Thursday, July 10, 2014

Large Quake Swarm at Long Valley Caldera, CA

After a few months of relative quiet at California's Long Valley Caldera, East of Mammoth Mountain volcano, activity has intensified with hundreds of small and shallow quakes at depths of around 4.7 miles. Many small tremors are occurring below the surface about 1.5 miles north of Yosemite Mammoth Airport. These are small quakes, and likely not able to be felt by anyone not at the epicenters. These quakes are interesting mostly due to the sheer numbers, not the magnitude.

More than likely these are hydrothermal 'spasmodic' quakes, related to liquid movement under the surface, and likely not a result of any serious magma intrusion. If there were a large intrusion of magma, you would expect to see the depths of the quakes change (these are all relatively consistent) to progressively shallower depths. Since this isn't occurring, it is reasonable to assume this is simply normal behavior for Long Valley's large hydrothermal system, rivaled only by Yellowstone in the US.

Image from Google Earth with USGS overlay detailing locations of quakes in Long Valley.

The Long Valley caldera is a so-called 'supervolcano', like Yellowstone, or the Valles Caldera in Mew Mexico. Long Valley was the source of one of the largest eruptions on Earth, approximately 760,000 years ago, which created the voluminous Bishop Tuff, a layer of ash and debris that spans most of the continental US. Like Yellowstone, Long Valley is capable of 'nation ending' eruptions, however this, like Yellowstone, would be extremely unlikely in our lifetimes. 

The last 'serious' activity at Long Valley was a 6.0+ mag quake in the late 70's, which was followed by rapid 'doming' in the center of the caldera. On average this 'resurgent doming' has added several centimeters in height per decade.

It is likely in the future that activity will resume at Long Valley, given the doming, active geothermal system, and persistent seismicity. For now, I wouldn't lose any sleep over this, as it is not only quite common, but completely normal activity. If larger quakes were to 'swarm' in the area, this would be a cause for concern.

*****UPDATE 7/11/14*****

Looks like the swarm is over for now. 

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