Long Valley Caldera and Mono-Inyo Chain: An earthquake swarm occurred beneath Mammoth Mountain, lasting from about February 3-18. Though Mammoth Mountain is the site of frequent earthquake swarms, this was one of the largest since a protracted swarm in 1989.
The February swarm included 166 earthquakes of M1.0 or larger, most at depths of ~5 km below the surface. The largest event was M 3.1 on Feb 5, which was felt by some residents of the town of Mammoth Lakes.
The swarm is likely related to migration of deep-seated hydrothermal fluids. No accompanying changes in surface deformation or gas emissions have yet been detected.
Elsewhere in the region, forty earthquakes of M1.0 or greater were located in the Long Valley Caldera, with a maximum M2.6. No earthquakes M1.0 or greater were detected under the Mono-Inyo chain.