Queen Charlotte Islands
October 28, 2012 by staff
Queen Charlotte Islands, Some people on the North Olympic Peninsula felt the magnitude 7.7 earthquake that struck just after 8 p.m. Saturday, Oct. 27 off the west coast of Canada. The U.S. Geological Survey reported the earthquake was near the Queen Charlotte Islands at a depth of about 3 miles (5 km) and was centered 96 miles (155 kilometers) south of Masset, British Columbia.
It was followed by a 5.8-magnitude aftershock a few minutes later.
No tsunami warning has been issued for Washington State coastal areas, but the quake did not go unnoticed.
“We were having dinner and I noticed the venetian blinds swinging,” a resident of uptown Port Townsend emailed The Leader. “Then I looked at the corner lamp in the living room, and the chain that hangs down from it was swinging too, so I knew it really was a quake. Hope everyone has a quake kit!”
The National Weather Service issued a tsunami warning for coastal areas of British Columbia and southern Alaska. An initial tsunami alert for the state of Hawaii was upgraded to a Tsunami Warning, due to the sea level readings received and the resulting change in the Hawaii tsunami forecast.
According to the USGS, the quake occurred as a result of oblique-thrust faulting near the plate boundary between the Pacific and North America plates. At the location of this event, the Pacific plate moves approximately north-northwest with respect to the North America plate at a rate of approximately 50 mm/yr.
This earthquake is likely associated with relative motion across the Queen Charlotte fault system offshore of British Columbia, Canada. According to the USGS, studies of tectonics in this region suggest plate motions are taken up by strike slip faulting parallel to the plate boundary, accompanied by lesser amounts of thrust motion to accommodate the oblique nature of the plate motion vector between the two plates with respect to the orientation of the main plate boundary fault structure. This oblique component of plate motion may involve either underthrusting of the western edge of the Pacific Plate beneath North America, or be taken up on crustal faults within the North America plate.
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