The most dangerous earthquake fault in the San Francisco Bay Area is connected to another, which means both could rupture simultaneously and unleash major devastation, a new study finds. The Hayward Fault has long been considered a threat because it runs under densely populated neighbourhoods east of San Francisco. The new work found that beneath San Pablo Bay, it joins with a second, less active underground fracture to the north. Scientists had already considered the possibility of both faults rupturing at once, whether they are connected or not. So the discovery doesn't change the estimated earthquake hazard much, although it confirms suspicions that the stage is set for what could be a massive quake. If the Hayward and Rodgers Creek faults broke simultaneously along their combined 118 miles, they could produce a magnitude 7.4 quake, said scientists from the U.S. Geological Survey. Such shaking would be more than five times stronger than the 1989 Loma Prieta quake on the San Andreas