Earthquake swarm: What caused hundreds of mini-quakes?

An earthquake swarm hit Mammoth Lakes late last week, with more than 600 earthquakes hitting the region within 24 hours. The earthquake swarm is not connected to volcanic activity, scientists say.

A seismologist says a series of more than 600 earthquakes during a 24-hour period – called an earthquake swarm – in the Mammoth Lakes region may have been caused by water pressure from area hot springs.

The Los Angeles Times reports Saturday that U.S. Geological Survey seismologist David Shelly says scientists don't believe the earthquake swarm is connected to any volcanic activity.

Shelly says the quakes may have been triggered as water pressure from area hot springs shifted through the ground surface, stressing tectonic plates.

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.