Mount St. Helens

Seen from Spirit Lake Memorial Highway, much of Mount St. Helens and its environs lay locked in snow and cold, but beneath the surface increasing numbers of small earthquakes have been rumbling.

Bill Wagner, The Daily News

A series of earthquakes occurred to the northeast of Mount St. Helens early Wednesday morning, according to the U.S. Geological Survey.

The first quake hit with a 3.9 magnitude at 12:36 a.m., USGS said. Weak tremors were reportedly felt from Portland all the way to Seattle.

A second 2.7 magnitude earthquake hit at 12:39 a.m., which was followed by a swarm of smaller quakes ranging in magnitude from 1.0 to 1.9, USGS reported.

Bill Steele, a seismology lab coordinator for the Pacific Northwest Seismic Network, said in an interview Wednesday that the cluster of earthquakes does not mean people should worry about Mount St. Helens erupting again anytime soon.

The quakes centered on the Bean Creek drainage northeast of Mount St. Helens and about 3 miles east of Spirit Lake, ranging in depth from 9.4 kilometers to 11.1 kilometers, according to USGS.

The 3.9 quake was the largest earthquake in the immediate area since USGS started monitoring the region in the 1970s, local seismologists said Wednesday.

Steele added that it’s normal for an area where the Earth’s crust is weak to produce tectonic quakes near a volcano.

“We’re in an area of crustal weakness that Mount St. Helens has exploited, but (the earthquakes) are not associated at all with the magmatic system that feeds the volcano,” he said.

On average, PNSN locates between four and fourteen earthquakes within 10 kilometers of the volcano each week.

Wes Thelen, a seismologist with the Cascades Volcano Observatory, said Wednesday that all signs pointed to a tectonic earthquake.

“This has all of the fingerprints of a typical tectonic sequence,” he told The Daily News.

Thelen said the earthquake was most likely a strike-slip fault — a vertical (or nearly vertical) fracture where the blocks have mostly moved horizontally.

The orientation of the fault was consistent with the regional tectonic stress states, Thelen said.

“That’s something that we would expect with any earthquake that wasn’t associated with a volcano,” he said.

Thelen said the area to the northeast of the St. Helens Seismic Zone typically gets about one to five earthquakes per month.

“There’s some scientific interest here but nothing societal really to speak of,” he said.



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