SAN RAMON, Calif. (AP) — A swarm of small earthquakes has been rattling an area east of San Francisco, with more than 200 recorded since last week.
All the quakes were centered around the city of San Ramon on either the Calaveras Fault or offshoots of it. The largest struck Monday and was logged as a magnitude-3.5, according to the U.S. Geological Survey. No injuries or major damage have been reported.
IS A SWARM LIKE THIS A PRECURSOR TO A BIGGER EARTHQUAKE?
The San Ramon, Danville and Alamo area has seen several swarms over the past 40 years, U.S. Geological Survey Research Geophysicist Brad Aagaard said. The largest earthquake in each was in the magnitude 3.5 to 4.4 range.
Based on this historical data, Aagaard says, the most recent swarm is unlikely to lead to a large, damaging earthquake. Several of the swarms have lasted about 30 to 40 days, so East Bay residents likely will continue to experience light shaking for a couple more weeks.
DOES A SWARM RELIEVE PRESSURE TO AVOID A BIGGER QUAKE?
These small earthquakes relieve only a very tiny amount of stress compared with a magnitude-6.0 or larger earthquake. As a result, they do not reduce the occurrence of larger earthquakes.
HOW LIKELY IS A LARGE EARTHQUAKE ON THE CALAVERAS FAULT?
The probability of a magnitude-6.7 or larger quake on the northern section of the Calaveras fault in the next 30 years is 8 percent.
The probability of a magnitude-6.7 or larger earthquake somewhere in the San Francisco Bay Area region in the next 30 years is 72 percent.
WHAT SHOULD PEOPLE DO TO PREPARE FOR A BIG EARTHQUAKE?
Experts suggest keeping a gallon of water per person per day for at least three days, for drinking and sanitation. They also recommend having a three-day supply of nonperishable food.
Officials say people should have an earthquake preparedness kit with a flashlight, extra batteries, a battery-powered or hand crank radio and a National Oceanic and Atmospheric Administration radio with tone alert.
Other items to have include a first-aid kit, a whistle to signal for help, a dust mask to help filter contaminated air, as well as plastic sheeting and duct tape to shelter in place. Maps, a can opener, a wrench or pliers to turn off utilities, as well as moist towels and garbage bags for personal sanitation are also advisable.