Aftershocks and memories of an exhilarating few seconds are all that remain of a moderate
By Rick Adair, Sierra Sun News Service
Aftershocks and memories of an exhilarating few seconds are all that remain of a moderate earthquake that shook the region Friday afternoon.
The quake measured magnitude 5.5 and was centered about 40 miles north of Truckee and about 5 miles northwest of the eastern Sierra town of Graeagle, near Portola, Calif. It struck at 1:19 p.m. at a depth of 9 miles, according to U.S. Geological Survey officials.
Strong shaking and light damage, but no injuries, were reported in Graeagle and Portola, and in Quincy 20 miles to the northwest of the quake.
The temblor was felt throughout western Nevada and central California, and startled some, but not all, with its relatively long and noticeable shaking.
“We had a number of calls (looking for information), but no reports of injuries,” said Nevada County Sheriff’s Office Capt. Gary Jacobson in Truckee.
Leslie Tigan, the Portola city clerk, said the quake rattled the city hall but produced no damage.
“It was like nothing I have ever felt before, but I am from southern New Jersey,” she said.
But despite the scare, no major damages were reported at area businesses.
“It didn’t faze us,” said a manager at the Truckee Albertson’s store.
Truckee’s most recent large earthquake was a magnitude 4.8 earthquake on Donner Summit on Dec. 2, 2000.
As a precaution, several dams near the quake were inspected for damage. Locke Hahne, manager of operations and maintenance for the Bureau of Reclamation’s Lahontan Basin Area Office, said his staff inspected the dams at Boca and Stampede Reservoirs, Lake Tahoe and Prosser Creek, and the Lahontan Dam on the Carson River, and found no problems.
“These are all ‘high hazard’ dams,” he said. “That means these may cause death or high property damage if they break. The Lake Tahoe dam at Tahoe City has only 6 feet of water behind it and wouldn’t cause many problems, but some of the other dams have 100 feet or more behind them, which would be a problem.”
Hahne said his staff routinely performs inspections within 24 hours at dams where a quake causes accelerations of 5 percent of gravity or more. But he added that even though Friday’s quake didn’t reach the acceleration threshold, the dams were inspected anyway.
“We really take public safety seriously,” he said. “When it comes to earthquakes, it’s important for the public to know we get on it as soon as possible.”
U.S.G.S. Officials have forecast up to 30 aftershocks in the magnitude 3 to 5 range through Friday, although only two in this range have struck so far, the strongest, at 5:01 a.m. Saturday, measuring 4.2. Thirteen aftershocks of magnitude 1 and greater have been identified, but nearly a dozen more of smaller size have struck, according to University of Nevada, Reno, sources.
UNR reports place Friday’s quake in the Mohawk Valley area, the site of several like-sized events in the past. The largest known quake there struck April 1, 1959, with magnitude 5.8. A consortium of scientists and engineers have preliminarily estimated that the fault there is capable of a magnitude 7.3 event, but with a very low probability.
Steve Wesnousky, director of UNR’s Center for Neotectonic Studies, says the valley is within a trend of quakes that stretch northwest from Lake Tahoe to Lassen Peak that probably reflects motion along the eastern side of the Sierra Nevada amounting to as much as 15 percent of the motion seen across the more famous San Andreas Fault Zone.
Teri Vance, Nik Dirga and Kurt Hildebrand contributed to this report.
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