Download or read book Methods of Improving Regional Seismic Event Locations written by and published by . This book was released on 2001 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this paper we investigate the effect that depth-dependent Source Specific Station Corrections (SSSC's) have on improving regional seismic event location accuracy. To accomplish this we have relocated events considered GT5 or less that occur within the region encompassed by Weston Geophysical's regional 3-D model of the India-Pakistan region (WINPAK3D) using different depth-dependent SSSC's. By comparing the hypocenters produced using SSSC's at different depths to the ground truth location, we have gained insight into the minimum number of depth-dependent SSSC's that must be implemented in current automatic processing routines for accurate and efficient regional event location. For a crustal earthquake, we generated SSSC's for a suite of depths by calculating travel times for WINPAK3D relative to the global IASPEI91 model (Kennett and Engdahl, 1991) to all regional stations. We then estimated the event hypocenter using the International Seismological Center (ISC) location as an initial hypocenter and two different but closely related methods of SSSC application and hypocenter location. For both location procedures, we compared the location derived from application of the different depth-dependent SSSC's to the ISC location in order to determine if there were significant differences in the hypocenters. Our initial results suggest that two SSSC's, one for the crust and one for the mantle, may be the minimum number of SSSC's to achieve the current goal in location accuracy in our study region.

Download or read book Improved Regional Seismic Event Locations Using 3 D Velocity Models written by and published by . This book was released on 1999 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this research is to develop improved methods for regional and local seismic event locations from 3-D velocity models. Improved hypocenter estimates and high resolution velocity models are critical to the successful seismic monitoring of potential nuclear tests. During Phase 1 of the study we have developed a nonlinear, multiple event location technique which uses primary and secondary phases (for P waves) and a 3-D regional velocity model to estimate event hypocenters. Travel times for the regional phases are calculated using a sophisticated eikonal finite difference scheme, and the locations are determined using an efficient grid search algorithm for 3-D media. We demonstrate its capabilities using synthetic data and a 3-D velocity model from a region of U.S. monitoring concern.

Download or read book Originalanmerkungen Herkunftsnachweise Nachwort written by and published by . This book was released on 1980 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advances in Seismic Event Location written by Cliffort H. Thurber and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 271 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in Seismic Event Location provides a broad overview of the fundamental issues involved in seismic event location, and presents a variety of state-of-the-art location methods and applications at a wide range of spatial scales. Three important themes in the book are: seismic monitoring for a Comprehensive Nuclear-Test-Ban Treaty (CTBT), seismic event location in three-dimensional Earth models, and methods for multiple-event location. Each chapter contains background material to help readers less familiar with the topics covered, as well as to provide abundant references for readers interested in probing deeper into a topic. However, most of the emphasis is on recent advances in methodology and their application. Audience: The book is intended primarily for academic and professional researchers and graduate students in seismology.

Download or read book Regional Seismic Event Identification and Improved Locations With Small Arrays written by and published by . This book was released on 1998 with total page 219 pages. Available in PDF, EPUB and Kindle. Book excerpt: We isolated the effect of structure immediately beneath seismic stations on seismic waveforms by determining the inference of velocity discontinuities beneath a single broadband 3-component seismic station using receiver functions, in which the P-to-S converted phases generated beneath a seismic station are isolated by deconvolution of the horizontal component seismograms by the vertical. We improve the deconvolution itself by the development of a time domain inversion for the receiver function. We extend the technique's application to an area of complex structure, using data collected at Pinon Flat Observatory, California, where we improve understanding of the region's structure and tectonic framework. We then used near-receiver- scattered component of teleseismic code to calibrate site amplifications for the southern California seismic network. We also developed and applied appropriate statistical analysis tools to permit accurate estimation of the site amplifications from the doubly censored non-Gaussian data. The main purpose of estimating site amplifications has been to enable isolation of propagation effects on Lg amplitudes, which is important to understand for accurate monitoring of nuclear testing. We conclude with the application of the site amplifications to Lg of regional events, demonstrating that they are successful in isolating propagation from site effects on Lg amplitudes.

Download or read book Regional Seismic Event Identification and Improved Locations with Small Arrays and Networks written by and published by . This book was released on 1995 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: This final report contains a summary of our work on the use of seismic networks and arrays to improve locations and identify small seismic event. The research can be divided into three main areas. We have developed techniques to migrate 3-component array records of local, regional and teleseismic wavetrains to directly image buried two- and three-dimensional heterogeneities (e.g. layer irregularities, volumetric heterogeneities) in the vicinity of the array. The initial intent of this research effort was to identify noise sources excited by incident signals and isolate their contributions to seismic coda. This technique has been applied to small-aperture array data collected in southern California. We have developed a technique to empirically characterize local and regional seismic code by binning and stacking network recordings of dense aftershock sequences. The principle motivation for this work was to look for robust coda phases dependent on source depth. We've used these empirical results, obtained by examining ANZA network recordings of Lande and Superstition Hills aftershocks, and have developed a technique to constrain sour depth. We have extended our ripple-fired event discriminant (based on the time-independence of coda produced by ripple firing) by looking for an independence of the coda from the recording direction (also indicative of ripple-firing). (MM).

Download or read book Grid Search Location Methods for Ground Truth Collection from Local and Regional Seismic Networks written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this project is to develop improved seismic event location techniques that can be used to generate more and better quality reference events using data from local and regional seismic networks. Their approach is to extend existing methods of multiple-event location with more general models of the errors affecting seismic arrival time data, including picking errors and errors in model-based travel-times (path corrections). Toward this end, they are integrating a grid-search based algorithm for multiple-event location (GMEL) with a new parameterization of travel-time corrections and new kriging method for estimating the correction parameters from observed travel-time residuals. Like several other multiple-event location algorithms, GMEL currently assumes event-independent path corrections and is thus restricted to small event clusters. The new parameterization assumes that travel-time corrections are a function of both the event and station location, and builds in source-receiver reciprocity and correlation between the corrections from proximate paths as constraints. The new kriging method simultaneously interpolates travel-time residuals from multiple stations and events to estimate the correction parameters as functions of position. They are currently developing the algorithmic extensions to GMEL needed to combine the new parameterization and kriging method with the simultaneous location of events. The result will be a multiple-event location method which is applicable to non-clustered, spatially well-distributed events. They are applying the existing components of the new multiple-event location method to a data set of regional and local arrival times from Nevada Test Site (NTS) explosions with known origin parameters. Preliminary results show the feasibility and potential benefits of combining the location and kriging techniques. They also show some preliminary work on generalizing of the error model used in GMEL with the use of mixture-of-Gaussians probability distributions fit to observed travel-time residuals.

Download or read book Methods of the Optimal Planning of Regional Seismic Networks written by Andrzej Kijko and published by . This book was released on 1978 with total page 70 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Grid Search Techniques for Seismic Event Location and Phase Association written by and published by . This book was released on 2007 with total page 49 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objectives of this project are to develop improved methods for locating seismic events and to develop new approaches to analyzing the seismic event location uncertainty. Our efforts are focused on the problems of both single and multiple event location. For a single event, we have formulated a statistical approach based on maximum-likelihood estimation and implemented it with grid-search and Monte Carlo techniques to yield an algorithm called "Grid-Search Single Event Location" (GSEL), which computes non-elliptical confidence regions on event locations for a wide class of assumed probability distributions (Gaussian and non-Gaussian) and for data picking errors. We have applied GSEL to regional arrival data from the 1991 Racha earthquake sequence and from the 1998 Adana (Turkey) earthquake sequence. Our multiple-event grid-search location algorithm (called GMEL) is also based on a maximum likelihood formulation of the location problem and it solves jointly for the location parameters (hypocenters and origin times) of seismic events in a cluster and travel-time corrections at the stations recording the events, GMEL accommodates non-Gaussian as well as Gaussian models of picking errors. We test this GMEL with clusters of 1999 Izmit/Duzce (Turkey) earthquake sequence. The approach we developed is based on the maximum- likelihood framework determines confidence regions on event locations under a general class of picking error models (Gaussian and non- Gaussian).

Download or read book Relative Seismic Event Location and Size Estimation Contributions to Earthquake Analysis and Seismic Discrimination at Local Distances written by Jonas Kintner and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Improving estimates of seismic source parameters is fundamental for understanding earthquake processes and enhancing current seismic event monitoring capabilities. In this dissertation I address several scientific challenges regarding the characterization (location, magnitude, etc.) of seismic events. Better source characterization allows us to relate seismic activity to observed surface deformation and to the broader tectonic implications of hazardous earthquakes. From a seismological perspective, I extend recently-developed surface-wave based methods to characterize seismic events across a wider range of tectonic environments, event sizes, station distributions, noise environments, and seismic source types. The first study documented is focused on constraining the relative locations and sizes of moderate-magnitude earthquakes in the 2013-2014 Minab sequence, Iran. We combinedsurface-wave cross correlation measurements, surface-wave spectra, and teleseismic body-wave modeling to constrain epicentroid locations, magnitudes, and depths. The results show that at least in some cases, we can use distant observations to improve the precision of relative earthquake epicentroid locations and magnitudes of remote earthquake sequences in tectonically complex regions. An appendix documents the results from relative relocations across the broad region including and surrounding Iran.Also included is a study of the 2014-15 Bushkan earthquake sequence, Iran. For this moderate-magnitude, shallow event, we used a combination of surface wave analysis, body wave modeling, and InSAR observations to characterize the mainshock and larger aftershocks. This study illuminates the opportunities provided by joint analysis of geodetic and seismological observations from modest-magnitude, shallow earthquakes in remote regions.Next I describe a study in which we characterize earthquake activity along the northwestern Caribbean plate boundary. We analyzed the earthquake processes along this margin by computing precise relative locations and magnitudes of moderate sized earthquakes from 1976 to 2018, and comparing the source-time functions and finite-fault models of the two largest recent earthquakes in the region. The relocation analysis allows us to improve relative event locations that help define the seismically active portions of the plate boundary more clearly. The finite-fault rupture models suggest that the large earthquakes along this strike-slip system may be influenced by faulting asperities and/or restraining bend features. The fourth study is an extension of the relative event location and magnitude estimation methods used in previous analyses. We estimate precise relative locations and magnitudes of small industrial explosions across Pennsylvania, USA using local and near-regional short-period shear-wave observations. The analysis is an effective illustration of the use of cross correlation of local-distance observations to compute high precision relative location and magnitude estimates of low-yield seismic sources.The final analysis described is an investigation of the potential to discriminate between earthquakes, mine blasts, and single shot borehole explosions using the amplitude ratio between local-distance (

Download or read book Improved Seismic Monitoring Improved Decision Making written by National Research Council and published by National Academies Press. This book was released on 2006-01-04 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: Improved Seismic Monitoringâ€"Improved Decision-Making, describes and assesses the varied economic benefits potentially derived from modernizing and expanding seismic monitoring activities in the United States. These benefits include more effective loss avoidance regulations and strategies, improved understanding of earthquake processes, better engineering design, more effective hazard mitigation strategies, and improved emergency response and recovery. The economic principles that must be applied to determine potential benefits are reviewed and the report concludes that although there is insufficient information available at present to fully quantify all the potential benefits, the annual dollar costs for improved seismic monitoring are in the tens of millions and the potential annual dollar benefits are in the hundreds of millions.

Download or read book The Use of Propagation Path Corrections to Improve Regional Seismic Event Location in Western China written by and published by . This book was released on 1999 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: In an effort to improve the ability to locate seismic events in western China using only regional data, the authors have developed empirical propagation path corrections (PPCs) and applied such corrections using both traditional location routines as well as a nonlinear grid search method. Thus far, the authors have concentrated on corrections to observed P arrival times for shallow events using travel-time observations available from the USGS EDRs, the ISC catalogs, their own travel-tim picks from regional data, and data from other catalogs. They relocate events with the algorithm of Bratt and Bache (1988) from a region encompassing China. For individual stations having sufficient data, they produce a map of the regional travel-time residuals from all well-located teleseismic events. From these maps, interpolated PPC surfaces have been constructed using both surface fitting under tension and modified Bayesian kriging. The latter method offers the advantage of providing well-behaved interpolants, but requires that the authors have adequate error estimates associated with the travel-time residuals. To improve error estimates for kriging and event location, they separate measurement error from modeling error. The modeling error is defined as the travel-time variance of a particular model as a function of distance, while the measurement error is defined as the picking error associated with each phase. They estimate measurement errors for arrivals from the EDRs based on roundoff or truncation, and use signal-to-noise for the travel-time picks from the waveform data set.

Download or read book Grid Search Location Methods for Ground Truth Collection From Local and Regional Seismic Networks written by Stephen C. Myers and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This project investigated new techniques for improving seismic eventlocations derived from regional and local networks. The technqiuesinclude a new approach to empirical travel-time calibration thatsimultaneously fits data from multiple stations and events, using ageneralization of the kriging method, and predicts travel-timecorrections for arbitrary event-station paths. We combined thiscalibration approach with grid-search event location to produce aprototype new multiple-event location method that allows the use ofspatially well-distributed events and takes into account correlationsbetween the travel-time corrections from proximate event-stationpaths. Preliminary tests with a high quality data set from NevadaTest Site explosions indicated that our new calibration/locationmethod offers improvement over the conventional multiple-eventlocation methods now in common use, and is applicable to more generalevent-station geometries than the conventional methods. The testswere limited, however, and further research is needed to fullyevaluate, and improve, the approach. Our project also demonstratedthe importance of using a realistic model for observational errors inan event location procedure. We took the initial steps in developinga new error model based on mixture-of-Gaussians probabilitydistributions, which possess the properties necessary to characterizethe complex arrival time error processes that can occur when pickinglow signal-to-noise arrivals. We investigated various inferencemethods for fitting these distributions to observed travel-timeresiduals, including a Markov Chain Monte Carlo technique forcomputing Bayesian estimates of the distribution parameters.

Download or read book Seismic Event Locations Using Multiple Phases written by A. C. Chang and published by . This book was released on 1985 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work evaluates the utility of a travel travel Covariance Matrix Method (COVMTX) for the improvement of the location of seismic events at regional distances using both Pn and Pg arrival times. Correlations between Pn and Pg travel time residuals are determined for the data set. The correlation of Pn and Pg times, rho sub PnPg for signals received at the same station from the same event was found to be very poor, less than 0.3 in all computations. The Covariance Matrix Method did not improve the results, possibly because the systematic bias due to the clustering of stations is small for the particular network of stations used in the relocation. Nevertheless, the method is still valuable because we must weight each signal differently, especially when multiple phases are used. The Simultaneous Inversion Method often resulted in erroneous depth estimates because the inversion for the depth dependent terms a sub Pn and a sub Pg in the linear travel time formula t = a + b delta may end up with some unacceptable values. By restricting the inversion for the a coefficients, the relocation resulted in the best results. This restriction is similar to the Successive Determinations Method devised by Chang et al. (1981), because it only improves the velocities or the b coefficients. This results suggests that a successive determinations approach may be very useful in locations using later phases, where large local variations in travel times are noted but are unpredictable prior to the location.

Download or read book Seismological Tables written by Sir Harold Jeffreys and published by . This book was released on 1988 with total page 43 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Integrated Approach to Seismic Event Location 2 Sources of Location Uncertainty for Teleseismic and Local Network Data written by and published by . This book was released on 1994 with total page 57 pages. Available in PDF, EPUB and Kindle. Book excerpt: The locations of seismic events determined from travel times by independent agencies differ for at least three reasons, including differences in picking of or availability of the phases, effects produced by individual structural peculiarities of each station, and systematic mislocations caused by the choice of the travel time model used for relocation. The present study evaluates earthquake locations for events in thin geographically diverse regions chosen to represent a broad spectrum of location problems. These are: Macquarie Ridge; Bucaramanga, Colombia; and Efate, Vanuatu. The evaluation methods include a comparison of locations reported by different agencies, an analysis of the sources of the variance of travel-time residuals, and a determination of the volume of groups of events thought to originate from a common source region. For the data analyzed it appears that station-dependent effects are a more significant source of location differences than are effects related to picking phase arrivals or choice of velocity model. Also, this study finds many situations where it seems inappropriate to utilize the strategy of minimizing travel time variance to improve location quality. Seismic event location, Seismic strain, Seismic discrimination.

Download or read book Seismic Event Location in Regional Distances written by and published by . This book was released on 1991 with total page 39 pages. Available in PDF, EPUB and Kindle. Book excerpt: Three-component data from regional seismic events recorded by the former NRDC-Soviet Academy of Sciences regional seismic network in Kazakhstan, USSR, have been analyzed with the primary goal of improving regional seismic event location capability. Data from these events were used in the investigation of the following problems related to regional event location: (1) determination of wave arrival azimuth; (2) observability and value of secondary phase arrivals; (3) evaluation and improvement of regional event location algorithms; (4) independent determination of 'master event' locations. Starting with very little prior information, we have demonstrated the potential for a sparse seismic network of three 3-component stations to locate events over a wide region with reasonable accuracy and precision, both for epicenter and depth. Our basic findings are: that arrival azimuth can be determined with reasonable precision, but the data provide little in the way of location constraint in most cases; secondary phase arrivals are routinely observable over a wide distance range, and they provide important location constraints; existing location algorithms perform well and provide appropriate estimates of location uncertainty, but must be modified for far-regional applications. Numerous master events have been identified and used to improve our location capability.