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 Improving Regional Seismic Event Location Through Calibration of the International Monitoring System written by and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: At Lawrence Livermore National Laboratory (LLNL), we are working to help calibrate the 170 seismic stations that are part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) monitoring network, in order to enhance the network's ability to locate small seismic events. These low magnitude events are likely to be recorded by only the closest of seismic stations, ranging from local to near teleseismic distances. At these distance ranges, calibration statistics become highly nonstationary, challenging us to develop more general statistical models for proper calibration. To meet the goals outlined above, we are developing a general nonstationary framework to accurately calibrate seismic travel-time predictions over the full distance range, from local, to regional, to teleseismic distances. The objective of this framework is to develop valid region-specific corrections for the Middle Fast, North Africa, and portions of the Soviet Union, to assess our progress towards meeting calibration goals, and to perform cost-benefit analysis for future calibrations. The framework integrates six core components essential to accurate calibration. First, is the compilation and statistical characterization of well located reference events, including aftershock sequences, mining explosions and rockbursts, calibration explosions, and teleseismically constrained events (Harris et al., SSA 1999; Hanley et al., SSA 1999). Second, is the development of generalized velocity models based on these reference events (McNamara et al., SSA 1998; Pasyanos, SSA 1999). Third, is the development of nonstationary spatial corrections (nonstationary Bayesian kriging) that refine the base velocity models (Schultz et al., SSA 1998). The fourth component is the development of a detection model on a station-by-station basis. The fifth component is the cross-validation of calibration results to ensure internal consistency along with the continual benchmarking of our nonstationary model where event locations are accurately known (Myers and Schultz., SSA 1999). Finally, the sixth component is the development of location uncertainty maps, demonstrating how calibration is helping to improve location accuracy across both seismically active and aseismic regions. Together, these components help us to ensure the accurate location of events, and just as important, help to ensure the accurate representation of bias uncertainty and random uncertainty in the predicted error ellipses.

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 Integrating Diverse Calibration Products to Improve 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: The monitoring of nuclear explosions on a global basis requires accurate event locations. As an example, under the Comprehensive Test Ban Treaty, the size of an on-site inspection search area is 1,000 square kilometers or approximately 17 km accuracy assuming a circular area. This level of accuracy is a significant challenge for small events that are recorded using a sparse regional network. In such cases, the travel-time of seismic energy is strongly affected by crustal and upper mantle heterogeneity and large biases can result. This can lead to large systematic errors in location and, more importantly, to invalid error bounds associated with location estimates. Corrections can be developed and integrated to correct for these biases. These path corrections take the form of both three-dimensional model corrections along with three-dimensional empirically based travel time corrections. LLNL is currently working to integrate a diverse set of three-dimensional velocity model and empirical based travel-time products into one consistent and validated calibration set. To perform this task, we have developed a hybrid approach that uses three-dimensional model corrections for a region and then uses reference events when available to improve the path correction. This Bayesian kriging approach uses the best apriori three-dimensional velocity model that is produced for a local region and uses this as a baseline correction. When multiple models are produced for a local region, uncertainties in the models are compared against each other using ground truth data and an optimal model is chosen. We .are in the process of combining three-dimensional models on a region-by-region basis and integrating the uncertainties to form a global correction set. The Bayesian kriging prediction combines this a priori model and its statistics with the empirical calibrations to give an optimal aposteriori calibration estimate. In regions where there is limited or no coverage by reference events the corrections will be based primarily on the model. The integrated a priori model is particularly important in these areas. In regions with adequate calibration events, we are demonstrating improvement in event location through the reduction of regional bias. In regions with sparse or no ground truth, the a priori model will need to be spot-validated with the use of dedicated calibration experiments or through the use of mining explosions, where available.

Download or read book LLNL s 3 D A Priori Model Constraints and Uncertainties for Improving Seismic Location written by and published by . This book was released on 2000 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate seismic event location is key to monitoring the Comprehensive Nuclear-Test-Ban Treaty (CTBT) and is largely dependent on our understanding of the crust and mantle velocity structure. This is particularly challenging in aseismic regions, devoid of calibration data, which leads us to rely on a priori constraints on the velocities. We investigate our ability to improve seismic event location in the Middle East, North Africa, and the Former Soviet Union (ME/NA/FSU) by using a priori three-dimensional (3-D) velocity models in lieu of more commonly used one dimensional (1-D) models. Event locations based on 1-D models are often biased, as they do not account for significant travel-time variations that result from heterogeneous crust and mantle; it follows that 3-D velocity models have the potential to reduce this bias. Here, we develop a composite 3-D model for the ME/NA/FSU regions. This fully 3-D model is an amalgamation of studies ranging from seismic reflection to geophysical analogy. Our a priori model specifies geographic boundaries and velocity structures based on geology, tectonics, and seismicity and information taken from published literature, namely a global sediment thickness map of 1{sup o} resolution (Laske and Masters, 1997), a regionalized crustal model based on geology and tectonics (Sweeney and Walter, 1998; Bhattacharyya et al., 2000; Walter et al., 2000), and regionalized upper mantle (RUM) models developed from teleseismic travel times (Gudmundsson and Sambridge, 1998). The components of this model were chosen for the complementary structures they provide. The 1{sup o} sediment map and regionalized crustal model provide detailed structures and boundaries not available in the more coarse 5{sup o} models used for global-scale studies. The RUM models offer improved resolution over global tomography, most notably above depths of 300 km where heterogeneity is greatest; however, we plan to test other published upper mantle models of both P- and S-wave velocity. We compute travel times through this integrated model for comparison with other standard 1-D models, as our goal is to evaluate whether the 3-D model can better predict the observed travel times. The arrival times are computed through the model using a 3-D finite-difference technique and are then compared with a declustered set of ISC P arrival times (Engdahl et al., 1998). Our ME/NA/FSU model predicts the P and Pn travel times very well, as measured by variance reduction, for three stations we tested: ARU, KVT, and GAR; these predicted times also resemble some patterns seen in Pn tomography models of this region. Such tests will allow us to identify parts of the model that may need modification. We also compute model-based correction surfaces for each station in the ME/NA/FSU regions that can be used as additional constraints in our event location algorithm to determine the improvement provided by using 3-D models. We use this method to relocate a set of ground truth events: the 1991 Racha aftershock sequence which was investigated by Myers and Schultz (2000) using empirical kriged correction surfaces and a 1-D velocity model. They find an epicenter mislocation bias of 42 km when no corrections are applied and that this mislocation is reduced to 13 km when their empirically derived correction surfaces are included. We relocate this same set of events using our model-based correction surfaces and produce a mislocation bias of only 26 km, a significant improvement. We are currently implementing methods to quantify uncertainties on the model-based corrections which will be required to compute representative error ellipses for the new locations. We also plan to combine both the model-based and empirical correction techniques to achieve the best improvement in location. This test case demonstrates the power of using 3-D velocity models to improve location capability for small, regionally recorded events. This example also shows how the model-based approach holds great potential for improving locations in aseismic regions where it may not be possible to compute empirical correction surfaces.

Download or read book The DOE Model for Improving Seismic Event Locations Using Travel Time Corrections written by and published by . This book was released on 1998 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The U.S. National Laboratories, under the auspices of the Department of Energy, have been tasked with improv- ing the capability of the United States National Data Center (USNDC) to monitor compliance with the Comprehen- sive Test Ban Trea~ (CTBT). One of the most important services which the USNDC must provide is to locate suspicious events, preferably as accurately as possible to help identify their origin and to insure the success of on-site inspections if they are deemed necessary. The seismic location algorithm used by the USNDC has the capability to generate accurate locations by applying geographically dependent travel time corrections, but to date, none of the means, proposed for generating and representing these corrections has proven to be entirely satisfactory. In this presentation, we detail the complete DOE model for how regional calibration travel time information gathered by the National Labs will be used to improve event locations and provide more realistic location error esti- mates. We begin with residual data and error estimates from ground truth events. Our model consists of three parts: data processing, data storage, and data retrieval. The former two are effectively one-time processes, executed in advance before the system is made operational. The last step is required every time an accurate event location is needed. Data processing involves applying non-stationary Bayesian kriging to the residwd data to densifi them, and iterating to find the optimal tessellation representation for the fast interpolation in the data retrieval task. Both the kriging and the iterative re-tessellation are slow, computationally-expensive processes but this is acceptable because they are performed off-line, before any events are to be located. In the data storage task, the densified data set is stored in a database and spatially indexed. Spatial indexing improves the access efficiency of the geographically-ori- ented data requests associated with event location. Finally, in the Data Retrieval phase, when an accurate location is needed, the densified data is retrieved and a quick interpolation is performed using natural neighbor interpolation with a gradient slope modification to guarantee continuous derivatives. To test our model, we use the residuals from a large set of synthetic events (441) that were created to have travel times consistent with the IASP91 radial base model plus perturbations of up to 2 seconds taken from spherical har- monic surfaces with randomly generated coefficients. Relocating these events using 3 stations with poor azimuthal coverage and IASP91 travel times alone yields dislocations of up 278 km with a mean value of 58 km. Using our model to apply travel time corrections we reduce the hugest dislocation to 151 km and the mean value to 13 km. Fur- ther, the error ellipses generated now accurately reflect the uncertainly associated with the composite model (base model + corrections), and as a result are small for events occurring near ground truth event points and large for events occurring where no calibration data is available.

Download or read book Research Required to Support Comprehensive Nuclear Test Ban Treaty Monitoring written by Panel on Basic Research Requirements in Support of Comprehensive Test Ban Monitoring and published by National Academies Press. This book was released on 1997-08-15 with total page 133 pages. Available in PDF, EPUB and Kindle. Book excerpt: On September 24, 1996, President Clinton signed the Comprehensive Nuclear Test Ban Treaty at the United Nations Headquarters. Over the next five months, 141 nations, including the four other nuclear weapon states -- Russia, China, France, and the United Kingdom -- added their signatures to this total ban on nuclear explosions. To help achieve verification of compliance with its provisions, the treaty specifies an extensive International Monitoring System of seismic, hydroacoustic, infrasonic, and radionuclide sensors. This volume identifies specific research activities that will be needed if the United States is to effectively monitor compliance with the treaty provisions.

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 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 Monitoring the Comprehensive Nuclear Test Ban Treaty written by Frode Ringdal and published by Springer Science & Business Media. This book was released on 2001-04 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt: In September 1996, the United Nations General Assembly adopted the Comprehensive Nuclear-Test-Ban Treaty (CTBT), prohibiting nuclear explosions worldwide, in all environments. The treaty calls for a global verification system, including a network of 321 monitoring stations distributed around the globe, a data communications network, an international data centre (IDC), and on-site inspections, to verify compliance. This volume contains research papers focusing on seismic ecent location in the CTBT context. The on-site inspection protocol of the treaty specifies a search area not to exceed 1000 square km. Much of the current research effort is therefore directed towards refining the accuracy of event location by including allowances for three-dimensional structure within the Earth. The aim is that the true location of each event will lie within the specified source zone regarding postulated location. The papers in this volume cover many aspects of seismic event location, including the development of algorithms suitable for use with three-dimensional models, allowances for regional structure, use of calibration events and source-specific station corrections. They provide a broad overview of the current international effort to improve seismic event location accuracy, and the editors hope that it will stimulate increased interest and further advances in this important field.

Download or read book Calibration of 3D Upper Mantle Structure in Eurasia Using Regional and Teleseismic Full Waveform Seismic Data written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Adequate path calibrations are crucial for improving the accuracy of seismic event location and origin time, size, and mechanism, as required for CTBT monitoring. There is considerable information on structure in broadband seismograms that is currently not fully utilized. The limitations have been largely theoretical. the development and application to solid earth problems of powerful numerical techniques, such as the Spectral Element Method (SEM), has opened a new era, and theoretically, it should be possible to compute the complete predicted wavefield accurately without any restrictions on the strength or spatial extent of heterogeneity. This approach requires considerable computational power, which is currently not fully reachable in practice. We propose an approach which relies on a cascade of increasingly accurate theoretical approximations for the computation of the seismic wavefield to develop a model of regional structure for the area of Eurasia located between longitudes of 30 and 150 degrees E, and latitudes of -10 to 60 degrees North. The selected area is particularly suitable for the purpose of this experiment, as it is highly heterogeneous, presenting a challenge for calibration purposes, but it is well surrounded by earthquake sources and, even though they are sparsely distributed, a significant number of high quality broadband digital stations exist, for which data are readily accessible through IRIS (Incorporated Research Institutions for Seismology) and the FDSN (Federation of Digital Seismic Networks). The starting models used will be a combination of a-priori 3D models recently developed for this region, combining various geophysical and seismological data, and a major goal of this study will be to refine these models so as to fit a variety of seismic waveforms and phases.

Download or read book Extending Regional Wave Form Modeling to Shorter Periods to Improve the Location and Identification of Small Seismic Sources written by and published by . This book was released on 2000 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: In an effort to improve the location of small seismic events near known test sites, we are determining source-station specific corrections (SSSC's) for regional P, S and Lg phases recorded at IMS stations within 20 deg of these locals, in particular the central Asian test sites of Lop Nor Semipalantinsk. To this end, we are calculating travel-time residuals between phase arrival information from various sources -- CEB and ISC values as well as direct waveform picks -- and IASP91 predictions using available ground-truth data for events in and near these test sites. These residuals are then averaged for each station to determine the empirical SSSC's. Ground-truth data for these events vary in accuracy; in particular, the level of ground truth for more recent Lop Nor explosions, which are the only ones recorded by many of the newer IMS stations, is not well constrained, being GT25 locations from the Reviewed and Calibration Event Bulletins (REB and CEB). As accurate hypocentral information is crucial to obtaining well-calibrated travel-time corrections, we re-evaluated these more poorly constrained ground-truth data. We found that the ISC locations were quite similar to those of GT5 Lop Nor events which were determined from joint epicenter determinations (JED). For m(b) greater than or equal to 5 explosions the average difference in epicentral locations is 2.9 km, with the maximum being 5.5 km; and differences in origin time being 0.1 sec on average, with the maximum being 0.3 sec. Epicentral errors for these ISC locations are small, being less than 5 km. Discrepancies and errors are significantly larger for the smaller (m(b) less than or equal to 4.7) explosions, and are assumed to be due to SNR phase picking problems and fewer observations used to determine locations. Consequently the ISC teleseismic locations for the m(b) is greater than or equal to 5 explosions can be considered to be of GT5 quality.

Download or read book Monitoring the Comprehensive Nuclear Test Ban Treaty Source Location written by Frode Ringdal and published by Birkhäuser. This book was released on 2013-03-07 with total page 414 pages. Available in PDF, EPUB and Kindle. Book excerpt: In September 1996, the United Nations General Assembly adopted the Comprehensive Nuclear-Test-Ban Treaty (CTBT), prohibiting nuclear explosions worldwide, in all environments. The treaty calls for a global verification system, including a network of 321 monitoring stations distributed around the globe, a data communications network, an international data centre (IDC), and on-site inspections, to verify compliance. This volume contains research papers focusing on seismic ecent location in the CTBT context. The on-site inspection protocol of the treaty specifies a search area not to exceed 1000 square km. Much of the current research effort is therefore directed towards refining the accuracy of event location by including allowances for three-dimensional structure within the Earth. The aim is that the true location of each event will lie within the specified source zone regarding postulated location. The papers in this volume cover many aspects of seismic event location, including the development of algorithms suitable for use with three-dimensional models, allowances for regional structure, use of calibration events and source-specific station corrections. They provide a broad overview of the current international effort to improve seismic event location accuracy, and the editors hope that it will stimulate increased interest and further advances in this important field.

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 Seismological Research Letters written by and published by . This book was released on 2006 with total page 436 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 Methods for the IMS Regional Kinematic Calibration written by and published by . This book was released on 2000 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Among the problems related to CTBT a very important role belongs to the calibration of the regional travel times (regional kinematic calibration). The success in solving this task would significantly improve the accuracy of the weak seismic event location by the system. The methods that are applied to perform this kind of calibration are assumed in the present paper. All these methods can be broken into two principal groups: methods for direct calibration and those utilizing the velocity model of the media that is to be developed in an intermediate stage. Direct methods are used to construct the time correction surfaces making use of previously learned seismological experience (regional travel time tables) or directly employing the experimental data. The first approach represents the try to perform the task through the linear combination of regional travel time tables (godographs) and their errors. Another technique is a kind of spatial interpolation of the regional observations for given station. Indirect methods solve the calibration problem in two steps. Initially the 3-D velocity model of the media is being produced by the inversion of the observations. Afterwards the field of travel times is generated on the base of the velocity model. Methods inside the group differ depending upon what way is chosen for the reverse kinematic problem solution. Currently the velocity models are being built by "try-and-drop" technique or by tomographic inversion. The tomographic P-models developed till now do not possess the horizontal resolution enough to be successfully applied in a regional scale. The main reason of poor lateral resolution for the uppermost mantle comes from low amount and uneven distribution of regional P-wave observations used to produce the global tomographic models. The reliability of 3-D model constructed by "try-and-drop" method is unknown but its using is still reasonable unless enough data for the area to be calibrated have been collected.