Kinematics of active deformation at the Mendocino Triple Junction

Kathryn Materna

UC Berkeley

Date & Time
Building 3, Rambo Auditorium

The Mendocino Triple Junction (MTJ) is a rapidly deforming plate boundary zone at the intersection of the San Andreas fault, the Cascadia Subduction Zone (CSZ), and the Mendocino Fault Zone. Earthquake cycle deformation in this region results in large present-day strain rates and seismicity rates. In this project, we analyze GPS time series in the region and find slight time dependence in the interseismic velocity field. We find that in one area, the GPS velocity field changes in spatially coherent patterns following large offshore earthquakes and we find that these changes cannot be fully explained by postseismic deformation, slow slip events, or hydrological loading. Instead, we believe that these observations present a rare example of dynamically triggered changes in interface coupling, and we speculate on the possible mechanical causes of these changes. We evaluate the relationship between coupling changes and tremor. These observations, together with similar examples elsewhere in the world, suggest that faults outside of the ETS zone may have time-dependent coupling during the interseismic period, a phenomenon that we need to understand and account for in future hazard models.

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