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

A 3.9-magnitude quake first struck northeast of the famed southwest Washington peak at 12:36 a.m. People reported feeling the quake in Portland, Seattle and elsewhere.

The temblor came before "a fairly vigorous earthquake aftershock sequence," the USGS said Wednesday morning, "and 15 events have been located so far by the Pacific Northwest Seismic Network."

Quakes are common in the area, and approximately one to five happen each month, the USGS said in a Facebook post.

"The earthquake is a tectonic earthquake aligned with regional stress and faulting in the area," the agency said. "There is no sign that this is connected to volcanic activity."

The 3.9-magnitude temblor is the second-largest in the immediate area of Mount St. Helens since 1981, the USGS said. The mountain is best known for erupting in 1980.

People in Seattle, Portland and Vancouver, Washington, are among those who reported feeling the 3.9-magnitude quake, according to the USGS "Did You Feel It?" feature.

-- Jim Ryan jryan@oregonian.com 503-221-8005; @Jimryan015