Measuring aseismic slip through characteristically repeating earthquakes at the Mendocino Triple Junction, Northern California

Kathryn Materna, Taka'aki Taira, & Roland Bürgmann

Published August 15, 2016, SCEC Contribution #6883, 2016 SCEC Annual Meeting Poster #238

The Mendocino Triple Junction (MTJ), at the transition point between the San Andreas fault system, the Mendocino Transform Fault, and the Cascadia Subduction Zone, undergoes rapid tectonic deformation and produces more large (M>6.0) earthquakes than any region in California. Most of the active faults of the triple junction are located offshore, making it difficult to characterize both seismic slip and aseismic creep. In this work, we study aseismic creep rates near the MTJ using characteristically repeating earthquakes (CREs) as indicators of creep rate. CREs are generally interpreted as repeated failures of the same seismic patch within an otherwise creeping fault zone; as a consequence, the magnitude and recurrence time of the CREs can be used to determine a fault’s creep rate through empirically calibrated scaling relations.

Using seismic data from 2010-2016, we identify CREs as recorded by an array of eight 100-Hz PBO borehole seismometers deployed in the Cape Mendocino area. For each event pair with epicenters less than 30 km apart, we compute the cross-spectral coherence of 20 seconds of data starting one second before the P-wave arrival. The most similar events (with median coherence above 0.95 at two or more stations) are selected as CREs and then grouped into CRE families. Each family is used to infer a local creep rate. On the Mendocino Transform Fault, we find relatively high creep rates of >5 cm/year that increase closer to the Gorda Ridge. Closer to shore and to the MTJ itself, we find many families of repeaters on and off the transform fault with highly variable creep rates, indicative of the complex deformation that takes place there.

Key Words
Repeating earthquakes, Mendocino Triple Junction

Citation
Materna, K., Taira, T., & Bürgmann, R. (2016, 08). Measuring aseismic slip through characteristically repeating earthquakes at the Mendocino Triple Junction, Northern California . Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology