The possibility of the Big One hitting along the "locked, loaded, and ready to go" San Andreas fault is an ever-present risk in southern California—and lately, it has been more present than usual. A cluster of more than 200 earthquakes hit a seismic zone under the Salton Sea at the southern end of the fault on Monday, the Los Angeles Times reports. The jolts, the strongest of which was magnitude 4.3, lasted for more than 24 hours and US Geological Survey experts say the activity has temporarily raised the risk of an earthquake 7.4 magnitude or stronger to as high as 1 in 100. The area has triggered other quakes in the past and experts say the increased risk will last until next Tuesday.
The California Office of Emergency Services has issued an earthquake advisory for the region, CBS Los Angeles reports. "California is earthquake country. We must always be prepared and not let our guard down," says OES Director Mark Ghilarducci, who describes the warning as an opportunity to revisit emergency plans. The Smithsonian reports that the increased risk came the same week that Gov. Jerry Brown approved an expansion of California's early warning system. The system will be able to provide up to a minute's warning ahead of major quakes, long enough for train drivers to slow down or for workers to move away from dangerous machinery. (Read more San Andreas Fault stories.)