space. Right hand waving gives the right answer; wrong hand waving gives the wrong answer. Many papers use wrong handwaving to get wrong answers. This talk explains how to do it right and also answers the following questions: (1) A neutrino which is a mixture of two mass eigenstates is emitted with muon in the decay of a pion atmore » rest. This is a ''missing mass experiment'' where the muon energy determines the neutrino mass. Why are the two mass states coherent? (2) A neutrino which is a mixture of two mass eigenstates is emitted at time t=0. The two mass eigenstates move with different velocities and arrive at the detector at different times. Why are the two mass states coherent? (3) A neutrino is a mixture of two overlapping wave packets with different masses moving with different velocities. Will the wave packets eventually separate? If yes, when?« less

SHORT COMMUNICATION: Time measurement device with four femtosecond stability

NASA Astrophysics Data System (ADS)

Panek, Petr; Prochazka, Ivan; Kodet, Jan

2010-10-01

We present the experimental results of extremely precise timing in the sense of time-of-arrival measurements in a local time scale. The timing device designed and constructed in our laboratory is based on a new concept using a surface acoustic wave filter as a time interpolator. Construction of the device is briefly described. The experiments described were focused on evaluating the timing precision and stability. Low-jitter test pulses with a repetition frequency of 763 Hz were generated synchronously to the local time base and their times of arrival were measured. The resulting precision of a single measurement was typically 900 fs RMS, and a timing stability TDEV of 4 fs was achieved for time intervals in the range from 300 s to 2 h. To our knowledge this is the best value reported to date for the stability of a timing device. The experimental results are discussed and possible improvements are proposed.

Auto Correlation Analysis of Coda Waves from Local Earthquakes for Detecting Temporal Changes in Shallow Subsurface Structures: the 2011 Tohoku-Oki, Japan Earthquake

NASA Astrophysics Data System (ADS)

Nakahara, Hisashi

2015-02-01

For monitoring temporal changes in subsurface structures I propose to use auto correlation functions of coda waves from local earthquakes recorded at surface receivers, which probably contain more body waves than surface waves. Use of coda waves requires earthquakes resulting in decreased time resolution for monitoring. Nonetheless, it may be possible to monitor subsurface structures in sufficient time resolutions in regions with high seismicity. In studying the 2011 Tohoku-Oki, Japan earthquake (Mw 9.0), for which velocity changes have been previously reported, I try to validate the method. KiK-net stations in northern Honshu are used in this analysis. For each moderate earthquake normalized auto correlation functions of surface records are stacked with respect to time windows in the S-wave coda. Aligning the stacked, normalized auto correlation functions with time, I search for changes in phases arrival times. The phases at lag times of <1 s are studied because changes at shallow depths are focused. Temporal variations in the arrival times are measured at the stations based on the stretching method. Clear phase delays are found to be associated with the mainshock and to gradually recover with time. The amounts of the phase delays are 10 % on average with the maximum of about 50 % at some stations. The deconvolution analysis using surface and subsurface records at the same stations is conducted for validation. The results show the phase delays from the deconvolution analysis are slightly smaller than those from the auto correlation analysis, which implies that the phases on the auto correlations are caused by larger velocity changes at shallower depths. The auto correlation analysis seems to have an accuracy of about several percent, which is much larger than methods using earthquake doublets and borehole array data. So this analysis might be applicable in detecting larger changes. In spite of these disadvantages, this analysis is still attractive because it can be applied to many records on the surface in regions where no boreholes are available.

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

NASA Astrophysics Data System (ADS)

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

2016-04-01

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

Evaluation of a dense seismic array for acquisition of high quality data in the ACROSS observation

NASA Astrophysics Data System (ADS)

Tsuruga, K.; Kunitomo, T.; Hasada, Y.; Kumazawa, M.; Shigeta, N.; Kasahara, J.

2004-12-01

ACROSS is an active monitoring methodology to detect any subtle temporal change of physical properties in the Earth's interior. We demonstrate the potentiality of the ACROSS observation with a dense sensor array. We have conducted a dense seismic array observation at the distance of 1 km from the ACROSS source since 2003. The array is composed of 36 three-component velocity seismometers buried at 1.8 m deep in an area 25 m square. All the data are recorded accurately referring to a GPS clock. We derived and analyzed a transfer function (TF) from the source to a receiver by the following steps: (1) evaluating a force vector as source characteristics, (2) converting the observed data to the displacement vectors by incorporating all the corrections of the instruments, (3) stacking the observed data for an enough time to suppress the temporal noise, (4) extracting ACROSS signal and evaluating noise level, (5) representing TF in a tensor form with the estimated errors, (6) slant-stacking with variable ray parameters, (7) estimating the travel times and amplitudes of the wave arrivals by Sompi Event Analysis (Hasada et al., 2001) and representing the result by a pulse sequence, and (8) deriving the polarization vector for each arrival to identify all the wave modes. We analyzed TF of SH-wave component from 16 to 20 Hz as an example. We obtained good quality TF with S/N ratio up to 104 by stacking for 12 days at the step (3). The spatial noise originated from the local heterogeneity around the array was eliminated by the step (6). Several arrivals were recognized within the time windows from 0.6 to 1.8 s. The maximum amplitude of event traces was detected at the travel time of 1.064 s with a ray parameter of 7.9x10-4 s/m. We also found the scattered waves probably generated by the heterogeneities around the array. The ACROSS dense array observation would provide a lot of information on the underground heterogeneities. Consequently, we have the important and challenging subjects: (1) optimum designing of ACROSS array to acquire the better data and (2) development of new theoretical method to deal with the variable types of the wave.

MULTI-VIEWPOINT OBSERVATIONS OF A WIDELY DISTRIBUTED SOLAR ENERGETIC PARTICLE EVENT: THE ROLE OF EUV WAVES AND WHITE-LIGHT SHOCK SIGNATURES

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

Kouloumvakos, A.; Patsourakos, S.; Nindos, A.

2016-04-10

On 2012 March 7, two large eruptive events occurred in the same active region within 1 hr from each other. Each consisted of an X-class flare, a coronal mass ejection (CME), an extreme-ultraviolet (EUV) wave, and a shock wave. The eruptions gave rise to a major solar energetic particle (SEP) event observed at widely separated (∼120°) points in the heliosphere. From multi-viewpoint energetic proton recordings we determine the proton release times at STEREO B and A (STB, STA) and the first Lagrange point (L1) of the Sun–Earth system. Using EUV and white-light data, we determine the evolution of the EUVmore » waves in the low corona and reconstruct the global structure and kinematics of the first CME’s shock, respectively. We compare the energetic proton release time at each spacecraft with the EUV waves’ arrival times at the magnetically connected regions and the timing and location of the CME shock. We find that the first flare/CME is responsible for the SEP event at all three locations. The proton release at STB is consistent with arrival of the EUV wave and CME shock at the STB footpoint. The proton release time at L1 was significantly delayed compared to STB. Three-dimensional modeling of the CME shock shows that the particle release at L1 is consistent with the timing and location of the shock’s western flank. This indicates that at L1 the proton release did not occur in low corona but farther away from the Sun. However, the extent of the CME shock fails to explain the SEP event observed at STA. A transport process or a significantly distorted interplanetary magnetic field may be responsible.« less

Time-localized frequency analysis of ultrasonic guided waves for nondestructive testing

NASA Astrophysics Data System (ADS)

Shin, Hyeon Jae; Song, Sung-Jin

2000-05-01

A time-localized frequency (TLF) analysis is employed for the guided wave mode identification and improved guided wave applications. For the analysis of time-localized frequency contents of digitized ultrasonic signals, TLF analysis consists of splitting the time domain signal into overlapping segments, weighting each with the hanning window, and forming the columns of discrete Fourier transforms. The result is presented by a frequency versus time domain diagram showing frequency variation along the signal arrival time. For the demonstration of the utility of TLF analysis, an experimental group velocity dispersion pattern obtained by TLF analysis is compared with the dispersion diagram obtained by theory of elasticity. Sample piping is carbon steel piping that is used for the transportation of natural gas underground. Guided wave propagation characteristic on the piping is considered with TLF analysis and wave structure concepts. TLF analysis is used for the detection of simulated corrosion defects and the assessment of weld joint using ultrasonic guided waves. TLF analysis has revealed that the difficulty of mode identification in multi-mode propagation could be overcome. Group velocity dispersion pattern obtained by TLF analysis agrees well with theoretical results.

Reduced rank models for travel time estimation of low order mode pulses.

PubMed

Chandrayadula, Tarun K; Wage, Kathleen E; Worcester, Peter F; Dzieciuch, Matthew A; Mercer, James A; Andrew, Rex K; Howe, Bruce M

2013-10-01

Mode travel time estimation in the presence of internal waves (IWs) is a challenging problem. IWs perturb the sound speed, which results in travel time wander and mode scattering. A standard approach to travel time estimation is to pulse compress the broadband signal, pick the peak of the compressed time series, and average the peak time over multiple receptions to reduce variance. The peak-picking approach implicitly assumes there is a single strong arrival and does not perform well when there are multiple arrivals due to scattering. This article presents a statistical model for the scattered mode arrivals and uses the model to design improved travel time estimators. The model is based on an Empirical Orthogonal Function (EOF) analysis of the mode time series. Range-dependent simulations and data from the Long-range Ocean Acoustic Propagation Experiment (LOAPEX) indicate that the modes are represented by a small number of EOFs. The reduced-rank EOF model is used to construct a travel time estimator based on the Matched Subspace Detector (MSD). Analysis of simulation and experimental data show that the MSDs are more robust to IW scattering than peak picking. The simulation analysis also highlights how IWs affect the mode excitation by the source.

Application of Seismic Array Processing to Tsunami Early Warning

NASA Astrophysics Data System (ADS)

An, C.; Meng, L.

2015-12-01

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

Fluid dynamic modeling of nano-thermite reactions

NASA Astrophysics Data System (ADS)

Martirosyan, Karen S.; Zyskin, Maxim; Jenkins, Charles M.; Yuki Horie, Yasuyuki

2014-03-01

This paper presents a direct numerical method based on gas dynamic equations to predict pressure evolution during the discharge of nanoenergetic materials. The direct numerical method provides for modeling reflections of the shock waves from the reactor walls that generates pressure-time fluctuations. The results of gas pressure prediction are consistent with the experimental evidence and estimates based on the self-similar solution. Artificial viscosity provides sufficient smoothing of shock wave discontinuity for the numerical procedure. The direct numerical method is more computationally demanding and flexible than self-similar solution, in particular it allows study of a shock wave in its early stage of reaction and allows the investigation of "slower" reactions, which may produce weaker shock waves. Moreover, numerical results indicate that peak pressure is not very sensitive to initial density and reaction time, providing that all the material reacts well before the shock wave arrives at the end of the reactor.

Fluid dynamic modeling of nano-thermite reactions

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

Martirosyan, Karen S., E-mail: karen.martirosyan@utb.edu; Zyskin, Maxim; Jenkins, Charles M.

2014-03-14

This paper presents a direct numerical method based on gas dynamic equations to predict pressure evolution during the discharge of nanoenergetic materials. The direct numerical method provides for modeling reflections of the shock waves from the reactor walls that generates pressure-time fluctuations. The results of gas pressure prediction are consistent with the experimental evidence and estimates based on the self-similar solution. Artificial viscosity provides sufficient smoothing of shock wave discontinuity for the numerical procedure. The direct numerical method is more computationally demanding and flexible than self-similar solution, in particular it allows study of a shock wave in its early stagemore » of reaction and allows the investigation of “slower” reactions, which may produce weaker shock waves. Moreover, numerical results indicate that peak pressure is not very sensitive to initial density and reaction time, providing that all the material reacts well before the shock wave arrives at the end of the reactor.« less

The vertical propagation of disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake over Taiwan

NASA Astrophysics Data System (ADS)

Liu, J. Y.; Chen, C. H.; Sun, Y. Y.; Chen, C. H.; Tsai, H. F.; Yen, H. Y.; Chum, J.; Lastovicka, J.; Yang, Q. S.; Chen, W. S.; Wen, S.

2016-02-01

In this paper, concurrent/colocated measurements of seismometers, infrasonic systems, magnetometers, HF-CW (high frequency-continuous wave) Doppler sounding systems, and GPS receivers are employed to detect disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake. No time delay between colocated infrasonic (i.e., super long acoustic) waves and seismic waves indicates that the triggered acoustic and/or gravity waves in the atmosphere (or seismo-traveling atmospheric disturbances, STADs) near the Earth's surface can be immediately activated by vertical ground motions. The circle method is used to find the origin and compute the observed horizontal traveling speed of the triggered infrasonic waves. The speed of about 3.3 km/s computed from the arrival time versus the epicentral distance suggests that the infrasonic waves (i.e., STADs) are mainly induced by the Rayleigh waves. The agreements in the travel time at various heights between the observation and theoretical calculation suggest that the STADs triggered by the vertical motion of ground surface caused by the Tohoku earthquake traveled vertically from the ground to the ionosphere with speed of the sound in the atmosphere over Taiwan.

Pn-waves Travel-time Anomaly beneath Taiwan from Dense Seismic Array Observations and its Possible Tectonic Implications

NASA Astrophysics Data System (ADS)

Lin, Y. Y.; Huang, B. S.; Ma, K. F.; Hsieh, M. C.

2015-12-01

We investigated travel times of Pn waves, which are of great important for understanding the Moho structure in Taiwan region. Although several high quality tomographic studies had been carried out, observations of Pn waves are still the most comprehensive way to elucidate the Moho structure. Mapping the Moho structure of Taiwan had been a challenging due to the small spatial dimension of Taiwan island with two subduction systems. To decipher the tectonic structure and understanding of earthquake hazard, the island of Taiwan have been implemented by several high density seismic stations, including 71 short-period stations of Central Weather Bureau Seismic Network (CWBSN) and 42 broardband stations of Broadband Array in Taiwan for Seismology (BATS). High quality seismic records of these stations would be used to identify precise Pn-wave arrival times. After station-elevation correction, we measure the difference between the observed and theoretical Pn arrivals from the IASPI 91 model for each station. For correcting uncertainties of earthquake location and origin time, we estimate relative Pn anomaly, ΔtPn , between each station and a reference station. The pattern of ΔtPn reflects the depth anomaly of Moho beneath Taiwan. In general, Pn waves are commonly observed from shallow earthquake at epicentral distance larger than 120 km. We search the global catalog since 2005 and the criteria are M > 5.5, focal depth < 30 km and epicentral distance > 150 km. The 12 medium earthquakes from north Luzon are considered for analysis. We choose a station, TWKB, in the most southern point of Taiwan as the reference station due to that all events are from the south. The results indicate obvious different patterns of ΔtPn from different back-azimuths. The ΔtPn pattern of the events in the first group from the south south-east indicates that the Pn arrivals delay suddenly when the Pn waves pass through the Central Range, suggesting the Moho becomes deep rapidly. However, we cannot recognize the same pattern when the events from due south in the second group. The ΔtPn pattern in the second group has a clear slow gradient from the south to north through Taiwan island. It may be relative to a smooth dipping structure of the Moho. Both ΔtPn patterns reveal large delays in northern Taiwan which may be related to the north subduction structure.

Using level set based inversion of arrival times to recover shear wave speed in transient elastography and supersonic imaging

NASA Astrophysics Data System (ADS)

McLaughlin, Joyce; Renzi, Daniel

2006-04-01

Transient elastography and supersonic imaging are promising new techniques for characterizing the elasticity of soft tissues. Using this method, an 'ultrafast imaging' system (up to 10 000 frames s-1) follows in real time the propagation of a low-frequency shear wave. The displacement of the propagating shear wave is measured as a function of time and space. Here we develop a fast level set based algorithm for finding the shear wave speed from the interior positions of the propagating front. We compare the performance of level curve methods developed here and our previously developed (McLaughlin J and Renzi D 2006 Shear wave speed recovery in transient elastography and supersonic imaging using propagating fronts Inverse Problems 22 681-706) distance methods. We give reconstruction examples from synthetic data and from data obtained from a phantom experiment accomplished by Mathias Fink's group (the Laboratoire Ondes et Acoustique, ESPCI, Université Paris VII).

Multiple Signal Classification for Gravitational Wave Burst Search

NASA Astrophysics Data System (ADS)

Cao, Junwei; He, Zhengqi

2013-01-01

This work is mainly focused on the application of the multiple signal classification (MUSIC) algorithm for gravitational wave burst search. This algorithm extracts important gravitational wave characteristics from signals coming from detectors with arbitrary position, orientation and noise covariance. In this paper, the MUSIC algorithm is described in detail along with the necessary adjustments required for gravitational wave burst search. The algorithm's performance is measured using simulated signals and noise. MUSIC is compared with the Q-transform for signal triggering and with Bayesian analysis for direction of arrival (DOA) estimation, using the Ω-pipeline. Experimental results show that MUSIC has a lower resolution but is faster. MUSIC is a promising tool for real-time gravitational wave search for multi-messenger astronomy.

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

NASA Astrophysics Data System (ADS)

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

2002-12-01

Waveform modeling of seismic fault zone (FZ) trapped waves has been claimed to provide a high resolution imaging of FZ structure at seismogenic depth. We analyze quantitatively a waveform data set generated by 238 Landers aftershocks recorded by a portable seismic array (Lee, 1999). The array consists of 33 three-component L-22 seismometers, 22 of which on a line crossing the surface rupture zone of the mainshock. A subset of 93 aftershocks were also recorded by the Southern California Seismic Network, while the other events were recorded only by the FZ array. We locate the latter subset of events with a "grid-search relocation method" using accurately picked P and S arrival times, a half-space velocity model, and back-azimuth adjustment to correct the effect of low velocity FZ material on phase arrivals. Next we determine the quality of FZ trapped wave generation from the ratio of trapped waves to S-wave energy for stations relatively close to and far from the FZ. Energy ratios exceeding 4, between 2 and 4, and less than 2, are assigned quality A, B, and C of trapped wave generation. We find that about 70% of nearby events with S-P time less than 2 sec, including many clearly off the fault, generate FZ trapped waves with quality A or B. This distribution is in marked contrast with previous claims that trapped waves at Landers are generated only by sources close to or inside the fault zone (Li et al., 1994, 2000). The existence of trapped waves due to sources outside the Landers rupture zone indicates that the generating structure is shallow, as demonstrated in recent 3D calculations of wave propagation in irregular FZ structures (Fohrmann et al., 2002). The time difference between the S arrivals and trapped wave group does not grow systematically with increasing source-receiver distance along the fault, in agreement with the above conclusion. The dispersion of trapped waves at Landers is rather weak, again suggesting a short propagation distance inside the low velocity FZ material. To put additional constraints on properties of the shallow trapping structure at Landers, we modeled FZ trapped waves with a genetic inversion algorithm (Michael and Ben-Zion, 2002) using the 2D analytical solution of Ben-Zion and Aki (1990) and Ben-Zion (1998) for a uniform FZ structure. The synthetic waveform modeling indicates an effective FZ waveguide with depth of about 3-5 km, width on the order of 200 m, shear velocity reduction relative to the host rock of about 40-50%, and S wave quality factor of about 30. The modeling also shows that the waveguide is not centered at the exposed fault trace (station C00), but at a distance of about 100 m east of C00. Shallow trapping structures with similar properties appear to characterize also the Karadere-Duzce branch of the north Anatolian fault (Ben-Zion et al., 2002) and the Parkfield segment of the San Andreas fault (Michael and Ben-Zion, 2002; Korneev et al., 2002).

Explosively Driven Shock Induced Damage in OFHC Copper

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

Koller, D. D.; Hixson, R. S.; Gray, G. T. III

OFHC Cu samples were subjected to shock loading using plane wave HE lenses to produce a uniaxial Taylor wave profile (shock followed by immediate release). Upon arrival of the shock wave at the free surface of the sample, the wave is reflected and propagates back into the sample as a release wave. It is the interaction of initial and reflected release waves that place the material in a localized state of tension which can ultimately result in damage and possibly complete failure of the material. The peak tensile stress and its location in the material are determined by the wavemore » shape. Damage evolution processes and localized behavior are discussed based on results from time-resolved free surface velocity (VISAR) interferometry and post shock metallurgical analysis of the soft recovered samples.« less

Ultrasonic input-output for transmitting and receiving longitudinal transducers coupled to same face of isotropic elastic plate

NASA Technical Reports Server (NTRS)

Williams, J. H., Jr.; Karagulle, H.; Lee, S. S.

1982-01-01

The quantitative understanding of ultrasonic nondestructive evaluation parameters such as the stress wave factor were studied. Ultrasonic input/output characteristics for an isotropic elastic plate with transmitting and receiving longitudinal transducers coupled to the same face were analyzed. The asymptotic normal stress is calculated for an isotropic elastic half space subjected to a uniform harmonic normal stress applied to a circular region at the surface. The radiated stress waves are traced within the plate by considering wave reflections at the top and bottom faces. The output voltage amplitude of the receiving transducer is estimated by considering only longitudinal waves. Agreement is found between the output voltage wave packet amplitudes and times of arrival due to multiple reflections of the longitudinal waves.

Modal analysis of wave propagation in dispersive media

NASA Astrophysics Data System (ADS)

Abdelrahman, M. Ismail; Gralak, B.

2018-01-01

Surveys on wave propagation in dispersive media have been limited since the pioneering work of Sommerfeld [Ann. Phys. 349, 177 (1914), 10.1002/andp.19143491002] by the presence of branches in the integral expression of the wave function. In this article a method is proposed to eliminate these critical branches and hence to establish a modal expansion of the time-dependent wave function. The different components of the transient waves are physically interpreted as the contributions of distinct sets of modes and characterized accordingly. Then, the modal expansion is used to derive a modified analytical expression of the Sommerfeld precursor improving significantly the description of the amplitude and the oscillating period up to the arrival of the Brillouin precursor. The proposed method and results apply to all waves governed by the Helmholtz equations.

Multi-hole seismic modeling in 3-D space and cross-hole seismic tomography analysis for boulder detection

NASA Astrophysics Data System (ADS)

Cheng, Fei; Liu, Jiangping; Wang, Jing; Zong, Yuquan; Yu, Mingyu

2016-11-01

A boulder stone, a common geological feature in south China, is referred to the remnant of a granite body which has been unevenly weathered. Undetected boulders could adversely impact the schedule and safety of subway construction when using tunnel boring machine (TBM) method. Therefore, boulder detection has always been a key issue demanded to be solved before the construction. Nowadays, cross-hole seismic tomography is a high resolution technique capable of boulder detection, however, the method can only solve for velocity in a 2-D slice between two wells, and the size and central position of the boulder are generally difficult to be accurately obtained. In this paper, the authors conduct a multi-hole wave field simulation and characteristic analysis of a boulder model based on the 3-D elastic wave staggered-grid finite difference theory, and also a 2-D imaging analysis based on first arrival travel time. The results indicate that (1) full wave field records could be obtained from multi-hole seismic wave simulations. Simulation results describe that the seismic wave propagation pattern in cross-hole high-velocity spherical geological bodies is more detailed and can serve as a basis for the wave field analysis. (2) When a cross-hole seismic section cuts through the boulder, the proposed method provides satisfactory cross-hole tomography results; however, when the section is closely positioned to the boulder, such high-velocity object in the 3-D space would impact on the surrounding wave field. The received diffracted wave interferes with the primary wave and in consequence the picked first arrival travel time is not derived from the profile, which results in a false appearance of high-velocity geology features. Finally, the results of 2-D analysis in 3-D modeling space are comparatively analyzed with the physical model test vis-a-vis the effect of high velocity body on the seismic tomographic measurements.

Chacterization of Teleseismic Earthquakes Observed on an Ice Shelf

NASA Astrophysics Data System (ADS)

Baker, M. G.; Aster, R. C.; Anthony, R. E.; Wiens, D.; Nyblade, A.; Bromirski, P. D.; Stephen, R. A.; Gerstoft, P.

2016-12-01

Broadband seismographs deployed atop large tabular icebergs and ice shelves record a rich superposition of atmospheric, oceanic, and solid earth signals. We characterize these signals, including body and surface wave arrivals from approximately 200 global earthquakes, using a 34-station broadband array spanning the Ross Ice Shelf, Antarctica. Teleseismic earthquake arrivals are essential for constructing models of crustal and upper mantle structure, and observations on the ice shelf are key to resolving the structure of the underlying West Antarctic Rift System. To test the plausibility of passive imaging in this unique environment, we examine seasonal and spatial dependence of signal-to-noise ratios of body wave arrivals and the impact of ice shelf dynamics on surface wave dispersion. We also note unusual phase mechanics arising from the floating platform geometry.

Determination of differential arrival times by cross-correlating worldwide seismological data

NASA Astrophysics Data System (ADS)

Godano, M.; Nolet, G.; Zaroli, C.

2012-12-01

Cross-correlation delays are the preferred body wave observables in global tomography. Heterogeneity is the main factor influencing delay times found by cross-correlation. Not only the waveform, but also the arrival time itself is affected by differences in seismic velocity encountered along the way. An accurate method for estimating differential times of seismic arrivals across a regional array by cross-correlation was developed by VanDecar and Crosson [1990]. For the estimation of global travel time delays in different frequency bands, Sigloch and Nolet [2006] developed a method for the estimation of body wave delays using a matched filter, which requires the separate estimation of the source time function. Sigloch et al. [2008] found that waveforms often cluster in and opposite the direction of rupture propagation on the fault, confirming that the directivity effect is a major factor in shaping the waveform of large events. We propose a generalization of the VanDecar-Crosson method to which we add a correction for the directivity effect in the seismological data. The new method allows large events to be treated without the need to estimate the source time function for the computation of a matched synthetic waveform. The procedure consists in (1) the detection of the directivity effect in the data and the determination of a rupture model (unilateral or bilateral) explaining the differences in pulse duration among the stations, (2) the determination of an apparent fault rupture length explaining the pulse durations, (3) the removal of the delay due to the directivity effect in the pulse duration , by stretching or contracting the seismograms for directive and anti-directive stations respectively and (4) the application of a generalized VanDecar and Crosson method using only delays between pairs of stations that have an acceptable correlation coefficient. We validate our method by performing tests on synthetic data. Results show that the error between theoretical and measured differential arrival time are significantly reduced for the corrected data. We illustrate our method on data from several real earthquakes.

Relative arrival-time upper-mantle tomography and the elusive background mean

NASA Astrophysics Data System (ADS)

Bastow, Ian D.

2012-08-01

The interpretation of seismic tomographic images of upper-mantle seismic wave speed structure is often a matter of considerable debate because the observations can usually be explained by a range of hypotheses, including variable temperature, composition, anisotropy, and the presence of partial melt. An additional problem, often overlooked in tomographic studies using relative as opposed to absolute arrival-times, is the issue of the resulting velocity model's zero mean. In shield areas, for example, relative arrival-time analysis strips off a background mean velocity structure that is markedly fast compared to the global average. Conversely, in active areas, the background mean is often markedly slow compared to the global average. Appreciation of this issue is vital when interpreting seismic tomographic images: 'high' and 'low' velocity anomalies should not necessarily be interpreted, respectively, as 'fast' and 'slow' compared to 'normal mantle'. This issue has been discussed in the seismological literature in detail over the years, yet subsequent tomography studies have still fallen into the trap of mis-interpreting their velocity models. I highlight here some recent examples of this and provide a simple strategy to address the problem using constraints from a recent global tomographic model, and insights from catalogues of absolute traveltime anomalies. Consultation of such absolute measures of seismic wave speed should be routine during regional tomographic studies, if only for the benefit of the broader Earth Science community, who readily follow the red = hot and slow, blue = cold and fast rule of thumb when interpreting the images for themselves.

Preadoption adversity and long-term clinical-range behavior problems in adopted Chinese girls.

PubMed

Tan, Tony Xing; Camras, Linda A; Kim, Eun Sook

2016-04-01

In this study, we report findings on the role of preadoption adversity on long-term clinical-range problems in adopted Chinese girls. Four waves (2005, 2007, 2009 and 2011) of problem behavior data on 1,223 adopted Chinese girls (M = 4.86 years, SD = 2.82 in 2005) were collected from the adoptive mothers with the Child Behavior Checklist (CBCL). At Wave 1 (2005), data on the following indicators of preadoption adversity was collected: age at adoption, physical signs/symptoms (e.g., sores) of preadoption adversity, developmental delays at arrival, refusal/avoidance behaviors and crying/clinging behaviors toward adoptive parents during the first 3 weeks of adoption. We found that the percentage of clinical-range internalizing problems was 11.1%, 16.5%, 11.3%, and 16.1% at Wave 1, Wave 2, Wave 3, and Wave 4, respectively; the corresponding percentage of clinical-range externalizing problems was 8.4%, 10.5%, 8.4% and 9.9% respectively; and the corresponding percentage of clinical-range total CBCL problems was 9.3%, 13.0%, 9.8% and 12.6% respectively. Analyses with Mplus showed that controlling for demographic variables, indicators of preadoption adversity, except age at adoption, increased the odds for clinical-range behavior problems. Longitudinal path models revealed that controlling for demographic variables and the children's adjustment status in the previous wave, refusal/avoidance remained significant in predicting clinical-range internalizing, externalizing and total CBCL problems at Wave 2, delays at arrival and signs/symptoms were significant in predicting clinical-range internalizing problems at Wave 3. Overall, adoptees with clinical-range CBCL problems in earlier waves were 9-28 times as likely to show clinical-range CBCL problems in subsequent waves. (c) 2016 APA, all rights reserved).

Microseisms at Palisades. III - Microseisms and microbaroms

NASA Technical Reports Server (NTRS)

Rind, D.

1980-01-01

Microseisms (seismic surface waves) in the frequency range of 0.1-1 Hz recorded at Palisades, N.Y., are compared with microbaroms (infrasound) in the same frequency range recorded simultaneously. Both are thought to be generated by interfering ocean waves, and the question addressed is how often does their comparison imply that they have the same source. Compared were their approximate regions of formation, the formation conditions (both meteorological and oceanographic), amplitude variations, and frequency spectra. It is concluded that for the signals recorded at this location the two phenomena appear to have the same ocean wave sources two-thirds of the times and at least some of the remaining times one of the signals is prevented from arriving owing to propagation difficulties.

Gravitational-wave bursts from the nuclei of distant galaxies and quasars: Proposal for detection using Doppler tracking of interplanetary spacecraft

NASA Technical Reports Server (NTRS)

Thorne, K. S.; Braginsky, V. B.

1974-01-01

Supermassive black holes which exist in the nuclei of many quasars and galaxies are examined along with the collapse which forms these holes and subsequent collisions between them which produce strong, broad-band bursts of gravitational waves. Such bursts might arrive at earth as often as 50 times per year--or as rarely as once each 300 years. The detection of such bursts with dual-frequency Doppler tracking of interplanetary spacecraft is considered.

Investigating Stimulated Wave-Particle Interaction of Radiation Belt Particles with Space-Borne Whistler Mode Transmitters

DTIC Science & Technology

2009-03-30

presented. ii Figure 12. Arrival time of electrons during the positive phase of charge on the antenna. ........ 15 The distances...relativistic electrons in the radiation belt. The target electrons are in the energy range of 0.5~3.0 MeV in the region between L = 1.7~2.2, where L is the...waves to pitch-angle diffuse the electrons into the loss-cone, i.e., to precipitate the relativistic electrons into the neutral atmosphere. There are

Wide-angle Marine Seismic Refraction Imaging of Vertical Faults: Pre-Stack Turning Wave Migrations of Synthetic Data and Implications for Survey Design

NASA Astrophysics Data System (ADS)

Miller, N. C.; Lizarralde, D.; McGuire, J.; Hole, J. A.

2006-12-01

We consider methodologies, including survey design and processing algorithms, which are best suited to imaging vertical reflectors in oceanic crust using marine seismic techniques. The ability to image the reflectivity structure of transform faults as a function of depth, for example, may provide new insights into what controls seismicity along these plate boundaries. Turning-wave migration has been used with success to image vertical faults on land. With synthetic datasets we find that this approach has unique difficulties in the deep ocean. The fault-reflected crustal refraction phase (Pg-r) typically used in pre-stack migrations is difficult to isolate in marine seismic data. An "imagable" Pg-r is only observed in a time window between the first arrivals and arrivals from the sediments and the thick, slow water layer at offsets beyond ~25 km. Ocean- bottom seismometers (OBSs), as opposed to a long surface streamer, must be used to acquire data suitable for crustal-scale vertical imaging. The critical distance for Moho reflections (PmP) in oceanic crust is also ~25 km, thus Pg-r and PmP-r are observed with very little separation, and the fault-reflected mantle refraction (Pn-r) arrives prior to Pg-r as the observation window opens with increased OBS-to-fault distance. This situation presents difficulties for "first-arrival" based Kirchoff migration approaches and suggests that wave- equation approaches, which in theory can image all three phases simultaneously, may be more suitable for vertical imaging in oceanic crust. We will present a comparison of these approaches as applied to a synthetic dataset generated from realistic, stochastic velocity models. We will assess their suitability, the migration artifacts unique to the deep ocean, and the ideal instrument layout for such an experiment.

The effect of abdominal wall morphology on ultrasonic pulse distortion. Part II. Simulations.

PubMed

Mast, T D; Hinkelman, L M; Orr, M J; Waag, R C

1998-12-01

Wavefront propagation through the abdominal wall was simulated using a finite-difference time-domain implementation of the linearized wave propagation equations for a lossless, inhomogeneous, two-dimensional fluid as well as a simplified straight-ray model for a two-dimensional absorbing medium. Scanned images of six human abdominal wall cross sections provided the data for the propagation media in the simulations. The images were mapped into regions of fat, muscle, and connective tissue, each of which was assigned uniform sound speed, density, and absorption values. Propagation was simulated through each whole specimen as well as through each fat layer and muscle layer individually. Wavefronts computed by the finite-difference method contained arrival time, energy level, and wave shape distortion similar to that in measurements. Straight-ray simulations produced arrival time fluctuations similar to measurements but produced much smaller energy level fluctuations. These simulations confirm that both fat and muscle produce significant wavefront distortion and that distortion produced by fat sections differs from that produced by muscle sections. Spatial correlation of distortion with tissue composition suggests that most major arrival time fluctuations are caused by propagation through large-scale inhomogeneities such as fatty regions within muscle layers, while most amplitude and waveform variations are the result of scattering from smaller inhomogeneities such as septa within the subcutaneous fat. Additional finite-difference simulations performed using uniform-layer models of the abdominal wall indicate that wavefront distortion is primarily caused by tissue structures and inhomogeneities rather than by refraction at layer interfaces or by variations in layer thicknesses.

Spatiotemporal changes of seismic attenuation caused by injected CO2 at the Frio-II pilot site, Dayton, TX, USA

NASA Astrophysics Data System (ADS)

Zhu, Tieyuan; Ajo-Franklin, Jonathan B.; Daley, Thomas M.

2017-09-01

A continuous active source seismic monitoring data set was collected with crosswell geometry during CO2 injection at the Frio-II brine pilot, near Liberty, TX. Previous studies have shown that spatiotemporal changes in the P wave first arrival time reveal the movement of the injected CO2 plume in the storage zone. To further constrain the CO2 saturation, particularly at higher saturation levels, we investigate spatial-temporal changes in the seismic attenuation of the first arrivals. The attenuation changes over the injection period are estimated by the amount of the centroid frequency shift computed by local time-frequency analysis. We observe that (1) at receivers above the injection zone seismic attenuation does not change in a physical trend; (2) at receivers in the injection zone attenuation sharply increases following injection and peaks at specific points varying with distributed receivers, which is consistent with observations from time delays of first arrivals; then, (3) attenuation decreases over the injection time. The attenuation change exhibits a bell-shaped pattern during CO2 injection. Under Frio-II field reservoir conditions, White's patchy saturation model can quantitatively explain both the P wave velocity and attenuation response observed. We have combined the velocity and attenuation change data in a crossplot format that is useful for model-data comparison and determining patch size. Our analysis suggests that spatial-temporal attenuation change is not only an indicator of the movement and saturation of CO2 plumes, even at large saturations, but also can quantitatively constrain CO2 plume saturation when used jointly with seismic velocity.

Logical synchronization: how evidence and hypotheses steer atomic clocks

NASA Astrophysics Data System (ADS)

Myers, John M.; Madjid, F. Hadi

2014-05-01

A clock steps a computer through a cycle of phases. For the propagation of logical symbols from one computer to another, each computer must mesh its phases with arrivals of symbols from other computers. Even the best atomic clocks drift unforeseeably in frequency and phase; feedback steers them toward aiming points that depend on a chosen wave function and on hypotheses about signal propagation. A wave function, always under-determined by evidence, requires a guess. Guessed wave functions are coded into computers that steer atomic clocks in frequency and position—clocks that step computers through their phases of computations, as well as clocks, some on space vehicles, that supply evidence of the propagation of signals. Recognizing the dependence of the phasing of symbol arrivals on guesses about signal propagation elevates `logical synchronization.' from its practice in computer engineering to a dicipline essential to physics. Within this discipline we begin to explore questions invisible under any concept of time that fails to acknowledge the unforeseeable. In particular, variation of spacetime curvature is shown to limit the bit rate of logical communication.

Seismic excitation by the space shuttle Columbia

USGS Publications Warehouse

Kanamori, H.; Mori, J.; Anderson, D.L.; Heaton, T.H.

1991-01-01

SEISMIC stations in southern California recorded the atmospheric shock waves generated by the space shuttle Columbia on its return to the Edwards Air Force base on 13 August 1989 (Fig. 1). In addition to the shock wave, the broad-band IRIS-TERRAscope station at Pasadena recorded a distinct pulse with a period of ???2-3 seconds, which arrived 12.5 seconds before the shock wave (Fig. 2). This pulse was also recorded at the University of Southern California, near downtown Los Angeles, where it arrived 3 seconds after the shock wave. The origin of this pulse could not be readily identified. We show here that it was a seismic P wave excited by the motion of high-rise buildings in downtown Los Angeles, which were hit by the shock wave. The proximity of the natural period of the high-rise buildings to that of the Los Angeles basin enabled efficient energy transfer from shock wave to seismic wave.

Time-dependent seismic tomography

USGS Publications Warehouse

Julian, B.R.; Foulger, G.R.

2010-01-01

Of methods for measuring temporal changes in seismic-wave speeds in the Earth, seismic tomography is among those that offer the highest spatial resolution. 3-D tomographic methods are commonly applied in this context by inverting seismic wave arrival time data sets from different epochs independently and assuming that differences in the derived structures represent real temporal variations. This assumption is dangerous because the results of independent inversions would differ even if the structure in the Earth did not change, due to observational errors and differences in the seismic ray distributions. The latter effect may be especially severe when data sets include earthquake swarms or aftershock sequences, and may produce the appearance of correlation between structural changes and seismicity when the wave speeds are actually temporally invariant. A better approach, which makes it possible to assess what changes are truly required by the data, is to invert multiple data sets simultaneously, minimizing the difference between models for different epochs as well as the rms arrival-time residuals. This problem leads, in the case of two epochs, to a system of normal equations whose order is twice as great as for a single epoch. The direct solution of this system would require twice as much memory and four times as much computational effort as would independent inversions. We present an algorithm, tomo4d, that takes advantage of the structure and sparseness of the system to obtain the solution with essentially no more effort than independent inversions require. No claim to original US government works Journal compilation ?? 2010 RAS.

Triggered Seismicity in Utah from the November 3, 2002, Denali Fault Earthquake

NASA Astrophysics Data System (ADS)

Pankow, K. L.; Nava, S. J.; Pechmann, J. C.; Arabasz, W. J.

2002-12-01

Coincident with the arrival of the surface waves from the November 3, 2002, Mw 7.9 Denali Fault, Alaska earthquake (DFE), the University of Utah Seismograph Stations (UUSS) regional seismic network detected a marked increase in seismicity along the Intermountain Seismic Belt (ISB) in central and north-central Utah. The number of earthquakes per day in Utah located automatically by the UUSS's Earthworm system in the week following the DFE was approximately double the long-term average during the preceding nine months. From these preliminary data, the increased seismicity appears to be characterized by small magnitude events (M = 3.2) and concentrated in five distinct spatial clusters within the ISB between 38.75°and 42.0° N. The first of these earthquakes was an M 2.2 event located ~20 km east of Salt Lake City, Utah, which occurred during the arrival of the Love waves from the DFE. The increase in Utah earthquake activity at the time of the arrival of the surface waves from the DFE suggests that these surface waves triggered earthquakes in Utah at distances of more than 3,000 km from the source. We estimated the peak dynamic shear stress caused by these surface waves from measurements of their peak vector velocities at 43 recording sites: 37 strong-motion stations of the Advanced National Seismic System and six broadband stations. (The records from six other broadband instruments in the region of interest were clipped.) The estimated peak stresses ranged from 1.2 bars to 3.5 bars with a mean of 2.3 bars, and generally occurred during the arrival of Love waves of ~15 sec period. These peak dynamic shear stress estimates are comparable to those obtained from recordings of the 1992 Mw 7.3 Landers, California, earthquake in regions where the Landers earthquake triggered increased seismicity. We plan to present more complete analyses of UUSS seismic network data, further testing our hypothesis that the DFE remotely triggered seismicity in Utah. This hypothesis is important to investigate because well-documented evidence for triggering of seismicity by distant earthquakes comes primarily from areas characterized by recent volcanic or geothermal activity. The regions of apparent triggered seismicity from the DFE in Utah fall into neither of these two categories.

Full-wave effects on shear wave splitting

NASA Astrophysics Data System (ADS)

Lin, Yu-Pin; Zhao, Li; Hung, Shu-Huei

2014-02-01

Seismic anisotropy in the mantle plays an important role in our understanding of the Earth's internal dynamics, and shear wave splitting has always been a key observable in the investigation of seismic anisotropy. To date the interpretation of shear wave splitting in terms of anisotropy has been largely based on ray-theoretical modeling of a single vertically incident plane SKS or SKKS wave. In this study, we use sensitivity kernels of shear wave splitting to anisotropic parameters calculated by the normal-mode theory to demonstrate that the interference of SKS with other phases of similar arrival times, near-field effect, and multiple reflections in the crust lead to significant variations of SKS splitting with epicentral distance. The full-wave kernels not only widen the possibilities in the source-receiver geometry in making shear wave splitting measurements but also provide the capability for tomographic inversion to resolve vertical and lateral variations in the anisotropic structures.

Thickness of the Descending Philippine Sea Plate Estimated from Tomographic Images beneath the Kumano Basin, along the Nankai Trough, Southwestern Japan

NASA Astrophysics Data System (ADS)

Kamiya, S.; Suzuki, K.; Takahashi, N.

2015-12-01

The Philippine Sea plate subducts northwestward beneath the Japanese islands from the south. The average thickness of the overall Philippine Sea plate has been investigated in the oceanic area using surface wave analyses [e.g. Abe and Kanamori, 1970], suggesting a thin (30-40 km thick) plate. On the other hand, several studies have indicated a thicker Philippine Sea plate based on source mechanisms and seismicity in the eastern rim of the plate [Seno, 1987; Moriyama et al., 1989]. From tomographic images, Kamiya and Kobayashi [2007] pointed out that the subducting Philippine Sea slab has thickness variation with a stepwise offset east of Izu Peninsula. The eastern (the Kanto district) and western (north of Izu Peninsula and the Tokai district) regions have respective thicknesses of 60 and 25 km. In the Kumano basin, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) developed the Dense Oceanfloor Network System for Earthquakes and Tsunami (DONET) in order to monitor seismic activity [Kaneda et al., 2009; Kawaguchi et al., 2010]. DONET ocean-bottom stations are connected with an optical fiber cable, and data are transferred in real time to our laboratory at JAMSTEC. The present study obtains three-dimensional P-wave and S-wave seismic velocity models beneath the Kumano basin by employing an travel time tomography technique. We pick arrival times of P and S waves from the waveform data recorded by the DONET system during the period from January 2011 to December 2014. In order to improve the resolution in the deeper regions than the seismic area inside of the descending slab, we also pick arrival times from the seismic events occurred outside of this district. We use these picked arrival times adding to the JMA catalogue data in seismic tomography. From the obtained tomographic images, we find high velocity anomalies corresponding to the descending Philippine Sea slab. We also find low velocity anomalies under the high velocity slab clearly. There seems to be a sharp velocity contrast between the anomalies. We can estimate the thickness of the descending slab at about 30 km, which is almost consistent with the thickness beneath the Tokai district estimated by Kamiya and Kobayashi [2007] and comparable to the effective elastic thickness beneath the eastern part of the Shikoku basin estimated by Yoshioka and Ito [2001].

Infrasonic and seismic signals from the Myanmar earthquake of November 11,2012

NASA Astrophysics Data System (ADS)

Su, Wei; Zhang, Dongning; Li, Ke

2013-04-01

On November 11, 2012, at 01:12:38 UTC (09:12:38 Beijing Time), a strong earthquake (Mw=6.8) occurred in Myanmar. The epicenter (23.0˚N,95.9˚E,focal depth ~10 km) was near the town of Male, 52 km NNE of the city of Shwebo. The earthquake with a rupture length of 60-70 km resulted from right lateral movement on the Sagaing Fault related to collision between the Indo-Australian Plate and the Eurasian Plate. At a distance of 366 km from the epicenter, infrasonic and seismic signals were recorded by Tengchong seismo-acoustic array located in southwest of China for monitoring volcanic and earthquake activity, which consists of four MB2005 microbarometers with bandwidth 0.01-27Hz and four BBVS-60 seismometers with bandwidth 0.01667-50Hz arranged in a centered triangle with an aperture of about 1.8 km. PMCC provided by CEA/DASE applied to analyze infrasound data. Comparison of the infrasonic and seismic signals produced by this earthquake showed infrasonic signals with different arrival times and azimuths may be classified as local, epicentral and diffracted or secondary sourced infrasound, but seismic signals only include P, S and surface waves can produce local infrasound through ground-coupled air waves at the station. The PMCC results indicated that the infrasonic waves showed a consistent acoustic trace velocity of approximately 0.348 km/s from 09:30 to 09:36 (Beijing Time) and the azimuth of arrival changed with time from 227 to 217 degrees. There are mountain chains with altitude more than 1000 m in the east of the epicenter. Mountains shaking induced by earthquake acted as a speaker and radiated the infrasound that traveled to Tengchong seismo-acoustic array. It was worth noting that PMCC detected a group infrasound with trace velocity of approximately 0.339 km/s and arrival azimuth of 237 degree from 09:23:31 to 09:24 (Beijing Time). It may be inferred that the seismic surface wave induced by earthquake reach the mountains on the border between China Yunnan and Myanmar, then acted as a secondary sources and generated diffracted infrasound. This work is supported by the fundamental research and development project of the Institute of Geophysics,CEA(DQJB10B28).

The effect of S-wave arrival times on the accuracy of hypocenter estimation

USGS Publications Warehouse

Gomberg, J.S.; Shedlock, K.M.; Roecker, S.W.

1990-01-01

We have examined the theoretical basis behind some of the widely accepted "rules of thumb' for obtaining accurate hypocenter estimates that pertain to the use of S phases and illustrate, in a variety of ways, why and when these "rules' are applicable. Most methods used to determine earthquake hypocenters are based on iterative, linearized, least-squares algorithms. We examine the influence of S-phase arrival time data on such algorithms by using the program HYPOINVERSE with synthetic datasets. We conclude that a correctly timed S phase recorded within about 1.4 focal depth's distance from the epicenter can be a powerful constraint on focal depth. Furthermore, we demonstrate that even a single incorrectly timed S phase can result in depth estimates and associated measures of uncertainty that are significantly incorrect. -from Authors

Emergency response and field observation activities of geoscientists in California (USA) during the September 29, 2009, Samoa Tsunami

NASA Astrophysics Data System (ADS)

Wilson, Rick I.; Dengler, Lori A.; Goltz, James D.; Legg, Mark R.; Miller, Kevin M.; Ritchie, Andy; Whitmore, Paul M.

2011-07-01

State geoscientists (geologists, geophysicists, seismologists, and engineers) in California work closely with federal, state and local government emergency managers to help prepare coastal communities for potential impacts from a tsunami before, during, and after an event. For teletsunamis, as scientific information (forecast model wave heights, first-wave arrival times, etc.) from NOAA's West Coast and Alaska Tsunami Warning Center is made available, federal- and state-level emergency managers must help convey this information in a concise, comprehensible and timely manner to local officials who ultimately determine the appropriate response activities for their jurisdictions. During the September 29, 2009 Tsunami Advisory for California, government geoscientists assisted the California Emergency Management Agency by providing technical assistance during teleconference meetings with NOAA and other state and local emergency managers prior to the arrival of the tsunami. This technical assistance included background information on anticipated tidal conditions when the tsunami was set to arrive, wave height estimates from state-modeled scenarios for areas not covered by NOAA's forecast models, and clarifying which regions of the state were at greatest risk. Over the last year, state geoscientists have started to provide additional assistance: 1) working closely with NOAA to simplify their tsunami alert messaging and expand their forecast modeling coverage; 2) creating "playbooks" containing information from existing tsunami scenarios for local emergency managers to reference during an event; and, 3) developing a state-level information "clearinghouse" and pre-tsunami field response team to assist local officials as well as observe and report tsunami effects. Activities of geoscientists were expanded during the more recent Tsunami Advisory on February 27, 2010, including deploying a geologist from the California Geological Survey as a field observer who provided information back to emergency managers.

3D P-Wave Velocity Structure of the Crust and Relocation of Earthquakes in 21 the Lushan Source Area

NASA Astrophysics Data System (ADS)

Yu, X.; Wang, X.; Zhang, W.

2014-12-01

The double difference seismic tomography method is applied to the absolute first arrival P wave arrival times and high quality relative P arrival times of the Lushan seismic sequence to determine the detailed crustal 3D P wave velocity structure and the hypocenter parameters in the Lushan seismic area. The results show that the Lushan mainshock locates at 30.28 N, 103.98 E, with the depth of 16.38 km. The leading edge of aftershock in the northeast of mainshock present a spade with a steep dip angle, the aftershocks' extended length is about 12 km. In the southwest of the Lushan mainshock, the leading edge of aftershock in low velocity zone slope gently, the aftershocks' extended length is about 23 km. The P wave velocity structure of the Lushan seismic area shows obviously lateral heterogeneity. The P wave velocity anomalies represent close relationship with topographic relief and geological structure. In Baoxing area the complex rocks correspond obvious high-velocity anomalies extending down to 15 km depth，while the Cenozoic rocks are correlated with low-velocity anomalies. Our high-resolution tomographic model not only displays the general features contained in the previous models, but also reveals some new features. An obvious high-velocity anomaly is visible in Daxing area. The high-velocity anomalies beneath Baoxing and Daxing connect each other in 10 km depth, which makes the contrast between high and low velocity anomalies more sharp. Above 20 km depth the velocity structure in southwest and northeast segment of the mainshock shows a big difference: low-velocity anomalies are dominated the southwest segment, while high-velocity anomalies rule the northeast segment. The Lushan mainshock locates at the leading edge of a low-velocity anomaly surrounded by the Baoxing and Daxing high-velocity anomalies. The Lushan aftershocks in southwest are distributed in low-velocity anomalies or the transition belt: the footwall represents low-velocity anomalies, while the hanging wall shows high-velocity anomalies. The northeastern aftershocks are distributed at the boundary between high-velocity anomalies in Baoxing and Daxing area. The main seismogenic layer dips to northwest.

Prediction system of the 1-AU arrival times of CME-associated interplanetary shocks using three-dimensional simulations

NASA Astrophysics Data System (ADS)

den, Mitsue; Amo, Hiroyoshi; Sugihara, Kohta; Takei, Toshifumi; Ogawa, Tomoya; Tanaka, Takashi; Watari, Shinichi

We describe prediction system of the 1-AU arrival times of interplanetary shock waves associated with coromal mass ejections (CMEs). The system is based on modeling of the shock propagation using a three-dimensional adaptive mesh refinement (AMR) code. Once a CME is observed by LASCO/SOHO, firstly ambient solar wind is obtained by numerical simulation, which reproduces the solar wind parameters at that time observed by ACE spacecraft. Then we input the expansion speed and occurrence position data of that CME as initial condtions for an CME model, and 3D simulation of the CME and the shock propagation is perfomed until the shock wave passes the 1-AU. Input the parameters, execution of simulation and output of the result are available on Web, so a person who is not familiar with operation of computer or simulations or is not a researcher can use this system to predict the shock passage time. Simulated CME and shock evolution is visuallized at the same time with simulation and snap shots appear on the web automatically, so that user can follow the propagation. This system is expected to be useful for forecasters of space weather. We will describe the system and simulation model in detail.

Diffraction of a plane wave by a three-dimensional corner

NASA Technical Reports Server (NTRS)

Ting, L.; Kung, F.

1971-01-01

By the superposition of the conical solution for the diffraction of a plane pulse by a three dimensional corner, the solution for a general incident plane wave is constructed. A numerical program is presented for the computation of the pressure distribution on the surface due to an incident plane wave of any wave form and at any incident angle. Numerical examples are presented to show the pressure signature at several points on the surface due to incident wave with a front shock wave, two shock waves in succession, or a compression wave with same peak pressure. The examples show that when the distance of a point on the surface from the edges or the vertex is comparable to the distance for the front pressure raise to reach the maximum, the peak pressure at that point can be much less than that given by a regular reflection, because the diffracted wave front arrives at that point prior to the arrival of the peak incident wave.

The Contribution of Coseismic Displacements due to Splay Faults Into the Local Wavefield of the 1964 Alaska Tsunami

NASA Astrophysics Data System (ADS)

Suleimani, E.; Ruppert, N.; Fisher, M.; West, D.; Hansen, R.

2008-12-01

The Alaska Earthquake Information Center conducts tsunami inundation mapping for coastal communities in Alaska. For many locations in the Gulf of Alaska, the 1964 tsunami generated by the Mw9.2 Great Alaska earthquake may be the worst-case tsunami scenario. We use the 1964 tsunami observations to verify our numerical model of tsunami propagation and runup, therefore it is essential to use an adequate source function of the 1964 earthquake to reduce the level of uncertainty in the modeling results. It was shown that the 1964 co-seismic slip occurred both on the megathrust and crustal splay faults (Plafker, 1969). Plafker (2006) suggested that crustal faults were a major contributor to vertical displacements that generated local tsunami waves. Using eyewitness arrival times of the highest observed waves, he suggested that the initial tsunami wave was higher and closer to the shore, than if it was generated by slip on the megathrust. We conduct a numerical study of two different source functions of the 1964 tsunami to test whether the crustal splay faults had significant effects on local tsunami runup heights and arrival times. The first source function was developed by Johnson et al. (1996) through joint inversion of the far-field tsunami waveforms and geodetic data. The authors did not include crustal faults in the inversion, because the contribution of these faults to the far-field tsunami was negligible. The second is the new coseismic displacement model developed by Suito and Freymueller (2008, submitted). This model extends the Montague Island fault farther along the Kenai Peninsula coast and thus reduces slip on the megathrust in that region. We also use an improved geometry of the Patton Bay fault based on the deep crustal seismic reflection and earthquake data. We propagate tsunami waves generated by both source models across the Pacific Ocean and record wave amplitudes at the locations of the tide gages that recorded the 1964 tsunami. As expected, the two sources produce very similar waveforms in the far field that are also in good agreement with the tide gage records. In order to study the near-field tsunami effects, we will construct embedded telescoping bathymetry grids around tsunami generation area to calculate tsunami arrival times and sea surface heights for both source models of the 1964 earthquake, and use available observation data to verify the model results.

Measuring the speed of sound in a solid

NASA Astrophysics Data System (ADS)

Key, Tony; Smidrovskis, Robert; From, Milton

2000-02-01

The speed of sound in a solid is measured using an oscilloscope, a square-wave oscillator and a piezo-electric pick-up. A study of the relationship between the distance traveled and the time of arrival of the sound pulse allows a graphical determination of the speed of the pulse in the lucite rod.

Fault zone structure determined through the analysis of earthquake arrival times

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

Michelini, A.

1991-10-01

This thesis develops and applies a technique for the simultaneous determination of P and S wave velocity models and hypocenters from a set of arrival times. The velocity models are parameterized in terms of cubic B-splines basis functions which permit the retrieval of smooth models that can be used directly for generation of synthetic seismograms using the ray method. In addition, this type of smoothing limits the rise of instabilities related to the poor resolving power of the data. V{sub P}/V{sub S} ratios calculated from P and S models display generally instabilities related to the different ray-coverages of compressional andmore » shear waves. However, V{sub P}/V{sub S} ratios are important for correct identification of rock types and this study introduces a new methodology based on adding some coupling (i.e., proportionality) between P and S models which stabilizes the V{sub P}/V{sub S} models around some average preset value determined from the data. Tests of the technique with synthetic data show that this additional coupling regularizes effectively the resulting models.« less

Fault zone structure determined through the analysis of earthquake arrival times

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

Michelini, Alberto

1991-10-01

This thesis develops and applies a technique for the simultaneous determination of P and S wave velocity models and hypocenters from a set of arrival times. The velocity models are parameterized in terms of cubic B-splines basis functions which permit the retrieval of smooth models that can be used directly for generation of synthetic seismograms using the ray method. In addition, this type of smoothing limits the rise of instabilities related to the poor resolving power of the data. V P/V S ratios calculated from P and S models display generally instabilities related to the different ray-coverages of compressional andmore » shear waves. However, V P/V S ratios are important for correct identification of rock types and this study introduces a new methodology based on adding some coupling (i.e., proportionality) between P and S models which stabilizes the V P/V S models around some average preset value determined from the data. Tests of the technique with synthetic data show that this additional coupling regularizes effectively the resulting models.« less

The P and S wave velocity structure of the mantle beneath eastern Africa and the African superplume anomaly

NASA Astrophysics Data System (ADS)

Mulibo, Gabriel D.; Nyblade, Andrew A.

2013-08-01

P and S relative arrival time residuals from teleseismic earthquakes recorded on over 60 temporary AfricaArray broadband seismic stations deployed in Uganda, Tanzania, and Zambia between 2007 and 2011 have been inverted, together with relative arrival time residuals from earthquakes recorded by previous deployments, for a tomographic image of mantle wave speed variations extending to a depth of 1200 km beneath eastern Africa. The image shows a low-wave speed anomaly (LWA) well developed at shallow depths (100-200 km) beneath the Eastern and Western branches of the Cenozoic East African rift system and northwestern Zambia, and a fast wave speed anomaly at depths ≤ 350 km beneath the central and northern parts of the East African Plateau and the eastern and central parts of Zambia. At depths ≥350 km the LWA is most prominent under the central and southern parts of the East African Plateau and dips to the southwest beneath northern Zambia, extending to a depth of at least 900 km. The amplitude of the LWA is consistent with a ˜150-300 K thermal perturbation, and its depth extent indicates that the African superplume, originally identified as a lower mantle anomaly, is likely a whole mantle structure. A superplume extending from the core-mantle boundary to the surface implies an origin for the Cenozoic extension, volcanism, and plateau uplift in eastern Africa rooted in the dynamics of the lower mantle.

Re-evaluation of Apollo 17 Lunar Seismic Profiling Experiment data

NASA Astrophysics Data System (ADS)

Heffels, Alexandra; Knapmeyer, Martin; Oberst, Jürgen; Haase, Isabel

2017-01-01

We re-analyzed Apollo 17 Lunar Seismic Profiling Experiment (LSPE) data to improve our knowledge of the subsurface structure of this landing site. We use new geometrically accurate 3-D positions of the seismic equipment deployed by the astronauts, which were previously derived using high-resolution images by Lunar Reconnaissance Orbiter (LRO) in combination with Apollo astronaut photography. These include coordinates of six Explosive Packages (EPs) and four geophone stations. Re-identified P-wave arrival times are used to calculate two- and three-layer seismic velocity models. A strong increase of seismic velocity with depth can be confirmed, in particular, we suggest a more drastic increase than previously thought. For the three-layer model the P-wave velocities were calculated to 285, 580, and 1825 m/s for the uppermost, second, and third layer, respectively, with the boundaries between the layers being at 96 and 773 m depth. When compared with results obtained with previously published coordinates, we find (1) a slightly higher velocity (+4%) for the uppermost layer, and (2) lower P-wave velocities for the second and third layers, representing a decrease of 34% and 12% for second and third layer, respectively. Using P-wave arrival time readings of previous studies, we confirm that velocities increase when changing over from old to new coordinates. In the three-layer case, this means using new coordinates alone leads to thinned layers, velocities rise slightly for the uppermost layer and decrease significantly for the layers below.

A novel time of arrival estimation algorithm using an energy detector receiver in MMW systems

NASA Astrophysics Data System (ADS)

Liang, Xiaolin; Zhang, Hao; Lyu, Tingting; Xiao, Han; Gulliver, T. Aaron

2017-12-01

This paper presents a new time of arrival (TOA) estimation technique using an improved energy detection (ED) receiver based on the empirical mode decomposition (EMD) in an impulse radio (IR) 60 GHz millimeter wave (MMW) system. A threshold is employed via analyzing the characteristics of the received energy values with an extreme learning machine (ELM). The effect of the channel and integration period on the TOA estimation is evaluated. Several well-known ED-based TOA algorithms are used to compare with the proposed technique. It is shown that this ELM-based technique has lower TOA estimation error compared to other approaches and provides robust performance with the IEEE 802.15.3c channel models.

Teleseismic and regional data analysis for estimating depth, mechanism and rupture process of the 3 April 2017 MW 6.5 Botswana earthquake and its aftershock (5 April 2017, MW 4.5)

NASA Astrophysics Data System (ADS)

Letort, J.; Guilhem Trilla, A.; Ford, S. R.; Sèbe, O.; Causse, M.; Cotton, F.; Campillo, M.; Letort, G.

2017-12-01

We constrain the source, depth, and rupture process of the Botswana earthquake of April 3, 2017, as well as its largest aftershock (5 April 2017, Mw 4.5). This earthquake is the largest recorded event (Mw 6.5) in the East African rift system since 1970, making one important case study to better understand source processes in stable continental regions. For the two events an automatic cepstrum analysis (Letort et al., 2015) is first applied on respectively 215 and 219 teleseismic records, in order to detect depth phase arrivals (pP, sP) in the P-coda. Coherent detections of depth phases for different azimuths allow us to estimate the hypocentral depths respectively at 28 and 23 km, suggesting that the events are located in the lower crust. A same cepstrum analysis is conducted on five other earthquakes with mb>4 in this area (from 2002 to 2017), and confirms a deep crustal seismicity cluster (around 20-30 km). The source mechanisms are then characterized using a joint inversion method by fitting both regional long-period surface-waves and teleseismic high-frequency body-waves. Combining regional and teleseismic data (as well as systematic comparisons between theoretical and observed regional surface-waves dispersion curves prior to the inversion) allows us to decrease epistemic uncertainties due to lack of regional data and poor knowledge about the local velocity structure. Focal mechanisms are both constrained as normal faulting with a northwest trending, and hypocentral depths are confirmed at 28 and 24 km. Finally, in order to study the mainshock rupture process, we originally apply a kymograph analysis method (an image processing method, commonly used in the field of cell biology for identifying motions of molecular motors, e.g. Mangeol et al., 2016). Here, the kymograph allows us to better identify high-frequency teleseismic P-arrivals inside the P-coda by tracking both reflected depth phase and direct P-wave arrivals radiated from secondary sources during the faulting process. Secondary P-arrivals are thus identified with a significant azimuthal variation of their arrival times (until 4s), allowing the localization of the source that generated these secondary waves. This analysis shows that the mainshock is probably a mix of at least two events, the second being 20-30 km further northwest along the fault.

Joint Inversion of Body-Wave Arrival Times and Surface-Wave Dispersion Data for Three-Dimensional Seismic Velocity Structure Around SAFOD

NASA Astrophysics Data System (ADS)

Zhang, H.; Thurber, C. H.; Maceira, M.; Roux, P.

2013-12-01

The crust around the San Andreas Fault Observatory at depth (SAFOD) has been the subject of many geophysical studies aimed at characterizing in detail the fault zone structure and elucidating the lithologies and physical properties of the surrounding rocks. Seismic methods in particular have revealed the complex two-dimensional (2D) and three-dimensional (3D) structure of the crustal volume around SAFOD and the strong velocity reduction in the fault damage zone. In this study we conduct a joint inversion using body-wave arrival times and surface-wave dispersion data to image the P-and S-wave velocity structure of the upper crust surrounding SAFOD. The two data types have complementary strengths - the body-wave data have good resolution at depth, albeit only where there are crossing rays between sources and receivers, whereas the surface waves have very good near-surface resolution and are not dependent on the earthquake source distribution because they are derived from ambient noise. The body-wave data are from local earthquakes and explosions, comprising the dataset analyzed by Zhang et al. (2009). The surface-wave data are for Love waves from ambient noise correlations, and are from Roux et al. (2011). The joint inversion code is based on the regional-scale version of the double-difference (DD) tomography algorithm tomoDD. The surface-wave inversion code that is integrated into the joint inversion algorithm is from Maceira and Ammon (2009). The propagator matrix solver in the algorithm DISPER80 (Saito, 1988) is used for the forward calculation of dispersion curves from layered velocity models. We examined how the structural models vary as we vary the relative weighting of the fit to the two data sets and in comparison to the previous separate inversion results. The joint inversion with the 'optimal' weighting shows more clearly the U-shaped local structure from the Buzzard Canyon Fault on the west side of SAF to the Gold Hill Fault on the east side.

Joint Inversion of Body-Wave Arrival Times and Surface-Wave Dispersion Data in the Wavelet Domain Constrained by Sparsity Regularization

NASA Astrophysics Data System (ADS)

Zhang, H.; Fang, H.; Yao, H.; Maceira, M.; van der Hilst, R. D.

2014-12-01

Recently, Zhang et al. (2014, Pure and Appiled Geophysics) have developed a joint inversion code incorporating body-wave arrival times and surface-wave dispersion data. The joint inversion code was based on the regional-scale version of the double-difference tomography algorithm tomoDD. The surface-wave inversion part uses the propagator matrix solver in the algorithm DISPER80 (Saito, 1988) for forward calculation of dispersion curves from layered velocity models and the related sensitivities. The application of the joint inversion code to the SAFOD site in central California shows that the fault structure is better imaged in the new model, which is able to fit both the body-wave and surface-wave observations adequately. Here we present a new joint inversion method that solves the model in the wavelet domain constrained by sparsity regularization. Compared to the previous method, it has the following advantages: (1) The method is both data- and model-adaptive. For the velocity model, it can be represented by different wavelet coefficients at different scales, which are generally sparse. By constraining the model wavelet coefficients to be sparse, the inversion in the wavelet domain can inherently adapt to the data distribution so that the model has higher spatial resolution in the good data coverage zone. Fang and Zhang (2014, Geophysical Journal International) have showed the superior performance of the wavelet-based double-difference seismic tomography method compared to the conventional method. (2) For the surface wave inversion, the joint inversion code takes advantage of the recent development of direct inversion of surface wave dispersion data for 3-D variations of shear wave velocity without the intermediate step of phase or group velocity maps (Fang et al., 2014, Geophysical Journal International). A fast marching method is used to compute, at each period, surface wave traveltimes and ray paths between sources and receivers. We will test the new joint inversion code at the SAFOD site to compare its performance over the previous code. We will also select another fault zone such as the San Jacinto Fault Zone to better image its structure.

Lamb wave detection of limpet mines on ship hulls.

PubMed

Bingham, Jill; Hinders, Mark; Friedman, Adam

2009-12-01

This paper describes the use of ultrasonic guided waves for identifying the mass loading due to underwater limpet mines on ship hulls. The Dynamic Wavelet Fingerprint Technique (DFWT) is used to render the guided wave mode information in two-dimensional binary images because the waveform features of interest are too subtle to identify in time domain. The use of wavelets allows both time and scale features from the original signals to be retained, and image processing can be used to automatically extract features that correspond to the arrival times of the guided wave modes. For further understanding of how the guided wave modes propagate through the real structures, a parallel processing, 3D elastic wave simulation is developed using the finite integration technique (EFIT). This full field, technique models situations that are too complex for analytical solutions, such as built up 3D structures. The simulations have produced informative visualizations of the guided wave modes in the structures as well as mimicking directly the output from sensors placed in the simulation space for direct comparison to experiments. Results from both drydock and in-water experiments with dummy mines are also shown.

Short-Term TEC Perturbations Associated With Planetary Waves Occurrence in the Ionosphere

NASA Astrophysics Data System (ADS)

Shagimuratov, I. I.; Karpov, I.; Krankowski, A.

2008-12-01

Analysis of TEC response to storm showed short-term perturbations which were observed after initial phase of geomagnetic storms. The perturbations demonstrated very well expressed latitudinal structure and were recognized on diurnal variations as surges of TEC enhancement of TEC. Ordinary such storm-time positive effect was associated with TAD. Duration of the perturbations was about 2-4 hours and their amplitude increased toward low latitudes. Such TEC perturbations have the longitudinal dependence. It is important that time location of surges have week dependence on latitude. The observed structure appeared to arrive from high latitudes, but at middle latitudes it was represented as a standing wave. It is assumed that such TEC perturbations can be produced due to superposition of the eastward and westward propagating planetary Poincare waves. The periods of these waves are usually several hours. Poincare waves can be excited at the atmosphere in storm time. At middle latitudes their superposition is as standing wave that forms observing TEC perturbations. In the report, the possibilities of application Poincare waves to the ionosphere dynamics studies are discussed and an explanation of the observed ionospheric effects is given.

Micro-crack detection in CFRP laminates using coda wave NDE

NASA Astrophysics Data System (ADS)

Dayal, Vinay; Barnard, Dan; Livings, Richard

2018-04-01

Coda Waves or diffuse field has been touted to be an NDE method that does not require the damage to be in the path of the ultrasound. The object is insonified with ultrasound and instead of catching the first or second arrival, the waves are allowed to bounce multiple times. This aspect is very important in structural health monitoring (SHM) where the potential damage development location is unknown. Researchers have used Coda waves in the interrogation of seismic damage and metallic materials. In this work we have applied the technique to composite material, and present the results herein. The coda wave and acoustic emission signals are recorded simultaneously and corroborated. Development of small incipient damage in the form of micro-crack and their detection is the objective of this work.

Investigation into the bistatic evolution of the acoustic scattering from a cylindrical shell using time-frequency analysis

NASA Astrophysics Data System (ADS)

Agounad, Said; Aassif, El Houcein; Khandouch, Younes; Maze, Gérard; Décultot, Dominique

2018-01-01

The time and frequency analyses of the acoustic scattering by an elastic cylindrical shell in bistatic method show that the arrival times of the echoes and the resonance frequencies of the elastic waves propagating in and around the cylindrical shell are a function of the bistatic angle, β, between the emitter and receiver transducers. The aim of this work is to explain the observed results in time and frequency domains using time-frequency analysis and graphical interpretations. The performance of four widely used time-frequency representations, the Smoothed Pseudo Wigner-Ville (SPWV), the Spectrogram (SP), the reassignment SPWV, and the reassignment SP, are studied. The investigation into the evolution of the time-frequency plane as a function of the bistatic angle β shows that there are the waves propagating in counter-clockwise direction (labeled wave+) and the waves which propagate in clockwise direction (labeled waves-). In this paper the A, S0, and A1 circumferential waves are investigated. The graphical interpretations are used to explain the formation mechanism of these waves and the acoustic scattering in monostatic and bistatic configurations. The delay between the echoes of the waves+ and those of the waves- is expressed in the case of the circumnavigating wave (Scholte-Stoneley wave). This study shows that the observed waves at β = 0 ° and β = 18 0 ° are the result of the constructive interferences between the waves+ and the waves-. A comparative study of the physical properties (group velocity dispersion and cut-off frequency) of the waves+, the waves- and the waves observed in monostatic configuration is conducted. Furthermore, it is shown that the ability of the time-frequency representation to highlight the waves+ and the waves- is very useful, for example, for the detection and the localization of defaults, the classification purposes, etc.

Multichannel analysis of surface waves

USGS Publications Warehouse

Park, C.B.; Miller, R.D.; Xia, J.

1999-01-01

The frequency-dependent properties of Rayleigh-type surface waves can be utilized for imaging and characterizing the shallow subsurface. Most surface-wave analysis relies on the accurate calculation of phase velocities for the horizontally traveling fundamental-mode Rayleigh wave acquired by stepping out a pair of receivers at intervals based on calculated ground roll wavelengths. Interference by coherent source-generated noise inhibits the reliability of shear-wave velocities determined through inversion of the whole wave field. Among these nonplanar, nonfundamental-mode Rayleigh waves (noise) are body waves, scattered and nonsource-generated surface waves, and higher-mode surface waves. The degree to which each of these types of noise contaminates the dispersion curve and, ultimately, the inverted shear-wave velocity profile is dependent on frequency as well as distance from the source. Multichannel recording permits effective identification and isolation of noise according to distinctive trace-to-trace coherency in arrival time and amplitude. An added advantage is the speed and redundancy of the measurement process. Decomposition of a multichannel record into a time variable-frequency format, similar to an uncorrelated Vibroseis record, permits analysis and display of each frequency component in a unique and continuous format. Coherent noise contamination can then be examined and its effects appraised in both frequency and offset space. Separation of frequency components permits real-time maximization of the S/N ratio during acquisition and subsequent processing steps. Linear separation of each ground roll frequency component allows calculation of phase velocities by simply measuring the linear slope of each frequency component. Breaks in coherent surface-wave arrivals, observable on the decomposed record, can be compensated for during acquisition and processing. Multichannel recording permits single-measurement surveying of a broad depth range, high levels of redundancy with a single field configuration, and the ability to adjust the offset, effectively reducing random or nonlinear noise introduced during recording. A multichannel shot gather decomposed into a swept-frequency record allows the fast generation of an accurate dispersion curve. The accuracy of dispersion curves determined using this method is proven through field comparisons of the inverted shear-wave velocity (??(s)) profile with a downhole ??(s) profile.Multichannel recording is an efficient method of acquiring ground roll. By displaying the obtained information in a swept-frequency format, different frequency components of Rayleigh waves can be identified by distinctive and simple coherency. In turn, a seismic surface-wave method is derived that provides a useful noninvasive tool, where information about elastic properties of near-surface materials can be effectively obtained.

Mapping the crustal thickness in Shillong-Mikir Hills Plateau and its adjoining region of northeastern India using Moho reflected waves

NASA Astrophysics Data System (ADS)

Bora, Dipok K.; Baruah, Saurabh

2012-04-01

In this study we have tried to detect and collect later phases associated with Moho discontinuity and used them to study the lateral variations of the crustal thickness in Shillong-Mikir Hills Plateau and its adjoining region of northeastern India. We use the inversion algorithm by Nakajima et al. (Nakajima, J., Matsuzawa, T., Hasegawa, A. 2002. Moho depth variation in the central part of northeastern Japan estimated from reflected and converted waves. Physics of the Earth and Planetary Interiors, 130, 31-47), having epicentral distance ranging from 60 km to 150 km. Taking the advantage of high quality broadband data now available in northeast India, we have detected 1607 Moho reflected phases (PmP and SmS) from 300 numbers of shallow earthquake events (depth ⩽ 25 km) in Shillong-Mikir Hills Plateau and its adjoining region. Notably for PmP phase, this could be identified within 0.5-2.3 s after the first P-arrival. In case of SmS phase, the arrival times are observed within 1.0-4.2 s after the first S-arrival. We estimated the crustal thickness in the study area using travel time difference between the later phases (PmP and SmS) and the first P and S arrivals. The results shows that the Moho is thinner beneath the Shillong Plateau about 35-38 km and is the deepest beneath the Brahmaputra valley to the north about 39-41 km, deeper by 4-5 km compared to the Shillong Plateau with simultaneous observation of thinnest crust (˜33 km) in the western part of the Shillong Plateau in the Garo Hills region.

Short Text Messages (SMS) as an Additional Tool for Notifying Medical Staff in Case of a Hospital Mass Casualty Incident.

PubMed

Timler, Dariusz; Bogusiak, Katarzyna; Kasielska-Trojan, Anna; Neskoromna-Jędrzejczak, Aneta; Gałązkowski, Robert; Szarpak, Łukasz

2016-02-01

The aim of the study was to verify the effectiveness of short text messages (short message service, or SMS) as an additional notification tool in case of fire or a mass casualty incident in a hospital. A total of 2242 SMS text messages were sent to 59 hospital workers divided into 3 groups (n=21, n=19, n=19). Messages were sent from a Samsung GT-S8500 Wave cell phone and Orange Poland was chosen as the telecommunication provider. During a 3-month trial period, messages were sent between 3:35 PM and midnight with no regular pattern. Employees were asked to respond by telling how much time it would take them to reach the hospital in case of a mass casualty incident. The mean reaction time (SMS reply) was 36.41 minutes. The mean declared time of arrival to the hospital was 100.5 minutes. After excluding 10% of extreme values for declared arrival time, the mean arrival time was estimated as 38.35 minutes. Short text messages (SMS) can be considered an additional tool for notifying medical staff in case of a mass casualty incident.

One-dimensional velocity model of the Middle Kura Depresion from local earthquakes data of Azerbaijan

NASA Astrophysics Data System (ADS)

Yetirmishli, G. C.; Kazimova, S. E.; Kazimov, I. E.

2011-09-01

We present the method for determining the velocity model of the Earth's crust and the parameters of earthquakes in the Middle Kura Depression from the data of network telemetry in Azerbaijan. Application of this method allowed us to recalculate the main parameters of the hypocenters of the earthquake, to compute the corrections to the arrival times of P and S waves at the observation station, and to significantly improve the accuracy in determining the coordinates of the earthquakes. The model was constructed using the VELEST program, which calculates one-dimensional minimal velocity models from the travel times of seismic waves.

The shallow elastic structure of the lunar crust: New insights from seismic wavefield gradient analysis

NASA Astrophysics Data System (ADS)

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

2016-10-01

Enigmatic lunar seismograms recorded during the Apollo 17 mission in 1972 have so far precluded the identification of shear-wave arrivals and hence the construction of a comprehensive elastic model of the shallow lunar subsurface. Here, for the first time, we extract shear-wave information from the Apollo active seismic data using a novel waveform analysis technique based on spatial seismic wavefield gradients. The star-like recording geometry of the active seismic experiment lends itself surprisingly well to compute spatial wavefield gradients and rotational ground motion as a function of time. These observables, which are new to seismic exploration in general, allowed us to identify shear waves in the complex lunar seismograms, and to derive a new model of seismic compressional and shear-wave velocities in the shallow lunar crust, critical to understand its lithology and constitution, and its impact on other geophysical investigations of the Moon's deep interior.

Multichannel analysis of surface-waves and integration of downhole acoustic televiewer imaging, ultrasonic Vs and Vp, and vertical seismic profiling in an NEHRP-standard classification, South of Concordia, Kansas, USA

NASA Astrophysics Data System (ADS)

Raef, Abdelmoneam; Gad, Sabreen; Tucker-Kulesza, Stacey

2015-10-01

Seismic site characteristics, as pertaining to earthquake hazard reduction, are a function of the subsurface elastic moduli and the geologic structures. This study explores how multiscale (surface, downhole, and laboratory) datasets can be utilized to improve "constrained" average Vs30 (shear-wave velocity to a 30-meter depth). We integrate borehole, surface and laboratory measurements for a seismic site classification based on the standards of the National Earthquake Hazard Reduction Program (NEHRP). The seismic shear-wave velocity (Vs30) was derived from a geophysical inversion workflow that utilized multichannel analysis of surface-waves (MASW) and downhole acoustic televiewer imaging (DATI). P-wave and S-wave velocities, based on laboratory measurements of arrival times of ultrasonic-frequency signals, supported the workflow by enabling us to calculate Poisson's ratio, which was incorporated in building an initial model for the geophysical inversion of MASW. Extraction of core samples from two boreholes provided lithology and thickness calibration of the amplitudes of the acoustic televiewer imaging for each layer. The MASW inversion, for calculating Vs sections, was constrained with both ultrasonic laboratory measurements (from first arrivals of Vs and Vp waveforms at simulated in situ overburden stress conditions) and the downhole acoustic televiewer (DATV) amplitude logs. The Vs30 calculations enabled categorizing the studied site as NEHRP-class "C" - very dense soil and soft rock. Unlike shallow fractured carbonates in the studied area, S-wave and P-wave velocities at ultrasonic frequency for the deeper intact shale core-samples from two boreholes were in better agreement with the corresponding velocities from both a zero-offset vertical seismic profiling (VSP) and inversion of Rayleigh-wave velocity dispersion curves.

Auto correlation analysis of coda waves from local earthquakes for detecting temporal changes in shallow subsurface structures - The 2011 Tohoku-Oki, Japan, earthquake -

NASA Astrophysics Data System (ADS)

Nakahara, H.

2013-12-01

For monitoring temporal changes in subsurface structures, I propose to use auto correlation functions of coda waves from local earthquakes recorded at surface receivers, which probably contain more body waves than surface waves. Because the use of coda waves requires earthquakes, time resolution for monitoring decreases. But at regions with high seismicity, it may be possible to monitor subsurface structures in sufficient time resolutions. Studying the 2011 Tohoku-Oki (Mw 9.0), Japan, earthquake for which velocity changes have been already reported by previous studies, I try to validate the method. KiK-net stations in northern Honshu are used in the analysis. For each moderate earthquake, normalized auto correlation functions of surface records are stacked with respect to time windows in S-wave coda. Aligning the stacked normalized auto correlation functions with time, I search for changes in arrival times of phases. The phases at lag times of less than 1s are studied because changes at shallow depths are focused. Based on the stretching method, temporal variations in the arrival times are measured at the stations. Clear phase delays are found to be associated with the mainshock and to gradually recover with time. Amounts of the phase delays are in the order of 10% on average with the maximum of about 50% at some stations. For validation, the deconvolution analysis using surface and subsurface records at the same stations are conducted. The results show that the phase delays from the deconvolution analysis are slightly smaller than those from the auto correlation analysis, which implies that the phases on the auto correlations are caused by larger velocity changes at shallower depths. The auto correlation analysis seems to have an accuracy of about several percents, which is much larger than methods using earthquake doublets and borehole array data. So this analysis might be applicable to detect larger changes. In spite of these disadvantages, this analysis is still attractive because it can be applied to many records on the surface in regions where no boreholes are available. Acknowledgements: Seismograms recorded by KiK-net managed by National Research Institute for Earth Science and Disaster Prevention (NIED) were used in this study. This study was partially supported by JST J-RAPID program and JSPS KAKENHI Grant Numbers 24540449 and 23540449.

Constraints for the subsurface structure at the Abydos site on 67P/Churyumov-Gerasimenko resulting from CASSE listening to the MUPUS insertion phase

NASA Astrophysics Data System (ADS)

Knapmeyer, M.; Fischer, H. H.; Joerg, K.; Seidensticker, K. J.

2016-12-01

During the more than 3 hours of the MUPUS PEN insertion phase at Abydos, the Comet Acoustic Surface Sounding Experiment (CASSE), part of SESAME, recorded hammer strokes of MUPUS with all three accelerometers, which are housed in Philae's feet. Stroke times recorded in the MUPUS housekeeping data, the identification of two adjacent strokes in a single recording, and laboratory experiments concerning the properties of sound transmission through Philae's legs and feet foster the identification of the recorded signals as hammer strokes, and as elastic waves transmitted through the comet. A hammer stroke exerted on a surface dominantly excites surface waves of the Rayleigh type. By comparison of arrival times at the individual feet, we estimate the propagation velocity of these Rayleigh waves to be at least 80 m/s. With the bulk density of 533 ± 6 kg/m3 as derived from tracking Rosetta (Pätzold et al., Nature, vol. 530, 2016), this velocity translates into a shear modulus of the comet material of at least 3.2 MPa. Shear modulus scales with velocity squared, so when taking into account the formal uncertainties arising from the arrival time inversion, the shear modulus may easily be as large as 10 MPa. This is still low compared to solid rock or monocrystalline ice, but is compatible with highly porous materials. The recorded signals are only weakly dispersive: Energy at frequencies below approx. 200 Hz arrives slightly later than at higher frequencies. This indicates the presence of a surface layer, to which the above propagation velocity and shear modulus apply, on top of a material with an even lower propagation velocity and shear modulus. The boundary between the two materials is likely more than 20 cm below the surface. We conclude that the results of CASSE listening to MUPUS support the hypothesis of surficial sintering at least for the Abydos site on 67P/Churyumov-Gerasimenko.

The U.S. East Coast Meteotsunami of June 13, 2013

NASA Astrophysics Data System (ADS)

Knight, W. R.; Whitmore, P.; Kim, Y.; Wang, D.; Becker, N. C.; Weinstein, S.; Walker, K.

2013-12-01

NOAA's two Tsunami Warning Centers (TWCs) provide advance notification to coastal communities concerning tsunami hazards. While the focus is primarily on seismic sources, the U.S. East Coast event of June 13, 2013 indicates the importance of understanding and forecasting atmospherically-driven tsunamis, or meteotsunamis, as well. Here we describe an approach which explains the generation of this event by atmospheric processes, and suggests that the causative forces can be monitored and used to forecast meteotsunami occurrence. The U.S. East Coast tsunami of June 13, 2013 was well recorded at tide gauges from North Carolina to Massachusetts as well as at Bermuda and Puerto Rico. It also triggered DART 44402, just east of the Atlantic shelf break at 39.4N. As there was no seismic energy release associated with the tsunami and an eastward propagating major weather system crossed the Atlantic coast just before the tsunami, the focus turned to atmospheric forcing. Tsunami forecast models used at the two U.S. TWCs were modified to introduce moving atmospheric pressure distributions as sources. In a simple case, a north-south oriented line air pressure jump of width 50 km and pressure of 4 mb at sea level was moved eastward at 20 m/s. The speed matched both the storm speed at the coast and the long wave speed for 40 m deep water, thus allowing for resonant coupling of atmosphere to ocean in the shelf region (Proudman Resonance). Considering the simplicity of the source, a reasonable comparison between the modeled and observed tsunami was obtained with regards to arrival time and height. The proposed source also offers an explanation of the later wave arrivals at US tide gauges. These typically lagged the arrival at Bermuda - a location much further east. This pattern can be explained within the context of Proudman resonance if the waves arriving at coastal stations originated at the shelf break as reflected waves. Model animations of wave dynamics corroborate this phenomenon. The contribution of edge waves generated as the system moves over the coast is also examined. Remaining questions include the importance of shelf parameters in setting the wave fetch and the 'Q' of Proudman resonance along the Atlantic coastline. In other words, are some stretches of shelf more conducive to tsunami formation than others? Wind stress was disregarded in the initial modeling work leaving its possible importance as another unanswered question. Operational questions include how to detect likely meteotsunami conditions with real-time meteorological measurements, and what form alerts should take. The minimum necessary temporal resolution of the pressure sensors along with their density and siting needs to be determined. Because details of the source, such as direction and speed of propagation, will likely subject unique sections of coastline to tsunami attack, the detailed analysis of data from sensor arrays to be used in forecasting will be important.

Inferring atmospheric weather conditions in volcanic environments using infrasound

NASA Astrophysics Data System (ADS)

Ortiz, H. D.; Johnson, J. B.; Ruiz, M. C.

2015-12-01

We use infrasound produced by Tungurahua Volcano (Ecuador) to infer local time-varying atmospheric conditions, which can be used to improve gas flux measurements and tephra dispersal modeling. Physical properties of the atmosphere, including wind and temperature (which controls adiabatic sound speed), can be quantified by studying the travel times of acoustic waves produced during volcanic activity. The travel times between Tungurahua's vent and five infrasound stations located in a network configuration over an area of 90 km2 were used in this study. We are able to quantify the arrival time differences of acoustic waves for ten unique station pairs and use this information to model the average speed of sound between source and receiver. To identify what parameters best fit the observed arrival times, we perform a grid search for a homogeneous two-dimensional wind velocity as well as for air temperature. Due to travel time dependence on the specific path taken by waves, we account for topography using a 5 meter resolution digital elevation model of Tungurahua. To investigate the time-varying atmospheric structure we use data recorded at Tungurahua volcano, during a strombolian eruptive phase in August 2012, however the methodology can be applied to continuous network infrasound data collected since July 2006 as part of the Japanese-Ecuadorian Cooperation Project: "Enhancement of the Volcano Monitoring Capacity in Ecuador". We propose that the computation of wind velocities will help to improve gas flux measurements that are based on remote sensing techniques like Differential Optical Absorption Spectroscopy (DOAS), resulting in better estimates of sulfur fluxes that can then be related to magma fluxing into the volcanic system. Further, wind field quantification close to the volcano can improve numerical models that are used to forecast tephra deposits, thereby helping to mitigate their effect on inhabitants, infrastructure, livestock, and crops.

Modelling guided waves in the Alaskan-Aleutian subduction zone

NASA Astrophysics Data System (ADS)

Coulson, Sophie; Garth, Thomas; Reitbrock, Andreas

2016-04-01

Subduction zone guided wave arrivals from intermediate depth earthquakes (70-300 km depth) have a huge potential to tell us about the velocity structure of the subducting oceanic crust as it dehydrates at these depths. We see guided waves as the oceanic crust has a slower seismic velocity than the surrounding material, and so high frequency energy is retained and delayed in the crustal material. Lower frequency energy is not retained in this crustal waveguide and so travels at faster velocities of the surrounding material. This gives a unique observation at the surface with low frequency energy arriving before the higher frequencies. We constrain this guided wave dispersion by comparing the waveforms recorded in real subduction zones with simulated waveforms, produced using finite difference full waveform modelling techniques. This method has been used to show that hydrated minerals in the oceanic crust persist to much greater depths than accepted thermal petrological subduction zone models would suggest in Northern Japan (Garth & Rietbrock, 2014a), and South America (Garth & Rietbrock, in prep). These observations also suggest that the subducting oceanic mantle may be highly hydrated at intermediate depth by dipping normal faults (Garth & Rietbrock 2014b). We use this guided wave analysis technique to constrain the velocity structure of the down going ~45 Ma Pacific plate beneath Alaska. Dispersion analysis is primarily carried out on guided wave arrivals recorded on the Alaskan regional seismic network. Earthquake locations from global earthquake catalogues (ISC and PDE) and regional earthquake locations from the AEIC (Alaskan Earthquake Information Centre) catalogue are used to constrain the slab geometry and to identify potentially dispersive events. Dispersed arrivals are seen at stations close to the trench, with high frequency (>2 Hz) arrivals delayed by 2 - 4 seconds. This dispersion is analysed to constrain the velocity and width of the proposed waveguide. The velocity structure of this relatively young subducting plate is compared to the velocity structure resolved in the older oceanic lithosphere subducted beneath Northern Japan. We also use guided wave observations to investigate the thickness and low velocity structure of the subducting Yakutat terrain. Additionally we discuss the dependence of the inferred slab geometry on the earthquake catalogues that are used.

Parameters of Higuchi's method to characterize primary waves in some seismograms from the Mexican subduction zone

NASA Astrophysics Data System (ADS)

Gálvez-Coyt, Gonzalo; Muñoz-Diosdado, Alejandro; Peralta, José; Balderas-López, José; Angulo-Brown, Fernando

2012-06-01

Higuchi's method is a procedure that, if applied appropriately, can determine in a reliable way the fractal dimension D of time series; this fractal dimension permits to characterize the degree of correlation of the series. However, when analyzing some time series with Higuchi's method, there are oscillations at the right-hand side of the graph, which can cause a mistaken determination of the fractal dimension. In this work, an appropriate explanation is given to this type of behaviour. Using the seismogram as a time series and the properties of the P and S waves, it is possible to use the properties of Higuchi's method to previously detect the arrival of the earthquake shacking stage, some seconds in advance, approximately 30-35 s in the case of Mexico City. Thus, we propose the Higuchi's method to characterize and detect the P waves in order to estimate the strength of the forthcoming S waves.

Regional variations in seismic boundaries

NASA Astrophysics Data System (ADS)

Shumlyanska, Ludmila

2010-05-01

Dividing of the Earth into zones in the frame one-dimensional velocity model was proposed Jeffreys and Gutenberg is the first half of XX century. They recovered the following zones: A - the crust; B - zone in the depth interval 33-413 km, C - zone 413-984 km, D - zone 984-2898 km, E - 2898-4982 km, F - 4982-5121 km, G - 5121-6371 km (centre of the Earth). These zones differ in their seismic properties. Later, zone D was divided to the areas D' (984-2700 km) and D" (2700-2900 km). At present, this scheme is significantly modified and only the layer D" is in wide use. The more seismological studies are carried out, the more seismic boundaries appear. Boundaries at 410, 520, 670, and 2900 km, at which increase in the velocity of the seismic waves is particularly noticeable are considered as having global significance. Moreover, there are indications of the existence of geophysical boundaries at 800, 1200-1300, 1700, 1900-2000 km. Using 3D P-velocity model of the mantle based on Taylor approximation method for solving of the inverse kinematics multi-dimensional seismic task we have obtained seismic boundaries for the area covering 20-55° E × 40-55° N. Data on the time of first arrivals of P waves from earthquakes and nuclear explosions recorded at ISC stations during 1964-2002 were used as input to construct a 3-D model. The model has two a priori limits: 1) the velocity is a continuous function of spatial coordinates, 2) the function v(r)/r where r is a radius in the spherical coordinate system r, φ, λ decreases with depth. The first limitation is forced since velocity leaps can not be sustainably restored from the times of first arrival; the second one follows from the nature of the observed data. Results presented as horizontal sections of the actual velocity every 25 km in the depth interval 850-2850 km, and as the longitudinal and latitudinal sections of the discrepancy on the 1-D reference model, obtained as a result of solving of the inversion task at 1° in the same depth interval [1, 2]. A general approach to the solving of the seismic tomography task by the method of Taylor's approximation is as follows: construction of a generalized field of mid-point of arrival times of waves at the observation station; construction of mid-points travel-time curves, i.e. cross-sections of the generalized field of mid-point of the arrival times of waves; inversion of travel time of the mid-point curve into speed curve. Due to the imposed limitations there are no abrupt velocity leaps in the model in use. First derivatives of the velocity for each curve were calculated points of local extreme were identified in order to determine the seismic boundaries. Maps of depths of occurrences of seismic boundaries at about 410 km, 670 km, 1700 km, and 2800 km were constructed. In general there is a deviation from generally accepted values beneath regions with different geodynamic regimes. There is a correlation of the 410 km and 670 km boundaries behaviour with the observed heat flow anomalies and gravitational field. [1] V.Geyko, T. Tsvetkova, L. Shymlanskaya, I. Bugaienko, L. Zaets Regional 3-D velocity model of the mantle of Sarmatia (south-west of the East European Platform). Geophysical Journal, 2005, iss. 6, P. 927-939. (In Russian) [2] V. Geyko, L. Shymlanskaya, T. Tsvetkova, I.Bugaenko, L.Zaets Three-dimensional model of the upper mantle of Ukraine constructed from the times of P waves arrival. Geophysical Journal, 2006, iss. 1, P. 3-16. (In Russian)

Subsurface images of the Eastern Rift, Africa, from the joint inversion of body waves, surface waves and gravity: investigating the role of fluids in early-stage continental rifting

NASA Astrophysics Data System (ADS)

Roecker, S.; Ebinger, C.; Tiberi, C.; Mulibo, G.; Ferdinand-Wambura, R.; Mtelela, K.; Kianji, G.; Muzuka, A.; Gautier, S.; Albaric, J.; Peyrat, S.

2017-08-01

The Eastern Rift System (ERS) of northern Tanzania and southern Kenya, where a cratonic lithosphere is in the early stages of rifting, offers an ideal venue for investigating the roles of magma and other fluids in such an environment. To illuminate these roles, we jointly invert arrival times of locally recorded P and S body waves, phase delays of ambient noise generated Rayleigh waves and Bouguer anomalies from gravity observations to generate a 3-D image of P and S wave speeds in the upper 25 km of the crust. While joint inversion of gravity and arrival times requires a relationship between density and wave speeds, the improvement in resolution obtained by the combination of these disparate data sets serves to further constrain models, and reduce uncertainties. The most significant features in the 3-D model are (1) P and S wave speeds that are 10-15 per cent lower beneath the rift zone than in the surrounding regions, (2) a relatively high wave speed tabular feature located along the western edge of the Natron and Manyara rifts, and (3) low (∼1.71) values of Vp/Vs throughout the upper crust, with the lowest ratios along the boundaries of the rift zones. The low P and S wave speeds at mid-crustal levels beneath the rift valley are an expected consequence of active volcanism, and the tabular, high-wave speed feature is interpreted to be an uplifted footwall at the western edge of the rift. Given the high levels of CO2 outgassing observed at the surface along border fault zones, and the sensitivity of Vp/Vs to pore-fluid compressibility, we infer that the low Vp/Vs values in and around the rift zone are caused by the volcanic plumbing in the upper crust being suffused by a gaseous CO2 froth on top of a deeper, crystalline mush. The repository for molten rock is likely located in the lower crust and upper mantle, where the Vp/Vs ratios are significantly higher.

Thermal-hydraulic behaviors of vapor-liquid interface due to arrival of a pressure wave

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

Inoue, Akira; Fujii, Yoshifumi; Matsuzaki, Mitsuo

In the vapor explosion, a pressure wave (shock wave) plays a fundamental role for triggering, propagation and enhancement of the explosion. Energy of the explosion is related to the magnitude of heat transfer rate from hot liquid to cold volatile one. This is related to an increasing rate of interface area and to an amount of transient heat flux between the liquids. In this study, the characteristics of transient heat transfer and behaviors of vapor film both on the platinum tube and on the hot melt tin drop, under same boundary conditions have been investigated. It is considered that theremore » exists a fundamental mechanism of the explosion in the initial expansion process of the hot liquid drop immediately after arrival of pressure wave. The growth rate of the vapor film is much faster on the hot liquid than that on the solid surface. Two kinds of roughness were observed, one due to the Taylor instability, by rapid growth of the explosion bubble, and another, nucleation sites were observed at the vapor-liquid interface. Based on detailed observation of early stage interface behaviors after arrival of a pressure wave, the thermal fragmentation mechanism is proposed.« less

Sequencing of tsunami waves: Why the first wave is not always the largest

NASA Astrophysics Data System (ADS)

Okal, Emile; Synolakis, Costas

2015-04-01

In many instances, the largest wave to hit a coastline during a tsunami is not the first one. Classical examples include the arrivals of the 1960 Chilean tsunami in Hilo, Hawaii, and of the 1964 Alaskan tsunami in Crescent City, California, where most casualties took place during later arrivals. This situation can be socially treacherous, since residents and civil defense authorities are led to believe that the worst is over after a first, relatively mild arrival, and to give an early "all clear" before the true largest wave, as was the case in Papeete, Tahiti during the 2011 Tohoku tsunami. We research this problem by using a number of simple models for which analytical solutions are available, as well as more realistic simulations of the large earthquake tsunamis of the past decade, and compare their results to a catalog of waveforms obtained at DART buoys spread over the Pacific Basin. Preliminary results indicate a transition from a regime of Maximum First Wave to one of Delayed Maximum when distance is increased, azimuth to receiver is moved away from the normal to fault strike, and/or source size is reduced.

Precise Hypocenter Determination around Palu Koro Fault: a Preliminary Results

NASA Astrophysics Data System (ADS)

Fawzy Ismullah, M. Muhammad; Nugraha, Andri Dian; Ramdhan, Mohamad; Wandono

2017-04-01

Sulawesi area is located in complex tectonic pattern. High seismicity activity in the middle of Sulawesi is related to Palu Koro fault (PKF). In this study, we determined precise hypocenter around PKF by applying double-difference method. We attempt to investigate of the seismicity rate, geometry of the fault and distribution of focus depth around PKF. We first re-pick P-and S-wave arrival time of the PKF events to determine the initial hypocenter location using Hypoellipse method through updated 1-D seismic velocity. Later on, we relocated the earthquake event using double-difference method. Our preliminary results show the distribution of relocated events are located around PKF and have smaller residual time than the initial location. We will enhance the hypocenter location through updating of arrival time by applying waveform cross correlation method as input for double-difference relocation.

Delivery and application of precise timing for a traveling wave powerline fault locator system

NASA Technical Reports Server (NTRS)

Street, Michael A.

1990-01-01

The Bonneville Power Administration (BPA) has successfully operated an in-house developed powerline fault locator system since 1986. The BPA fault locator system consists of remotes installed at cardinal power transmission line system nodes and a central master which polls the remotes for traveling wave time-of-arrival data. A power line fault produces a fast rise-time traveling wave which emanates from the fault point and propagates throughout the power grid. The remotes time-tag the traveling wave leading edge as it passes through the power system cardinal substation nodes. A synchronizing pulse transmitted via the BPA analog microwave system on a wideband channel sychronizes the time-tagging counters in the remote units to a different accuracy of better than one microsecond. The remote units correct the raw time tags for synchronizing pulse propagation delay and return these corrected values to the fault locator master. The master then calculates the power system disturbance source using the collected time tags. The system design objective is a fault location accuracy of 300 meters. BPA's fault locator system operation, error producing phenomena, and method of distributing precise timing are described.

Quantum control via a genetic algorithm of the field ionization pathway of a Rydberg electron

NASA Astrophysics Data System (ADS)

Gregoric, Vincent C.; Kang, Xinyue; Liu, Zhimin Cheryl; Rowley, Zoe A.; Carroll, Thomas J.; Noel, Michael W.

2017-08-01

Quantum control of the pathway along which a Rydberg electron field ionizes is experimentally and computationally demonstrated. Selective field ionization is typically done with a slowly rising electric field pulse. The (1/n*)4 scaling of the classical ionization threshold leads to a rough mapping between arrival time of the electron signal and principal quantum number of the Rydberg electron. This is complicated by the many avoided level crossings that the electron must traverse on the way to ionization, which in general leads to broadening of the time-resolved field ionization signal. In order to control the ionization pathway, thus directing the signal to the desired arrival time, a perturbing electric field produced by an arbitrary wave-form generator is added to a slowly rising electric field. A genetic algorithm evolves the perturbing field in an effort to achieve the target time-resolved field ionization signal.

A novel fault location scheme for power distribution system based on injection method and transient line voltage

NASA Astrophysics Data System (ADS)

Huang, Yuehua; Li, Xiaomin; Cheng, Jiangzhou; Nie, Deyu; Wang, Zhuoyuan

2018-02-01

This paper presents a novel fault location method by injecting travelling wave current. The new methodology is based on Time Difference Of Arrival(TDOA)measurement which is available measurements the injection point and the end node of main radial. In other words, TDOA is the maximum correlation time when the signal reflected wave crest of the injected and fault appear simultaneously. Then distance calculation is equal to the wave velocity multiplied by TDOA. Furthermore, in case of some transformers connected to the end of the feeder, it’s necessary to combine with the transient voltage comparison of amplitude. Finally, in order to verify the effectiveness of this method, several simulations have been undertaken by using MATLAB/SIMULINK software packages. The proposed fault location is useful to short the positioning time in the premise of ensuring the accuracy, besides the error is 5.1% and 13.7%.

Acoustic ranging of small arms fire using a single sensor node collocated with the target.

PubMed

Lo, Kam W; Ferguson, Brian G

2015-06-01

A ballistic model-based method, which builds upon previous work by Lo and Ferguson [J. Acoust. Soc. Am. 132, 2997-3017 (2012)], is described for ranging small arms fire using a single acoustic sensor node collocated with the target, without a priori knowledge of the muzzle speed and ballistic constant of the bullet except that they belong to a known two-dimensional parameter space. The method requires measurements of the differential time of arrival and differential angle of arrival of the muzzle blast and ballistic shock wave at the sensor node. Its performance is evaluated using both simulated and real data.

Study of Rayleigh-Love coupling from Spatial Gradient Observation

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Tsunami waves generated by dynamically triggered aftershocks of the 2010 Haiti earthquake

NASA Astrophysics Data System (ADS)

Ten Brink, U. S.; Wei, Y.; Fan, W.; Miller, N. C.; Granja, J. L.

2017-12-01

Dynamically-triggered aftershocks, thought to be set off by the passage of surface waves, are currently not considered in tsunami warnings, yet may produce enough seafloor deformation to generate tsunamis on their own, as judged from new findings about the January 12, 2010 Haiti earthquake tsunami in the Caribbean Sea. This tsunami followed the Mw7.0 Haiti mainshock, which resulted from a complex rupture along the north shore of Tiburon Peninsula, not beneath the Caribbean Sea. The mainshock, moreover, had a mixed strike-slip and thrust focal mechanism. There were no recorded aftershocks in the Caribbean Sea, only small coastal landslides and rock falls on the south shore of Tiburon Peninsula. Nevertheless, a tsunami was recorded on deep-sea DART buoy 42407 south of the Dominican Republic and on the Santo Domingo tide gauge, and run-ups of ≤3 m were observed along a 90-km-long stretch of the SE Haiti coast. Three dynamically-triggered aftershocks south of Haiti have been recently identified within the coda of the mainshock (<200 s) by analyzing P wave arrivals recorded by dense seismic arrays, parsing the arrivals into 20-s-long stacks, and back-projecting the arrivals to the vicinity of the main shock (50-300 km). Two of the aftershocks, coming 20-40 s and 40-60 s after the mainshock, plot along NW-SE-trending submarine ridges in the Caribbean Sea south of Haiti. The third event, 120-140 s was located along the steep eastern slope of Bahoruco Peninsula, which is delineated by a normal fault. Forward tsunami models show that the arrival times of the DART buoy and tide gauge times are best fit by the earliest of the three aftershocks, with a Caribbean source 60 km SW of the mainshock rupture zone. Preliminary inversion of the DART buoy time series for fault locations and orientations confirms the location of the first source, but requires an additional unidentified source closer to shore 40 km SW of the mainshock rupture zone. This overall agreement between earthquake and tsunami analyses suggests that land-based earthquake ruptures and/or non-thrust main shocks can generate tsunamis by means of dynamically-triggered aftershocks. It also provides an independent verification to the back-projection seismic method, and it indicates that the active NE-SW shortening of Hispaniola extends southward into the Caribbean Sea.

The focusing effect of P-wave in the Moon's and Earth's low-velocity core. Analytical solution

NASA Astrophysics Data System (ADS)

Fatyanov, A. G.; Burmin, V. Yu

2018-04-01

The important aspect in the study of the structure of the interiors of planets is the question of the presence and state of core inside them. While for the Earth this task was solved long ago, the question of whether the core of the Moon is in a liquid or solid state up to the present is debatable up to present. If the core of the Moon is liquid, then the velocity of longitudinal waves in it should be lower than in the surrounding mantle. If the core is solid, then most likely, the velocity of longitudinal waves in it is higher than in the mantle. Numerical calculations of the wave field allow us to identify the criteria for drawing conclusions about the state of the lunar core. In this paper we consider the problem of constructing an analytical solution for wave fields in a layered sphere of arbitrary radius. A stable analytic solution is obtained for the wave fields of longitudinal waves in a three-layer sphere. Calculations of the total wave fields and rays for simplified models of the Earth and the Moon with real parameters are presented. The analytical solution and the ray pattern showed that the low-velocity cores of the Earth and the Moon possess the properties of a collecting lens. This leads to the emergence of a wave field focusing area. As a result, focused waves of considerable amplitude appear on the surface of the Earth and the Moon. In the Earth case, they appear before the first PKP-wave arrival. These are so-called "precursors", which continue in the subsequent arrivals of waves. At the same time, for the simplified model of the Earth, the maximum amplitude growth is observed in the 147-degree region. For the Moon model, the maximum amplitude growth is around 180°.

Combined mine tremors source location and error evaluation in the Lubin Copper Mine (Poland)

NASA Astrophysics Data System (ADS)

Leśniak, Andrzej; Pszczoła, Grzegorz

2008-08-01

A modified method of mine tremors location used in Lubin Copper Mine is presented in the paper. In mines where an intensive exploration is carried out a high accuracy source location technique is usually required. The effect of the flatness of the geophones array, complex geological structure of the rock mass and intense exploitation make the location results ambiguous in such mines. In the present paper an effective method of source location and location's error evaluations are presented, combining data from two different arrays of geophones. The first consists of uniaxial geophones spaced in the whole mine area. The second is installed in one of the mining panels and consists of triaxial geophones. The usage of the data obtained from triaxial geophones allows to increase the hypocenter vertical coordinate precision. The presented two-step location procedure combines standard location methods: P-waves directions and P-waves arrival times. Using computer simulations the efficiency of the created algorithm was tested. The designed algorithm is fully non-linear and was tested on the multilayered rock mass model of the Lubin Copper Mine, showing a computational better efficiency than the traditional P-wave arrival times location algorithm. In this paper we present the complete procedure that effectively solves the non-linear location problems, i.e. the mine tremor location and measurement of the error propagation.

Large-scale magnetic field perturbation arising from the 18 May 1980 eruption from Mount St. Helens, Washington

USGS Publications Warehouse

Mueller, R.J.; Johnston, M.J.S.

1989-01-01

A traveling magnetic field disturbance generated by the 18 may 1980 eruption of Mount St. Helens at 1532 UT was detected on an 800-km linear array of recording magnetometers installed along the San Andreas fault system in California, from San Francisco to the Salton Sea. Arrival times of the disturbance field, from the most northern of these 24 magnetometers (996 km south of the volcano) to the most southern (1493 km S23?? E), are consistent with the generation of a traveling ionospheric disturbance stimulated by the blast pressure wave in the atmosphere. The first arrivals at the north and the south ends of the array occurred at 26 and 48 min, respectively, after the initial eruption. Apparent average wave velocity through the array is 309 ?? 14 m s-1 but may have approached 600 m s-1 close to the volcano. The horizontal phase and the group velocity of ??? 300 m s-1 at periods of 70-80 min, and the attenuation with distance, strongly suggest that the magnetic field perturbations at distances of 1000-1500 km are caused by gravity mode acoustic-gravity waves propagating at F-region heights in the ionosphere. ?? 1989.

A repeating source of infrasound from the Wells, Nevada earthquake sequence

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

Arrowsmith, Stephen J.; Whitaker, Rod; Randall, George

2009-01-01

The Wells, Nevada earthquake of February 21, 2008, generated a complex seismoacoustic wakefield. In addition to epicentral infrasound, the earthquake triggered a secondary source of infrasound, which was also initiated by subsequent aftershocks. By applying simple constraints on the propagation of seismic and infrasound waves, we show that the secondary source is an isolated peak that appears to efficiently generate infrasound through the interaction with seismic surface waves. By measuring peak-to-peak amplitudes of epicentral and secondary arrivals and correcting them for the effects of distance and winds, we find that epicentral arrivals lit with empirical relationships of Mutschlecner and Whitakermore » (2005) and Le Pichon et al. (2006), which form the basis for a proposed infrasound discriminant (Anderson et al., Pers. Comm.). In contrast, the secondary arrivals are much higher in amplitude, highlighting the importance of being able to separate epicentral and secondary arrivals for infrasonic event discrimination.« less

Ultrasonic guided wave interpretation for structural health inspections

NASA Astrophysics Data System (ADS)

Bingham, Jill Paisley

Structural Health Management (SHM) combines the use of onboard sensors with artificial intelligence algorithms to automatically identify and monitor structural health issues. A fully integrated approach to SHM systems demands an understanding of the sensor output relative to the structure, along with sophisticated prognostic systems that automatically draw conclusions about structural integrity issues. Ultrasonic guided wave methods allow us to examine the interaction of multimode signals within key structural components. Since they propagate relatively long distances within plate- and shell-like structures, guided waves allow inspection of greater areas with fewer sensors, making this technique attractive for a variety of applications. This dissertation describes the experimental development of automatic guided wave interpretation for three real world applications. Using the guided wave theories for idealized plates we have systematically developed techniques for identifying the mass loading of underwater limpet mines on US Navy ship hulls, characterizing type and bonding of protective coatings on large diameter pipelines, and detecting the thinning effects of corrosion on aluminum aircraft structural stringers. In each of these circumstances the signals received are too complex for interpretation without knowledge of the guided wave physics. We employ a signal processing technique called the Dynamic Wavelet Fingerprint Technique (DFWT) in order to render the guided wave mode information in two-dimensional binary images. The use of wavelets allows us to keep track of both time and scale features from the original signals. With simple image processing we have developed automatic extraction algorithms for features that correspond to the arrival times of the guided wave modes of interest for each of the applications. Due to the dispersive nature of the guided wave modes, the mode arrival times give details of the structure in the propagation path. For further understanding of how the guided wave modes propagate through the real structures, we have developed parallel processing, 3D elastic wave simulations using the finite integration technique (EFIT). This full field, numeric simulation technique easily examines models too complex for analytical solutions. We have developed the algorithm to handle built up 3D structures as well as layers with different material properties and surface detail. The simulations produce informative visualizations of the guided wave modes in the structures as well as the output from sensors placed in the simulation space to mimic the placement from experiment. Using the previously developed mode extraction algorithms we were then able to compare our 3D EFIT data to their experimental counterparts with consistency.

Offset-vertical seismic profiling for marine gas hydrate exploration: Is it a suitable technique? First results from ODP Leg 164

USGS Publications Warehouse

Pecher, I.A.; Holbrook, W.S.; Stephen, R.A.; Hoskins, H.; Lizarralde, D.; Hutchinson, D.R.; Wood, W.T.

1997-01-01

Walkaway vertical seismic profiles were acquired during Ocean Drilling Project (ODP) Leg 164 at the Blake Ridge to investigate seismic properties of hydrate-bearing sediments and the zone of free gas beneath them. An evaluation of compressional (P-) wave arrivals Site 994 indicates P-wave anisotrophy in the sediment column. We identified several shear (S-) wave arrivals in the horizontal components of the geophone array in the borehole and in data recorded with an ocean bottom seismometer deployed at the seafloor. S-waves were converted from P-waves at several depth levels in the sediment column. One of the most prominent conversion points appears to be the bottom simulating reflector (BSR). It is likely that other conversion points are located in the zone of low P-wave reflectivity above the BSR. Modeling suggests that a change of the shear modulus is sufficient to cause significant shear conversion without a significant normal-incidence P-wave reflection.

3D P-wave velocity structure of the crust and relocation of earthquakes in the Lushan, China, source area

NASA Astrophysics Data System (ADS)

Yu, Xiangwei; Wang, Xiaona; Zhang, Wenbo

2016-04-01

Many researchers have investigated the Lushan source area with geological and geophysical approaches since the 2013 Lushan, China, earthquake happened. Compared with the previous tomographic studies, we have used a much large data set and an updated tomographic method to determine a small scale three-dimensional P wave velocity structure with spatial resolution less than 5km, which plays the important role for understanding the deep structure and the genetic mechanism beneath the Lushan area. The double difference seismic tomography method is applied to 50,711 absolute first arrival P wave arrival times and 7,294,691 high quality relative P arrival times of 5,285 events of Lushan seismic sequence to simultaneously determine the detailed crustal 3D P wave velocity structure and the hypocenter parameters in the Lushan seismic area. This method takes account of the path anomaly biases explicitly by making full use of valuable information of seismic wave propagation jointly with absolute and relative arrival time data. Our results show that the Lushan mainshock locates at 30.28N, 103.98E, with the depth of 16.38km. The front edge of aftershock in the northeast of mainshock present a spade with a steep dip angle, the aftershocks' extended length is about 12km. In the southwest of Lushan mainshock, the front edge of aftershock in low velocity zone slope gently, the aftershocks' extended length is about 23km. Our high-resolution tomographic model not only displays the general features contained in the previous models, but also reveals some new features. The Tianquan, Shuangshi and Daguan line lies in the transition zone between high velocity anomalies to the southeast and low velocity anomalies to the northwest at the ground surface. An obvious high-velocity anomaly is visible in Daxing area. With the depth increasing, Baoxing high velocity anomaly extends to Lingguan, while the southeast of the Tianquan, Shuangshi and Daguan line still shows low velocity. The high-velocity anomalies beneath Baoxing and Daxing connect each other in 10km depth, which makes the contrast between high and low velocity anomalies more sharp. Above 20km depth the velocity structure in southwest and northeast segment of mainshock shows a big difference: low-velocity anomalies are dominated the southwest segment, while high-velocity anomalies rule the northeast segment. Lushan aftershocks in southwest are distributed in low-velocity anomalies or the transition belt: the footwall represents low-velocity anomalies, while the hanging wall shows high-velocity anomalies. The northeastern aftershocks are distributed at the boundary between high-velocity anomalies in Baoxing and Daxing area. The P wave velocity structure of Lushan seismic area shows obviously lateral heterogeneity. The P wave velocity anomalies represent close relationship with topographic relief and geological structure. In Baoxingarea the complex rocks correspond obvious high-velocity anomalies extending down to 15km depth，while the Cenozoic rocks are correlated with low-velocity anomalies. Lushan mainshock locates at the leading edge of a low-velocity anomaly surrounded by the Baoxing and Daxing high-velocity anomalies. The main seismogenic layer dips to northwest. Meanwhile, a recoil seismic belt dips to southeast above the main seismogenic layer exists at the lower boundary of Baoxing high-velocity anomaly.

Gravitational waves from binary supermassive black holes missing in pulsar observations.

PubMed

Shannon, R M; Ravi, V; Lentati, L T; Lasky, P D; Hobbs, G; Kerr, M; Manchester, R N; Coles, W A; Levin, Y; Bailes, M; Bhat, N D R; Burke-Spolaor, S; Dai, S; Keith, M J; Osłowski, S; Reardon, D J; van Straten, W; Toomey, L; Wang, J-B; Wen, L; Wyithe, J S B; Zhu, X-J

2015-09-25

Gravitational waves are expected to be radiated by supermassive black hole binaries formed during galaxy mergers. A stochastic superposition of gravitational waves from all such binary systems would modulate the arrival times of pulses from radio pulsars. Using observations of millisecond pulsars obtained with the Parkes radio telescope, we constrained the characteristic amplitude of this background, A(c,yr), to be <1.0 × 10(-15) with 95% confidence. This limit excludes predicted ranges for A(c,yr) from current models with 91 to 99.7% probability. We conclude that binary evolution is either stalled or dramatically accelerated by galactic-center environments and that higher-cadence and shorter-wavelength observations would be more sensitive to gravitational waves. Copyright © 2015, American Association for the Advancement of Science.

S-wave triggering of tremor beneath the Parkfield, California, section of the San Andreas fault by the 2011 Tohoku, Japan earthquake: observations and theory

USGS Publications Warehouse

Hill, David P.; Peng, Zhigang; Shelly, David R.; Aiken, Chastity

2013-01-01

The dynamic stresses that are associated with the energetic seismic waves generated by the Mw 9.0 Tohoku earthquake off the northeast coast of Japan triggered bursts of tectonic tremor beneath the Parkfield section of the San Andreas fault (SAF) at an epicentral distance of ∼8200  km. The onset of tremor begins midway through the ∼100‐s‐period S‐wave arrival, with a minor burst coinciding with the SHSH arrival, as recorded on the nearby broadband seismic station PKD. A more pronounced burst coincides with the Love arrival, followed by a series of impulsive tremor bursts apparently modulated by the 20‐ to 30‐s‐period Rayleigh wave. The triggered tremor was located at depths between 20 and 30 km beneath the surface trace of the fault, with the burst coincident with the S wave centered beneath the fault 30 km northwest of Parkfield. Most of the subsequent activity, including the tremor coincident with the SHSH arrival, was concentrated beneath a stretch of the fault extending from 10 to 40 km southeast of Parkfield. The seismic waves from the Tohoku epicenter form a horizontal incidence angle of ∼14°, with respect to the local strike of the SAF. Computed peak dynamic Coulomb stresses on the fault at tremor depths are in the 0.7–10 kPa range. The apparent modulation of tremor bursts by the small, strike‐parallel Rayleigh‐wave stresses (∼0.7  kPa) is likely enabled by pore pressure variations driven by the Rayleigh‐wave dilatational stress. These results are consistent with the strike‐parallel dynamic stresses (δτs) associated with the S, SHSH, and surface‐wave phases triggering small increments of dextral slip on the fault with a low friction (μ∼0.2). The vertical dynamic stresses δτd do not trigger tremor with vertical or oblique slip under this simple Coulomb failure model.

Sounds of earthquakes in West Bohemia: analysis of sonic and infrasonic records

NASA Astrophysics Data System (ADS)

Fischer, Tomáš; Vilhelm, Jan; Kuna, Václav; Chum, Jaroslav; Horálek, Josef

2013-04-01

Earthquake sounds are usually observed during the occurrence of small earthquakes. The observations of audible manifestations of earthquakes date back to the ancient age and have been recently analyzed in more detail based both on macroseismic observations and audio recordings. In most cases the earthquake sounds resemble low-frequency underground thundering that is generated by seismic-acoustic conversion of P and SV waves at the earth surface. This is also supported by the fact that earthquake sounds usually precede shaking caused by S-waves. The less frequent are explosion-type sounds whose origin remains unclear. We analyze the observations of sounds associating the occurrence of earthquake swarms in the area of West Bohemia/Vogtland, Central Europe. Macroseismic data include 250 reports of sounds with 90% thundering and 10% of explosions. Additional data consist of sonic and infrasonic records acquired by microphones and microbarographs at seismic stations in the area. All the sonic and infrasonic records correspond to sounds of the thunder type; no explosions were recorded. Comparison of these records enabled to determine the seismic wave - air pressure transfer function. The measurements using a 3D microphone array confirm that in the epicentral area the sonic wave is propagating subvertically. We also compared the coda of seismograms and sonic records. It turned out that additional to seismo-acoustic coupling, a later acoustic wave of thunder type arrives at the observation site whose arrival time corresponds to sonic propagation from the epicenter. We analyse the possible generation mechanisms of this type of sonic wave.

A Study of the Effects of Seafloor Topography on Tsunami Propagation

NASA Astrophysics Data System (ADS)

Ohata, T.; Mikada, H.; Goto, T.; Takekawa, J.

2011-12-01

For tsunami disaster mitigation, we consider the phenomena related to tsunami in terms of the generation, propagation, and run-up to the coast. With consideration for these three phenomena, we have to consider tsunami propagation to predict the arrival time and the run-up height of tsunami. Numerical simulations of tsunami that propagates from the source location to the coast have been widely used to estimate these important parameters. When a tsunami propagates, however, reflected and scattered waves arrive as later phases of tsunami. These waves are generated by the changes of water depth, and could influence the height estimation, especially in later phases. The maximum height of tsunami could be observed not as the first arrivals but as the later phases, therefore it is necessary to consider the effects of the seafloor topography on tsunami propagation. Since many simulations, however, mainly focus on the prediction of the first arrival times and the initial height of tsunami, it is difficult to simulate the later phases that are important for the tsunami disaster mitigation in the conventional methods. In this study, we investigate the effects of the seafloor topography on tsunami propagation after accommodating a tsunami simulation to the superposition of reflected and refracted waves caused by the smooth changes of water depths. Developing the new numerical code, we consider how the effects of the sea floor topography affect on the tsunami propagation, comparing with the tsunami simulated by the conventional method based on the liner long wave theory. Our simulation employs the three dimensional in-equally spaced grids in finite difference method (FDM) to introduce the real seafloor topography. In the simulation, we import the seafloor topography from the real bathymetry data near the Sendai-Bay, off the northeast Tohoku region, Japan, and simulate the tsunami propagation over the varying seafloor topography there. Comparing with the tsunami simulated by the conventional method based on the liner long wave theory, we found that the amplitudes of tsunamis are different from each other for the two simulations. The degree of the amplification of the height of tsunami in our method is larger than that in the conventional one. The height of the later phases of the tsunamis shows the discrepancy between the two results. We would like to conclude that the real changes of water depth affect the prediction of tsunami propagation and the maximum height. Because of the effects of the seafloor topography, the amplitude of the later phases is sometimes larger than the former ones. Due to the inclusion of such effects by the real topography, we believe our method lead to a higher accuracy of prediction of tsunami later phases, which would be effective for tsunami disaster mitigation.

Broadband bearing-time records of three-component seismic array data and their application to the study of local earthquake coda

NASA Astrophysics Data System (ADS)

Wagner, Gregory S.; Owens, Thomas J.

1993-09-01

High-frequency three-component array d, are used to study the P and S coda produced by* cal earthquakes. The data are displayed as broadba bearing-time records which allow us to examine a compl, time history of the propagation directions and arrival tin of direct and scattered phases crossing the array. This ~ sualization technique is used to examine the wavefield ~ two scale lengths using two sub-arrays~of sensors. Resu suggest that P coda is dominated by P energy propag, ing sub-parallel to the direct P arrival. The S coda pro agates in all directions and appears to be composed p~ dominantly of S and/or surface wave energy. Significant more 0e coda appears on the smaller scale length sub-art relative to the larger scale array suggesting that much, the ~, coda remains coherent for only very short distanc

Sensitivity of tsunami evacuation modeling to direction and land cover assumptions

USGS Publications Warehouse

Schmidtlein, Mathew C.; Wood, Nathan J.

2015-01-01

Although anisotropic least-cost-distance (LCD) modeling is becoming a common tool for estimating pedestrian-evacuation travel times out of tsunami hazard zones, there has been insufficient attention paid to understanding model sensitivity behind the estimates. To support tsunami risk-reduction planning, we explore two aspects of LCD modeling as it applies to pedestrian evacuations and use the coastal community of Seward, Alaska, as our case study. First, we explore the sensitivity of modeling to the direction of movement by comparing standard safety-to-hazard evacuation times to hazard-to-safety evacuation times for a sample of 3985 points in Seward's tsunami-hazard zone. Safety-to-hazard evacuation times slightly overestimated hazard-to-safety evacuation times but the strong relationship to the hazard-to-safety evacuation times, slightly conservative bias, and shorter processing times of the safety-to-hazard approach make it the preferred approach. Second, we explore how variations in land cover speed conservation values (SCVs) influence model performance using a Monte Carlo approach with one thousand sets of land cover SCVs. The LCD model was relatively robust to changes in land cover SCVs with the magnitude of local model sensitivity greatest in areas with higher evacuation times or with wetland or shore land cover types, where model results may slightly underestimate travel times. This study demonstrates that emergency managers should be concerned not only with populations in locations with evacuation times greater than wave arrival times, but also with populations with evacuation times lower than but close to expected wave arrival times, particularly if they are required to cross wetlands or beaches.

Upper-mantle seismic structure in a region of incipient continental breakup: northern Ethiopian rift

NASA Astrophysics Data System (ADS)

Bastow, Ian D.; Stuart, Graham W.; Kendall, J.-Michael; Ebinger, Cynthia J.

2005-08-01

The northern Ethiopian rift forms the third arm of the Red Sea, Gulf of Aden triple junction, and marks the transition from continental rifting in the East African rift to incipient oceanic spreading in Afar. We determine the P- and S-wave velocity structure beneath the northern Ethiopian rift using independent tomographic inversion of P- and S-wave relative arrival-time residuals from teleseismic earthquakes recorded by the Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE) passive experiment using the regularised non-linear least-squares inversion method of VanDecar. Our 79 broad-band instruments covered an area 250 × 350 km centred on the Boset magmatic segment ~70 km SE of Addis Ababa in the centre of the northern Ethiopian rift. The study area encompasses several rift segments showing increasing degrees of extension and magmatic intrusion moving from south to north into the Afar depression. Analysis of relative arrival-time residuals shows that the rift flanks are asymmetric with arrivals associated with the southeastern Somalian Plate faster (~0.65 s for the P waves; ~2 s for the S waves) than the northwestern Nubian Plate. Our tomographic inversions image a 75 km wide tabular low-velocity zone (δVP~-1.5 per cent, δVS~-4 per cent) beneath the less-evolved southern part of the rift in the uppermost 200-250 km of the mantle. At depths of >100 km, north of 8.5°N, this low-velocity anomaly broadens laterally and appears to be connected to deeper low-velocity structures under the Afar depression. An off-rift low-velocity structure extending perpendicular to the rift axis correlates with the eastern limit of the E-W trending reactivated Precambrian Ambo-Guder fault zone that is delineated by Quaternary eruptive centres. Along axis, the low-velocity upwelling beneath the rift is segmented, with low-velocity material in the uppermost 100 km often offset to the side of the rift with the highest rift flank topography. Our observations from this magmatic rift zone, which is transitional between continental and oceanic rifting, do not support detachment fault models of lithospheric extension but instead point to strain accommodation via magma assisted rifting.

Using P-wave Triplications to Constrain the Mantle Transition Zone beneath Central Iranian Plateau and Surrounding Area

NASA Astrophysics Data System (ADS)

Chi, H. C.; Tseng, T. L.

2014-12-01

The Iranian Plateau is a tectonically complex region resulting from the continental collision between the African and Eurasian plates. The convergence of the two continents created the Zagros Mountains, the high topography southwest of Iran, and active seismicity along the Zagros-Bitlis suture. Tomographic studies in Iran reveal low seismic speeds and high attenuation of Sn wave in the uppermost mantle beneath the Iranian Plateau relative to adjacent regions. The deeper structure, however, remains curiously inconclusive. By contrast, a prominent fast seismic anomaly is found under central Tibet near depth of 600 km in the mantle transition zone (TZ), and it is speculated to be the remnant of lithosphere detached during the continental collision. We conduct a comparative study that utilizes triplicate arrivals of high-resolution P waveforms to investigate the velocity structure of mantle beneath the central Iranian Plateau and surroundings. Due to the abrupt increase in seismic wave speeds and density across the 410- and 660-km discontinuities, seismic waves at epicentral distances of 15-30 degrees would form multiple arrivals and the relative times and amplitudes between them are most sensitive to the variations in seismic speeds near the TZ. We combine several broadband arrays to construct 8 seismic profiles, each about 800 km long, that mainly sample the TZ under central Iranian Plateau, Turan shield and part of South Caspian basin. Move-outs between arrivals are clear in the profiles. Relative timings suggest a slightly smaller 660-km contrast under stable Turan shield. In the next stage, it is necessary to model waveforms after the source effect being removed properly. Our preliminary tests show that the F-K method can efficiently calculate the synthetic seismograms. We will determine the 1D velocity model for each sampled sector by minimizing the overall misfits between observed and predicted waveforms. The lateral variations may be further explored by comparing adjacent sectors. The results are important for understanding the lithosphere-mantle interaction during the process of continental collision.

Acoustic multipath arrivals in the horizontal plane due to approaching nonlinear internal waves.

PubMed

Badiey, Mohsen; Katsnelson, Boris G; Lin, Ying-Tsong; Lynch, James F

2011-04-01

Simultaneous measurements of acoustic wave transmissions and a nonlinear internal wave packet approaching an along-shelf acoustic path during the Shallow Water 2006 experiment are reported. The incoming internal wave packet acts as a moving frontal layer reflecting (or refracting) sound in the horizontal plane. Received acoustic signals are filtered into acoustic normal mode arrivals. It is shown that a horizontal multipath interference is produced. This has previously been called a horizontal Lloyd's mirror. The interference between the direct path and the refracted path depends on the mode number and frequency of the acoustic signal. A mechanism for the multipath interference is shown. Preliminary modeling results of this dynamic interaction using vertical modes and horizontal parabolic equation models are in good agreement with the observed data.

Role of Compressibility on Tsunami Propagation

NASA Astrophysics Data System (ADS)

Abdolali, Ali; Kirby, James T.

2017-12-01

In the present paper, we aim to reduce the discrepancies between tsunami arrival times evaluated from tsunami models and real measurements considering the role of ocean compressibility. We perform qualitative studies to reveal the phase speed reduction rate via a modified version of the Mild Slope Equation for Weakly Compressible fluid (MSEWC) proposed by Sammarco et al. (2013). The model is validated against a 3-D computational model. Physical properties of surface gravity waves are studied and compared with those for waves evaluated from an incompressible flow solver over realistic geometry for 2011 Tohoku-oki event, revealing reduction in phase speed.