Towards a Comprehensive Understanding of Episodic Tremor and Slip

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In this research we develop and apply techniques to improve our understanding of a recently discovered phenomenon known as deep, non-volcanic tremor. Deep tremor is a more or less incessant, but weak, shaking of the ground that has been associated with large, but very slow earthquakes. The nature of tremor, with long, but not impulsive, episodes of ground motion requires new and innovative approaches from seismologists because the usual analysis applied to ordinary earthquakes cannot be applied to tremor. We are currently improving methods that have already been developed by the PI and his colleagues, and applying them to tremor in different areas. We are also continue to develop new and improved methods for tremor analysis. Among these are matched-filter analysis of low frequency earthquakes, a running auto-correlation analysis of tremor episodes to detect low frequency earthquakes, and a ''sub-space'' detection algorithm for identifying similar, but not identical small low frequency earthquakes. We use the understanding that emerges from this analysis to address the systematics of tremor behavior of the mechanics of the tremor process. The areas of the proposed study are all areas where tremor occurrence is well documented, specifically: Cascadia, Southwest Japan, and Central California. The strategic location of tremor -- at the boundary of the locked zone where we expect future large earthquakes to initiate -- and the emerging understanding that it represents shear slip on the plate boundary, makes this an important research target with significant potential implications for earthquake forecasting. In particular, an improved understanding should help scientists to assess the significance of deep tremor for earthquake hazard in the Cascadia subduction zone and in central California, where tremor is observed deep under the Cholame segment of the San Andreas Fault, a segment that has not ruptured in over 150 years. Another important broader impact is the international flavor of this work: U.S. researchers and graduate students will collaborate with researchers at the University of Tokyo, the National Institute for Earth Sciences and Disaster Prevention, and other institutions in Japan on significant portions of this research.