Photo courtesy of Pacific Northwest Seismic Network — A 3.4 earthquake hit in Useless Bay Thursday morning, being felt by residents from Freeland to Langley.

Useless Bay earthquake sounded like ‘sonic boom’ to some, went unnoticed by others

A small earthquake that originated in Useless Bay Thursday morning was one of about 60 to shake Puget Sound over the past week. And though the number may seem alarming, experts say Whidbey Island residents have nothing to fear.

Having so many in so short of time isn’t common, but it’s not unheard of, according to Doug Gibbons, a research engineer at Pacific Northwest Seismic Network. They aren’t a forecast for a massive event either.

“I don’t think any people need to leave town because an earthquake is around the corner,” Gibbons said. “But it’s always a good time to double check your preparedness kit or emergency plan, especially on an island like Whidbey that could become isolated if something happens to the bridge or ferry dock.”

Gibbons doesn’t think the earthquakes are related to “the big one,” the quake scientists say is long overdue for the region. He says the crustal faults in Puget Sound are the likely source of the recent quakes, due to north and south compression. “The big one” is said to occur along the subduction zone that’s caused by the Juan de Fuca Plate moving eastward, beneath the North American Plate.

The series of earthquakes began May 3 in the Bremerton area with an event that measured 3.3 on the Richter scale. Gibbons says about 20 smaller aftershocks occurred in the following 24-hour period. A “small handful” of tremors shook Puget Sound between May 5 and May 10, before an uptick in quakes — at least 30 — began Wednesday morning.

Most registered magnitudes between 1.5 to 2.5 and occurred about 15 miles under the ground.

Thursday’s quake in Useless Bay measured 3.4 on the Richter scale. It hit at 10:56 a.m. and was felt by people across the South End. In Freeland, Record reporters noticed their desks and chairs gently shaking while they were working on this story for Saturday’s paper. It caused one to stop what he was doing and utter in surprise, “Did you feel that? I think we just had another earthquake.”

Monica Falso, who lives near Whidbey Air Park, said she heard it before she felt it. She thought it was a plane flying overhead.

“My husband and I both work from home, and I heard what sounded like a low, sonic-boom sound from my window,” Falso said. “I thought I was the only one who heard it before my husband yelled from across the hall, ‘Did you hear that?’”

Falso says in her 15 years of living on Whidbey Island, she’s never heard of so many earthquakes occurring so frequently. According to Gibbons, she’s right. There hasn’t been a series of recorded quakes like this in “quite a while.”

“It’s not an anomaly when we think of the long-term history of the Puget Sound area,” Gibbons said. “But, we have not had a series like this for a while, especially in an area that would be felt by people.”

Nearly all of the tremors have occurred in Sinclair Inlet, which is close to Bremerton and is the waterway spanned by the Seattle-to-Bremerton ferry route. The Bremerton area has seen three slightly larger earthquakes with magnitudes of 3.6, 3.4 and the original tremor. No damage has been reported.

It’s also likely that many went by unnoticed by the public.

“We had hundreds of ‘felt’ reports, but if you were in a car or sleeping, you probably wouldn’t feel them,” Gibbons said. “The threshold to feel the earthquakes is a magnitude 2, at least, and it probably wouldn’t be widely felt until we get to magnitude 4.”

Experts at Pacific Northwest Seismic Network are still looking into the exact cause of the tremors.