The Physical Mechanism of Deep-Focus Earthquakes from Broadband Waveforms

点击翻译按钮获取中文摘要

This research is to systematically determine temporal source properties of deep earthquakes including the source spectrum, seismic energies, stress drops, rise times, and durations from teleseismic broadband waveforms. Recently available broadband digital seismograms from the Global Digital Seismic Network (GDSN) supported by NSF provide a valuable data set of waveforms from deep earthquakes. Preliminary results show no systematic change in stress drop with depth or moment for events from 10 to 670 km deep within subducting oceanic slabs, although the scatter is large. Rise times, however, become shorter for events deeper that about 550 km. Below 100 to 200 km depth, pressure and temperature in the subducting slab inhibit the brittle failure that causes earthquakes at shallower depths. The goal of this research is to determine the physical process that allows deep earthquakes to occur, one of the outstanding problems in solid earth geophysics.