M4.4 "Sierra Block" earthquake west of Mammoth Lakes

Release Date:

At 10:36:54 PST (18:36:54 UTC on) 1 February, a M4.4 earthquake occurred under McGee Mountain near Toms Place, CA, at a depth of 10 km.

Earthquakes are represented by colored, scaled circles on a shaded relief map of the Long Valley Caldera.

Location of the 1 February 2020 earthquake south of the Long Valley Caldera

(Public domain.)

This area, sometimes referred to as the "Sierra Block" commonly produces earthquakes in the range of M3 with a M4+ every few years. These earthquakes are generally unrelated to volcanic activity, and the alert level at all Long Valley Volcanic Center volcanoes remains at Normal/Green. The current earthquake poses no immediate hazard, but aftershocks like the M3.1 that occurred shortly after at 10:55:36 PST (18:55:36 UTC) may still occur.