Systematic Differences in the Spectral Excitation of Pn and Lg by the Last Lop Nor Explosions and Nearby Earthquakes: Implications on the Pn/Lg Spectral Ratio Discriminant

摘要

PD and Lg spectra from the last eight Lop Nor explosions and many nearby earthquakes are collected from many broadband seismic stations, and analyzed to obtain source spectral characteristics and path Q. Pn spectra are unstable in amplitude with varying paths and source mechanisms. Much improvement has been made to stablize Pn spectral analysis. The main findings of this study include: (1) Pn spectra from explosions have a spectral overshoot that is more significant than predicted by the theoretical source model used, (2) for explosions, Pn M0 tends to be higher than Lg M0; (3) for both Pn and Lg, M0 scales with f(c)(bar)alpha, with alpha being close to 4 for explosions, and 3 for earthquakes; (4) for both explosions and earthquakes, at the same M0 level, Pn f(c) are much higher than Lg f(c), and (5) for explosions, the significant spectral overshoot in Pn causes the Pn/Lg ratio to reach maximum around Pn f(c). This maximum is the dominant cause for that ratio to be significantly higher for explosions than for earthquakes in the frequency band of roughly 3 to 6 hz, a phenomenon previously reported for the same region.