Pair of earthquakes rattle Seattle area

(Update: Expert says Washington, California quakes unrelated)

Two earthquakes shook the Puget Sound region in Washington state early Friday morning, with the temblors felt into British Columbia and across the Cascade Mountains into the eastern part of the state.

There were no immediate reports of damage or injuries.

The U.S. Geological Survey reports that a 4.6 magnitude earthquake rattled the Three Lakes area, about 40 miles (64 kilometers) northeast of Seattle. That was followed minutes later by a 3.5 magnitude aftershock near the city of Monroe, some 30 miles (48 kilometers) northeast of Seattle.

The initial jolt was recorded at 2:51 a.m. Friday.

The state Department of Transportation said the agency would be inspecting bridges, but had no reports of damage.

The USGS said it received reports of people feeling the shaking from Vancouver to near Wenatchee, Washington.

The Northwest is especially prone to earthquakes. The most recent large one to shake the Seattle area occurred in 2001, when a 6.8 magnitude quake happened just north of Olympia, Washington. That quake caused some injuries and widespread damage, including to the air traffic control tower at Sea-Tac Airport.

Further south along the Pacific coast, a magnitude 4.9 aftershock of last week’s Southern California earthquakes was felt widely in the region on Friday morning. There have been thousands of aftershocks of the magnitude 6.4 earthquake on July 4 and the 7.1 quake that occurred the next day.

David Caruso, a USGS geophysicist, told The Seattle Times the Washington state quake was due to a thrust fault, in which one side of a fault pushed upward relative to its opposite side. Such quakes are common in the Cascade Mountain range.

Caruso said the Northwest quake had no connection to the recent earthquakes in California.