3.4 earthquake off Whidbey Island joins swarm of Kitsap County quakes

A swarm of earthquakes in Kitsap County is still growing, and now there's another one in a different spot--a 3.5 near Whidbey Island. All of them near known earthquake faults that could cause major damage.

A magnitude 3.4 earthquake west of the southern tip of Whidbey Island hit Thursday morning about 11 a.m.  This comes after a swarm of quakes hit the Kitsap County area near Bremerton over the past week.

People reported feeling the quake, which struck at 10:56 a.m., as far away as Bellevue some 40 miles away.

There were no immediate reports of injuries.

It comes hours after a new round of earthquakes struck the Kitsap County region Thursday morning, in the same vicinity where some other quakes hit within the past week. Hundreds of people reported feeling a 3.6 magnitude quake at 12:35 a.m. all the way from Bremerton to Seattle.

A map from the Pacific Northwest Seismic Network shows where all the quakes have been over the past few days. 

Thursday morning two earthquakes were recorded at magnitudes 3.6 and 2.6. On Wednesday morning a series of quakes measured between magnitude 3.4 and 1.1.

The strongest of the Wednesday morning quakes struck beneath the waters of Puget Sound along the Seattle-Bremerton ferry route.

All of the quakes were deep underground, around 16 to 18 miles, and all in the vicinity of known fault zones capable of causing serious damage in the Puget Sound region.  The Kitsap quakes, mostly under Rich Passage, are between two branches of the Seattle Fault, considered capable of a magnitude 7.2 magnitude earthquake. 

While the quakes are in a concerning neighborhood, are they tied to these major faults? 

"We think the Seattle Fault is complicated,"  said John Vidale of the Pacific Northwest Seismic Network. Vidale also serves as the official seismologist for the state of Washington.  "It could be in that system of faults, but we don't know if there's a primary fault down there, and if there is if these earthquakes are on it." 

What makes the Seattle Fault so dangerous is that it's very shallow, rising to the surface.  It's expected the northern part of the Seattle Fault dips at a fairly shallow angle to the south, which could put it well above the kind of depths scientists believe the swarm of new quakes is at. 

"These are really small earthquakes. They really don't have an influence on the faults above," says PNSN seismologist Renata Hartog. 

But scientists want to learn more, and each quake becomes another data point for study, bringing the inaccessible depths under Puget Sound into sharper focus. 

"It's very interesting of course," said Hartog.  "Because how the Seattle Fault is driven from below is interesting to know.  We don't know that very well at the moment."  

© 2017 KING-TV


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