Earthquakes recorded near Mount St. Helens; Wash. residents report feeling tremors

A 2.7-magnitude earthquake, left, and a 3.9-magnitude earthquake were recorded near Mount St. Helens on Jan. 3, 2018. Images courtesy USGS

MOUNT ST. HELENS, Wash. – Two earthquakes shook the area northeast of Mount St. Helens shortly after midnight Wednesday and people felt the tremor from Battle Ground to Camas.

The U.S. Geological Survey website said the initial quake occurred at 12:36 a.m., and the first aftershock around 12:40 a.m.

They measured at 3.9- and 2.7-magnitude.

The Pacific Northwest Seismic Network continued to track 13 more aftershocks of much lesser magnitude in the same area. The last measured just 1.1 magnitude shortly before 4 a.m.

Earthquakes can be caused by movement deep within the volcano, but these quakes had nothing to do with the volcano.

Wes Thelen is a seismologist with the U.S. Geological Survey Cascade Volcano Observatory in Vancouver. He told KATU's Mary Loos, “This particular earthquake and the aftershocks have all the fingerprints of a typical tectonic sequence, and we don’t have any evidence that it’s related at all to what’s going on underneath the volcano there.”

Mount St. Helens and the area around it are constantly monitored for earthquake activity and changes to the surface. Seismologist look into the data to determine a quake's location, radius, and depth. That information helps them determine what caused the quake.

Thelen says in the case of this swarm of quakes, "This happened at about 6 or 7 miles deep, so we know that's a very common depth for tectonic earthquakes."

The Cascade volcanoes are generally pretty quiet. Some, like St. Helens, Mt. Hood and Mt. Rainier continue to have earthquakes, but nothing that indicates an eruption is imminent. There would have to be much more activity to indicate that. “A big increase in the number of earthquakes underneath Mount St. Helens and the size of earthquakes underneath Mount St. Helens," Thelen said.

If anything, these earthquakes are a good reminder that we should always be prepared living in a place with this kind of activity.

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