Analysis of the Effects of Eurasian Crustal and Upper Mantle Structure on Regional Phases Using Broadband Seismic Data

Abstract

Abstract : This report presents the results of the second phase of a two-year effort to investigate the effects of upper mantle structure on the propagation of regional phases. The first year investigation was directed at improving our understanding of the behavior of the PP phase at upper mantle distances, and developing methods to map large-scale variations in uppermost mantle velocity structure. During the second year investigation presented here, we successfully applied the techniques developed to a dataset of 45 PP waveforms for paths traversing China. We determined a first order P wave velocity model for the crust and upper mantle under China, which best explains the overall dataset. Next, we investigated the data on a path-by-path basis to constrain lateral deviations from this average model and to map large-scale variations in absolute velocities and velocity gradients in the uppermost mantle under China. Our final effort was directed at exploring the effect of our regionalized velocity models, on the propagation of the P sub n and Lg regional phases to assess how variations in the velocity structure under China influence P sub n/Lg ratios for earthquakes and explosion sources.