Shaking 'swarm' fuels California's quake jittersAugust 28, 2012 by Michael Thurston in Earth / Earth Sciences
A "quake swarm" that has shaken southern California with hundreds of moderate temblors in quick succession is fueling jitters in the Golden State, long braced for the Big One.
The quakes, which began Sunday and could last for a few days according to experts, were mostly moderate but included several over 5.0 in magnitude, causing minor damage in the town of Brawley, near the Mexican border.
While nobody was injured—and as seismologists stress it does not increase the risk of a massive earthquake the region has long feared—it has inevitably fueled anxiety.
"Glad I've stocked up on food, water, fuel, and ammo. Have you?" commented SteadHead on the website of local broadcaster KTLA.
On Sunday, quakes could be felt as far away as San Diego on the West Coast and inland east into Arizona, as well as Orange County further north towards Los Angeles.
In Brawley itself there was minor damage to town center buildings, while products were knocked from shelves in some stores and amateur video showed the alarming jolt of the biggest shakes.
Seismologists say the latest quake cluster is the biggest in 30 years. A 2005 swarm peaked with a 5.1-magnitude shake, whereas the largest judder on Sunday reached 5.5 on the Richter scale.
The town at the epicenter of the shaking has a quake phenomenon named after it: the Brawley Seismic Zone. It sits between the San Andreas and Imperial faults.
"This is a classic Brawley Seismic Zone swarm," she told the Los Angeles Times newspaper. "It's relatively hot."
But she said a Brawley swarm has never produced anything bigger than a 5.8 quake in 1981. "We've never seen a Brawley swarm followed by a big earthquake on another fault," she said.
Earthquakes are regular events in California, mostly triggered by activity along the San Andreas Fault that runs through much of the western state, the most populous in the United States.
Geologists say a quake capable of causing widespread destruction is 99 percent certain of hitting California within the next three decades. A magnitude 7.8 quake could kill 1,800 people, injure 50,000 more and damage 300,000 buildings.
A 6.7-magnitude earthquake in Los Angeles left at least 60 people dead and did an estimated $10 billion damage in 1994, while a 6.9 quake in San Francisco in 1989 claimed the lives of 67 people.
Los Angeles is on the so-called earthquake-prone Ring of Fire, which circles the Pacific and which has produced temblors including Japan's killer quake and tsunami in March last year.
California is arguably due for the Big One even more than usual. While major quakes have in recent years shaken Japan, Indonesia, Chile, New Zealand and Mexico, the US West Coast has been spared.
Following the latest quake cluster, emergency services were quick Monday to remind Californians of what most of them already know—the need to be ready at any time.
"It's best to think first about the basics of survival—fresh water, food, clean air and warmth," said San Diego Fire-Rescue Department Assistant Chief Ronnie Hicks.
(c) 2012 AFP
"Shaking 'swarm' fuels California's quake jitters" August 28, 2012 http://phys.org/news/2012-08-swarm-fuels-california-quake-jitters.html