Swarm of 90 Minor Quakes Shakes Mammoth Lakes Area
A swarm of about 90 earthquakes has shaken the volcanic Mammoth Lakes area of the Eastern Sierra in the last three days, the U.S. Geological Survey reported Monday.
The strongest of the comparatively weak temblors occurred at 3:39 a.m. Monday, measured magnitude 3.2 and was centered 11 miles southeast of Mammoth Lakes, south of the Long Valley caldera.
Quite a few of the quakes, however, occurred within the caldera--a huge volcanic crater--six miles southeast of Mammoth Lakes. The caldera was created during an eruption 760,000 years ago and has been the locale of scientific monitoring for a possible renewal of volcanic activity.
The term “swarm” refers to an episode of frequent quakes that can last several days. There have been two other swarms this year.
One took place in February, when about 100 quakes triggered a low-level D volcano hazards notice by the geological survey. The other occurred in April, when a stronger swarm, including a magnitude 4.3 quake, led to a Level C notice of “strong or persistent unrest.”
No such notices have been issued in the most recent swarm.
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