Aseismic slip at the Mendocino Triple Junction from characteristically repeating earthquakes

Kathryn Materna

UC Berkeley Earth and Planetary Science

Date & Time
Building 3, Rambo Auditorium
Tom Brocher

The Mendocino Triple Junction (MTJ) lies at the transition point between the San Andreas Fault system, the Mendocino Transform Fault, and the Cascadia Subduction Zone. Many of the active faults of the triple junction are located offshore, making it especially difficult to characterize aseismic creep. In this work, we study aseismic creep rates near the MTJ using characteristically repeating earthquakes (CREs) as indicators of creep rate. Using seismic data from 2008-2017, we identify CREs as recorded by an array of eight 100-Hz borehole seismometers deployed 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 estimates of coupling on other 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 an important plate boundary region outside the coverage of current geodetic networks.

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