SAN FRANCISCO (CBS SF) — The United States Geological Survey announced on its website Friday it was “closely tracking” a swarm of hundreds of earthquakes that began Thursday, located in Long Valley about 7 miles east of the Sierra Nevada resort town of Mammoth Lakes.

The region, known to geologists as the Long Valley Caldera, is the site of one of North America’s greatest pre-historic eruptions and is surrounded by a chain of recently-active volcanos. Earthquake swarms are fairly common in the area.

Geologists are careful to determine if the quakes indicate the movement of magma deep below the surface — possibly signaling another eruption — or if they are shallower, less-ominous quakes, sometimes called “tectonic quakes” or “brittle-failure earthquakes.”

The USGS California Volcano Observatory site states that these most-recent quakes “do not result from the underground movement of magma” and “pose no immediate hazard.”

Seismologist David Shelley told the Los Angeles Times the quakes may have been triggered by water pressure from area hot springs, heated by the magma far underground.

Shelly says at least 109 of the earthquakes reported since Thursday were magnitude 2.0 or greater and smaller quakes made up the bulk of the activity.

COMPLETE QUAKE COVERAGE: CBS Earthquake Resource Center

This article will be updated as information warrants, and follow KPIX 5 on Twitter at @CBSSF or KCBS Radio on Twitter at @KCBSNews for updates on breaking news anytime.

DID YOU FEEL IT?: USGS Shake Map For Northern California
LIVE QUAKE MAP: Track Real-Time Hot Spots
BAY AREA FAULTS: Interactive Map Of Local Faults

Strong earthquakes with an epicenter off the coast can trigger tsunamis, depending on the size and type of the fault movement. The Pacific Tsunami Warning Center tracks earthquake data for the West Coast.
status low USGS Closely Tracking Earthquake Swarm In Mammoth Lakes Volcanic Area
Tsunami Alerts & Maps


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