Volcano Update from Archive

Wednesday, June 20, 2007 15:07 PDT (Wednesday, June 20, 2007 22:07 UTC)

37.70°N 118.87°W, Summit Elevation 11122 ft (3390 m)
Volcano Alert Level: NORMAL
Aviation Color Code: GREEN

Earthquake sequence of 12 June 2007 south of Long Valley caldera

At 12:22 AM (PDT) on June 12, a magnitude M=3.6 earthquake was followed within less than a minute by a M=4.6 earthquake and a rich aftershock sequence that continues to gradually decay through June 20. These earthquakes are centered at depths of 7- to 10-km beneath the west shore of Lake Dorothy in the Sierra Nevada 7 km south of the caldera boundary (14 km southeast of Mammoth Lakes). This sequence has included over 150 M>1 earthquakes, eight of which had magnitudes in excess of M=3.0. The larger of these earthquakes produced felt shaking in the Mammoth Lakes-Bishop area of eastern California. This is the most energetic earthquake sequence in the vicinity of the caldera since 2000. It occurred within the part of the Sierra Nevada south of the caldera that maintained elevated levels of seismic activity during recurring unrest episodes within Long Valley caldera from 1980 through 1999. We have seen no evidence for increased earthquake activity or ground deformation within the caldera associated with this earthquake sequence in the nearby Sierra Nevada.

The Long Valley Observatory (LVO) monitors and studies earthquakes, ground deformation, degassing, and other types of geologic unrest in and around the Long Valley Caldera. The 15 by 30 km Long Valley Caldera was formed during an eruption 760,000 years ago and is located 20 km south of Mono Lake along the east side of the Sierra Nevada in east-central California. There have been multiple smaller eruptions since the caldera-forming eruption with the most recent occurring 250 years ago in Mono Lake at the north end of Mono-Inyo Craters volcanic chain. LVO is one of the five USGS Volcano Observatories that monitor volcanoes within the United States for science and public safety.