Bill Steele, a University of Washington seismologist, has spent a lot years warning anyone who will listen that the region is overdue for a damaging earthquake. He fears the Feb. 28 magnitude 6.8 quake may not have been nasty enough to galvanize folks into better disaster planning. That would be a mistake, he said. The Ash Wednesday quake was deep in the earth, situated along a stress point in the Juan de Fuca plate, which dips beneath the North American continental plate. The depth helped cushion the blow.
Deep earthquakes are the most common in the Pacific Northwest.
Take the same earthquake and place it close to the Earth's surface, and the ground motion could be 10 times worse, he said. Worse yet could be a subduction zone earthquake of magnitude 8 or higher, triggered by the oceanic and continental plates jamming together then wrenching apart. It could be many times stronger and last for minutes, not seconds. The last one occurred 300 years ago. The art of designing buildings to withstand earthquakes has changed dramatically over time, said state Department of Natural Resources geologist Tim Walsh.