UW News

March 20, 2001

Seismic network uses schools, public facilities to chart ground shaking

News and Information

While the Puget Sound region was being shaken by the magnitude 6.8 Nisqually earthquake, George Thomas and his University of Washington team were preparing for the next temblor – and the one after that.

They scout out appropriate locations for, and then install, strong-motion sensors throughout western Washington. Their goal is to provide scientists with an ever-more-complete picture of what happens to the ground when an earthquake strikes.

“Our geologic picture is a little fuzzy, mostly because of the dense vegetation around here,” said Thomas, a research scientist in the UW’s Earth and space sciences department who heads what is dubbed the Strong Motion Urban Team.

Strong-motion sensors are designed to accurately record ground motion from moderate and large earthquakes. Conventional seismographs are intended to record the motion from small earthquakes and often are overwhelmed by large quakes.

The information from the remote strong-motion seismographs can give engineers a better idea of specific construction needs in a particular area, or let companies with sensitive equipment know when their machinery was shaken enough by an earthquake that it probably should be recalibrated.

The sensors comprise parts of three different networks – the Pacific Northwest Seismic Network operated by the UW and the United States Geological Survey, one geared primarily toward tsunami warnings here and in Alaska, and a growing national system operated by regional networks.

“The plan is eventually to have thousands of seismographs all over the country coming into the regional networks, and the regional networks are now at a point where they can share data in real time,” said Thomas. He would like to see 200 to 300 of them in western Washington.

The three-person team last year installed 22 monitors throughout the region, many in schools. The sensors all recorded data on the Feb. 28 Nisqually quake, and most transmitted it to the UW.

“We made all the data available publicly the next day,” Thomas said.

He hopes to install another 25 or so stations this year. The big quake eliminated one worry – he now has more than enough volunteer hosts from which to select locations. They are spread through Island, King, Kitsap, Pierce, San Juan, Snohomish, Whatcom, and Thurston counties. The final choices have to pass engineering muster before stations can be installed this summer.

The biggest responses have been from schools and community colleges. Coincidentally, they often are the easiest places to install stations, since the approval process can be a matter of minutes rather than months, and they have ready access to the Internet.

“Communications are the real snag,” Thomas said. “Before last year we were using mostly dedicated phone lines, which was effective but very expensive. Then last year we decided to go strictly with the Internet.”

Now the seismographs are installed with communications hardware that transmits the information through Internet connections. Total cost for a seismograph system is about $10,500.

Typically the devices are placed alongside a school’s main data facilities. A device at Finn Hill Junior High School north of Kirkland is in a break room, while at Holy Rosary School in West Seattle it’s in a closet. Sometimes the seismographs are placed in basements or crawlspaces, and occasionally concrete slabs have to be built for the devices.

A major advantage of the network, Thomas said, is that a number of scientific and other institutions have access to real-time data. Often they have different ways of analyzing the information, which means that more detailed analysis is available more quickly.

“In this last quake it was actually the National Earthquake Information Center (in Golden, Colo.) that calculated the magnitude using data from the Pacific Northwest network and other seismic networks,” Thomas said.

Of course, things don’t always go smoothly in an earthquake. The shaking can knock out power or communications. In that case, the seismograph can save information in its memory until someone shows up with a laptop computer to download it. After the Nisqually quake, information had to be recovered that way from eight sites where power failed or Internet connections were lost.

“We used the ‘sneaker net’ to get the data,” Thomas joked.


For more information, contact Thomas at (206) 543-9024 or george@geophys.washington.edu

A list of current strong-motion sensor locations, http://spike.geophys.washington.edu/SEIS/PNSN/SMO/smosta.html