No clear answer in thousands of Nevada quakes

Seismologists studying a yearlong swarm of thousands of mostly minor earthquakes in northwest Nevada say they could be the precursor for a “big one,” although speculation that they’re related to a series of extinct volcanoes can’t be ruled out.

The University of Nevada, Reno’s Nevada Seismological Laboratory announced Tuesday there have been 5,610 earthquakes in a swarm that started in July 2014 in the Sheldon National Wildlife Refuge near the Oregon border.

More than 200 have registered at a magnitude of 3 or greater, which is enough to be felt by ranchers and residents nearby.

“It’s kind of unusual that it has lasted so long,” seismologist Ken Smith said.

It’s been a topic of discussion whether the quakes stem from the extinct volcanos in the Sheldon refuge collectively known as the High Rock Caldera.

That hasn’t been conclusively ruled out, but Smith said there’s no direct evidence of volcanic activity driving the earthquakes.

Such a repetition of small earthquakes is often associated with volcanic activity, but the latest ones point to a fairly typical tectonic sequence that is characteristic of the western Great Basin region.

A swarm of thousands of little earthquakes could also lead to a big one. Three magnitude 7.0 earthquakes each century and one magnitude 6.0 or larger each decade are expected in Nevada.