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  1. #1
    Senior Member JohnDoe2's Avatar
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    'Volcanic unrest' shakes California

    'Volcanic unrest' shakes California

    Earthquakes reported near Mammoth Mountain volcano

    By Amanda Watts, CNN
    updated 9:09 PM EDT, Fri September 26, 2014

    STORY HIGHLIGHTS

    • Three dozen earthquakes in last 2 days near Fresno, California
    • Swarms of earthquakes not uncommon in the region
    • Last swarm of earthquakes produced over 2500 between 1997-98


    (CNN) -- A flurry of small earthquakes rumbling near the Mammoth Mountain Volcano, have been categorized as "volcanic unrest" by the United States Geological Survey.

    Nearly three dozen earthquakes ranging from magnitude 2.6 to 3.8 have swarmed the area, northeast of Fresno, California, over the last two days.


    Earthquake swarms in this region are not uncommon. David Shelly, a seismologist with California Volcano Observatory, said this swarm is "bigger than we've seen recently, but normal in the area." He adds they are keeping a close eye on the movement, "but in the larger scheme of things, it's within in the range of activity over the last several decades."


    Mammoth Mountain is in an area called the Long Valley Caldera. The center of the caldera has been uplifting slowly over the last several decades and seismologists continuously monitor it. "We think there is fluid coming up from the crust triggering the earthquakes," said Shelly.


    The last swarm of quakes from 1997 to 1998 produced over 2,500 earthquakes per week at its height, according to the USGS. Since then, the region has been relatively quiet.


    In July, USGS scientists installed a volcanic-gas monitoring station on the mountain. It tracks gases that fluctuate with earthquake activity to better track the changes in real-time.


    The awareness level on the USGS website remains at green/normal.

    Mammoth Mountain, standing at 11,053 feet, last erupted about 57,000 years ago, according to the USGS.

    http://www.cnn.com/2014/09/26/us/mam...html?hpt=hp_t2

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  2. #2
    Senior Member JohnDoe2's Avatar
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    Mammoth Lakes earthquake swarm tied to water pressure, tectonic stress


    The Long Valley caldera, where more than 600 earthquakes have been reported since Thursday. (United States Geological Survey's Volcano Hazards Program)

    By VERONICA ROCHA

    600-plus earthquakes have shaken Mammoth Lakes region over the last 24 hours, USGS says

    The more than 600 earthquakes that have struck the Mammoth Lakes region over the last 24 hours are an indication of tectonic, not volcanic, stress, an expert said Friday.

    At least 109 of the earthquakes were magnitude 2.0 or greater, with smaller quakes making up the bulk of the activity, said David Shelly, a seismologist at the U.S. Geological Survey's Volcano Science Center.

    At least six, however, were greater than magnitude 3.0.


    We are not having any eruptions in California ... in the near future.- David Shelly, seismologist at USGS Volcano Science Center

    The largest, a 3.8 temblor six miles from Mammoth Lakes, occurred at 9:21 p.m. Thursday.

    The swarm of quakes, which began Thursday in the 20-by-10-mile Long Valley caldera east of the central Sierra Nevada Range, isn't uncommon for the region. About 200 small quakes -- the largest a magnitude 2.7 -- shook in Long Valley Caldera in July.


    Still, Shelly said, “this one is a bit more energetic than what we have seen in a while."


    The earthquakes may have been triggered by water pressure from area hot springs shifting through the ground surface, stressing tectonic plates. Scientists, Shelly said, are closely watching the earthquake swarm, but don’t believe it's connected to any magmatic activity.

    lRelated
    L.A. NOW 'Volcanic unrest' in Mammoth Lakes: Nearly 3 dozen small quakes in 24 hours SEE ALL RELATED

    Shelly said seismic analysts plan to review the swarm and update locations and magnitudes of the quakes, but the activity is not nearly on the size and scale of what was measured in the 1980s and 1990s.
    In the 1980s, the area was hit with a swarm of multiple 6.0-magnitude temblors, but they were overshadowed by the Mount St. Helens eruption in Washington, Shelly said.

    A decade later, in 1997, the area was rocked with another series of mostly 4.9-magnitude quakes over the course of several months.


    The Long Valley caldera is one of the most seismically active regions in the state, and is part of a quiet network of 17 volcanoes throughout California. Many of the older volcanoes haven't been active for thousands of years.


    The last time the Long Valley caldera erupted was 50,000 years ago.

    Some volcanoes, like the Clear Lake Volcanic Field just 90 miles north of San Francisco, and Salton Buttes, which lies within the Salton Sea Geothermal Field 90 miles east of Palm Springs, experience some seismic activity, but nothing near the shaking in the Long Valley caldera.


    "We are not having any eruptions in California ... in the near future," Shelly said.


    Scientists rate a volcano's potential threat by assigning one of three different categories -- high to very high, moderate, or low to very low.

    The USGS created the measurement to ensure hazardous volcanoes are monitored so scientists can better develop forecasts and warnings for residents.

    The Long Valley caldera carries high to very high threat potential, likely because it rests near the community of Mammoth Lake.

    The breakdown for the rest of California's volcanoes:

    High to very high threat potential

    Clear Lake Volcanic Field
    Lassen Volcanic Center
    Medicine Lake
    Mono-Inyo Chain
    Mount Shasta
    Salton Buttes


    Moderate threat potential

    Coso Volcanic Field
    Soda Lakes (NV)
    Ubehebe Craters


    Low to very low threat potential

    Brushy Butte
    Eagle Lake Volcanic Field
    Golden Trout Creek Volcanic Field
    Lavic Lake Volcanic Field
    Silver Lake Volcanic Field
    Tumble Buttes
    Twin Buttes

    http://www.latimes.com/local/lanow/l...926-story.html
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  3. #3
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