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March 2, 2024

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Tremor event arrives early, as thousands of quakes recorded west of Whatcom last 2 weeks


BELLINGHAM – The 2021 Episodic Tremor and Slip Event seems to have hit the Puget Sound region a little earlier than expected and could be signaling that Vancouver Island is slowly pulling away from Bellingham and most of the rest of Washington state, experts say.

“We think ETS 2021 has begun,” the Pacific Northwest Seismic Network said in a tweet Tuesday, Oct. 5. “An Episodic Tremor and Slip (ETS) Event occurs beneath N WA — S Vancouver Island about every 14 months. But wait, wasn’t the last one only ~12 months ago?”

There is no denying the area has been active the past couple of weeks.

Since Sept. 20, the Pacific Northwest Seismic Network’s tremor map tracked 2,834 epicenters — all smaller than 2.0 magnitude and many smaller than 1.0 — beneath the southern end of Vancouver Island, the San Juan Islands, the Strait of Juan de Fuca, the Kitsap Peninsula and the western edge of the Olympic Peninsula.

“This 2021 ETS is not supposed to start until about 14 months after the last one started which would make it due to start sometime in Dec. 2021,” PNSN Professor Emeritus Steve Malone wrote in his ETS blog. “Yet it looks as if something has already started. As of today significant tremor has been going on in the central Puget Sound region since Sep 21 or 22. Typically we feel that if tremor goes on every day for 10 days then a real/significant ETS is under way. So, it now seems that is the case.”

While Malone said that an ETS event this early — approximately 12 months since the last event in September and October of 2020 — is unusual, it’s is not unheard of. In 2013, a similar year-long gap was seen between tremor and slip events, he wrote.

In February, another, “out of the ordinary” tremor event was tracked under Vancouver Island.

“Because of the variability of the way these ETS events take place we have no idea if there is any special significance to this early start,” Malone wrote. “It may be just another slightly different way these events unfold.”

John Cassidy, an earthquake seismologist with Natural Resources Canada, told Canadian media organization Black Press Media that the tremor and slip event could signal that Vancouver Island is slowly sliding west.

Using global positioning data, Cassidy said researchers found that Vancouver Island shifted a few millimeters — or the thickness of five dimes — to the west during the one- to two-week tremor and slip event, according to the story. Usually, the island is moving slowly to the east.

“It’s really tiny and it’s really slow but it’s remarkable we can see this with our instruments,” Cassidy told Black Press Media.

Though we can’t feel the effects of the events, the tremor should serve as a reminder that we live in a seismic zone, where much larger earthquakes have and will happen again.

A reminder of where we live

The episodic tremor and slip event also comes at a perfect time to serve as a reminder, as Whatcom County and Washington state prepare to participate in the Great ShakeOut in less than a month.

At 10:21 a.m. Oct. 21, residents are invited to “drop, cover and hold wherever they are,” according to a release from the Whatcom County Sheriff’s Office’s Division of Emergency Management, as a reminder of what to do when a large earthquake strikes the region.

At approximately the same time, the state’s 122 coastal tsunami sirens will be tested using the wailing sound of a tsunami warning instead of the sound of the Westminster Chimes usually used during tests. National Oceanic and Atmospheric Administration radios also will sound the alarm at that time.

The are 13 tsunami sirens located along Whatcom County’s coasts, according to a state map.

Residents are asked not to call 911 when they hear the siren during the ShakeOut.

“Of note, there are many new sirens on the coast so the sound could come from new directions,” the release stated. “Some new tsunami sirens are still being worked on and may not be used during the test.”

Residents are encouraged to register for the earthquake and tsunami drill at shakeout.org/washington/ and to use #ShakeOut on social media to post pictures of themselves under desks using proper earthquake protection techniques during the drill.

“If you’re continuing to work from home, take this opportunity to examine your environment for hazards and talk to family about where everyone would gather if your home was damaged and you were separated,” the release states. “If you’re at a workplace or have kids in school, ask about what plans are in place for when an earthquake happens.”

Residents also are encouraged to download the free “Prepare in a Year” guide, to learn how they can take little steps each month to get prepared at mil.wa.gov/preparedness, or walk their tsunami evacuation route if they live near the coast. Maps and information about how tsunami sirens work can be found at mil.wa.gov/tsunami.

During the Great ShakeOut on Oct. 21, the Washington Emergency Management Division will answer earthquake-related questions on their Facebook page or by email.