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Waveform modeling techniques are applied to several recent, moderate sized earthquakes recorded by the broadband TERRAscope array in southern California. A method for the determination of source parameters at regional distances with three-component, sparse network data is described. The sensitivity of the method to source mislocations and velocity model is investigated. The method is relatively insensitive to source mislocation. The choice of velocity model can affect the inversion results, but it appears that for a number of paths throughout southern California, a simple plane layered velocity model derived from travel-time studies explains much of the observed waveforms. The broadband waveforms of two small earthquakes that occurred in 1988 near Upland, California are forward modeled to determine Green's functions for the path to Pasadena, California. The effects of near surface gradients, crustal interface sharpness, and two-dimensional basin-ridge structures were studied. This analysis resulted in a simple plane layered velocity model that best fit the data. The Green's functions are then used to study the source characteristics of the 1990 Upland mainshock (M_L = 5.2). The long-period body waves are inverted to determine the orientation and seismic moment. Comparisons of the 1990 mainshock with the 1988 events revealed that the mainshock was a relatively complicated event. Multi-point source and distributed finite slip models show that the mainshock ruptured down dip (6 km to 9km) with a non-uniform slip distribution in which 30 % of the total seismic moment was released from a relatively small area at 9 km depth. The overall area of the mainshock was found to be significantly smaller than the aftershock zone. The source process of the June 28, 1991 Sierra Madre earthquake (M_L = 5.8) is investigated using the broadband data recorded at 6 TERRAscope stations. The long-period body waves are inverted to determine the orientation and seismic moment. Ratios of the

We build on our earlier results (DE-FC52-06NA27324, Dreger et al., 2008; Ford et al., 2010; Ford et al., 2009a, b Ford et al., 2008) in which it has been demonstrated that regional distance moment tensor analysis can discriminate explosions from naturally occurring earthquakes and mine collapses. In this project, as an effort to refine procedures for implementation we develop a more complete understanding of uncertainties, and define robust methods for their characterization. In Ford et al., 2008, it was found that populations of explosions, earthquakes and collapses in the Western U.S. separated on a Hudson et al. (1989) diagram enabling source-type discrimination. A question the current research addresses is whether these populations remain separated for other regions of the world. We have compiled a database of naturally occurring, and induced seismicity to examine the distribution of non-double-couple seismic moment tensors in a Hudson source-type diagram to be used as an a priori constraint. The results indicate the region of tradeoff between a pure explosion monopole and a compressional major vector dipole (CLVD) is relatively devoid of natural and induced seismicity, which is favorable for seismic moment tensor source-type discrimination. In addition, we present new results for the North Korean test combining regional and teleseismic observations to further restrict tradeoff between pure explosion and pure CLVD solutions for nuclear explosions. We are investigating the velocity model dependence of vanishing free-surface traction effects on seismic moment tensor inversion of shallow sources, and are working on developing a damped inversion to suppress these effects and reduce bias in scalar moment estimates for shallow sources. Finally, we are working toward extending the regional seismic moment tensor database for nuclear explosions and natural seismicity for the Korean Peninsula and Kazakhstan., Published in the Proceedings of the 2011 Monitoring Research Review - Ground-Based Nuclear Explosion Monitoring Technologies, 13-15 September 2011, Tucson, AZ. Volume I. Sponsored by the Air Force Research Laboratory (AFRL) and the National Nuclear Security Administration (NNSA). U.S. Government or Federal Rights License

Inversions for regional attenuation (1/Q) of Lg are performed in two different regions. The path attenuation component of the Lg spectrum is isolated using the coda-source normalization method, which corrects the Lg spectral amplitude for the source using the stable, coda-derived source spectra. Tomographic images of Northern California agree well with one-dimensional (1-D) Lg Q estimated from five different methods. We note that there is some tendency for tomographic smoothing to increase Q relative to targeted 1-D methods. For example, in the San Francisco Bay Area, which contains high attenuation relative to the rest of the region, Q is overestimated by tilde 30. Coda-source normalized attenuation tomography is also carried out for the Yellow Sea/Korean Peninsula (YSKP), where output parameters (site, source, and path terms) are compared with those from the amplitude tomography method of Phillips et al. (2005), as well as with a new method that ties the source term to the magnitude and distance amplitude corrections (MDAC) formulation (Walter and Taylor, 2001). The source terms show similar scatter between coda-source corrected and MDAC source perturbation methods, whereas the amplitude method has the greatest correlation with estimated true-source magnitude. The coda-source better represents the source spectra compared to the estimated magnitude and could be the cause of the scatter. The similarity in the source terms between the coda-source and MDAC-linked methods shows that the latter method may approximate the effect of the former, and therefore could be useful in regions without coda-derived sources. The site terms from the MDAC-linked method correlate slightly with global Vs30 measurements. While the coda-source and amplitude ratio methods do not correlate with Vs30 measurements, they do correlate with one another, which provides confidence that the two methods are consistent., Proceedings of the Monitoring Research Review (30th): Ground-Based Nuclear Explosion Monitoring Technologies, Portsmouth, VA on 23-25 Sep 2008, sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). Prepared in collaboration with the Los Alamos National Laboratory, the Berkeley Seismological Laboratory, Weston Geophysical, and the Instituto Nazionale di Geofisica e Vulcanologia. The original document contains color images.

We present progress in the development of a new approach to develop and evaluate earth models at the regional scale that utilizes full waveform seismograms. We have implemented an approach which relies on a cascade of increasingly accurate theoretical approximations for the computation of the seismic wavefield, with the goal to develop a model of regional structure for a subregion of Southeast Asia (longitude 75 to 150 degrees and latitude 0 to 45 degrees). The selected area is highly heterogeneous, presenting a challenge for calibration purposes, but is well surrounded by earthquake sources and includes high quality broadband digital stations. In previous years, we developed preliminary models based on successively more sophisticated theoretical approaches to time domain inversion of long period seismograms, in the framework of normal mode theory: (1) a 3D model based on the Nonlinear Asymptotic Coupling Theory (NACT), which includes the consideration of 2D kernels in the vertical plane containing source and receiver. This model was developed for a larger region (longitude 30-150 degrees and latitude -10 to 60 degrees); (2) a 3D model based on the "NBorn" approximation. This approach combines the 3D Born approximation with the path average approximation (PAVA) and allows to accurately account for large accumulated phase delays on paths that sample large scale smooth anomalies. The resulting model has a horizontal resolution of about 200 km. In parallel, a regional version of the Spectral Element Method (SEM) code, in spherical geometry, RegSEM.1, was completed. This code uses Perfectly-Matched Layers (PMLs) at the borders of the region, and includes general 3D anisotropy, Moho and surface topography, ocean bathymetry, attenuation, and ellipticity. Because each SEM run (i.e., for one event) is time consuming, we proposed implementing an approach in which the wavefields for several events are computed simultaneously., Proceedings of the 30th Monitoring Research Review (30th) : Ground-Based Nuclear Explosion Monitoring Technologies, Portsmouth, VA on 23-25 Sep 2008, p241-250, sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). Prepared in collaboration with Rice University and Lawrence Livermore National Laboratory. The original document contains color images.

The deviatoric and isotropic source components for 17 explosions at the Nevada Test Site, as well as 12 earthquakes and 3 collapses in the surrounding region of the western US, are calculated using a regional time-domain full waveform inversion for the complete moment tensor. The events separate into specific populations according to their deviation from a pure double-couple and ratio of isotropic to deviatoric energy. The separation allows for anomalous event identification and discrimination between explosions, earthquakes, and collapses. Confidence regions of the model parameters are estimated from the data misfit by assuming normally distributed parameter values. We investigate the sensitivity of the resolved parameters of an explosion to imperfect Earth models, inaccurate event depths, and data with a low signal-to-noise ratio (SNR) assuming a reasonable azimuthal distribution of stations. In the band of interest (0.02-0.10 Hz) the source-type calculated from complete moment tensor inversion is insensitive to velocity model perturbations that cause less than a half-cycle shift (<5 sec) in arrival time error if shifting of the waveforms is allowed. The explosion source-type is insensitive to an incorrect depth assumption (for a true depth of 1 km), but the goodness-of-fit of the inversion result cannot be used to resolve the true depth of the explosion. Noise degrades the explosive character of the result, and a good fit and accurate result are obtained when the SNR is greater than 5. We assess the depth and frequency dependence upon the resolved explosive moment. As the depth decreases from 1 km to 200 m, the isotropic moment is no longer accurately resolved and is in error between 50% and 200%. However, even at the most shallow depth the resultant moment tensor is dominated by the explosive component when the data has a good SNR., 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, p593-602, 2008. Prepared in collaboration with Berkeley Seismological Laboratory. Sponsored in part by the National Nuclear Security Administration (NNSA). Proposal no. BAA06-42. The original document contains color images.

We present progress in the development of a new approach to develop and evaluate earth models at the regional scale that utilizes full waveform seismograms. We have recently implemented a non-linear three-dimensional (3-D) Born approximation and constructed a 3-D shear velocity model of a subregion of Southeast Asia (longitude 75 to 150 degrees and latitude 0 to 45 degrees) based on this approach for the forward modeling part of the problem and linear Born kernels for the inverse part. Our initial model in the large region (longitude 30 to 150 and latitude -10 to 60 degrees) is derived from a large data set of teleseismic surface waveforms (fundamental mode and overtones in the period range 60-300 s) using the Nonlinear Asymptotic Coupling Theory (NACT), an approach used successfully for global and regional mantle tomography at Berkeley since 1995. In the subregion of study, our "N-Born" model is parameterized at relatively short wavelengths on the order of 200 km. The NACT approach assumes two-dimensional (2-D) sensitivity kernels, confined to the vertical plane containing the source and the receiver, and is adequate for the development of a smooth velocity model. We first developed a model for Southeast Asia using NACT. Using this model as a starting model, we performed one iteration using the N-Born approach. This approach computes synthetic seismograms including the effects of single scattering (linear) as well as a non-linear part, as in the standard "path average approximation," that accounts for large accumulated phase delays on paths that sample large scale smooth anomalies. The inversion kernels are complete 3-D Born kernels. A regional version of the Spectral Element Method (SEM) code, RegSEM.1, has been completed. This version of the code accepts a non-conformal grid, uses PML (Perfectly Matched Layers) at the borders of the region, and includes general 3-D anisotropy, Moho and surface topography, ocean bathymetry, attenuation, and ellipticity., Presented at the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies (29th) held in Denver, CO on 25-27 Sep 2007. Published in Proceedings of the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies (29th), p247-255, Sep 2007. The original document contains color images.

Using a regional time-domain waveform inversion for the complete moment tensor we calculate the deviatoric and isotropic source components for several explosions at the Nevada Test Site (NTS) as well as earthquakes, and collapses in the surrounding region of the western U.S. The events separate into specific populations according to their deviation from a pure double-couple and ratio of isotropic to deviatoric energy. The separation allows for anomalous event identification and discrimination between explosions, earthquakes, and collapses. Error in the moment tensor solutions and source parameters is also calculated. We investigate the sensitivity of the moment tensor solutions to Green's functions calculated with imperfect Earth models, inaccurate event locations, and data with a low signal-to-noise ratio. We also test the performance of the method under a range of recording conditions from excellent azimuthal coverage to cases of sparse station availability, as might be expected for smaller events. Finally, we assess the depth and frequency dependence upon event size. This analysis will be used to determine the range where well-constrained solutions can be obtained., Published in the Proceedings of the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies (29th), held in Denver, CO on 25-27 September 2007, p561-570, 2007. The original document contains color images.

The measurement of regional attenuation Q(1) can produce method dependent results. The discrepancies among methods are due to differing parameterizations (e.g., geometrical spreading rates), employed data sets (e.g., choice of path lengths and sources), and methodologies themselves (e.g., measurement in the frequency or time domain). We apply the coda normalization (CN), two-station (TS), reverse two-station (RTS), source-pair/receiver-pair (SPRP), and the new coda-source normalization (CS) methods to measure Q of the regional phase, Lg (Q(Lg)), and its power-law dependence on frequency of the form Q(Of) with controlled parameterization in the well-studied region of northern California using a high-quality data set from the Berkeley Digital Seismic Network. We test the sensitivity of each method to changes in geometrical spreading, Lg frequency bandwidth, the distance range of data, and the Lg measurement window. For a given method, there are significant differences in the power-law parameters, Q(o) and eta, due to perturbations in the parameterization when evaluated using a conservative pairwise comparison. The CN method is affected most by changes in the distance range, which is most probably due to its fixed coda measurement window. Since, the CS method is best used to calculate the total path attenuation, it is very sensitive to the geometrical spreading assumption. The TS method is most sensitive to the frequency bandwidth, which may be due to its incomplete extraction of the site term. The RTS method is insensitive to parameterization choice, whereas the SPRP method as implemented here in the time-domain for a single path has great error in the power-law model parameters and eta is greatly affected by changes in the method parameterization. When presenting results for a given method it is best to calculate Q(of) for multiple parameterizations using some a priori distribution., Presented at the Monitoring Research Review (29th): Ground-Based Nuclear Explosion Monitoring Technologies held in Denver, Colorado on 25-27 September 2007. Published in the Proceedings of the Monitoring Research Review (29th): Ground-Based Nuclear Explosion Monitoring Technologies, p34-43, 2007. Sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). The original document contains color images.