A magnitude 4.3 quake at 10:35 a.m. Monday at Mount St. Helens was felt in southwest Washington and the Portland area.
There are no reports of damage.
The Pacific Northwest Seismic Network reports the quake was centered about three miles deep. There were two aftershocks of 2.3 and 2.5 and dozens of smaller aftershocks.
Spokesman Bill Steele with the University of Washington seismology lab in Seattle says there are no signs of volcanic activity, but the quakes could represent changes in the stress field at the volcano.
There were more than 700 reports the quake was felt in the region.