New research published by University of Washington seismologists reports the results of monitoring they have been recording of a slow-moving and unfelt seismic event under the Olympic Peninsula. It promises to be the best-documented such event in the eight years since the regularly occurring phenomena were first discovered.
“It appears to be right on time,” Steve Malone, a UW Earth and space sciences professor, said of the most recent of what are termed episodic tremor-and-slip, or slow-slip, events. “The first signals were mostly fairly weak, but they were easily detected.”

The first ground motion associated with the event was recorded very early Sunday morning in an area north of Olympia and west of Tacoma. By Monday afternoon the signals were substantially stronger. If the event behaves like past occurrences, the source of the rumbling will move north through the Olympic Peninsula during the next week before crossing the Strait of Juan de Fuca to Canada’s Vancouver Island