Yorba Linda earthquake a likely aftershock from earlier cluster
The 4.1 earthquake that jolted Yorba Linda on Wednesday afternoon appears to be an aftershock of the cluster of quakes that hit the region earlier this month, seismologists said.
The jolted area included southeastern Los Angeles County, Orange County and the Inland Empire. The quake occurred in about the same location of an earthquake doublet, two 4.5 quakes that occurred on Aug. 7 at 11:23 p.m. and Aug. 8 at 9:33 a.m. The area was also hit by a 4.0 quake on June 14.
Wednesday's quake, which hit at 1:31 p.m., was located near the center point of the magnitude-5.5 Chino Hills earthquake that reverberated through the Los Angeles Basin in the summer of 2008, U.S. Geological Survey seismologist Lucy Jones told The Times.
Wednesday's quake appeared to be located in the "Yorba Linda trend," a seismic area identified by Caltech geophysicist Egill Hauksson in 1990, that might be a buried fault.
Many who felt the quake said it was relatively mild.
At Vinjon's Kennel in Yorba Linda, the quake hit just as Carisa Feeney, 22, was giving a bath to a year-and-a-half-old boxer mix. When the quake delivered its single strong jolt, the dog leaped up in the tub –- and both quickly ran outside.
"I'm pretty much covered in water," Feeney said.
Nancy Ferguson, who owns SGO Designer Glass in Old Town Yorba Linda, said, "We had a big jolt, just for a few seconds, then everything just kind of swayed."
Ferguson, who has hundreds of pieces of glass on display in her store, said she holds her breath every time there's an earthquake. "But nothing fell over today, so we're feeling pretty lucky," she said.
It is unlikely that the earthquake swarm that has hit Imperial County with hundreds of quakes since the weekend is related to Wednesday's quake in Yorba Linda, Jones said.
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Earthquake swarms prompt emergency declaration in Brawley
Updated: New earthquake hits Orange County Wednesday afternoon
Earthquake swarms continued Wednesday in Imperial County as the city of Brawley declared an emergency to deal with the damage.
The swarm that began Sunday morning showed signs of slowing down Wednesday, with fewer quakes reported by the U.S. Geological Survey than on recent days. The magnitude of the quakes is also declining.
There was scattered damage around Brawley, but officials have not yet compiled a full estimate of the costs. The Brawley City Council on Tuesday declared a local emergency, according to the Imperial Valley Press.
PHOTOS: Earthquake swarm damages Imperial County buildings
More than 400 earthquakes greater than magnitude 1.0 have been recorded in Imperial County since Saturday evening, said U.S. Geological Survey geophysicist Elizabeth Cochran. The largest were a 5.3 and a 5.5 about midday Sunday.
Scientists say the reason is not fully understood, but there is a clue: Earthquake faults work much differently south of the Salton Sea than they do closer to Los Angeles.
Take, for instance, the San Andreas fault as it runs through Los Angeles County. It's a fault where, generally speaking, two plates of the Earth's crust are grinding past each other. The Pacific plate is moving to the northwest, while the North American plate is pushing to the southeast.
South of the Salton Sea, the fault dynamic changes. The Pacific and North American plates start to pull away from each other, Cochran told The Times from her Pasadena office. (That movement is what created the Gulf of California, which separates Baja California from the rest of Mexico.)
So Imperial County is caught between these two types of faults in what is called the "Brawley Seismic Zone," which can lead to an earthquake swarm, Cochran said.
The last major swarm was in 2005, Cochran said, when the largest magnitude was a 5.1. The largest swarm before last weekend's occurred in 1981, when the biggest quake topped out at 5.8. Before that, there were swarms in the 1960s and 1970s.Brawley school officials told the Imperial Valley Press that Palmer Auditorium, a performance facility it manages with a local arts group, has been shut down after an inspection.
"We were told by engineers it needs to be shut down because there were huge structural damages," school Supt. Hasmik Danielian told the paper.
Crews would have a better idea of the total damage caused by the quakes in the coming days, said Maria Peinado, a spokeswoman for the Imperial County Public Health Department, but so far the list of affected structures includes about 20 mobile homes shifted from their foundations.
The earthquakes also caused "cosmetic" damage to at least three buildings dating to the 1930s in downtown Brawley, said Capt. Jesse Zendejas of the Brawley Fire Department.A few displaced residents spent Sunday night at an American Red Cross shelter at the Imperial Valley College gymnasium, Peinado said.
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Yorba Linda earthquake comes amid a 'cluster' of temblors
The magnitude 4.1 Yorba Linda earthquake that jolted residents around Southern California on Wednesday afternoon came amid a earthquake swarm in Imperial County.
But it remains unclear whether the two events are connected. Seismologists have said there was no evidence the Imperial swarm would cause bigger quakes closer to L.A.
Yorba Linda has experienced several moderate quakes this month.
Seismologists referred to this earlier Yorba Linda quakes as a "cluster." They struck near the Whittier fault, but preliminary data suggested that that fault was not responsible for the cluster. The strongest was a magnitude 4.5. The cluster seemed to end Aug. 9.
More than 400 earthquakes greater than magnitude 1.0 have been recorded in Imperial County since Saturday evening. The largest were a 5.3 and a 5.5 about midday Sunday.
For all the ground movement, experts said there was no evidence the earthquake swarms were a precursor of much larger quakes on longer, more dangerous faults. And scientists don't see any immediate signs of added pressure to the San Andreas fault, which is not far from the location of the earthquake swarm.
That makes this weekend's swarm different from the one that occurred after the 2010 Easter Sunday quake that shook up the California-Mexico border. The 7.2 quake appeared to have directed tectonic stress northward, toward populated areas in Southern California. Three months after the Mexicali quake, a 5.4 quake that centered south of Palm Springs rattled the region.
Scientists said the Easter Sunday quake and its aftershocks triggered movement on at least six faults, including the Elsinore and San Jacinto faults, which run close to heavily populated areas in eastern Los Angeles County and the Inland Empire.
As on Monday, officials said there is no evidence that this weekend's swarm will trigger quakes elsewhere.
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After 4.1 earthquake, aftershocks keep Yorba Linda shaking
Two small aftershocks have been reported in Yorba Linda, shortly after a magnitude 4.1 earthquake hit the area at 1:31 p.m. on Wednesday.
A shallow 2.1 earthquake registered at 1:34 p.m. and a second 1.5 aftershock was reported at 1:44 p.m.
The Richard Nixon Library in Yorba Linda reported there was no damage.
"It's a beautiful day to visit, we're open -- as usual -- til 5 p.m.," spokesman Jonathan Movroydis said.
Jeff Heel, whose parents own the Winery at Main Street in Yorba Linda, said they lost no bottles to the latest shaker but did feel it.
"It rolled for a little while, but this time we weren't really affected," Heel said. Even so, in a spirit of caution, he said he was taking down the winery's displays to protect as much stock as possible in case of an aftershock.
Earlier in the month the winery lost about 10 bottles when a cluster of earthquakes struck the same area, he said.
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