Earthquake tests hammer home shaking danger to Aberdeen schools

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by GLENN FARLEY / KING 5 News

NWCN.com

Posted on July 28, 2010 at 2:26 PM

Updated Wednesday, Jul 28 at 10:39 PM

ABERDEEN, Wash. - If there's a county with a front row seat for the biggest earthquakes known to occur in Washington state, it's Grays Harbor County.

Because coastal counties sit on top of the so-called subduction zone, they can experience magnitude 9-plus earthquakes, typically 300 to 500 years apart, say scientists. It's already been 310 years since the last one.

A big question is how will schools hold up in shaking of a magnitude 9.1?  To find out, geologists and seismologists with the Washington State Department of Natural Resources are testing the soil under Aberdeen Public Schools.

DNR Chief Hazards Geologist Tim Walsh and Geophysicist Ray Cakir showed us what they're looking for in the field behind the Central Park Elementary School.  A string of geophones designed to pick up sound waves coming through the earth are connected to a laptop computer. Scientific tech Christopher Maffucci then slams an 18 pound hammer down onto a steel plate dozens of times at different locations, sending sound waves into the earth. Those sound waves are reflected differently by different soil layers.

By using this and other techniques, DNR will be able to construct a profile of the ground and its susceptibility to shaking.  Because of the differences in the different kind of soils underground, two identical school buildings could suffer different levels of damage in a quake.

Next month, engineers will come in and assess the strength of the buildings based on the new shaking data the geologists will simulate using a sophisticated computer program. A similar program is also being used in Walla Walla that could face a potential magnitude 6.8, according to Walsh.

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