A magnitude 2.9 earthquake was recorded about four miles from Monroe at 2:41 a.m. Monday, according to the Pacific Northwest Seismic Network (PNSN.)
It was felt by at least 91 people who reported it to the U.S. Geological Survey's "Did You Feel It" web page.
No injuries or damage were reported.
The Puget Sound region is prone to earthquakes because it lies near the edge of the North American tectonic land plate and the Juan de Fuca, a large oceanic plate. The 700-mile boundary, a fault known as the Cascadia Subduction Zone, runs from Northern California to Canada. Scientists say the Juan de Fuca plate is trying to force its way under the North American plate, which they also say is ultimately inevitable.
Two years ago, thousands of tiny tremors pushed parts of Washington and Vancouver Island westward. It's a near-annual event that backs some scientists' expectations that a big earthquake may hit the Seattle area harder than their previous models suggested.
The waves of seismic activity are part of a process known as episodic tremor and slip, which is thought to increase stress on locked faults — areas where tectonic plates cannot move past each other, University of Washington earth-sciences professor Ken Creager has said.
Western Washington is also crisscrossed by more than a dozen large, shallow faults — cracks in the Earth's crust capable of unleashing damaging earthquakes.
Seattle, Tacoma, Everett, Olympia and Bremerton all sit uncomfortably close to crustal faults. And evidence suggests that in the aggregate, those faults might rupture more frequently than previously thought.
On Dec. 15, a magnitude 3.2 earthquake hit 16 miles below Bremerton at 8:27 a.m. and was felt as far away as Kent.
It was followed by 13 smaller, unfelt aftershocks, according to the Pacific Northwest Seismic Network, which wrote about the renewed seismic activity near Bremerton in a blog post.
