For years, scientists believed the mighty San Andreas—the 800-mile-long fault running the length of California where the Pacific and North American plates meet—could only rupture in isolated sections. But a recent study by federal, state and academic researchers showed that much of the fault could unzip all at once, unleashing a rare, singular catastrophe. Now,

insurers have used that research to come up with a new analysis of the damage that could be caused by statewide break of the San Andreas. The analysis, by CoreLogic Inc., a real-estate analytics firm in Irvine, Calif., lays out an alarming scenario of destruction. As many as 3.5 million homes could be damaged in an 8.3-magnitude quake along a roughly 500-mile portion of the fault—compared with 1.6 million homes damaged if only the northern part of the fault were to break, or 2.3 million if the southern piece ruptured. CONTINUE