Quake rumbles near Coupeville
June 25, 2008 · Updated 5:32 PM
Many Whidbey Island residents awoke Thursday morning with a shake and a rumble from the islands most recent earthquake.
At 6:08 a.m., a 3.1-magnitude earthquake was detected on the South Whidbey Island fault line. Bill Steele, a spokesman for the Pacific Northwest Seismograph Network and the University of Washington geophysics department, said the small quake felt unusually large for its size because of the extreme depth of the strike/slip earthquake motion. The quake occured about 30 kilometers below the earths surface.
Its a little unusual, Steele said. I think it was larger than a 3.0 magnitude earthquake.
He said the earthquake was probably closer to a magnitude 3.5. Earthquakes in the Puget Sound region usually occur 10-20 kilometers below the earths surface. Comparatively, earthquakes in California around the San Andreas Fault are usually in the upper 10 kilometers of the Earths crust.
The South Whidbey Island fault cuts directly across the southern half of Whidbey Island, Steele said. Though it has not seen much major activity in years past, the threat of a large quake is a possibility. When that quake will occur is difficult to estimate.
Its a very large fault structure, he said. Its uncertain but its kind of interesting to wonder.
People looking for information about the areas earthquakes can visit the Pacific Northwest Seismograph Network Web site at www.pnsn.org. In addition to viewing recent and historical area quakes, residents can also register whether or not they felt the most recent earthquake.
We have had a number of earthquakes that fall in the Whidbey Island fault zone, Steele said. This is just a little deep in the crust.
Steele will be on Whidbey Island today as a presenter for the the WSU Beach Watchers program, Sound Waters. The all day program will be held 8:30 a.m.-4 p.m. at Coupeville Middle School.
Steele will be just one of the speakers at the one-day university. Topics on the agenda include seminars on beach debris, tsunamis and earthquakes, and Puget Sound seafood.
Steele said in his presentation he will give an overview of the Puget Sound earthquake hazards, identifying fault lines and discussion of the Whidbey Island fault zone area.