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Geologists to test Whidbey earthquake faults in July
"A University of Idaho earthquake scientist who measured faults on both north and south Whidbey Island in 1996 will be back this summer to determine if the island should expect a future earthquake, and how big that quake could be.John Oldow, head of the university's Geology Department, said this week that he and a team of graduate students will spend much of July on Whidbey to measure the movement of the Devil's Mountain and South Whidbey faults. Using National Geological Survey monuments and the Global Positioning Satellite system (GPS), the researchers will be able to determine down to two or three millimeters -- the width of a nickel -- how far the fault has moved since Oldow made the last set of GPS measurements four years ago.Oldow said the Whidbey faults are getting more attention than most around the nation because of the active geologic history of the Puget Sound region. About 1,100 years ago, the Seattle fault moved 21 inches in a big quake. Oldow said measuring movement along the Whidbey faults could reveal if they have the same future.We don't know how fast they're moving, Oldow said Thursday.In all, Oldow and his team will take measurements on 27 monuments during the study. Twenty-three of those monuments are in the San Juan Islands or on Whidbey Island. Little more than stamped brass caps anchored in stone, the monuments are used as permanent reference points.Oldow said his team must first find each monument, clear away any debris that may have piled up around it, then make several hundred separate electronic measurements. If this new set of measurements show that the faults are moving, Oldow said, that might mean an earthquake is in the island's future -- a big earthquake. He said a temblor hitting as high as 7 on the Richter scale would not be inconceivable.If the faults are not moving, Oldow said he will have reason to conclude that the fault is inactive and poses no danger to people living nearby. However, those studying the fault do not think that is the case. Both Oldow and geologist Sam Johnson presented papers on the earthquake risks of the two faults at the Geological Society of America's annual conference in Vancouver last April. The two scientists agree that the faults are potentially active.Oldow said he will spend the next few months contacting Whidbey Island property owners who have Geological Survey monuments on their land. He said he needs to get permission to bring his team on to private property to make GPS measurements.Oldow said he has more than a passing interest in the Whidbey faults. He grew up in Anacortes and his father still lives in La Conner. Results of the fault survey will be posted on the Internet after the results have been examined. To find a map of the major Puget Sound faults, go to geohazards.cr.usgs.gov/pacnw/actflts/sfzfig1.html. "