Earthquake swarm reported at California's Coso Volcanic Field

December 4, 2012 – CALIFORNIA - An energetic earthquake swarm centered beneath rhyolite domes in the Coso Volcanic Field (CA) continues, with over 20 earthquakes ranging between M1 and M3 so far today. Many smaller events (hundreds) are recorded as well. The swarm initiated on 27 November and has included earthquakes as large as M3.7. The Coso Volcanic Field is located in Inyo County, California, at the western edge of the Basin and Range geologic province and northern region of the Mojave Desert. The Coso Volcanic Field is one of the most seismically active regions in the United States, producing dozens of tremors in the M1 and M2 range each week. Tremors in the M3 range occur at a rate of 2-6 per month and M4 quakes occur two-three times each year. Recent activity in the M5 range happened in 1996 and 1998 when tremors of M5.3, M5.1, M5.2, and M5.0 occurred with a day of each other. These tremors were actually recorded along the eastern side of the Coso Volcanic Field, 15 miles (24 km). September 30, 2009 to October 6, 2009 there have been 429 earthquakes ranging from 0.1 up to a 5.2. Some days have activity just about one every minute. On October 2, 2009 there were three earthquakes (5.2, 4.7, and a 4.9) all within one hour of each other. Earthquake swarms are common in the Coso area, often producing hundreds of tremors over periods of time as short as a few days. This kind of brisk and robust seismic activity is common in volcanic areas, such as Long Valley Caldera located near Mammoth Lakes, and Yellowstone Caldera at Yellowstone. Geologists say the last eruption of the volcanic fields occurred 30 to 40,000 years ago. –Earthquake Report, Wikipedia

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