PDN News Sources Compiled by Leah Leach, managing editor/news
Felt by at least one person as far away as Port Angeles, a 3.7 magnitude earthquake under Whidbey Island that came about an hour before most alarm clocks were set to go off today should serve as a wake-up call that a much bigger quake is likely in the future, say University of Washington scientists.
The deep quake — 36.2 miles deep, in the Juan de Fuca tectonic plate — at 5:09 a.m. came from the same zone that produced the destructive 6.8 Nisqually quake in 2001, which cracked the state Capitol dome and rained bricks down from historic buildings in Seattle’s Pioneer Square neighborhood.
“Every 20 to 30 years, we have one at 6.5 or greater,” said UW seismology lab coordinator Bill Steele. “It is the most frequent source of damaging earthquakes in the region and it will produce big ones in the future.”
The quake, which hit 2 miles southeast of Coupeville on Whidbey Island, was felt on the North Olympic Peninsula, according to the U.S.Geological Survey earthquake hazards Web site at http://earthquake.usgs.gov/.
Thirty-two people in Port Townsend, 30 miles from the quake’s epicenter, reported to the Web site that they had felt shaking, while one person in Port Angeles, 59 miles away, filed such a report.
Shaking also was reported by 12 people in Port Ludlow, four in Port Hadlock, two each in Nordland and Sequim, and one each in Chimacum and Quilcene.
The quake was felt in Victoria. Honn Kao, duty seismologist with Natural Resources Canada at the Pacific Geoscience Centre in Sidney, told the Times Colonist ( www.timescolonist.com ) that the office received a number of reports from Victoria.
No damage was reported.
Nobody was disturbed enough to phone the Jefferson County Emergency Management office in Port Townsend, said Bob Hamlin, program manager.
“We did not get any ‘felt’ reports,” he said Wednesday afternoon.
Hamlin said that was due probably both to the early hour the quake struck and to its relatively small magnitude.
“It starts to get noticeable at a 4.0,” he said.
“It was just a little reminder that it’s still there.”
The Juan de Fuca plate is the same source from which a 7.1 quake hit Olympia in 1949.
The “big one” could come from that plate slipping under the North America plate, scientists have said.
That interface has produced quakes of magnitude 8 or 9 about every 500 years. The last one was about 300 years ago.
Each whole number increase on the magnitude scale describes ground motion that is 10 times greater than the previous whole number.
Western Washington experiences frequent quakes of about magnitude 3.0 — about 10 a year — Steele said.
Most of these are not felt by many people because the quakes are so deep under Puget Sound that they create little shaking.
The Nisqually quake, under the Nisqually River delta south of Seattle between Tacoma and Olympia, was the largest quake to shake Western Washington in more than a half-century.
But that quake, which disrupted operations at Seattle-Tacoma International Airport and damaged the Alaska Way Viaduct through downtown Seattle, was not a “megathrust” quake that would cause catastrophic damage on the West Coast.
A megathrust quake would involve the breaking of a tectonic plate — a piece of the earth’s outer shell — and would likely have a magnitude of about 9. The last “megathrust” quake — commonly referred to as “the big one” — happened in the Northwest in 1700.
