By Brian Hackney

SAN FRANCISCO (KPIX) – The 7.1 magnitude earthquake that struck Ridgecrest is a reminder to people living in Northern California that the ‘Big One’ could strike here.

In fact, the biggest natural disaster threat facing everyone in the Bay Area is a quake on the Hayward fault.

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The Hayward fault springs to life behind Fremont and continues into San Pablo Bay. Geologists say at any time, it could trigger an even bigger quake than the two that just hammered Southern California.

“One of the scenarios that we think is very credible is that an earthquake actually starts in San Pablo Bay and ruptures in two different directions,” says geologist David P. Schwartz.

He says if both ruptures happened at once, it could be a magnitude “7.2 or 7.3” temblor.

“We really haven’t had an earthquake of that size in a modern American city. The Hayward fault is really the most highly-populated fault in the United States,” said Schwartz.

USGS geophysicist Ole Kaven said shaking like what we are seeing in Southern California may last for the next few days. He wouldn’t be surprised to see more large magnitude activity in the 4s and 5s.

He says it is quite normal for that area.

“This however is far enough from the San Andreas that we don’t expect any interaction between faults in our area,” said Kaven.

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So far, geophysicists haven’t seen anything out of the norm here — nothing over magnitude 3, or what they would consider “significant.”

As for what the next big one may feel like, the Ridgecrest fault orientation is a lot like what we have in the Bay Area.

“The depth of the earthquake is more or less what we would expect in the Bay Area,” said Kaven. “So the shaking that was felt locally in the Ridgecrest area is very similar to what we would feel in a San Andreas, Hayward or Calaveras event of this magnitude.”

(California Earthquake Authority)

Earthquake experts say there’s about a 3% chance of a larger earthquake happening from now over the next couple of days and the likelihood will continue to decrease as time passes.

“We’re on the boundary between the Pacific plate and the North American plate,” said Kaven. “The San Andreas is sort of the main player in accommodating the deformation between the two. But there are other zones across California and even Nevada that take up some of the relative motion between those two plates.”

So the bottom line is that, so far, all has remained normal in the Bay area, but the motion down south is very consistent with what we could expect to happen here.

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The Bay Area would experience a similar scenario — cell towers out, water lines down, electricity gone for days, and no way to contact their loved ones. It may be a good idea to plan for that and more, before the ‘Big One’ hits.