Aseismic Slip at the Mendocino Triple Junction From Repeating Earthquakes

Date: 4/26/2019

Time: 02:30 PM

Room: Elliott Bay

The Mendocino Triple Junction (MTJ) is a seismically active region at the transition between the San Andreas Fault system, the Mendocino Transform Fault, and the Cascadia Subduction Zone. The triple junction itself is located offshore, making it especially difficult to study using land-based methods. In this work, we document the occurrence of aseismic creep near the MTJ using characteristically repeating earthquakes (CREs) as indicators of creep rate. Using seismic data from 2008-2018, we identify CREs as recorded by an array of seismometers, including eight 100-Hz borehole instruments in the Cape Mendocino area. We apply a repeating earthquake detection criterion to the waveforms, and identify several dozen sequences of repeating earthquakes. The CRE data implies a creep rate of ~3 cm/yr on the downgoing extension of the Mendocino Transform Fault, consistent with other estimates of coupling on oceanic transform faults. We also find repeating earthquakes on the southern margin of the North American accretionary wedge. The creep rates are mostly steady over the study period, although we investigate the potential for small transients due to stress interactions between moderate-sized earthquakes and the CRE sequences. This project demonstrates the ability of CREs to monitor aseismic creep and its time-dependent features in a plate boundary region outside the coverage of current geodetic networks.

Presenting Author: Kathryn Materna

Authors