There's about a 76% chance that the San Francisco Bay Area could experience a 7.0 magnitude earthquake within the next 30 years, according to some recent reports.

Experts from the USGS think that the biggest earthquake threat is from the Hayward Fault, rather than the better-known San Andreas Fault.

That fault is like a "tectonic time bomb," according to scientists.



On this day 112 years ago, the San Andreas Fault under San Francisco rumbled apart, causing the devastating 1906 earthquake that swallowed city blocks, broke water mains, and triggered massive fires that burned for days.

The threat of another major quake for the Bay Area is "real and could happen at any time," according to researchers for the US Geological Survey. But the scariest scenario for the next major earthquake may not be from the San Andreas Fault (though that one still threatens), but from the Hayward Fault that runs along the east side of the San Francisco Bay.

The Hayward Fault is a "tectonic time bomb, due anytime for another magnitude 6.8 to 7.0 earthquake," according to a 2008 USGS report. Since then, research has indicated that the likelihood of a Hayward quake is greater and more threatening to the 7 million Bay Area residents than a San Andreas quake would be.

"It's just waiting to go off," USGS earthquake geologist emeritus David Schwartz told the Los Angeles Times.

The Hayward Fault USGS/Public Domain

The HayWired Earthquake Scenario

To better understand what might happen in the case of a quake on the Hayward Fault, researchers from the USGS partnered with a group called the HayWired Coalition. They modeled a hypothetical 7.0 magnitude quake with an epicenter beneath Oakland — a hypothetical event they call the HayWired Scenario.

The projections are sobering.

According to that model, the violent shaking from the earthquake could cause the two sides of the fault to split six feet apart in some places. Some aftershocks could continue for several months. Cities in the East Bay would be hit hard, including Berkeley, Oakland, San Leandro, and Hayward.

More than 300 buildings sit atop the Hayward Fault, including the stadium at the University of California Berkeley. Property damage in the HayWired Scenario is estimated by USGS to be more than $82 billion.

The human toll from such an event could be greater. The quake would displace 77,000 households, a number that could rise to 152,000 if fires and utility outages were counted. That means nearly half a million people would be forced from their homes.

A major earthquake in 1989 rocked the San Francisco Bay area and damaged parts of the Bay Bridge. AP Photo

The scientists think such an event would kill around 800 people and cause 18,000 nonfatal injuries. More than 2,500 people might need to be pulled from collapsed buildings, and around 22,000 could be trapped in elevators.

Most counties in the area would have full water service restored within 30 days, the researchers estimate, but it might take up to 210 days before the hardest hit counties would see full service restored.

More than 400 gas- and electric-related fires would likely ignite because of the main shock of the quake, and experts think those blazes could burn an area big enough to consume 52,000 homes, kill hundreds, and do another $30 billion in damage.

The 72 percent probability of a magnitude (M) 6.7 or greater earthquake in the region includes well-known major plate-boundary faults, lesser-known faults, and unknown faults. The percentage shown within each colored circle is the probability that a M 6.7 or greater earthquake will occur somewhere on that fault system by the year 2043. The dark, thick lines outlined in various colors represent major plate boundary faults; the thinner, yellow lines mark lesser-know, smaller faults. USGS/Public Domain

Another quake is coming

The last time a major quake hit the Hayward Fault was in 1868, when a 6.8-magnitude tremor raced through the region and leveled several towns. The region was sparsely populated then, but 30 people died and the impact was powerful enough that the 1868 quake is considered one of the most destructive in California history. People felt the shakes as far north as Nevada.

The devastation from the next quake will be worse given the current density of the East Bay.

The idea behind the HayWired Scenario is to present a realistic model of something experts think is likely to happen — and inspire more investment in earthquake safety.

There are steps that experts think could improve the situation. An early warning system could prevent at least 1,500 injuries if people followed alerts. If water utilities replace brittle pipes, acquire emergency generators, and create a fuel-management plan, water service could be restored more quickly. Retrofitting buildings could also reduce the number of fires.

But the researchers behind the analysis want people to understand that this scenario is just one of many possibilities. There are seven significant fault lines running through the Bay Area. The risk from a Hayward quake might be highest, but there are worse scenarios that would involve multiple faults rupturing simultaneously.

Overall, researchers think there's about a 76% chance the region could get hit by a 7.0 magnitude quake within the next 30 years.

As Schwartz told the LA Times, "You can't hide — there's really going to be very little places in the greater Bay Area that won't be affected."