Shake, rattle and roll

Mammoth experiences flurry of earthquakes last weekend.

The earthquake swarm that rattled through Mammoth Lakes from September 25 to September 28 is quieting down as of this week. The swarm, located seven miles from Mammoth Lakes near the Mammoth Yosemite Airport, grew to more than 700 earthquakes by Sept. 28, according to the U.S. Geological Survey (USGS).

Fortunately, most of those earthquakes were between magnitude 1 and 2, although eight were between magnitude 3 and 3.8 (for perspective, the 2011 Christchurch earthquake was a magnitude 6.3).

“Despite the several felt earthquakes, this is still rather modest activity compared with the much more energetic swarms occurring in the 1980s and 1990s,” the USGS said in a statement.

The Mammoth Lakes area was hit by multiple magnitude 6 earthquakes in the 1980s, and by a series of magnitude 4.9 earthquakes in 1997.

The USGS was also quick to clarify that the swarm was tectonic (relating to the earth’s crust), not volcanic. “The earthquakes themselves are small, brittle-failure (rock breaking) events,” the USGS stated. “The earthquakes do not result from the underground movement of magma.”

Such earthquake swarms are commonplace in the area, said USGS Volcano Science Center seismologist David Shelly in an interview with the Los Angeles Times.

Shelly theorized that this swarm might have been triggered by water pressure from the local hot springs shifting through the ground surface, putting pressure on tectonic plates.

The last swarm, composed of about 200 small quakes, shook the Long Valley Caldera in July.

However, Shelly admitted, “this one is a bit more energetic than what we have seen in a while.”

The USGS said it will continue “closely tracking” the tectonic activity.