Isotropic sources and attenuation structure: Nuclear tests, mine collapses, and Q

This dissertation investigates two different, but related, topics: isotropic sources and attenuation structure. The first section reports the analysis of explosions, earthquakes, and collapses in the western US 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. We find that in the band of interest (0.02-0.10 Hz) the source-type is insensitive to small velocity model perturbations and several kilometers of incorrect depth when the signal-to-noise ratio (SNR) is greater than 5. However, error in the isotropic moment grows from 50% to 200% as the source depth decreases from 1 km to 200 m. We add an analysis of the Crandall Canyon Mine collapse that occurred on 6 August 2007 in Utah to our dataset. The results show that most of the recorded seismic wave energy is consistent with an underground collapse in the mine. We contrast the waveforms and moment tensor results of the Crandall Canyon Mine seismic event to a similar sized tectonic earthquake about 200 km away near Tremonton, Utah, that occurred on September 1, 2007 demonstrating the low frequency regional waveforms carry sufficient information to distinguish the source-type. Finally, confidence in the regional full moment tensor inversion solution is described via the introduction of the network sensitivity solution (NSS), which takes into account the unique station distribution, frequency band, and signal-to-noise ratio of a given event scenario. The method is tested for the well-recorded nuclear test, JUNCTION, at the Nevada Test Site and the October 2006 North Korea test, where the station coverage is poor and the event magnitude is small. Both events contain large isotropic components that are 60% of the total moment, though the NTS event is much better constrained than the North Korea test. The network solutions illustrate the effect of station coverage on the ability to recover the seismic moment tensor, and to distinguish events of different source types, Importantly, the network solutions may also be used in synthetic cases to evaluate where stations are needed in order to improve moment tensor based source type identification.;The attenuation (parameterized as Q) structure section begins with an analysis of five one-dimensional (1-D) attenuation measurement methods methodologies to a Northern California dataset. The methods are: (1) coda normalization (CN), (2) two-station (TS), (3) reverse two-station (RTS), (4) source-pair/receiver-pair (SPRP), and (5) coda-source normalization (CS). The methods are used to measure Q of the regional phase, Lg (QLg), and its power-law dependence on frequency of the form Q0feta. All methods return similar power-law parameters, though the range of the joint 95% confidence regions is large (Q0 = 85 +/- 40; eta = 0.65 +/- 0.35). The RTS and TS methods differ the most from the other methods and from each other. We also 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 0 and eta. We conclude that when presenting results for a given method we suggest calculatingQ0f eta for multiple parameterizations using some a priori distribution. The analysis is extended for lateral variation in crustal attenuation of California by inverting 25,330 synthetic Wood-Anderson amplitudes from the California Integrated Seismic Network (CISN) for site, source, and path effects. Q ranges from 66 to 1000 (high to low attenuation) with an average of 143. The average Q is consistent with an amplitude decay function (logA0) for California when combined with a simple geometrical spreading rate. Attenuation in California is consistent with the tectonic structure of California, with low attenuation in the Sierra batholith and high attenuation at The Geysers, at Long Valley, and in the Salton Trough possibly due to geothermal effects. Finally, we perform inversions for regional attenuation of the crustal phase in the Yellow Sea/Korean Peninsula (YSKP) using a new method that attempts to solve the path/source amplitude trade-off by correcting the Lg spectral amplitude for the source using the stable, coda-derived source spectra. We compare the site, source and path terms produced to traditional methods and find good agreement. Regions of low Q correlate well with increased sediment thickness in the basins, particularly Bohai Basin located in the northern Yellow Sea. Regions of increased Q occur along topographic highs in the YSKP.