REGIONAL SEISMIC AMPLITUDE MODELING AND TOMOGRAPHY FOR EARTHQUAKE-EXPLOSION DISCRIMINATION

• Main Authors: Walter, W R, Pasyanos, M E, Matzel, E, Gok, R, Sweeney, J, Ford, S R, Rodgers, A J
• Language: unknown
• Published: 2021
• Subjects: 58 GEOSCIENCES; AMPLITUDES; APPROXIMATIONS; ATTENUATION; EARTHQUAKES; EXPLOSIONS; MINING; MONITORING; NUCLEAR EXPLOSIONS; NUCLEAR WEAPONS; POINT SOURCES; REFINING; SEISMIC EVENTS; SIMULATION; TECTONICS; TESTING; TOMOGRAPHY; WAVE FORMS; Novaya Zemlya
• Online Access: http://www.osti.gov/servlets/purl/945662; https://www.osti.gov/biblio/945662

We continue exploring methodologies to improve earthquake-explosion discrimination using regional amplitude ratios such as P/S 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 P/S 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 P/S discrimination behavior appears similar in both events using the limited regional data available. While regional amplitude ratios such as P/S 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 MDAC (Magnitude Distance Amplitude Correction, Walter and Taylor, 2001) technique 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. Monitoring the world for potential nuclear explosions requires characterizing seismic events and discriminating between natural and ...