After a two-day lull, a swarm of small earthquakes resumed Wednesday in the eastern Sierra, six miles east of Mammoth Lakes, prompting the U.S. Geological Survey to declare a volcano hazards watch for the third time this year.
The Level D notice, indicating "moderate unrest," came as more than 150 quakes, the strongest a magnitude 3.3 at 5:13 a.m., shook the area between 9 p.m. Tuesday and 3 p.m. Wednesday.
Geological Survey seismologist David Hill noted that the three-day watch is the fourth lowest of five levels of seriousness.
A Level C notice, indicating "strong or persistent unrest," was issued 2 1/2 months ago. Level A means a volcanic eruption is likely within hours to days.
The seismologist said there was no immediate cause for alarm. "These are areas that we've seen produce most of the earthquakes around Mammoth back to 1980," he said. "But we're not seeing any ground deformation, and there is no indication of magma [lava] near the surface."