California ancient volcano site rattled by swarm of tremors

August 28, 2011 – LOS ANGELES – A cluster of mild earthquakes rumbled early on Saturday near Pinnacles National Monument, site of an ancient volcano in central California, and were widely felt in and around the Monterrey Bay area. The largest of the tremors, measured at a magnitude of 4.6, struck shortly after midnight Friday local time just northwest of Pinnacles, which lies in the San Andreas seismic fault zone about 100 miles southeast of San Francisco Bay, the U.S. Geological Survey said. Quakes of that size cause noticeable shaking of furniture and some rattling noises, but there were no reports of damage or injuries from Saturday’s temblors, which were typical for the seismically active region. “It’s not uncommon to see clusters, or what we call swarms, of earthquakes in many places around California,” USGS spokeswoman Leslie Gordon said. The quake cluster near Pinnacles began at about 11 p.m. and numbered in the dozens. But only seven registered a magnitude 3.0 or higher as of noon on Saturday, USGS data showed. A National Park Service ranger reached by telephone at Pinnacles, known for its monolithic rock formations, spires and sheer-walled canyons, said the quakes were noticed but shrugged off by residents accustomed to such tremors. “Most of the residents here felt it, but we’re so used to having small earthquakes all the time that it was no big deal,” she said. A USGS mapping system that records citizen reports of where quakes are felt showed the largest of Sunday’s tremors was noticed as weak to light shaking throughout the Monterrey Bay region along a 200-mile-long corridor of central California. The California quake swarm occurred days after a rare 5.8 earthquake shook much of the U.S. East Coast on Tuesday, centered in Mineral, Virginia. That shock damaged the U.S. Capitol and Washington Monument and sent thousands of jittery residents and office workers out onto the streets. –Reuters