Download or read book A Plan for Seismic Location Calibration of 30 IMS Stations in Eastern Asia written by and published by . This book was released on 2000 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: In March 2000, a collaborative academic-industry research consortium comprised of five institutions started an integrated series of projects, all with the goal of improving the capability to locate seismic events based on data acquired by International Monitoring System (IMS) stations in Eastern Asia. The focus of this effort is to develop and deliver validated high-resolution travel time grids for operational use in support of the location estimates made by the International Data Centre (IDC) of the Comprehensive Test Ban Treaty Organization. These are to be used for the specified stations to locate on the order of a hundred events per day around the world. The basic approach is to use thousands of so-called "ground truth" seismic events in Eastern Asia that have been accurately located by regional or local networks. These will be used to obtain the travel times of key seismic phases from any point in the region to any of the 30 IMS stations that are the focus of the project. These travel-times will in general be a function of distance and azimuth -- and depth. They must be determined as a continuous function of position, from the empirical discrete ground truth data; and they must be demonstrated to improve location estimates of new events, over the estimates obtained on the basis of current procedures (typically, based on the Earth model IASP91). In the first project, the Lamont-Doherty Earth Observatory of Columbia University will contribute numerous newly obtained ground truth locations in Eastern Asia whose errors are thought to be of the order of five km or better (so called GT5 events) and that are expected to be large enough for detection at IMS stations. In most cases these events are recent enough for inclusion in the Reviewed Event Bulletin of the PIDC (since 1995).
Download or read book Seismic Calibration of Group 1 IMS Stations in Eastern Asia for Improved IDC Event Location written by and published by . This book was released on 2006 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt: The determination of accurate seismic locations for detected events is one of the most important functions of nuclear test monitoring because location plays such a key role in nuclear test monitoring. In order to establish a robust nuclear test monitoring capability, it is necessary to calibrate the IMS seismic stations used in monitoring, to account for systematic deviations from the nominal travel time curves. This report presents a summary of the research which has been accomplished during the three year program directed at the seismic calibration of the 30 Group 1 IMS stations of Eastern Asia. A Consortium of institutions, led by SAIC (formerly Maxwell Technologies, Inc.) was assembled to address this calibration effort. This consortium included the Massachusetts Institute of Technology's Earth Resources Laboratory, Weston Geophysical Corporation and the Russian Institute for Dynamics of the Geospheres. The consortium approach used a three dimensional velocity model to estimate SSSC at each station, supplemented with empirical corrections to take rigorous account of all the calibration data available for source regions surrounding each station. P-wave and S-wave SSSCs now have been determined and delivered to DTRA for all 30 Group 1 stations for surface focus and ten additional source depths.
Download or read book Seismic Calibration of Group One International Monitoring System Stations in Eastern Asia for Improved Event Location written by and published by . This book was released on 2001 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: A consortium of institutions that includes SAIC, the Massachusetts Institute of Technology (MIT) Earth Resources Laboratory (ERL), Weston Geophysical Corporation, the Russian Institute for Dynamics of the Geospheres (IDG), and the Chinese Seismological Bureau of Sichuan Province is engaged in a research program directed toward the seismic travel-time calibration of the 30 Group 1 International Monitoring System (IMS) stations of eastern Asia. We have assembled a preliminary 3-D velocity model of the entire region, which is composed of a global background model on a 5?-by-5? grid derived from surface wave analyses, supplemented by more detailed models in regions where they are available. At present, such detailed models have been identified for a large portion of the Former Soviet Union (FSU) for which Deep Seismic Sounding (DSS) data have been used to define a 3-D velocity model of the crust and upper mantle on a roughly 40-km by 40-km grid, and for an approximately 25?-by-30? area centered on the Pakistan/Afghanistan region for which a 3-D velocity model has been defined on a 1? by 1? grid. Regional phase travel times through these 3-D models are being computed using the Podvin and Lecomte finite difference algorithm to obtain preliminary SSSC estimates for the IMS stations in this region. These initial estimates are being tested using various calibration data sets that have been assembled for this study. These include a unique set of regional arrival-time data at FSU permanent network stations from some 60 Soviet Peaceful Nuclear Explosion (PNE) tests, as well as numerous Semipalatinsk and Novaya Zemlya explosions with precisely known locations and origin times.
Download or read book Collaborative Research Calibration for IMS Stations in Eastern Asia written by and published by . This book was released on 2007 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have competed a three-year consortium effort led by Lamont to improve the capability to locate seismic events based on data acquired by 30 International Monitoring System (IMS) stations in East Asia We have developed and tested Source Specific Station Corrections (SSSCs) for Pn and Sn travel times at these 30 IMS stations (or suitable surrogates), and for 127 other stations used for validation testing. First we developed SSSCs via a 3-D model of the P-wave velocity for East Asia, and then we refined them empirically by applying a kriging algorithm to travel-time residuals for 525 Ground-Truth (GT) events whose epicenters in East Asia we showed are known to within 5 km. Using a leave-one-out approach, we relocated these 525 events recorded by various combinations of 140 regional stations. Miclocations were reduced for 66% of the events using the model-based SSSCs and for 85% of the events using kringed SSSCs. Meridian miclocation improved from 16.9 km to 11.4 km and 6.5 km respectively. Median error ellipse area was reduced from 2616 sq. km to 1633 sl.km, respectively. Error ellipse coverage was maintained at close to 90%.
Download or read book Spring Meeting written by American Geophysical Union. Meeting and published by . This book was released on 2000 with total page 544 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Calibration of Regional Seismic Stations in the Middle East With Shots in Turkey written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: OAK-B135 The Eastern Mediterranean, Caucasus, and many parts of the Middle East are characterized by complex tectonics, and lateral variations of crust/upper mantle structures and seismic velocities. These complexities affect the detection, location, and characterization of seismic events. The primary objective of this project is to improve event location capabilities in the Middle East using calibration shots in Turkey. Specific objectives are: (1) calibrate regional travel-times and propagation characteristics of seismic waves across the Middle East and Eastern Mediterranean; (2) calibrate local and regional models for specific IMS stations in Turkey; (3) conduct reciprocity experiments where feasible; and (4) provide data and models to enhance IMS detection and location capabilities in the region. The calibration data will be generated by two shots in Turkey, one in central Anatolia, and another in eastern Turkey.
Download or read book Commerce Business Daily written by and published by . This book was released on 1999-05 with total page 1974 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research on Seismic Calibration of the International Monitoring System in Northern Eurasia written by and published by . This book was released on 2004 with total page 572 pages. Available in PDF, EPUB and Kindle. Book excerpt: The main goals of the "Russian Seismoacoustic Research for CTBT Monitoring" project were: Calibration of seismic stations of the Russian Academy of Sciences (RAS) included in the International Monitoring System (IMS), Development of travel time data for calibration studies in northern Eurasia, Collection data on peaceful nuclear explosions (PNEs) in the former Soviet Union, The Geophysical Survey (GS) of RAS and the Complex Seismological Expedition (CSE) of the Joint Institute of Physics of the Earth of the RAS, collected Northern Eurasian data on time arrivals for regional seismic phases. Tables for Pn, Pg, Sn and Lg waves have been updated. From travel-time residual analysis, we conclude that the LASPEI-91-91 predicted travel times are substantially biased in comparison with those predicted by Source Specific Station Corrections developed in this report. We review recently published and historical data on the parameters of PNEs' in the former Soviet Union. The seismic locations of the International Seismological Center (ISC) for some PNEs' show large misallocations (greater than 101cm) according to newly found information on these PNEs' actual locations. For ISC estimates of origin times for some PNEs' in the paper of Sultanov et. al., 1999, we provide adjusted data.
Download or read book Calibration of Seismic Wave Propagation in Jordan written by and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Natural Resources Authority of Jordan (NRA), the USGS and LLNL have a collaborative project to improve the calibration of seismic propagation in Jordan and surrounding regions. This project serves common goals of CTBT calibration and earthquake hazard assessment in the region. These objectives include accurate location of local and regional earthquakes, calibration of magnitude scales, and the development of local and regional propagation models. In the CTBT context, better propagation models and more accurately located events in the Dead Sea rift region can serve as (potentially GT5) calibration events for generating IMS location corrections. The detection and collection of mining explosions underpins discrimination research. The principal activity of this project is the deployment of two broadband stations at Hittiyah (south Jordan) and Ruweishid (east Jordan). These stations provide additional paths in the region to constrain structure with surface wave and body wave tomography. The Ruweishid station is favorably placed to provide constraints on Arabian platform structure. Waveform modeling with long-period observations of larger earthquakes will provide constraints on 1-D velocity models of the crust and upper mantle. Data from these stations combined with phase observations from the 26 short-period stations of the Jordan National Seismic Network (JNSN) may allow the construction of a more detailed velocity model of Jordan. The Hittiyah station is an excellent source of ground truth information for the six phosphate mines of southern Jordan and Israel. Observations of mining explosions collected by this station have numerous uses: for definition of templates for screening mining explosions, as ground truth events for calibrating travel-time models, and as explosion populations in development and testing discriminants. Following previously established procedures for identifying explosions, we have identified more than 200 explosions from the first 85 days of recording. In addition, Hittiyah is being calibrated for coda magnitude estimation and is placed favorably to estimate mechanism and magnitude for earthquakes along the Dead Sea Rift and the Gulf of Aqaba.
Download or read book Regional Model Calibration for Improving Seismic Location written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate seismic event location is integral to the effective monitoring of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), as well as being a fundamental component of earthquake source characterization. To account for the effects of crustal and mantle structure on seismic travel times, and to improve seismic event location in the Middle East and North Africa (MENA), we are developing a set of radially heterogeneous and azimuthally invariant travel-time models of the crust and upper mantle for each MENA seismic station. We begin by developing an average one-dimensional velocity model that minimizes the P-phase travel-time residuals from regional through teleseismic distance at each station. To do this we (1) generate a suite of 1-D velocity models of the earth, (2) compute travel times through the 1-D models using a tau-p formulation to produce standard travel-time tables, and (3) minimize the root-mean-square (rms) residuals between the P-phase arrivals predicted by each model and a groomed set of ISC P-phase arrival times (Engdahl et al., 1991). Once we have an average one-dimensional velocity model that minimizes the P-phase travel-time residuals for all distances, we repeat steps 1 through 3, systematically perturbing the travel-time model and using a grid search procedure to optimize models within regional, upper mantle, and teleseismic distance ranges. Regionalized models are combined into one two-dimensional model, using indicator functions and smoother methodologies to reduce distance and depth discontinuity artifacts between the individual models. Preliminary results of this study at a subset of MENA stations show that we are improving predictability with these models. Cross-validating the travel-time predictions with an independent data set demonstrates a marked reduction in the variance of the travel-time model error distributions. We demonstrate the improvement provided by these 2-D models by relocating the 1991 Racha aftershock sequence. We will extend our investigation to additional MENA stations, and will use our model in tandem with nonstationary empirical corrections (nonstationary Bayesian kriging) to further improve our ability to accurately predict travel times and locate seismic events in this region.
Download or read book The Use of Imperfect Calibration for Seismic Location written by and published by . This book was released on 2000 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: Efforts to more effectively monitor nuclear explosions include the calibration of travel times along specific paths. Benchmark events are used to improve travel-time prediction by: (1) improving models, (2) determining travel times empirically, or (3) using a hybrid approach. Even velocity models that are determined using geophysical analogy (i.e. models determined without the direct use of calibration data) require validation with calibration events. Ideally, the locations and origin times of calibration events would be perfectly known. However, the existing set of perfectly known events is spatially limited and many of these events occurred prior to the installation of current monitoring stations, thus limiting their usefulness. There are, however, large numbers of well (but not perfectly) located events that are spatially distributed, and many of these events may be used for calibration. Identifying the utility and limitations of the spatially distributed set of imperfect calibration data is of paramount importance to the calibration effort. In order to develop guidelines for calibration utility, we examine the uncertainty and correlation of location parameters under several network configurations that are commonly used to produce calibration-grade locations. We then map these calibration uncertainties through location procedures with network configurations that are likely in monitoring situations. By examining the ramifications of depth and origin time uncertainty, we expand on previous studies that focus strictly on epicenter accuracy. Particular attention is given to examples where calibration events are determined with teleseismic or local networks and monitoring is accomplished with a regional network.
Download or read book A Unified Approach to Joint Regional Teleseismic Calibration and Event Location with a 3D Earth Model written by and published by . This book was released on 2008 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: This newly initiated project will develop and test a methodology for locating seismic events from combined data sets of regional and teleseismic arrival times, based on consistent travel-time predictions from a unified 3D Earth model. One focus of the project is to address the practical difficulty of raytracing in 3D models, which has been a serious impediment to the pursuit of 3D event location methods. We will investigate whether, for teleseismic travel-time prediction, approximate techniques, in particular linearization around rays calculated in a 1D reference model, are adequate for the purpose of event location as they are commonly assumed to be for the purpose of global tomography. A second focus of the project is tomographic calibration of a 3D model with combined regional and teleseismic data from earthquakes and ground-truth events. We will investigate the hypothesis that a joint regional/teleseismic calibration will lead to a noticeable improvement in location accuracy over the modest and inconsistent improvements 3D models have yielded to date. Additionally, we will consider whether travel-time prediction errors inferred from a tomographic uncertainty analysis can provide an appropriate weighting of various teleseismic and regional phases to optimize location accuracy even further. We plan to validate our methodology with catalog data from Asia, the Middle East and North Africa, using available regional crust/upper mantle models for these areas in conjunction with published 3D global models of the deeper mantle. Special attention will be given to south-central Asia, where Weston Geophysical and MIT are currently applying body-wave and surface-wave tomography to develop a regional model of the crust and upper mantle. This project will attempt to improve and extend the Weston/MIT model by adding teleseismic constraints.
Download or read book Source Specific Station Corrections SSSCS for International Monitoring System IMS Seismic Stations in North Africa Middle East and Western Asia written by and published by . This book was released on 2000 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: To date, IDC regional travel time corrections have been successfully implemented for Fennoscandia and North America. Corrections and associated modeling errors to Pn, Pg, Sn, and Lg IASPEI91 travel time tables are specified on 1 by 1 degree latitude and longitude "source specific" grids within 20 degrees of each International Monitoring System (IMS) station. International Data Center (IDC) location software is configured to read and apply these grids when locating events in the Reviewed Event Bulletin (REB). In order to develop regional travel time corrections for IMS stations in North Africa, Middle East, and Western Asia, a consortium was formed of experts in IDC software integration/testing/validation, regional/global body/surface-wave tomography, tectonic regionalization, 3D ray-tracing, and ground truth (GT) data collection with the goal to improve location accuracy and precision while maintaining honest 90% coverage ellipses. The three-year R & D program will provide Source Specific Station Corrections (SSSCs) for all IMS primary and auxiliary seismic stations in the region. Corrections will be developed, tested, and validated in two phases. A preliminary set of SSSCs will be delivered and tested by late 2001. A refined set of SSSCs will be delivered and tested by early 2003. The preliminary set will develop corrections for surface sources only based on an initial preliminary regionalization and set of crustal and upper mantle models. The 3D model will be based on a hierarchy of global 3D models, regional models, and tectonic regionalization. Travel times will be computed by 3D ray tracing from each station to a grid of source locations. Modeling errors for the initial correction set may be conservatively large. Meanwhile, a concerted effort has begun to gather ground truth (GT) location data in the region for validation. All GT origins, GT arrivals, velocity models, regionalizations, SSSCs, and metadata will be delivered for testing and validation.
Download or read book Source Spectra Moment and Energy for Recent Eastern Mediterranean Earthquakes written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In the past several years there have been several large (M{sub w}> 7.0) earthquakes in the eastern Mediterranean region (Gulf of Aqaba, Racha, Adana, etc.), many of which have had aftershock deployments by local seismological organizations. In addition to providing ground truth data (GT “5 km) that is used in regional location calibration and validation, the waveform data can be used to aid in calibrating regional magnitudes, seismic discriminants, and velocity structure. For small regional events (m{sub b} “4.5), a stable, accurate magnitude is essential in the development of realistic detection threshold curves, proper magnitude and distance amplitude correction processing, formation of an M{sub s}:m{sub b} discriminant, and accurate yield determination of clandestine nuclear explosions. Our approach provides a stable source spectra from which M{sub w} and m{sub b} can be obtained without regional magnitude biases. Once calibration corrections are obtained for earthquakes, the coda-derived source spectra exhibit strong depth-dependent spectral peaking when the same corrections are applied to explosions at the Nevada Test Site (Mayeda and Walter, 1996), chemical explosions in the recent ''Depth of Burial'' experiment in Kazahkstan (Myers et al., 1999), and the recent nuclear test in India. For events in the western U.S. we found that total seismic energy, E, scales as M{sub o}{sup 0.25} resulting in more radiated energy than would be expected under the assumptions of constant stress-drop scaling. Preliminary results for events in the Middle East region also show this behavior, which appears to be the result of intermediate spectra fall-off (f{sup 1.5}) for frequencies ranging between (almost equal to)0.1 and 0.8 Hz for the larger events. We developed a Seismic Analysis Code (SAC) coda processing command that reads in an ASCII flat file that contains calibration information specific for a station and surrounding region, then outputs a coda-derived source spectra, moment estimate, and energy estimate.
Download or read book Living on an Active Earth written by National Research Council and published by National Academies Press. This book was released on 2003-09-22 with total page 431 pages. Available in PDF, EPUB and Kindle. Book excerpt: The destructive force of earthquakes has stimulated human inquiry since ancient times, yet the scientific study of earthquakes is a surprisingly recent endeavor. Instrumental recordings of earthquakes were not made until the second half of the 19th century, and the primary mechanism for generating seismic waves was not identified until the beginning of the 20th century. From this recent start, a range of laboratory, field, and theoretical investigations have developed into a vigorous new discipline: the science of earthquakes. As a basic science, it provides a comprehensive understanding of earthquake behavior and related phenomena in the Earth and other terrestrial planets. As an applied science, it provides a knowledge base of great practical value for a global society whose infrastructure is built on the Earth's active crust. This book describes the growth and origins of earthquake science and identifies research and data collection efforts that will strengthen the scientific and social contributions of this exciting new discipline.
Download or read book Nuclear Test Ban written by Ola Dahlman and published by Springer Science & Business Media. This book was released on 2009-04-21 with total page 284 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nuclear tests have caused public concern ever since the first such test was conducted, more than six decades ago. During the Cold War, however, con- tions were not conducive to discussing a complete ban on nuclear testing. It was not until 1993 that negotiations on such a treaty finally got under way. From then on, things moved relatively quickly: in 1996, the United Nations General Assembly adopted the Comprehensive Nuclear-Test-Ban Treaty (CTBT). To date, the Treaty has been signed by 178 states and ratified by 144, though it has yet to enter into force, as nine out of 44 ‘‘Annex 2 states’’, whose ratification is mandatory, have not heeded the call. Nevertheless, the CTBT verification system is already provisionally operational and has proven its effectiveness. We commend the CTBT organisation in Vienna for its successful efforts to build a verification network. This book is an excellent overview of the evolution of the CTBT and its verification regime. The authors are eminent scholars from the Netherlands, Norway and Sweden who have been intimately involved with the CTBT and its verification agency, the CTBTO Preparatory Commission, from their inc- tion to the present day. They have written a thorough and engaging narrative of the long road that led to the CTBT. Their story will appeal to both the layman and the expert and provide useful lessons for future negotiations on disarmament issues.
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:
