Swarm of 6 Earthquakes Shakes Region Near Mammoth Lakes

A swarm of six earthquakes, the strongest a magnitude 4.0, struck just north of the Eastern Sierra town of Bridgeport on Wednesday afternoon, the U.S. Geological Survey reported.

The sharpest temblor was the latest, at 4:20 p.m., and it was centered, like the others, three miles north of town.

There were no reports of damage or injury.

The first jolt, a magnitude 3.5, was felt at 1:17 p.m. Other quakes, ranging from 2.1 to 2.9, occurred at 1:23 p.m., 1:24 p.m., 1:45 p.m. and 2:44 p.m.

A “swarm” is a scientific term for a series of quakes in which stronger temblors usually follow weaker ones. They can last days, although most swarms last just hours.

Bridgeport, on U.S. Highway 395, is 40 miles north of Mammoth Lakes, where a history of volcanic activity has led to close monitoring of seismicity and signs of intrusion of magma underneath the surface. Four earthquakes in the magnitude 6 range occurred within two days at Mammoth in 1980, and were followed by frequent recurrence of other temblors in ensuing years. But there have been fewer earthquakes in the Mammoth area since the late 1990s.

Volcanic cones are visible from U.S. 395 from Mammoth Lakes north to Mono Lake, but do not continue as far north as Bridgeport.