Crustal Deformation Near the Mendocino Triple Junction Inferred From GPS-Derived Strain Rate Maps

Date: 4/24/2019

Time: 02:15 PM

Room: Puget Sound

Crustal deformation in southernmost Cascadia represents the confluence of transpressive and convergent tectonics around the Mendocino Triple Junction (MTJ), which defines the intersection of the North American, Gorda, and Pacific plates. The transition between these major systems is achieved in part by faulting and deformation along the North American plate boundary, as well as large-scale rotation of the crust in southern Cascadia. However, the spatiotemporal history of deformation around the MTJ is poorly resolved due to previously sparse instrument coverage. Fortunately, GPS instrumentation in this area has increased significantly over the past decade, providing improved resolution on long enough time series to discern and refine steady strain rates. This work uses GPS data to investigate horizontal strain rates in southern Cascadia. To achieve this, we generate regional strain rate maps from horizontal GPS time series data collected over the past decade. We use multiple methods to clean the time series, including applying a monthly moving average, removing offsets from earthquakes and common mode signals, and employing a seasonal decomposition technique. We examine strain rate maps spanning from 2007-2017 to explore the heterogeneity of strain and correlation with quaternary fault zones around the MTJ. Our results indicate that strain rates change across the MTJ from north to south, with compressional signals to the north and extensional signals to the south. We observe high maximum shear strain rates broadly across the San Andreas fault system, indicating that strain is distributed across multiple major fault strands. Lastly, we observe a band of high maximum shear strain rates north of the MTJ around the vicinity of the Mad River fault zone. We examine the interseismic slip rates in this region to gain insight into the seismic hazards associated with these faults.

Presenting Author: Carolyn Nuyen

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