Nature Sends Reminder: This Is Quake Country

The strongest earthquake to hit the Puget Sound region in 30 years caused plenty of jitters but no serious damage or injuries. It was a jarring reminder that the Pacific Northwest is prime earthquake country, scientists say.

The magnitude 5.0 quake struck at 7:11 p.m. Saturday and was centered 10 to 15 miles south-southwest of Seattle. It was felt as far north as Vancouver Island in Canada, as far south as Salem, Ore., west to the Olympic Peninsula and east to Yakima.

The temblor wasn’t strong enough to cause any major damage. But it rattled plenty of nerves.

“It started shaking the whole trailer,” said Scott Shabaz, who lives near Federal Way, about 2-1/2 miles south of the epicenter. “I have a rude friend who comes by once in a while and likes to do that with his truck.”

On Vashon Island, close to the epicenter, Tristan Ruegamer, 19, was in his car when the quake hit.

“It felt like someone was standing behind my car and shaking it,” he said. “We freaked out because we thought somebody was shaking the car.”

The quake shattered a few store windows, knocked groceries off shelves and carved some minor hairline cracks along the walls of two aging brick fire stations in Tacoma.

Seattle’s Kingdome, where a fishing and hunting show was under way, was closed 45 minutes early as a precaution, but no structural damage was found.

The state Department of Transportation plans to send crews to inspect bridges and highways in the region today, but no structural damage is expected, said Myint Lwin, bridge and structures engineer for the state.

The state’s newer bridges are designed to withstand quakes as strong as magnitude 7.5 and, even older bridges are likely to survive a magnitude 5 quake unscathed, Lwin said.

“We certainly wouldn’t expect a lot of damage, but it is a reminder that we live in a seismic area,” said Bill Steele, coordinator of the University of Washington’s seismology laboratory.

Ruth Ludwin, a research scientist with the UW seismology lab, said the quake occurred less than 10 miles from the Earth’s surface. Aftershocks of up to magnitude 4.0 can be expected for months but probably won’t be strong enough to cause any damage, Ludwin said Sunday.

At least two minor aftershocks, neither of which could be felt, were recorded late Saturday night.

The temblor was the strongest to hit the Seattle area since a magnitude 6.5 earthquake struck April 29, 1965. That quake injured at least 31 people and caused an estimated $12.5 million in property damage.

In 1949, a 7.1 quake centered near Olympia killed eight people and rained bricks and debris onto city streets.

The 1949 and 1965 quakes were much deeper and originated within the Juan de Fuca plate, a huge, thick slab of rock that is pushing under North America, Ludwin said. Saturday’s quake, on the other hand, was a “crustal” quake, occurring closer to the surface within the crust of the overlying North American plate.

Had the magnitude of Saturday’s quake been 6.0 or greater, it could have caused significant damage, Ludwin said.

“Shallow earthquakes pose a particular hazard because they’re closer to the people and the homes that are above them,” Ludwin said. “The type of quakes in ‘49 and ‘65 … the closest people to them are 35 miles away.”

Scientists say the Pacific Northwest also is prone to a third type of quake that would be “The Big One” - a “subduction zone” quake of magnitude 8 or greater originating off the Northwest coast at the boundary between the Juan de Fuca and North American plates.

“We appreciate we can have all these types of earthquakes, but for a damaging quake in the Puget Sound region, historically the deep earthquakes have been the most frequent,” Ludwin said.

Washington and Oregon average about 1,000 earthquakes a year, but only a half dozen to three dozen are felt.

Tags: geology

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