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A new study finds the most dangerous earthquake fault in the San Francisco Bay Area is connected to another fault. Together, they could produce a major quake.

A team from the U.S. Geological Survey has discovered a previously unknown strand of the Hayward Fault that connects to a less active fault to the north.

It's the first direct evidence that the two faults are linked. The discovery was published Wednesday in the journal Science Advances.

The Hayward Fault has long been considered a threat because it runs under densely populated neighborhoods east of San Francisco.

Scientists say if the Hayward and neighboring Rodgers Creek faults broke simultaneously along their combined 188 miles, they could produce a magnitude 7.4 quake.

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Online:

Science Advances: http://advances.sciencemag.org