LOS ANGELES (AP) — Scientists are virtually certain that California will be rocked by a strong earthquake in the next 30 years. Now they say the risk of a mega-quake is more likely than previously thought. 
 
 FILE - This Jan. 17, 1994 file photo shows several trailer homes that were burned to the ground at the Oak Ridge Trailer Park in Sylmar, Calif., after a magnitude-6.7 earthquake struck southern California.... (Associated Press) 
 
 FILE - In this Jan. 17, 1994 file photo, the covered body of Los Angeles Police Officer Clarence Wayne Dean, 46, lies near his motorcycle which plunged off the State Highway 14 overpass that collapsed... (Associated Press) 
 
 FILE - In this Jan. 17, 1994 file photo, a Los Angeles police officer stands in front of the Northridge Meadows Apartment building, after the upper floors of the structure collapsed onto the open garages... (Associated Press) 
 
 The chance of a magnitude-8 quake striking the state in the next three decades jumped to 7 percent from 4.7 percent, mainly because scientists took into account the possibility that several faults can shake at once, releasing seismic energy that results in greater destruction. 
 
 While the risk of a mega-quake is higher than past estimates, it's more likely — greater than 99 percent chance — that California will be rattled by a magnitude-6.7 jolt similar in size to the 1994 Northridge disaster. The chance of a Northridge-size quake was slightly higher in Northern California than Southern California — 95 percent versus 93 percent, according to a report released Tuesday by the U.S. Geological Survey. 
 
 "California is earthquake country, and residents should live every day like it could be the day of a big one," USGS geophysicist and lead author Ned Field said. 
 
 The latest seismic calculations largely mirror previous findings issued by the USGS in 2008. Back then, scientists also determined that California faced an almost certain risk of experiencing a Northridge-size quake. 
 
 The new report included newly discovered fault zones and the possibility that a quake can jump from fault to fault. Because of this knowledge, the odds of a catastrophic quake — magnitude 8 or larger — in the next 30 years increased. 
 
 There is a 93 percent chance of a magnitude 7 or larger occurring over the same period and a 48 percent chance of a magnitude 7.5 — similar to previous estimates. 
 
 Thousands of quakes every year hit California, sandwiched between two of Earth's major tectonic plates, the Pacific and North American plates. Most are too small to be felt. 
 
 Of the more than 300 faults that crisscross the state, the southern segment of the San Andreas Fault — which runs from central California to the Salton Sea near the U.S.-Mexico border — remains the greatest threat because it hasn't ruptured in more than three centuries. 
 
 The report found there is a 19 percent chance in the next 30 years that a Northridge-size quake will unzip the southern section compared to a 6.4 percent chance for the northern section, partly because it last broke in 1906. 
 
 The southern San Andreas is "ready to have an earthquake because it's really locked and loaded," Field said. 
 
 The report is a forecast, but it is not a prediction. Experts still cannot predict exactly where or when a quake will hit anywhere in the world. 
 
 In recent years, the USGS and several universities have been testing an early warning system designed to detect the first waves of a jolt and send out an alert before the slower-moving damaging waves. Proponents have said a few seconds of notice can allow trains to slow down, utilities to shut off gas lines and people to duck for cover. The public alert system — still in pilot phrase — needs more funding before it can be rolled out statewide. 
 
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 Contact the reporter on Twitter: http://www.twitter.com/SciWriAlicia ||||| Angelenos live under constant threat of a major earthquake, but a controversial new study from NASA's Jet Propulsion Laboratory puts a number on that threat. The scientific paper claims there is a 99.9 percent chance of an earthquake between magnitude 5 and 6.3 in less than three years. 
 
 The study was published earlier this month by the American Geophysical Union's Earth and Space Science journal. The bold claim has taken many in the seismic community by surprise. 
 
 Lead author, Andrea Donnellan of JPL, said this study used GPS and airborne radar data to look at land deformation caused by last year's 5.1 La Habra earthquake. Her team determined that, based on the surface changes, there is still a fair amount of pent-up seismic energy in the region that needs to be released. 
 
 “It’s almost like using the surface of the Earth as an instrument to understand what is going on deeper," she explained. 
 
 That energy could spawn shaking associated with a magnitude 5 or 6 temblor, she added, but that energy could crop up on any number of faults within a 100-kilometer range of last year's quake. 
 
 This sort of prediction is quite common. What isn't common is claiming a 99.9 percent chance of such a quake in a window of time as small as three years. 
 
 Donnellan said her team arrived at the conclusion by looking at the number of magnitude 5 earthquakes in the region over the last 81 years. There were 32 such events. 
 
 “So if you just look at that on average, it's about an earthquake every three years," Donnellan said. 
 
 Lucy Jones with the U.S. Geological Survey said that methodology doesn't fully explain the prediction, and the study doesn't adequately address this either. 
 
 The USGS conducts its own look at quake risk in California — the most recent version is called Uniform California Earthquake Rupture Forecast, Version 3. 
 
 Jones said that, according to those models, there is only an 85 percent chance of a magnitude 5 or 6 quake in the same region over a three-year period. 
 
 "It's nowhere near a 99.9 percent number," Jones said. 
 
 USGS released a statement on its Facebook page saying that the lack of details on how this number was reached "makes a critical assessment of this approach very difficult." 
 
 While the AGU journal the JPL paper appeared in conducts peer review of studies, Jones said it's custom that quake prediction studies are also sent to the National Earthquake Prediction Evaluation Council or its California counterpart. 
 
 However, she said this paper was not submitted to those organization for review. She added that there is no scientific consensus on this issue. 
 
 "This is the opinion of a small group of scientists — it has not been reviewed for action as a prediction, and I wouldn't be changing any behavior on the basis of this study," Jones said. 
 
 Several earthquake researchers approached by KPCC said they were surprised by this study and its conclusions, among them Michael Blanpied with the USGS Earthquake Hazards Program. 
 
 However, he noted that it should come as no surprise to people in Southern California that earthquakes are a real threat to the region. 
 
 “But I would say in general we want to give them the most credible and authentic information that we can,” he added. 
 
 JPL's Donnellan defended the research, saying that it's now up to the larger scientific community to evaluate the claims and see if different ones are called for. 
 
 “In science, individual methods are always controversial to somebody, but that’s how we make forward progress,” she said. 
 
 The study, titled "Potential for a large earthquake near Los Angeles inferred from the 2014 La Habra earthquake," was first published by AGU online on Oct. 1. 
 
 This story has been updated.
– The latest US Geological Survey forecast for California doesn't contain much that will reassure people worried about earthquakes—unless they find fatalism reassuring. The report says there is not only a 99% chance of a 6.7 magnitude or greater quake like the 1994 Northridge one hitting the state in the next 30 years, the chances of a mega-quake of 8 magnitude or greater are significantly higher than earlier thought, the AP reports. "California is earthquake country, and residents should live every day like it could be the day of a big one," says lead author Ned Field, a USGS geophysicist. He says that out of the state's hundreds of faults, the "locked and loaded" San Andreas Fault is still the biggest threat. Field says the odds of a mega-quake in the next three decades have risen to 7% from 4.7% since the 2008 forecast because scientists now have a better understanding of the fault system and how quakes can jump from fault to fault, the Los Angeles Times reports. In California, "it has become increasingly apparent that we are not dealing with a few [well-separated] faults, but with a vast interconnected fault system," he says. The USGS still can't predict exactly when an earthquake will hit, but it's testing an early warning system that will give authorities vital seconds to do things like shut off gas lines and slow down trains, the AP reports. (Another federal study warns that small, fracking-linked quakes in Oklahoma and Kansas are making a big one more likely.)