Aftershocks of the magnitude 7.1 earthquake near Ridgecrest have been creeping into areas close to two major earthquake faults, a development that is generating interest and some concern among seismologists over whether it could trigger another huge temblor.

Both faults are capable of producing new earthquakes of magnitude 7 or greater. The U.S. Geological Survey says the chance of an earthquake of magnitude 7 or greater from the July 5 earthquake is 1 in 300 — “possible, but with a low probability.”

Some aftershocks have rumbled northwest of the Searles Valley earthquake, approaching the Owens Valley fault. That fault triggered an earthquake of perhaps magnitude 7.8 or 7.9 in 1872, one of the largest in California’s modern record.

Felt as far away as Los Angeles and Sacramento, the 1872 earthquake killed 27 people — 1 out of every 10 people in the mining camp of Lone Pine — and destroyed 52 of 59 houses there.


The Ridgecrest aftershocks have also headed southeast toward the Garlock fault, a lesser-known fault capable of producing an earthquake of magnitude 8 or more. The fault along the northern edge of the Mojave Desert can send shaking south and west into Bakersfield and Ventura and Los Angeles counties.

“Those are places we would be more concerned,” U.S. Geological Survey research geophysicist Morgan Page said. “Little earthquakes are telling us where big earthquakes are more likely.”

(Rahul Mukherjee / Los Angeles Times)

No one can predict exactly when and where the next big earthquake will occur in California. Some quakes can trigger seismic activity on nearby faults, but it’s not a given.


Triggered temblors

Perhaps the most famous example of triggered earthquakes in California occurred in 1992. An April 22 magnitude 6.1 earthquake in Joshua Tree National Park began a quake sequence that migrated north in the coming months.

Then on June 28, an earthquake 63 times stronger ruptured — the magnitude 7.3 Landers earthquake with an epicenter more than 25 miles northeast of Palm Springs. A sleeping 3-year-old toddler died after being struck by a collapsing chimney during a sleepover.

Three hours later, a magnitude 6.3 quake struck about 20 miles west, just a few miles away from Big Bear.

“We always worry when seismicity picks up very close to a major fault or if it’s at the end of a major fault — whether it’ll push it enough to start a major rupture,” Caltech seismologist Egill Hauksson said.


Sometimes fears of seismic triggering don’t materialize.

The Easter Sunday magnitude 7.2 quake of 2010 directed tectonic stress toward Southern California from Mexico. There was concern about a potential triggered quake on the Elsinore fault, capable of a magnitude 7 quake, which extends into Orange County and the Los Angeles area and could produce devastating damage to the region.

But seismic activity eventually ended before it reached that fault, Hauksson said.

Quake epidemic

There’s a rule to seismology that will probably come as a disappointment to many — earthquakes don’t actually reduce the risk of future quakes; they increase them.


“Every earthquake actually increases the probability of more earthquakes,” Page said.

In fact, earthquake scientists actually model quakes like disease epidemics. “It’s based on the idea on how a contagion spreads to a population,” she said. “Earthquakes are like that … in general, if there are a lot of earthquakes going on, it’s more probable for a large earthquake to go on.”

While earthquakes do relieve stress to some areas around them, we become less safe after earthquakes because they “redistribute the stress and can push other faults in the area to failure,” Page said.

One big observation so far has been that there’s now a line of seemingly missing earthquakes between the northern end of the July earthquakes and the southern end of where the Owens Valley fault finished rupturing in 1872.


“That’s a kind of thing seismologists can get nervous looking at. It’s got to be filled in,” said USGS seismologist Susan Hough, who has researched the Owens Valley fault extensively. “There’s certainly room to put another earthquake.”

1 / 42 Dan Tolbert, 62, spends time with his dogs as he and his wife, Ronnie, 60, prepare to bed down for the night on a pair of mattresses in front of their earthquake-damaged home in Trona on July 10. Their night was interrupted when a scorpion crawled on their mattresses and they ended up spending the night in their truck. “If we keep feeling tremors tomorrow we’ll be out here again,” Ronnie said. (Genaro Molina / Los Angeles Times) 2 / 42 Karen Byrd, 39, collects photo frames knocked off the wall at her home in Trona, Calif. (Irfan Khan / Los Angeles Times) 3 / 42 Ronnie Tolbert, left, delivers food to Robert VanHorn, 81, almost a week after a 7.1 earthquake near Trona. (Genaro Molina / Los Angeles Times) 4 / 42 Benny Eldridge, 76, looks at a quake-damaged room in his Trona home, which he helped build with his father-in-law in 1961. The house has been red-tagged. (Genaro Molina / Los Angeles Times) 5 / 42 Benny Eldridge, 76, and his wife, Anna Sue, 75, sit in front of their damaged home in Trona. (Genaro Molina / Los Angeles Times) 6 / 42 Joyce Harrison Moore, 72, looks out from her damaged home almost a week after a pair of earthquakes battered Trona. “This town will either die or get back on its feet,” Moore said. (Genaro Molina / Los Angeles Times) 7 / 42 Ronnie Tolbert stands beside her damaged fireplace. (Genaro Molina / Los Angeles Times) 8 / 42 Valerie Helton, 60, facing the camera, receives a hug of support from Ronnie Tolbert. Helton and her daughter Jessica Sizemore Helton, left, have refused to leave their home since last week’s quakes. “This is all I have,” said Sizemore Helton. (Genaro Molina / Los Angeles Times) 9 / 42 Ralph “Zeb” Haleman, 67, carries cases of water home Sunday in Trona, Calif., where residents were still without water and electricity was spotty after last week’s quakes. (Irfan Khan / Los Angeles Times) 10 / 42 Kay Byrd, 64, gives herself an insulin shot. Byrd and her family are camping outside in Trona, Calif., wary of returning home after major earthquakes. (Irfan Khan / Los Angeles Times) 11 / 42 Brooke Thompson, 8, plays on the sleeping bag that her family slept in after a pair of major earthquakes drove them out of their home in Trona, Calif. (Irfan Khan / Los Angeles Times) 12 / 42 The Byrd family has breakfast next to where they spent the night under a salt cedar tree, afraid to return to their Trona, Calif., home of 21 years after major earthquakes. (Irfan Khan / Los Angeles Times) 13 / 42 Ronnie Tolbert, left, and her husband, Danny, sleep on mattresses in the front yard of their Trona home, which was damaged in a 7.1 magnitude earthquake. (Robert Gauthier / Los Angeles Times) 14 / 42 The Horta family sleeps in the back of their pickup truck in a fire station parking lot in Trona as the sun rises hours after being forced from their home by a magnitude 7.1 earthquake. (Robert Gauthier / Los Angeles Times) 15 / 42 Kathy Vander Housen, 76 hugs her friend Claire Barker, 76, after Barker told her that she had found her two cats. Vander Housen’s mobile home in Trona had been yellow-tagged by county inspectors, but she did not want to leave without the cats, which had been hiding since the earthquake (Irfan Khan / Los Angeles Times) 16 / 42 Buckled asphalt courses through a parking lot near Trona Rd. in Argus. (Robert Gauthier / Los Angeles Times) 17 / 42 Sammy Chute cuddles Gerard as her family in Trona prepares to evacuate to Ridgecrest, abandoning their home that was knocked off its foundation during a 7.1 earthquake. (Robert Gauthier / Los Angeles Times) 18 / 42 Charles Ware, 68, in his Trona front yard the morning after a 7.1 magnitude earthquake severely damaged his home. Ware said he invested all he had into this house two years ago, doesn’t have earthquake insurance and is afraid he may not be able to rebuild. He was on the phone with his brother in San Diego when the quake hit. “I got to ride it out with my brother,” he said. (Robert Gauthier / Los Angeles Times) 19 / 42 A customer rummages for a six-pack of beer at a damaged Shell food mart in Trona the day after a 7.1 earthquake. (Robert Gauthier / Los Angeles Times) 20 / 42 Hundreds of residents of Ridgecrest, Calif., and surrounding communities attend a town hall meeting at Kerr McGee Community Center about the response to recent major earthquakes. (Irfan Khan / Los Angeles Times) 21 / 42 Christian Fellowship of Trona congregants pray after holding a quick meeting on how to help other community members. (Irfan Khan / Los Angeles Times) 22 / 42 Kern County firemen tackle a fire on Saturday morning at Town and Country Mobile Home Park in Ridgcrest. (Irfan Khan / Los Angeles Times) 23 / 42 Jamie L. Acevedo sits outside her damaged Trona home, waiting to evacuate to Ridgecrest the morning after a 7.1 magnitude earthquake knocked her home off its foundation. (Robert Gauthier / Los Angeles Times) 24 / 42 Gas station owner Roger Sandoval faces the possibility of having to shut his Trona business after a 7.1 earthquake apparently damaged the supply tanks near the pumps. (Robert Gauthier / Los Angeles Times) 25 / 42 Chavela Padilla, left, an emergency response team volunteer, walks with Ronnie Tolbert amid quake-toppled items in Tobert’s Trona home. The damage occurred in a 7.1 temblor hours earlier. (Robert Gauthier / Los Angeles Times) 26 / 42 Chavela Padilla, a Trona emergency response team volunteer, enters her car after checking on a neighbor as her two young boys, Joey, 8, right, and Jimmy, 5, sleep in the back seat at close to 3 a.m. The boys were too scared to be home after experiencing a 7.1 earthquake hours earlier. (Robert Gauthier / Los Angeles Times) 27 / 42 Chavela Padilla, right, an emergency response team member walks with Ronnie Tolbert amid quake-toppled items in Tolbert’s Trona home. (Robert Gauthier / Los Angeles Times) 28 / 42 Brothers Joey, 8, right, and Jimmy Raya, 5, sleep in the back seat of their mother’s car in the parking lot of San Bernardino County Fire Station 57 in Trona after their home was damaged in a 7.1 magnitude earthquake hours earlier. (Robert Gauthier / Los Angeles Times) 29 / 42 Chavela Padilla, a Trona emergcency response team volunteer, assists her neighbor Alicia Marines, 72, who was injured while trying to escape her home during a 7.1 magnitude earthquake. Marines was evacuated to the local fire station. James Raya, Padilla’s husband and also a volunteer, looks on. (Robert Gauthier / Los Angeles Times) 30 / 42 Chavela Padilla, a Trona emergency response team volunteer, stands in the bloody footprints left by homeowner Alicia Marines, 72, who was injured during a 7.1 magnitude earthquake. Padilla volunteered to check on Marines’ residence and collect some fresh clothes. (Robert Gauthier / Los Angeles Times) 31 / 42 Ronnie Tolbert sorts through toppled belongings in her Trona home, damaged in a 7.1 magnitude earthquake hours earlier. (Robert Gauthier / Los Angeles Times) 32 / 42 The aftermath of Friday’s earthquake at a Ridgecrest liquor store. (Robyn Beck / AFP/Getty Images) 33 / 42 Work on Route 178 between Trona and Ridgecrest. (Etienne Laurent / EPA-EFE/REX ) 34 / 42 Workers fill large holes left in Highway 178 between Trona and Ridgecrest by Friday night’s 7.1 earthquake. (Etienne Laurent / EPA-EFE/REX ) 35 / 42 Highway workers repair roadway near Ridgecrest on Saturday morning. (Robyn Beck / AFP/Getty Images) 36 / 42 Police and emergency services respond to a fire at a building on Highway 178. (Etienne Laurent / EPA-EFE/REX ) 37 / 42 Firefighters respond to a fire at a building on Highway 178 after Friday night’s earthquake near Ridgecrest. (Etienne Laurent / EPA-EFE/REX ) 38 / 42 In Ridgecrest, Davia Speed and Peyton Speed, holding 1-month-old Lillian, get into their car after Friday night’s 7.1 earthquake. (Irfan Khan / Los Angeles Times) 39 / 42 Dawn Inscore leaves her apartment on Ridgecrest Boulevard with her child after the Friday night earthquake. (Irfan Khan / Los Angeles Times) 40 / 42 A fire burns behind Casa Corona restaurant in Ridgecrest after Friday’s earthquake. (Jessica Weston / The Daily Independent/Associated Press) 41 / 42 Carmen Rivera, 65, walks her dog Ash past a dislodged home in Torusdale Estates mobile home park in Ridgecrest. (Irfan Khan / Los Angeles Times) 42 / 42 Zoe Pineda, 7, helps clean up the library in Ridgecrest after the Fourth of July quake. (Irfan Khan / Los Angeles Times)

A seismic boundary

Both the July quakes and the 1872 Owens Valley quake lie in one of California’s great seismic zones, the Eastern California Shear Zone, which generates earthquakes as a result of the southwestern part of California sliding up northwest, toward Alaska, compared with the northeastern part of the state. (Yes, that does mean that eventually, L.A. will be right next to San Francisco a long time from now.)

The San Andreas fault gets the most attention because it’s the main boundary between the Pacific and North American plates. But “there’s other fault systems that slice California into ribbons,” Hough said, including the Eastern California Shear Zone, which carries a good chunk of the earthquake burden needed to accommodate that tectonic plate movement.


The zone covers a swath of California from Palm Springs to the Owens Valley east of the Sierra Nevada, “and we know there have to be big earthquakes eventually everywhere across this zone,” she said.

But it’s far from certain that the next big earthquake will happen on either of these two faults.

The Eastern California Shear Zone isn’t just one single through-going fault; there’s a bunch of faults there that slip over time. And it’s possible that other faster-moving faults might be better candidates to move in big quakes next, Hough said.

One might be the Garlock fault. A simulation of a hypothetical magnitude 7.7 earthquake on that fault would bring severe shaking to towns across the Mojave Desert and send strong shaking to Santa Clarita and the San Fernando Valley.


Another fault might be one underneath the valley sandwiched between Owens Valley and Death Valley — the Panamint Valley fault, according to some recent analysis conducted in recent weeks, Hough said.

But there are other plausible scenarios as well — earthquakes lighting up south of the July earthquakes and north of the 1992 Landers quake. Or the next big quake could strike somewhere with no connection to the July quakes at all, say, a devastating temblor on the San Francisco Bay Area’s Hayward fault.

“The bottom line is we don’t ever have a crystal ball,” Hough said. “The next earthquake may be something that no one sees is coming.”

Aftershock clues

Despite the limitations in what scientists can glean from tracking aftershocks, it’s still worth doing.


“Most big earthquakes have foreshocks. It’s extremely common,” Page said. One notable example was small quakes before the magnitude 6.3 Big Bear quake of 1992. “It’s lighting up areas where there’s more stress to be relieved.”

The reason why the Garlock fault is one that scientists are concerned about is that the seismic strain on it accumulates at one of the faster rates in California. It’s in a category a notch below the most worrisome faults in the state — the San Andreas, San Jacinto and Hayward.

The Garlock fault hasn’t ruptured in a big way in the modern historical record, but paleoseismic work suggests that the average time between earthquakes of at least magnitude 7 on the central part of the fault is about every 1,200 years, Page said.

But there’s huge variation in that average. Sometimes, only 200 years can pass between major quakes there; other times, 2,000 years can go by before a repeat performance.


The last time a big earthquake is believed to have hit the Garlock fault is roughly 465 years ago, give or take about a century.