Patches of tremor around the Mendocino Triple Junction

Andrew Tran and Richard M. Allen
University of California Berkeley

AGU Fall Meeting, San Francisco, December 2007.

Episodic Tremor and Slip (ETS) has been observed all along the Cascadia Subduction Zone. Here we focus on Non-Volcanic Tremor (NVT) in the southern part of the Cascadia around the Mendocino Triple Junction. Continuous data from the Northern California Seismic Network has recently been made available at NCEDC, allowing for a more extensive study of tremor in the Mendocino area. In this study, data from 56 stations for the January 2006 to June 2007 period was analyzed for tremor using an automated approach similar to that used by Brudzinski and Allen (2007).

More than 10 distinct NVT events with durations between 1.5 and 3 weeks were identified during the 18 month period. A distinct event is identified by clear peaks that rise above the noise level in the processed time series. Typically these events are visible on more than five stations. While some events show a single patch of tremor, other events can be divided into phases showing migration of the tremor activity. For example, an event in May 2006 begins as two distinct patches ~100 km apart which then migrate towards one another to form a single large patch. In late October 2006 tremor initiates north of the Mendocino triple junction and then propagates south of the triple junction over a period of ~5 weeks.

© Richard M Allen