Californians may expect the earth to move, but a new study of the San Andreas Fault suggests that the LA area is overdue for a Big One. The study by the US Geological Survey of a section of the fault in the Grapevine area found that major quakes strike there on average once every 100 years—and the last one hit 160 years ago, per a USGS release. Only two people were killed in the old quake, but a similar one today would surely have a much higher toll, while also damaging aqueducts, the electric grid, and highways. In fact, "it would impact our ability to be a world-class city," a USGS geologist tells the Los Angeles Times. Geologists examined a previously unstudied area of the fault, close to the juncture of Los Angeles, Ventura, and Kern counties.
They dug down deep to get 1,200 years of data, finding evidence of 10 major earthquakes that happened at irregular intervals, making the timing of the next one difficult to predict. Some intervals were as short as 20 years, some as long as 200 years. The quakes were generally in the 7 to 7.5 range in magnitude, though the 1857 quake was 7.9, significantly larger. A CalTech seismologist says that's actually good news because the quake released a lot of energy, which could explain why there's been such a relatively long lull. Still, "the stress is building up along the San Andreas and a large earthquake is inevitable," another geologist tells KABC-TV.