Big Isle to learn lesson from a thumpin’
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HILO » An 11-ton machine, affectionately called "Thumper," is helping scientists figure out why Waimea felt five times as much shaking as Waikoloa during the Oct. 15, 2006, earthquake, even though the resort area was much closer to the source.
"Thumper" shakes the ground like an earthquake but in a much less violent manner.
Seismologist Ivan Wong from the URS Corp. in California is using the machine to create a model of how various parts of the Big Island react to a real quake.
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ROD THOMPSON / RTHOMPSON@STARBULLETIN.COM
University of Texas at Austin engineering technician Cecil Hoffpauir checked the miniearthquake- producing machine, named "Thumper," yesterday in Hilo. The machine will provide data to help protect against future earthquakes.
Earthquake simulator to assess vulnerabilities on Big Island
HILO » "Thumper," a miniearthquake-producing machine named after the Walt Disney rabbit, has come from Texas to help protect the Big Island from earthquakes.
By producing controlled vibrations at a network of earthquake measuring stations on the Big Island, Thumper will help create more accurate data about past earthquakes and help protect against futures ones, said Ivan Wong, a seismologist with URS Corp. of Oakland, Calif., an engineering firm that consults with the U.S. government on disaster-response planning.
After the magnitude-6.7 quake and 6.0 aftershock of Oct. 15, 2006, Wong convinced the Federal Emergency Management Agency that it did not have enough information to understand exactly what happened when the ground shook.
Several dozen seismometers from the summit of Mauna Kea to Oahu recorded the earthquake, Wong said.
But there is a problem with the data. "We don't know what's under the instruments. We don't know if it's soil or rock," Wong said.
"Soft soils amplify earthquakes, typically," he said.
In fact, during the Oct. 15 quake, the Waimea area, known for its deep soil, experienced 1.05 g's of shaking, with 1 g being the force of Earth's gravity.
"That's very high, very surprising," Wong said.
But another instrument at the seaside Waikoloa resort, closer to the 6.7 quake epicenter, recorded only 0.19 g's.
Wong did not have a number at hand for hard-hit Kawaihae Harbor, but the effects there were obvious.
The sand the harbor sits on flowed like a liquid, he said. Some permanent repairs still remain to be made, he said. With data from Thumper, Wong plans to produce a model of how various parts of the island react to earthquakes, and how building requirements should respond to the dangers.
To get their measurements, Wong, University of Arkansas engineering professor Brady Cox and University of Texas at Austin technician Cecil Hoffpauir set out sensors along a 300-foot line, then measure how fast the shaking produced by Thumper arrives at each point.
As a general rule, high velocities mean rock and low velocities mean soil, Wong said. Low velocities also can mean trouble, as the Waimea example showed.
Stationing Thumper at various Hilo locations this week, Wong got four times as much shaking on the deep soil north of the Wailuku River compared with the hard rock on the south side.
Wong begins several days of testing at West Hawaii sites today. The FEMA contract did not provide enough money to take Thumper to seismometer sites on Maui and Oahu.