Sept. 19, 2004
By Associated Press

MAMMOTH LAKES, Calif. -- An earthquake swarm continued to shake a sparsely populated area along the eastern Sierra Nevada on Sunday.

Mono County sheriff's dispatchers reported no injuries or damage from the temblors centered along the California-Nevada line 30 miles northeast of Mammoth Lakes.

David Oppenheimer, a seismologist with the U.S. Geological Survey in Menlo Park, said there were 275 quakes Saturday and 206 temblors Sunday as of 5 p.m.

A magnitude 5.5 temblor Saturday afternoon was the most powerful in the swarm. Two magnitude 3.0 quakes -- one at 5:06 a.m. and the other at 6:29 a.m. -- were the strongest Sunday.

"In terms of energy release, it looks like it's dying down," Oppenheimer said. "In terms of the number of quakes, the sequence is still robust."

It's uncertain how much longer the quakes will continue, he said.

"They (swarms) all eventually die down," he said. "It could take a week. Some take up to six weeks."

Oppenheimer said it's premature to say whether the swarm is related to volcanic activity.

"Being so close to the Mono Craters and Long Valley Caldera, some people are thinking this could be volcanic. But it's too soon to know," he said. "If the swarm continues another week, we'll think about putting geodedic instruments out there to monitor the activity."

Oppenheimer stressed that there was volcanic unrest in the 1990s in the Mammoth Lakes area but never an eruption.

The eastern Sierra has been a seismically active area. A similar sequence was centered in the same area over a one-week period in 1980, Oppenheimer said. The activity died down in 1984 before picking up again in 1992.

http://www.dailynews.com/Stories/0,1413,200~20954~2413488,00.html