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The purpose of this research is to develop and test a novel method of regional seismic event location based on exploiting Empirical Green's Functions (EGF) that are produced from ambient noise. Elastic EGFs between pairs of seismic stations are determined by cross-correlating long ambient noise time-series recorded at the two stations. The EGFs principally contain Rayleigh and Love wave energy and our focus is placed on utilizing these signals between 5- and 15-sec periods. By comparing the tabulated EGFs in the frequency-time domain with similarly transformed records of seismic events (earthquakes, explosions, mine collapses) obtained by a network of remote stations, we have tested the method by locating events in the western USA for which other methods provide accurate locations (Californian Ground Truth earthquakes, the mine collapse in Utah). Data from the EarthScope USArray were used primarily. The location errors for GT1 earthquakes in California and the Crandall mine collapse in Utah were on average less than 1 km with origin time errors less than 1 s. These results were described in detail in Ritzwoller et al. (2009). During the past year we continued to refine the method and evaluate its capabilities. The ability of this approach to locate seismic events using a limited number of recording stations with significant open azimuth has been shown. We applied this method to less ideal environments locating small seismic events with magnitude 3.0-3.7 in Utah, with location accuracy better than 0.5 km relative to the University of Utah network locations. The effects of unknown source mechanism and depth on location were studied and are presented here. All research to date is described in detail by Barmin et al. (2010). Future work will continue to refine the location procedure and explore it ability to constrain depth and the moment tensor using ambient noise., Published in Proceedings of the 2010 Monitoring Research Review - Ground-Based Nuclear Explosion Monitoring Technologies, 21-23 September 2010, Orlando, FL. Volume I. Sponsored by the Air Force Research Laboratory (AFRL) and the National Nuclear Security Administration (NNSA). U.S. Government or Federal Rights License

We report on the progress toward the development of attenuation models for short-period (12-22 sec) Rayleigh waves in Asia and surrounding regions. These models are defined by maps of attenuation coefficients across the region of study in the specified period band. These models are designed to calibrate the regional surface-wave magnitude scale and to extend the teleseismic surface-wave magnitude body-wave magnitude (Ms-mb) discriminant to regional distances. In order to obtain accurate attenuation estimates, we must first measure surface-wave amplitudes reliably. Taking advantage of certain characteristics of Rayleigh waves, such as the dispersion and the elliptical particle motion, we employed a suite of techniques in making accurate fundamental-mode Rayleigh-wave amplitude measurements. We first analyze the dispersion of the surface wavetrain using a spectrogram. Based on the characteristics of the data dispersion, we design a phase-matched filter by using either a manually picked dispersion curve, or a model-predicted dispersion curve, or the dispersion of the data, and apply the filter to the seismogram. Intelligent filtering of the seismogram and windowing of the resulting cross-correlation based on the spectrogram analysis and the comparison between the spectrum of phase-match filtered data and raw-data and source spectra effectively reduces amplitude contaminations from surface-wave higher modes, multipathing, body-wave energy and other noise sources, and results in reliable amplitude measurements in many cases. We implemented these measuring techniques in a graphic-user-interface tool called Surface Wave Amplitude Measurement Tool (SWAMTOOL). Using the tool, we collected and processed waveform data for 200 earthquakes occurring throughout 2003-2006 inside and around Eurasia. The records from 135 broadband permanent and temporary stations were used., Presented at the Conference on Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies (30th), held in Portsmouth, VA, on 23-25 Sep 2008. Published in the proceedings of the conference, p108-117, 2008. Prepared in collaboration with Los Alamos National Laboratory. Sponsored in part by the National Nuclear Security Administration (NNSA). The original document contains color images.

We report on progress toward an attenuation model for short-period (10-20 s) Rayleigh waves in Central Asia and surrounding regions. This model will be defined by maps of attenuation across the region of study in the specified period band. The model is designed to calibrate the regional surface-wave magnitude scale and to extend the teleseismic 'surface-wave magnitude-body-wave magnitude' (Ms-mb) discriminant to regional distances (Marshall and Basham, 1971; Bonner et al., 2006; Russell, 2006). Work is progressing in three stages: (1) data accumulation and amplitude measurements, (2) estimation of attenuation coefficients, and (3) tomographic inversion of attenuation data. The first stage in model construction was the measurement of Rayleigh wave spectral amplitudes. To overcome inherent difficulties due to multipathing and scattering of short-period surface waves we applied the Surface Wave Amplitude Measurement Tool (SWAMTOOL) designed at Los Alamos National Laboratory (LANL) (Yang et al., 2005), which incorporates dispersion analysis, phase-matched filtering, and additional means to estimate the quality and reliability of the measurements. We enhanced SWAMTOOL by providing different options for phase-matched filtering of surface wave signals (Levshin et al., 2006). We collected and processed waveform data for 200 earthquakes occurring throughout 2003-2006 inside and around Eurasia. The records of about 140 broadband permanent and temporary stations were used. The existing broadband station distribution and the pattern of seismicity provided sufficient number of spectral amplitude measurements between 12 and 20 s periods for the construction of the two-dimensional (2-D) tomographic maps of attenuation coefficients. Measurements at periods below about 12 s are too scarce for tomographic inversion., Presented at the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies Conference (29th) held in Denver, CO on 25-27 September 2007. Published in the Proceedings of the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies Conference (29th), p111-122, September 2007. The original document contains color images.

The objective of this research was to construct surface wave group velocity maps at intermediate periods for the Near East, Central Asia and the Far East and to estimate the possibility of using these maps to extract weak surface wave signals and measure their amplitude spectra. To reach these goals we acquired broadband digital records of more than 1600 events that occurred in and around Eurasia during the period 1976-1998 and recorded by about 170 stations of global and regional networks, and PASSCAL deployments. All data were processed by seismic analysts using the frequency-time analysis package developed at the Univ. of Colorado. Altogether more than 23,000 dispersion curves of Rayleigh waves and 18,500 dispersion curves of Love waves were obtained. We developed a new method for tomographic inversion of these measurements. We studied effects of source group time delays and off-path propagation on tomographic images., The original document contains color images. All DTIC reproductions will be in black and white.

We have assembled a data set of nearly 1000 events across Eurasia and N. Africa whose locations and origin times are known with high accuracy. These events which occur in 23 event clusters, the groomed P and Pn arrival time data observed at regional distances, and about 1000 empirical phase path anomalies create a Ground Truth (CT) data base to be used to assess the quality of 3-D models and their applicability to regional locations. We assessed several seismic models of the crust and upper mantle, concentrating on the 1-D model AK135 and the 3-D $v_s$ model CUB2.0, in two ways: (1) the fit of model predicated travel times to the empirical path anomalies and (2) the ability to locate the CT events. The 3-D Vp model converted from CUB2.0 Vs model using the thermoelastic properties of an assumed mantle composition fits regional P and Pn travel times remarkably well. Our findings underscore the importance of GT data bases in assessing 3-D models, and show that global 3-D Vs models provide a sound basis on which to build improvements in regional location capabilities.

As an intermediate step to producing a integrated P and S model of the crust and upper mantle beneath most of Eurasia to predict regional station specific travel time correction surfaces, we present maps of isotropic Pn and Sn velocities across Eurasia. These maps are constructed using a groomed version of the ISC/NEIC data that are described, in part, by Engdahl et al. (1998). The locations and origin times of the events are replaced with local ground truth locations whenever possible (e.g., Sultanov et al., 1999). We use the tomographic method of Barmin et al. (2000) to estimate Pn and Sn maps on a 1.5 x 1.5 degree grid, augmented to include station and event static corrections and an epicentral distance or range correction. The starting model is CRUST5.1 (Mooney et al., 1998). We call the Pn and Sn maps together with these corrections the CU Pn=Sn model. Data are used in the inversion if the residual relative to the prediction from the spherical model AK135 (Kennett et al., 1995) is less than 7.5 s for P and 15 s for S, if the event depth is within the crust or less than 50 km deep, if the azimuthal gap to all reporting stations for the event is less than 180 degrees, and if the nominal error ellipse is less than 1000 km2 in area. We define the phases Pn and Sn as arriving between epicentral distances of 3 and 15 degrees. The resulting data set consists of about 1,600,000 Pn and 400,000 Sn travel times inhomogeneously distributed across Eurasia., Proceedings of the 22nd Annual DoD/DOE Seismic Research Symposium: Planning for Verification of and Compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) held in New Orleans, Louisiana on September 13-15, 2000. U.S. Government or Federal Rights. The original document contains color images.

This report presents the results of a study of the dispersion characteristics of intermediate period broadband fundamental surface waves propagating across Central Asia, Western China, and parts of the Middle East. We present group velocity maps from 10 s to 40 s period for both Rayleigh and Love waves. Broadband waveform data from about 600 events from 1988 - 1995 recorded at 83 individual stations from several global and regional networks (MEDNET, KNET, KAZNET) have produced about 9,000 paths for which individual dispersion curves have been estimated. These data break into two sets of measurements: those from about 400 large (Ms > 5.0) earthquakes from around the continent recorded on both global and regional networks and those from about 200 additional smaller (Ms < 5.0) events recorded regionally at KNET and KAZNET. The combination of measurements on these two spatial scales helps to optimize path coverage and azimuthal distribution which together determine resolution. This study displays denser and more uniform data coverage and demonstrates higher resolution (-4 deg) than previous studies that have been performed on this scale and at these periods.

Earthquake seismograms recorded by several global and regional networks between 1988 and late 1995 were used to measure the group velocity dispersion of fundamental Rayleigh and Love waves crossing Eurasia. More than 9,000 three component long period seismograms following more than 600 events with Ms greater than 4.5 were processed. This data set was reduced by clustering observations along similar paths into measurements along the unique path, and rejecting outliers. The resulting curves were used to construct group velocity maps from 20s period to 200s period for Rayleigh waves and up to 150s period for Love waves. These maps have better resolution and are more reliable than globally estimated dispersion maps or such maps computed from current global models of the crust and mantle. In particular, they contain new information about large sedimentary features, lower crustal and upper mantle structures, Moho topography. These maps guide the identification and extraction of surface waveforms which emanate from small seismic events. They should be added to the Knowledge Base used to monitor clandestine nuclear tests. More accurate and detailed crustal and upper mantle models derived from these maps are very important for improvement of location/depth estimation in the strategic areas of Eurasia characterized by complex geology.

This research is dedicated to the investigation of the relevance and use of intermediate period (5 - 25 s) surface wave data in problems of detection, discrimination, and the accurate location of small events using regional array data. It is focused on analysis of data from earthquakes throughout Central and Southern Asia and the Middle East and nuclear explosions at Lop Nor within 15 - 25 degrees of the Kyrghiz Telemetered Seismic Network. The main efforts during the 6.5-month time period covered by this report were directed to data collection and preprocessing, software development, measurements of surface wave characteristics, and constructing 'master curves' for clusters of events in specific regions. In the next year, we will greatly increase the volume of processed data and construct group velocity maps for Central and Southern Asia. The expected weak surface wave signals recorded by a network and improvement of the regional model of the lithosphere. This will provide means to enhance detection and location capabilities.

This research is dedicated to investigating the relevance and use of intermediate period (10 - 40 s) surface wave data in problems of detection, discrimination, and the accurate location of small events using regional array data. It is focused on the analysis of data from events throughout Central and Southern Asia within 27 degrees of the Kyrgyz Telemetered Seismic Network. The main efforts during the 1 year time period covered by this report were directed to data collection and preprocessing, software development, measurements of surface wave characteristics, and constructing group velocity maps. More than 1400 wave paths for Rayleigh waves and 900 paths for Love waves have been used for this purpose. The spatial resolution of obtained maps is 250-400 km, and they exhibit many features related to local tectonic structures, unresolved by previous studies. The inversion of these maps for the 3D shear-velocity structure of the region is in progress. Such models will provide the means to enhance existing detection and location capabilities in Central and Southern Asia.

The resolving power and the noise resistance· of the computer procedure called "frequency-time analysis", or briefly "FTAN" are investigated. The applications of FTAN to analysis of surface and body seismic waves and electromagnetic waves in the magnetosphere are demonstrated.