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Regional Seismic Amplitude Modeling and Tomography for Earthquake-Explosion Discrimination
LAWRENCE LIVERMORE NATIONAL LAB CA
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We continue exploring methodologies to improve earthquake-explosion discrimination using regional amplitude ratios such as PS in a variety of frequency bands. Empirically, we demonstrate that such ratios separate explosions from earthquakes, using closely located pairs of earthquakes and explosions recorded on common, publicly available stations at test sites around the world e.g., Nevada, Novaya Zemlya, Semipalatinsk, Lop Nor, India, Pakistan, and North Korea. We are also examining if there is any relationship between the observed PS and the point source variability revealed by longer period full waveform modeling e.g., Ford et al., 2008. For example, regional waveform modeling shows strong tectonic release from the May 1998 India test, in contrast with very little tectonic release in the October 2006 North Korea test, but the PS discrimination behavior appears similar in both events using the limited regional data available. While regional amplitude ratios such as PS can separate events in close proximity, it is also empirically well known that path effects can greatly distort observed amplitudes and make earthquakes appear very explosion like. Previously we have shown that the Magnitude Distance Amplitude Correction MDAC technique Walter and Taylor, 2001 can account for simple 1-D attenuation and geometrical spreading corrections, as well as magnitude and site effects. However, in some regions, 1-D path corrections are a poor approximation, and we need to develop 2-D path corrections. Here we demonstrate a new 2-D attenuation tomography technique using the MDAC earthquake source model applied to a set of events and stations in both the Middle East and the Yellow Sea Korean Peninsula regions. We believe this new 2-D MDAC tomography has the potential to greatly improve earthquake-explosion discrimination, particularly in tectonically complex regions such as the Middle East.
APPROVED FOR PUBLIC RELEASE