August’s Episodic Tremor and Slip Now in Progress

Detail from PNSN’s tremor map

When I interviewed the UW’s Steve Malone back in May, he was looking ahead to this summer’s predicted episodic tremor and slip (ETS) event.

Now UW News says the seismic game is afoot once more:

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.

The seismologists at the Pacific Northwest Seismic Network have installed a huge “array of arrays” (eight arrays with ten seismic recording stations) that should help them “see” downward into the earth and triangulate on where exactly the ETS is emanating from. As I learned in the May interview:

What fascinates seismologists is that this kind of ETS event, in its slow-motion way, unleashes energy equivalent to a 6.5 magnitude quake or greater. It just does it with such nuance that no one noticed until recently.

Nuanced or not, this time the seismologists are dialed in. Hopefully we will soon know a little more about ETS and any connection if may have to our much-anticipated Big One. Scientists still don’t know exactly what is going on down there in the subduction zone–it’s not clear if the tremor and slip is relieving stress, adding to it, or simply moving it around.