Earthquake Swarm in Mammoth Lakes

Earthquake swarm Mammoth Lakes, CA

We have been closely tracking an earthquake swarm in Long Valley Caldera, which started yesterday at around 4AM on (September 25, 2014). The swarm is located 7 miles east of the town of Mammoth Lakes, about a quarter mile north of the airport. From about 4AM on the September 25th to 12:30AM on September 26th there have been more than 70 earthquakes of magnitude M2.0 and above, including 8 earthquakes between M3.0 to M3.8 that produced locally felt shaking. This is one of several earthquake swarms that have occurred in the caldera this year. We do not see any evidence for anomalous ground deformation associated with the swarm at this time.

Despite the several felt earthquakes, this is still rather modest activity, compared with the much more energetic levels that we witnessed through the 1980s and 1990s. In that sense, it is not out of the ordinary for this geologically active area. We'll contInue to closely track this activity, and provide updates as appropriate.

Margaret T Mangan, PhD
Scientist-in-Charge
California Volcano Observatory
US Geological Survey