Stress Transfer Between the Cascadia Megathrust and the Northern San Andreas Fault

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The west coast of the North America from the Gulf of California to British Columbia is characterized by high earthquake activity. That great earthquakes occur in California is well known. Less well known is the fact that northernmost California, and western Washington and Oregon (the Cascadia Margin) are subject to truly great, "megathrust" earthquakes, the last of which occurred in about 1700. It is of vital importance to understand both the frequency of these events, and any linkage between events in Cascadia and those that occur to the south, on the San Andreas Fault in California. Earthquakes commonly produce turbidite (submarine landslide) deposits offshore. One way to address these issues is to establish chronologies by dating these deposits. This project will acquire new cores and date turbidites along the Cascadia Margin to improve high-resolution paleoseismic chronologies in this active margin setting and test a proposed model of interaction between two plate boundary fault systems. Long paleoseismic records afford the opportunity to make such comparisons, test models of recurrence, and establish long term records of behavior and plate boundary interaction that are not possible with earthquake records that are typically much too short. A primary aim of this work is to test the hypothesis that earthquakes along the Cascadia Margin have triggered events on the Northern San Andreas Fault repeatedly during the Holocene. Broader impacts of this work arise in part from the fact that the Cascadia Margin is expected to produce truly great "megathrust" earthquakes, with attendant tsunami hazards, this work has enormous societal relevance. This work should have a major, direct impact on the assessment of earthquake and tsunami hazards in the U.S. and Canada. Other benefits are training graduate students and the involvement of undergraduates in the project.