la-me-ln-mammoth-earthquake-swarm-largest-in-a-001More than 600 small earthquakes have rattled the Mammoth Lakes region in less than 36 hours as ripple effects continued across one of the most seismically active volcanic regions in California, according to the U.S. Geological Survey. The swarm of quakes — ranging from magnitude 1.0 to 3.8 — began just before 5 a.m. Thursday, according to the USGS.  “This is one of the largest earthquake swarms we’ve seen in the past decade or so,” said David Shelly, a USGS research seismologist who has been studying the volcanic system near Mammoth Lakes. “We’ll be tracking it closely.” Residents reported periodic rattles through the day but said they were used to the shaking given that Mammoth is a seismically active area. Earthquake swarms are not uncommon to this region in California’s Eastern Sierra. Countless small faults crisscross the area known as the Long Valley Caldera, Shelly said. This roughly 20-mile-wide crater-like depression, adjacent to Mammoth Mountain, was formed from ash and pumice deposits during a volcanic “super eruption” about 760,000 years ago. More