Discrimination between NTS explosions, earthquakes and the non-proliferation experiment at the Pinedale Seismic Research Facility

摘要

As the United States moves into an atmosphere of concern about the spread of nuclear weapons to non-nuclear countries, the focus on monitoring nuclear explosions is changing from looking at specific test sites and yields to looking for tests of large and small yields from anywhere in the world. Discrimination of small events then becomes important and regional seismic monitoring the best method to detect and identify suspicious events. At the Pinedale Seismic Research Facility (PSRF) in Wyoming we have the opportunity to try different regional discriminants with nuclear tests from NTS, western US (W-US) earthquakes and the Non-Proliferation Experiment (NPE). Four discriminants that gave the best results in a study by Taylor et al. were tried: m(sub b):M(sub s), M(sub b):M(sub s)(sup h), log(L(sub g)/P(sub g)) and spectral ratios. The different discriminants were applied to the data (14 NTS explosions, the NPE, one Department of Defense (DOB) explosion and 34 NWS earthquakes) regardless of signal-to-noise. When the NTS explosions and NPE were only compared to four earthquakes located on or near the Test Site, all the discriminants except log(L(sub g)/P(sub g)) worked fairly well at PSRF. When the other WUS earthquakes and DOD explosion are included, only m(sub b):M(sub s) shows any promise. Because of frequent physical variations in the earth's crust, regional signals are complex and easily influenced by site and path characteristics. Looking at events from one specific area reduces the effects of the path, which is why three discriminants work well when the data set is restricted to events on or near NTS. The only discriminant not adversely affected from variations in path is m(sub b):M(sub s). This is probably because it is believed that source dimension, source time function and/or source mechanism is the cause for the differences between earthquakes and explosions with this discriminant, rather than any path effects.