Mammoth Lakes Area Is Skaken by More Earthquakes

A series of small earthquakes rumbled through the Mammoth Lakes area over the weekend, prompting increased vigilance from seismologists but probably no immediate danger, scientists said.

Since Friday, the region has been hit with 17 quakes of magnitude 3 or greater. The largest of the swarm of temblors, a magnitude 4.3 quake, jolted the area about 5:50 p.m. Monday. Authorities said no damage or injuries were reported from the quakes. All were centered six miles southeast of Mammoth Lakes, U.S. Geological Survey seismologist David Hill said.

Late Friday, the geological survey issued a Level C report of “strong or persistent unrest” for the area, indicating increased chances for a volcanic eruption. Mammoth Lakes is at the edge of a collapsed volcanic crater and has had a number of quake swarms since May 1980, when four magnitude 6 earthquakes struck in a short time.

However, scientists have not detected any bulges in the ground that would indicate molten lava pushing its way to the surface, Hill said. “In the absence of ground deformation, there is no concern for imminent volcanic activity,” he said.

Even in a worst-case scenario, an eruption would be days to weeks away, and scientists would have plenty of warning, he said. “The fact is, for magma to get to the surface, it has to push aside the rocks that are in the way,” Hill said.

The USGS issued a Level D watch, “moderate unrest,” on Feb. 15 after 100 small earthquakes, mostly in the unnoticeable magnitude 2 range, struck the area. The upgrade to Level C merely signals to scientists to keep closer watch on their instruments over the next few days, Hill said. “People shouldn’t get panicky over it,” he said.

Occasionally, a flurry of small earthquakes precedes a larger quake. “There is always a possibility that things will escalate,” Hill said. But, he added, the vast majority of such flurries simply die away.

The volcano watch will continue at least until Wednesday afternoon, Hill said, but could be extended if quakes greater than magnitude 3 continue to strike the area.

Times wire services contributed to this story.