Northwest Nevada has been hit by a year-long swarm of thousands of mostly minor earthquakes. The University of Nevada's Reno Nevada Seismological Laboratory said today that 5,610 earthquakes have registered since 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. The largest one hit on Nov. 6 with a magnitude of 4.7, although there's also been a recent flare-up since mid-July. "It's kind of unusual that it has lasted so long," says Ken Smith, a seismologist.
It's been a topic of discussion whether the quakes stem from ancient volcanos in the Sheldon refuge collectively known as the High Rock Caldera, which is at least 15 million years old. That hasn't been ruled out, but Smith says there's no direct evidence of volcanic activity driving the earthquakes. The latest ones point to a fairly typical tectonic sequence that is characteristic of the western Great Basin region. "The activity appears to be primarily associated with a fault, or faults, dipping steeply to the southeast and striking north-northeast," says Smith. Of note to residents: A swarm of thousands of little earthquakes could lead to a big one. (Read more earthquake swarm stories.)