Precise Relocation of Deep Double Earthquake Subevents

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Below a depth of 70 km, the high confining pressure and temperature should prevent brittle failure from occurring. To explain the occurrence of deep earthquakes down to nearly 700 km depth, three mechanisms have been proposed: dehydration embrittlement, transformational faulting, and thermal shear instability. Each mechanism has a different implication for the rupture process of the earthquake, including whether or not the same fault segment can slip more than once. Overlapping rupture zones may result in repeating earthquakes. For three earthquakes in the Tonga and Kuril subduction zones, ranging in depth from 102-539 km and magnitude from 6.2-6.7, we observe repeating earthquakes separated by ~3 s. These events, which we call double earthquakes, have two subevents of similar duration and amplitude separated by nearly the same amount of time at all stations. For each double earthquake, we download from IRIS all available vertical-component seismograms recorded at epicentral distances of 0°-95° and use cross-correlation to measure the relative arrivals times of the two events for the P and pP arrivals. We use the relative arrival times to locate the subevents relative to one another and compare the subevent offset with the rupture dimensions. If the same patch of fault slipped twice, it would be compatible with the thermal shear instability model.

Presenting Author: Junjie Liu

Authors