Tremor

Episodic Tremor and Slip (ETS) episodes have been observed from British Columbia to northern California. This phenomenon is believed to be slip along the boundary between the subducting oceanic plate and the North American plate at depth. However, this slipping is slow compared to slip during a regular earthquake and takes place over days rather than seconds. When the slow slip is large enough, it can be observed using data from GPS sensors. While this slow slip is happening, tiny earthquakes radiate shaking that can be observed by seismic sensors, we call that tremor. We observe tremor very frequently. The PNSN monitors the non-volcanic tremor associated with slow slip and has deployed additional seismometers from time to time to record expected tremor events to gain insight into the process and into the stresses that eventually will lead to the region's next major earthquake. The Tremor Map shows the continuously detected tremor and allows a user to download tremor information. The Tremor Log page lists a collection of log entries for individual large tremor episodes, mostly in northwestern Washington and British Columbia. For information about research on ETS performed at the University of Washington, see this page: ETS Research, which has a fairly comprehensive list of journal publications by UW Earth and Space Sciences researchers on ETS and other miscellaneous information.

Natural Resources Canada (NRCan) also monitors ETS under Vancouver Island and the Salish Sea: