More Earthquake Coverage:-

Five Most Dangerous U.S. Earthquake Hotspots Beyond California

When the next big earthquake hits the San Francisco Bay Area, it will be a catastrophe of Hurricane Katrina proportions. Hundreds, perhaps thousands of people will die, and hundreds of thousands will become homeless. Economic losses will be on the order of $200 billion, the vast majority of it uninsured. Outside help will be desperately needed, but difficult to coordinate and execute.

And just as before Hurricane Katrina, scientists have been sounding the alarm, warning that the disaster is inevitable. It's not a matter of if, but when the "Big One" will strike.

"The reality is that we could have a large earthquake at any time," said geologist David Schwartz of the U.S. Geological Survey.

The Bay Area is lined with faults capable of delivering a knock-out blow. But one in particular is poised to rupture sooner than later. Geologists have determined that the average time between major earthquakes on the Hayward fault is 140 years. The last big one was October 21, 140 years ago.

The 1868 Hayward fault earthquake measured around a magnitude 7 and offset the ground laterally more than six feet in places. It killed 30 people in the sparsely populated area and leveled or severely damaged nearly every structure in a wide swath along its 43-mile length. It was known as the Great San Francisco Earthquake until the 1906 earthquake took that title away.

But if the 1868 quake were to strike again today, it would do exponentially more damage. The Hayward fault lies along the hills on the eastern side of the San Francisco Bay in one of the most densely populated areas of the state. It runs beneath homes, schools, senior centers, hospitals, businesses and through the campus of UC Berkeley, bisecting the football stadium.

"A Hayward fault earthquake will change the Bay Area," said USGS geologist Tom Brocher. "It's likely to be one of the nation's biggest natural disasters."

During the last 140 years, the population of the Bay Area has mushroomed to around seven million people. As many as five million of them would be impacted by a major Hayward fault quake. The Association of Bay Area Governments estimates that 220,000 people will be displaced from their homes, as many as 70,000 of those will seek public shelter.

But unlike in the areas affected by Katrina where more than half of the $125 billion in losses was insured, only around 8 percent of homes and businesses in the Bay Area are insured against earthquake damage, according to new research by Risk Management Solutions in Hayward.

"Our models suggest less than $10 billion will flow into the Bay

Area from insurance," said seismologist Mary Lou Zoback of RMS. "And the insurance money comes fairly quickly compared to money from federal and state programs."

The region's transportation infrastructure will take a major hit. More than a thousand roads could be closed. The Oakland and San Francisco International Airports, as well as the Port of Oakland, all lie on top of man-made fill, which is prone to liquefaction — where sediment acts like a liquid when shaken causing structures to founder.

Damage to the water delivery system may be the most worrisome because the Hetch Hetchy aqueduct, which supplies water for 2.4 million people, crosses the Hayward fault and could be ruptured in a major earthquake. As in the 1906 earthquake, damaged gas lines could start fires, which will be difficult to fight without a working water supply. And what water there is will need to be pumped to the firefighters using electricity that will likely be out in the immediate aftermath of the quake.

"All of these things cascade together," Zoback said. The $210 billion dollar damage that RMS estimates will result from a magnitude 7 Hayward fault quake doesn't even take into account fire damage. "I think our models way underestimate that impact."

The Bay Area is prone to earthquakes because it straddles the boundary between two massive tectonic plates. The Pacific plate is moving north relative to the North American plate at the rate of about 2 inches a year, but friction between the two plates keeps them from sliding smoothly past each other. Over time, stress builds up, eventually overcoming the friction and releasing in an earthquake. Much of the stress release happens on the San Andreas fault, the main seam between the plates, but some of it is relieved by the Hayward fault and other smaller parallel faults.

During the 1906 earthquake, 300 miles of the San Andreas ruptured and the two sides of the fault snapped past each other, moving as much as 20 feet in some places. The energy released during that massive quake was the equivalent of 15 million tons of TNT.

Since then, with the accumulated stress of the plate motion relieved, the Bay Area has enjoyed a century of relative quiet, seismically speaking. But all the while the plates have continued their inexorable march, slowly building up stress like a tightening spring. And there are signs that the region may be emerging from this "stress shadow."

The 1989 Loma Prieta earthquake could be one of those signs. The magnitude 6.9 quake, the area's largest since 1906, struck the San Andreas in the Santa Cruz mountains. That quake cast its own, smaller stress shadow, but models of the stress build up in the Bay Area due to plate motion suggest enough has accumulated to generate another major quake.

"The region is at a much higher stress level because the effects of the 1906 earthquake have worn off," Schwartz said.

The U.S. Geological Survey estimates there is a 63 percent chance that a magnitude 6.7 or greater earthquake will hit one of the Bay Area faults in the next 30 years. The Hayward fault, combined with its northern neighbor the Rogers Creek fault, accounts for 31 percent of that chance, more than any other fault including the San Andreas.

A major Hayward fault quake would severely cripple the Bay Area. The epicenter of the Loma Prieta earthquake was more than 60 miles south of San Francisco and yet it killed 63 people, most of them on a highway that collapsed in Oakland, injured nearly 4,000, did $6 billion in damage and knocked out a section of the Oakland Bay Bridge.

If the quake had struck at 5:04 p.m. on a normal weekday during rush hour, rather than on that unusual Tuesday afternoon when many had gone home early to watch the Bay Area's two baseball teams slug it out in the third game of the World Series that had just started at San Francisco's Candlestick Park, the death toll would have been significantly higher.

Move the epicenter of that quake, or a larger one, to the Hayward fault in the heart of the Bay Area, and it will make Loma Prieta look like a bad hair day.

So how do people in the Bay Area cope with this hazard? Though awareness of the potential for earthquakes is relatively high in the area, the USGS estimates only 10 percent of residents have a disaster plan and less than half have set aside supplies such as water, food and first aid. A quick survey of the Wired.com office found that the staff is behind even that modest curve – just a third have done anything at all to prepare, and less than 10 percent have something resembling a comprehensive plan.

This may be because for some, it takes a certain amount of denial to live in earthquake country. And many residents who lived through the 1989 quake, think they have already survived a major Bay Area earthquake.

They are wrong.

"They have the same expectations for the next one," Brocher said. "But a Hayward fault earthquake will be much closer to many of them, and it will be much more damaging."

Image: USGS/Google Earth