Scientists Say Nevada, Mammoth Quakes May Be Linked

This week’s moderately strong temblors in western Nevada could be connected to a quake swarm about 30 miles away east of Mammoth Lakes, scientists monitoring volcanic earthquakes near Mammoth said Wednesday.

The U.S. Geological Survey reported 34 quakes of magnitude 3.0 or greater in California and Nevada this past week--an unusually high number--including 24 in Nevada and five at Mammoth Lakes.

Other quakes of this magnitude have occurred in such widely separate areas as San Clemente Island and near Quincy in Northern California. The latter quake, which occurred at 9:49 a.m. Wednesday, was felt as far away as Sacramento. It was first measured at magnitude 4.8 but was later downgraded to 4.3. A 4.5 quake also occurred Wednesday afternoon 30 miles southeast of Bishop, Calif.

The seismic events in Nevada included quakes of magnitudes 5.3, 4.8, 4.3 and 4.2 in a remote mountainous area.

Hundreds of smaller quakes--the strongest was 3.4--have occurred along the same northeast-southwest lineal alignment near the eastern Sierra town of Mammoth Lakes.

Scientists said there is no connection between the San Clemente Island quake and the Quincy quake. But they viewed the Mammoth and Nevada quakes differently.

David Hill of the Geological Survey, the chief monitor of volcanic precursors in the Mammoth region, said that scientific monitoring of Mammoth has increased since June in the wake of repeated swarms of quakes, some increased ground uplift and small changes in hot springs.

“We are certainly watching things more closely now,” Hill said. “But . . . there is no evidence that things are moving toward [an eruption in the short term].”

Hill said that research into “sympathetic” earthquakes in the eastern Sierra after the comparatively distant Landers quake of 1992 could mean there is a possible connection between the Nevada and Mammoth quakes.

Ross Stein, another Geological Survey scientist, said, “Mammoth is basically straining the whole area, and quakes that have taken place north of Bishop in the Chalfant Valley and in Nevada over the last 15 to 20 years could be related.”

He added: “This week the San Andreas fault [closer to the Pacific] seems to be sleeping, and what is known as the Eastern California Shear Zone has been active. In that respect, he said, even the Quincy quake [which is along the shear zone] could be connected to Mammoth.”

Allan Lindh, a former director of Geological Survey earthquake research for the Western states, said, “We know from what happened after Landers that there are long-distance connections between quakes.

“The Nevada quakes in the Great Basin are related to volcanic processes,” he said. “Probably all of this is related, we just don’t know exactly how.”

Chris Farrar, another monitor of Mammoth, said he believes scientific concern about a Mammoth eruption would rise “if the deformation keeps going on at its current rate and moves into a shallower depth.”

But Hill said: “We don’t see any short-term, localized deformation that might be associated with magma [molten rock] moving into the shallower crust.”

Hill, Farrar and another survey specialist, Michael Sorey, said they have looked intensively into reports of recent changes in hot springs near Mammoth. But they have not been able to establish any overall increase in hot water emissions, which could be caused by injections of magma into the ground water system.