They call it a “slow slip,” a silent earthquake on the deep part of the Cascadia subduction zone.
That silence one day could trigger a catastrophic temblor across the North Olympic Peninsula, Western Washington and Vancouver Island.
The slow slip — now taking place under the Strait of Juan de Fuca and heading north under Vancouver Island — is so subtle that it has gone mostly undetected by Peninsula residents, though it has lingered for weeks.
Scientists call it an ETS, for “episodic tremor and slip.”
Detected for the first time during the past year, the silent ETS moved again July 8 beneath the North Olympic Peninsula — roughly from the western edge of the Dungeness Valley to the eastern shores of Clallam Bay, and into north-central Olympic National Park.
One of the seismographs installed to help detect the slip is in the Olympic foothills south of Sequim, said Steve Malone, a University of Washington geophysics professor who works for the Pacific Northwest Seismograph Network.
The Sequim-area detection device is part of a triangulation of seismography set up by UW seismologists in cooperation with the Geological Survey of Canada.
It includes seismographs on Lopez Island and in Sooke on British Columbia’s Vancouver Island.
“The location of it is pretty crude, but we think it’s some place in the North Olympic Peninsula or the Strait of Juan de Fuca,” Malone said of the slow slip’s geologic confines.
