The first cycle of seismic waves recorded at distances of 45, 300 and 355 km. from the GNOME nuclear explosion was used to determine whether the near source wave characteristics at 0.3 km. could be determined from distance measurements. Both head wave and body wave propagation were considered. First the recorded signals at distance were inversely propagated back to the near source region as head waves, and secondly, the measured source at 0.3 km. was propagated out to 300 km. from the source as a body wave. In both cases, restricted comparisons between theory and observation can be made, but the comparison appears to favor the body wave type of propagation. More research is needed to make a more conclusive choice between the two modes of propagation. Methods were developed which can be used to determine source motion from distance measurements when the data are sufficient to do so. / Graduation date: 1965

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We address questions related to the parameterization of two distinct types of seismic sources: earthquakes and underground nuclear explosions. For earthquakes, we focus on the improvement of location parameters, latitude and longitude, using relative measurements of spatial cluster of events. For underground nuclear explosions, we focus on the seismic source model, especially with regard to the generation of surface waves. We develop a procedure to improve relative earthquake location estimates by fitting predicted differential travel times to those measured by cross-correlating Rayleigh- and Love-wave arrivals for multiple earthquakes recorded at common stations. Our procedure can be applied to populations of earthquakes with arbitrary source mechanisms because we mitigate the phase delay that results from surface-wave radiation patterns by making source corrections calculated from the source mechanism solutions published in the Global CMT Catalog. We demonstrate the effectiveness of this relocation procedure by first applying it to two suites of synthetic earthquakes. We then relocate real earthquakes in three separate regions: two ridge-transform systems and one subduction zone. In each scenario, relocated epicenters show a reduction in location uncertainty compared to initial single-event location estimates. We apply the relocation procedure on a larger scale to the seismicity of the Eltanin Fault System which is comprised of three large transform faults: the Heezen transform, the Tharp transform, and the Hollister transform. We examine the localization of seismicity in each transform, the locations of earthquakes with atypical source mechanisms, and the spatial extent of seismic rupture and repeating earthquakes in each transform. We show that improved relative location estimates, aligned with bathymetry, greatly reduces the localization of seismicity on each of the three transforms. We also show how improved location estimates enhance the ability to use earthquake locations to address geophysical questions such as the presence of atypical earthquakes and the nature of seismic rupture along an oceanic transform fault. We investigate the physical basis for the mb-MS discriminant, which relies on differences between amplitudes of body waves and surface waves. We analyze observations for 71 well-recorded underground nuclear tests that were conducted between 1977-1989 at the Balapan test site near Semipalatinsk, Kazakhstan in the former Soviet Union. We combine revised mb values and earlier long-period surface-wave results with a new source model, which allows the vertical and horizontal forces of the explosive source to be different. We introduce a scaling factor between vertical and horizontal forces in the explosion model, to reconcile differences between body wave and surface wave observations. We find that this parameter is well correlated with the scaled depth of burial for UNEs at this test site. We use the modified source model to estimate the scaled depth of burial for the 71 UNEs considered in this study.

Underground nuclear explosions (UNEs) produce anthropogenic isotopes that provide the only definitive means by which to determine whether a nuclear explosion has taken place. Verification of a suspected test under the Comprehensive Nuclear-Test-Ban Treaty (CTBT) includes both on-site and atmospheric sampling of specific noble gas radioisotopes for analysis of origin. It is well-established that the processes of subsurface transport can affect the rate at which such gases will reach the surface. However, the relative abundance of anthropogenic isotopes reaching the surface following transport is currently assumed to rely solely on their direct fission yield, decay rate, and their production from precursor decay, making no account for the influence of transport processes on isotopic ratios. The Underground Transport of Environmental Xenon (UTEX) model has been developed to examine the possible effects of subsurface transport on radioxenon isotopic ratios as well as to consider a number of on-site inspection-related applications. In this work, background on the UTEX model's development, evolution and vetting is presented. This is followed by the characterization and analysis of a number of applications of the model for consideration of CTBT-relevant scenarios. Specifically, the UTEX model's capability to analyze CTBT on-site inspection concept of operations is demonstrated. This is accomplished through an examination of generalized UNE source terms, geological stratigraphy, UNE impact on local geology, natural soil-gas radionuclide backgrounds, atmospheric infiltration, and sampling methodology. It is shown that the processes driving noble gas transport through geological media can significantly skew the ratios of key radioxenon isotopes that are used to help verify whether or not a well-contained underground test has taken place. This result emphasizes the need for a broader understanding of radionuclide signatures used for CTBT verification purposes and the mechanisms that can alter them. / text