A magnitude 6.0 earthquake hit northern California’s San Francisco Bay area Sunday morning. The tremor struck just before 3:30 a.m. about 10 miles northwest of American Canyon. It was the largest tremor to shake the Bay Area since 1989.

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Now, residents of Napa Valley are bracing for aftershocks and, possibly, an even bigger earthquake at some point in the future. Experts say the area is overdue for an earthquake of at least 7.0 magnitude.

A 7-magnitude temblor would be 30 times more powerful than the one that shook northern California on Sunday. Richard Allen, director of the seismological laboratory at UC-Berkeley, joined Jeanine Pirro Sunday night, explaining that early-warning systems are helping to lower the number of injuries.

Allen said the Sunday quake was not "truly big," but at the university's lab in Berkeley they had 10 seconds of warning. Allen said the system worked and did issue an alert yesterday.

He said the warning system gives people enough time to shelter from falling debris, which was the cause of most injuries on Sunday.

Additional funding, however, is still needed to fully implement the system, Allen explained.

"We know that there's a bigger earthquake coming. The issue is we just don't know when," said Allen, adding that a larger quake along the Hayward Fault is "already overdue."

Watch the interview above.

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