When will the next big Bay Area earthquake be?

SAN FRANCISCO (KGO) -- We live in a region where the next big earthquake isn't a question of if, but when?

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For proof, look no further than the Hayward Fault, which ruptures predictably every 140 years, give or take a few.

Based on that, the Bay Area is overdue, and the next quake will be big...at least 7.1 in magnitude, equal to what rumbled through Mexico City, yesterday.

"7.1 is predictable," said UC Berkeley seismologist, Dr. Peggy Hellweg, of our pending big one.

"Could it be more," I asked.

"Yes," she replied.

"Are we ready?"

"No. A lot of buildings will collapse. There will be infrastructure damage. Many water pipes and sewers will collapse," she added, "And much of San Francisco's infrastructure runs through the East Bay."

VIDEO: Gas explosion fills Mexico City sky with fire following earthquake
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A man in Mexico City captured a dramatic explosion on camera following Tuesday's deadly earthquake.

In short, it will be a disaster unlike any this region has seen since 1906. So, in looking at the footage from Mexico City, are we seeing an inevitable Bay Area future?

"The energy from a 7.1 will be six times a strong as Loma Prieta, which was 6.9," said Hellweg.

Like Mexico City, our region has strict building codes designed to prevent structures from collapsing during large quakes. And yet, many buildings in Mexico City failed.
Structural engineers note that building codes both here and there are designed to survive one, 2,500 year event. But, in places with quake after quake after quake, damage has a cumulative effect.

Buildings do not repair themselves. Mexico has suffered two major quakes in less than two weeks.

"The first earthquake weakened the buildings," said Dr. Khalid M. Moslem, who runs UC Berkeley's Pacific Engineering Research Center. "The other caused them to collapse. This is a theory that needs to be proven."

It's worth noting that more people could have died in Mexico City, yesterday. After the 1985 quake, which killed at least 10,000 people, the city installed a warning system, which provided 20 seconds advance notice. Yesterday, tens of thousands of people escaped buildings before the quake waves arrived.

The San Francisco Bay Area does not have such a system. Will it take a disaster to make this happen?"

"It would be nice if it didn't," said Dr. Hellweg.

Click here for more stories, photos, and video on the Mexico earthquake.
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