Improving Earthquake and Explosion Discrimination by Using Love and Rayleigh Wave Magnitudes (Postprint) Annual Report 3.

摘要

Since the 1960s, comparing a Rayleigh-wave magnitude, Ms, to the body-wave magnitude, mb, has been a robust tool for the discrimination of earthquakes and explosions (e.g., Ms:mb). In this study, a Rayleigh-wave formula has been applied as is to Love waves and examine the possibilities for discrimination using only surface wave magnitudes (e.g., Ms(Rayleigh):Ms(Love)). The magnitudes were calculated by applying the time- domain magnitude technique called Ms(VMAX) to Rayleigh and Love waves from explosions and earthquakes. Results indicate that for the majority of the earthquakes studied (>75%), the Ms(VMAX) obtained from Love waves is greater than the estimate from Rayleigh waves. Conversely, 79 of 82 nuclear explosions analyzed (96%) have network-averaged Ms(VMAX)-Rayleigh equal to or greater than the Ms(VMAX)-Love. Logistic regression was used to develop an Ms(Rayleigh):Ms(Love) discriminant. Cross-validation analysis of the new discriminant correctly identifies 57 of 82 explosions and 246 of 264 earthquakes while misidentifying 22 explosions as earthquakes and 11 earthquakes as explosions. The majority of these misidentified earthquakes are either deep (sub-crustal) earthquakes or the events with normal or thrust focal mechanisms. Results also suggest that incorporation of Love waves into the analysis requires a re-examination of the period limits currently used for the Ms(VMAX) technique; while the Ms(VMAX)-Rayleigh method is currently operational using periods between 8 and 25 seconds, future processing should be extended to 40 seconds, especially in regions with deep earthquakes and complex paths.