Seismic tests aim to reveal earthquake risk
USGS using vibrations to assess mile-long stretch on North Side
June 23, 2012
The ground is shaking this weekend on Spokane’s North Side.
A team from the U.S. Geological Survey is in town to conduct seismic reflection tests on a mile-plus path along East Baldwin and West Shannon avenues.
The tests will help determine earthquake risks in Spokane, which was hit by a swarm of small to moderate quakes in 2001 in the vicinity of the current test.
On Friday, a four-ton “vibroseis” machine was sending vibrations into the ground every five meters on Baldwin.
It sounded like a motorcycle or maybe a wood chipper each time the signals were activated.
The shaking and noise got neighbors’ attention.
Eric Beaulaurier, a student at Spokane Falls Community College, showed up shirtless on his front porch. “I wanted to know what’s going on,” he said.
Across the street, Jason Inks said he remembers being “freaked out” in 2001 when the earthquakes hit the city. He said those quakes knocked bricks off the top of his chimney.
The team from the USGS Geologic Hazard Science Center in Golden, Colo., travels throughout the country conducting tests to determine earthquake risk. They arrived in Spokane from similar testing near Ellensburg last week.
A series of sensors was laid out next to the street and linked to computers to measure the return waves, or echoes, from the vibrations. The sensors were plotted using GPS.
The data will be used to create an underground map of soils and rock layers, including deformations and fractures in the layers.
Scientists believe that small, shallow faults run in a north-south direction across the North Side and are responsible for periodic earthquakes in Spokane.
“We should be able to image that deformation above the fault and along the fault,” said Bill Stephenson of the USGS.
The earthquake swarm in 2001 produced shocks of magnitude 3.7 and 4, plus dozens of smaller quakes. They appeared to be centered somewhere near Corbin Park, less than a mile north of the study area.
In addition, news files show that small earthquakes have occurred periodically in Spokane in 1941, 1948, 1952 and the early 1960s.
The study comes on the heels of a request two weeks ago seeking Spokane residents willing to place a seismograph in their homes for ongoing monitoring through the NetQuakes program of USGS.
Chris Cothrun, a scientist at the applied geophysics center at the University of Nevada at Las Vegas, said the study could give a glimpse of Spokane’s future earthquake risk. That, in turn, might justify changes in building codes to make structures safer in an earthquake, he said.
“We can assess the general risk over time,” he said.