Two magnitude 4.0s in earthquake swarm |

Two magnitude 4.0s in earthquake swarm

by Natalie Savidge
University of Nevada, Reno

The Nevada Seismological Laboratory reported magnitude 4.0 and 4.1 earthquakes in a swarm of 40 located events about 13 miles northwest of Truckee, Calif. on Tuesday. The two largest events were separated by seven minutes. Location parameters for event one: 39.468 north latitude, -120.349 west longitude, depth of 4.3 miles, at 2:02 a.m. , and for event two: 39.469 north latitude, -120.347 west longitude, depth of five miles (8.1 km), at 2:09 a.m. The swarm included a magnitude 3.2 event and six events between magnitude 2.0 and 2.9.

As of 1:32 p.m. Tuesday, the Nevada Seismological Laboratory located a total of 40 events in this sequence of earthquakes. The swarm is not directly associated with mapped faults, but occurs in a step-over between the Mohawk Valley and the Polaris fault zones along the eastern Sierra Basin-Range boundary region.

The largest earthquakes were felt in the Truckee, Lake Tahoe, Reno and western Sierra region. There is a slight increase in the probability of a larger event during an ongoing sequence of earthquakes such as this one. The Nevada Seismological Laboratory continues to closely monitor the activity.

“I like to remind everyone that it is always appropriate to make a plan for what to do during a disaster, in this case: secure your home before; drop, cover, hold on during; and assess damage after,” said Aaron Kenneston of tht Washoe County Emergency Management and Homeland Security Program. “Assemble a kit with at least 72 hours of water, food, first aid supplies, flashlight and battery-powered radio in case of utility disruption, and stay informed about our earthquake risks.”

Updated information for activity associated with this earthquake is available at

Nevada and eastern California regions have a history of large, damaging earthquakes, and citizens should always consider earthquake preparedness. Residents are encouraged to practice aspects of emergency plans and to “secure your space,” which includes retrofitting buildings to reduce damage and securing things within buildings to prevent injury. For more information on how to prepare for an earthquake, go to