A swarm of more than 500 earthquakes that began July 12 in northwest Nevada near the California and Oregon borders has increased in intensity in the last few days, prompting a warning Thursday to “prepare for the potential for strong ground-shaking.”
The quake activity is in a remote, high-desert area near the Sheldon National Wildlife Refuge in northern Washoe County.
While some shaking has been felt by people in the nearest communities, Cedarville in Modoc County, and Lakeview, Ore., “I haven’t heard of any damage,” said Ken Smith, seismic network manager at the Nevada Seismological Laboratory at the University of Nevada, Reno.
“It’s in an extremely remote location, but we’re keeping a very close eye on it,” Smith said. “I just hope it tapers off and there are no larger quakes.”
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“Following any sequence of earthquakes similar to what is occurring in northwest Nevada, there is a small increase in the probability of a larger event,” he said.
“Whether a larger event will occur in the northwest Nevada swarm cannot be predicted,” Smith said. “However, large earthquakes can happen anywhere in Nevada, and we encourage citizens to take steps to prepare for the potential for strong ground-shaking.”
Since Oct. 30, five earthquakes of magnitude 4 or higher have been reported in the swarm, with the largest quake occurring at 12:34 a.m. Thursday. It was preliminarily reported at a magnitude of 4.9 but is subject to a seismologist’s review.
A 4.5, also subject to review, was reported at 7:58 a.m. Thursday. A 4.6 quake jolted the area Tuesday.
During the past three months, 46 earthquakes larger than magnitude 3 have been recorded, one late Wednesday and three on Thursday. About 550 quakes larger than magnitude 2 have occurred, Smith said.
The current activity resembles the 1968 Adel, Ore., swarm, which lasted several months and included three events of approximately magnitude 5, Smith said. The Adel swarm caused moderate damage.
In 2008, the “Mogul-Somersett” swarm in west Reno consisted of an increasingly vigorous series of earthquakes over a two-month period, leading to a magnitude 5 event that caused moderate damage.
All residents in earthquake-prone states should read up on earthquake preparedness, Smith said. Two websites with information are http://www.seismo.unr.edu or http://earthquake.usgs.gov/learn/preparedness.php.