Detection of Long-Period S from Earthquakes and Explosions at LASA and LRSM Stations with Application to Positive and Negative Discrimination of Earthquakes and Underground Explosions.

摘要

An improved distance-amplitude relation for long-period S waves is developed and applied to long-period S waves measured from megaton-range explosions. The difference between magnitude determined from the maximum amplitude long-period S waves and the magnitude determined from Rayleigh waves is found to be a good discriminant between worldwide earthquakes and explosions at NTS and Amchitka. The long-period SH/SV ratio is not a discriminant. The 90% incremental threshold for detection of earthquake long-period S waves at LASA from Japan and the Kuril Islands is m sub b = 5.2. Beamforming and program FKCOMB were found to be equal in detection capability. Previously reported data imply a 90% incremental threshold of m sub b = 4.7 for detection of long-period S waves at ALPA from the Kuril Islands and Kamchatka. The difference between LASA and ALPA capability can be explained by the average distance-amplitude relation together with the lower noise level at ALPA. For possible seismic network, the use of negative discriminants (no detection of S waves) with .01 probability of a false alarm for explosions is shown to result in an M sub s threshold approximately equal to the threshold of 90% probability of detection of S waves from earthquakes by two or more stations (positive discrimination). A significant lowering of the negative threshold is possible if one station of the network has an especially low detection threshold.