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Earthquake swarm under Mammoth Mountain

February 6, 2014

An earthquake swarm under Mammoth Mountain (Mono County, CA), which started slowly on February 3, 2014 intensified in the early hours of February 5 with many small-magnitude earthquakes occurring in rapid succession, a phenomenon known as "spasmodic bursts."

The largest earthquake over the ~ 4 hours of heightened activity, a magnitude 3.0, occurred shortly after 1am local time. The swarm is emanating from depths of about 5 km (~ 3 miles) below the surface. Most earthquakes in the swarm are too small to be felt, but the magnitude 3.0 earthquake was felt by a few people in the town of Mammoth Lakes. Presently, earthquake activity beneath the mountain remains above background levels. Earthquake swarms, including spasmodic bursts, occur periodically beneath Mammoth Mountain. The current swarm is notable, however, because it includes the largest magnitude event (M3.0) observed in ~15 years. The attached plot shows the numbers of earthquakes under Mammoth Mountain over the last three months. 

CalVO deformation monitoring sensors at Mammoth Mountain show no significant change. In the adjacent Long Valley Caldera, the modest, quasi-steady inflation that has been observed for the last couple of years, also appears unchanged by the Mammoth Mountain swarm. CalVO scientists continue to closely monitor seismic, deformation, and gas emission signals. 

View Plot: Mammoth Mountain Hypocenter Counts - Feb. 2014 Swarm