Physical Basis for the Lg/P Discriminant: General Properties and PreliminaryModeling

摘要

A critical problem for reliable implementation of regional discrimination isincomplete understanding of how regional seismic signals depend on physical characteristics of the source and propagation path to the recording station. This research is directed at improving understanding of effects of these characteristics on an important regional discriminant, the Lg/P ratio. An empirical element in this research program has aimed at describing behavior of Lg/P ratios and their dependence on frequency for nuclear explosions, earthquakes, rockbursts, and other sources in various tectonic environments. Observations indicate differences between event types which appear to be enhanced at higher frequencies, but sources of scatter in the observations need further study. The theoretical element of this project seeks to explain the main features of the Lg/P observations in terms of source mechanisms and propagation models for the regional signals. Initial focus of the theoretical studies has been on effectiveness of mechanisms for generation of Lg by explosive sources. The studies indicate that, even though Rg-to-Lg scattering might explain observed frequency dependence and other features of explosion Lg/P ratios, it probably provides only a minor contribution to explosion Lg signals compared to other mechanisms.