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RENO, Nev. (AP) — Seismologists have taken steps to better track an earthquake swarm in the sparsely populated northwest corner of Nevada near Oregon and California.
The placement of seismographs closer to the activity will improve experts' ability to locate temblors and gain more information about them, said officials at the University of Nevada, Reno's Nevada Seismological Laboratory.
No major damage has been reported since the swarm began in July around the Sheldon National Wildlife Refuge, about 40 miles southeast of Lakeview, Oregon, and 250 miles north of Reno. The area is home to scattered ranches and farms.
"We've been in contact with local residents, and they've been very helpful in finding locations to install this additional instrumentation," lab director Graham Kent said in a statement. "Residents expressed an eagerness to help, as they are feeling the daily barrage of magnitude 3 and 4 quakes."
About 1,350 quakes have been recorded during the swarm, but seismologists have been unable to locate thousands more because of the small number of seismic stations in the remote desert region.
They're calling it the strongest such swarm in Nevada's recent history, with 12 magnitude-4.0-plus temblors and 112 quakes magnitude 3 or above. The largest two events — both magnitude 4.7 — shook the area on Nov. 6 and Nov. 7. Other swarms were felt near Hawthorne in 2011 and in Reno in 2008.
This week saw about 50 small quakes, including several measuring magnitude 3 and others measuring magnitude 4.0 on Friday and 4.3 on Nov. 17, said Ken Smith, seismic network manager of the seismological lab.
"The activity has quieted down somewhat this week, but it has had slowdown periods throughout, so we are still closely monitoring the sequence," Smith said. "The sequence, although slowing down somewhat, is still not over."
There's a small increase in the probability of a larger event following such swarms, experts said, but large quakes can't be predicted.
"Right now, it's not making much impact on the nearest communities, but if this gets into the magnitude 5 range a couple of communities will start to see an impact, and if it reaches magnitude 6.0, which is always a possibility in Nevada, we could see some impacts on people and damage to structures," Kent said.
Nevada, which is laced by faults, is the third most seismically active state in the nation behind California and Alaska.
Seven temblors of magnitude 6.5 or higher jolted the state from 1900 to 1954, with the last occurring east of Fallon in 1954 when two of magnitude 7 hit four minutes apart. A magnitude-6.0 temblor near the northeast Nevada town of Wells on Feb. 21, 2008, was the biggest in the state in four decades, causing nearly $10 million in damage.
Bill Hammond of the university's Nevada Geodetic Laboratory said that while some residents wonder if the latest swarm is related to an extinct volcano in the Sheldon wildlife refuge, experts think it stems from the region's faults.
"However, conclusively ruling out a volcanic source will require the additional seismic and geodetic measurements closer to the events," he said.
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