Yesterday evening, Wednesday, two small quakes occurred within 300 miles of Ferndale. Earthquakes measured as between Magnitude 4 and 5 are officially designated “small” earthquakes, more powerful than “minor” quakes but less than “moderate” ones.
First, about 9pm, there was a M4.2 quake at a depth of 10 miles with an epicenter 20 miles west-southwest of Bremerton (100 miles from Ferndale). Being near populated areas and of a magnitude greater than M2, this quake was reported to have been felt by thousands but no significant damage was reported.
Later, a few minutes after 10pm, a M4.8 quake at a depth of 6 miles occurred 150 miles west-northwest of Tofino, in the Pacific Ocean west of Vancouver Island (275 miles from Ferndale).
According to Pacific Northwest Seismic Network Director John Vidale, the Puget Sound quake fell into a decades-long pattern of earthquakes which occur every few years in the Puget Sound (see timeline below).
In addition to the recent quakes, a recent 5-day swarm of tremors west of West Seattle has at least one seismologist, Steve Malone, thinking an episodic tremor and slip (ETS) may be beginning within a month or two.
An ETS is an episode of tectonic plate movement often simply referred to as a slip. An ETS typically occurs over weeks and happens without detection by people as compared with quakes that only last a few seconds but can be felt and can result in damage at the surface.
Malone says the last Puget Sound ETS began in December of 2015.