Short-lived Long Valley earthquake swarm does not indicate heightened volcanic unrest

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A short-lived earthquake swarm occurred overnight under the Long Valley Caldera in eastern California about 4 km (2.5 mi) ESE of the town of Mammoths Lakes. The swarm does not appear to be related to increased volcanic unrest.

The swarm started with a M2.76 at 11:28 PM PST last night in the South Moat of Long Valley Caldera. This event was followed by a M3.87, the largest event in the swarm, about 15 minutes later. More than forty earthquakes between M1.0 to M3.17 occurred over the ensuing hour. The swarm gradually decayed in numbers of events and earthquake magnitudes over the course of the night to about 10 events of M1.0 or less per hour. Focal depths of earthquakes in the swarm cluster are between about 5-6 km (3-3.8 mi) below Route 203 just west of the junction with Route 395. Swarms of this type are common under the South Moat of Long Valley Caldera. At present, we see no indication of increased volcanic threat to the region.

View current monitoring data on the Long Valley Caldera Monitoring webpage.

December 13 - 14, 2016 Long Valley Caldera earthquake swarm recorde...

December 13 - 14, 2016 Long Valley Caldera earthquake swarm recorded on instrument MDH1 webicorder. Swarm begins at 23:28 PST.

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