Recent Nevada Quakes May or May Not Mean Big One Coming

April 3, 2008

There’s no way to know whether recent swarms of earthquakes in northeast Nevada and near Reno are an indicator that a bigger quake is coming, experts say.

“We can say with 100 percent certainty that large earthquakes are going to happen in western Nevada. We can’t say when,” said John G. Anderson, director of the Nevada Seismological Laboratory.

Earthquakes occur in Nevada because as the state ages, it spreads out. That spreading, coupled with a constant grinding along the San Andreas fault as the Pacific Ocean floor tries to move northwest toward the Oregon coast, is why Nevada is the second most seismically active state in the lower 48 states, Anderson said.

A magnitude 6.0 earthquake Feb. 21 severely damaged much of old downtown Wells in Elko County. It was followed by a swarm of smaller earthquakes around the town and also around Mogul, between Reno and Verdi, including a 3.1 temblor at 8:42 p.m. Wednesday 5 miles west of Reno.

Anderson said there’s no cause for alarm.

“The bottom line is that it is not unusual,” he told the Reno Gazette-Journal. “The swarm by Wells is a little more unusual than the swarm by Mogul.”

Contrary to popular belief, little quakes do not release energy and prevent bigger ones, he said.

“Small earthquakes are a reminder that we live in an active area, but they’re not useful for releasing the pent-up energy. They’re just too small,” Anderson said.

“When you look at all the energy released, 90 percent of the energy released is released in the big earthquake,” he said.

In an average year, Nevada has one earthquake of magnitude 5.3 or greater and a magnitude 6 about every three or four years, he said, and a magnitude 7 about once every 30 years.

The last ones registering 7 were in 1915 in Pleasant Valley south of Winnemucca, 1934 near Gabbs and in 1954 when two struck about four minutes apart in the Dixie Valley area near Fallon.

“During the 20th century, we were lucky that all of the largest earthquakes that occurred within the state occurred within pretty remote areas,” Anderson said.

So, if the last magnitude 7 quake was in 1954, isn’t the state due for another monster quake?

“It would certainly be no scientific surprise if it happened, but the occurrence of earthquakes is so irregular that we can’t really say that we’re due,” he said.

Before 1915, the last major quake in the Reno area that was a magnitude 7 was probably in 1860, Anderson said.

Magnitude 7 quakes occurred along the east side of Mount Rose just south of Reno about 600 years ago and about 1,900 years ago, he said.

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