October 15, 1999 - Scientists issued a new forecast that the Bay Area has a 70 percent chance of experiencing a destructive earthquake by the year 2030. The way experts see it now, there is no single Big One threatening the Bay Area. No, it's worse: There are a number of potential big ones lurking along eight major faults, including the San Andreas and the Hayward and the Calaveras and the San Gregorio, and perhaps on faults we don't know about because they are hidden beneath the folds of the hills. Any one of them could do to them what the 1995 quake did to Kobe.
The high number of faults slicing through the area makes it more likely that a quake will happen, and when it does, the dense population of the area will render the quake more damaging.
The U.S. Geological Survey puts the estimate at a slightly greater chance than a 1990 study because it includes a broader region and lowers the magnitude range for the quake. The 1990 study said there was a 67 percent chance of a magnitude 7 quake hitting the area by 2020. The new study lowered the bar to a 6.7 magnitude quake — the size of the 1994 Northridge quake, which killed 57 people and caused $20 billion in damage in Southern California.
The Hayward-Rodgers Creek fault, which stretches from Fremont to Santa Rosa, cutting through the heavily populated East Bay area, was given the highest probability for an earthquake. The team rated the likelihood at 32 percent.
The San Andreas fault, which runs from San Jose to north of San Francisco, had a 21 percent chance of a large quake.
The rate of large quakes dropped in the area after the devastating 1906 San Francisco earthquake. The new study suggests that the San Andreas fault slipped so much during the rupture that the strain was reduced over most faults in the region.
October 13 - Ready or not, San Francisco will be hit sooner rather than later by an earthquake potentially far more destructive than the Loma Prieta quake of 1989. And despite the lessons Loma Prieta drove home 10 years ago, the next "big one" could transform America's favourite city into its worst-ever natural disaster in a matter of seconds.
The quake that hit on Oct. 17, 1989, was centred near Loma Prieta in the sparsely populated Santa Cruz mountains about 50 miles (80 km) south of San Francisco, just far enough to put the urban core out of range of the most destructive shaking.
Still, it was by far the worst earthquake to strike San Francisco since the great quake of 1906, killing nearly 70 people and causing an estimated $6 billion in damage as buildings cracked, houses tilted and freeways and bridges collapsed across the San Francisco Bay Area.
The next "big one," as locals call it, is likely to be much worse because it is expected to hit closer to home. Two of the most dangerous faults in the world -- the San Andreas and the Hayward -- run up either side of San Francisco Bay and either one could trigger a major seismic disaster.
With more than 6.5 million people, the Bay Area is the fifth largest metropolitan area in the United States and includes the cities of Oakland and San Jose as well as Silicon Valley, the world centre of the high technology industry.
The Hayward Fault in particular worries seismic experts. Stretching under Oakland and Berkeley, it is seen as the most likely spot for the next major rupture between the Pacific and North American tectonic plates. Increasing the risk is the fact that most of the residential and business districts of East Bay cities are built on loose landfill, which magnifies the shaking and can even liquefy in the event of a major earthquake.
USGS scientists say geologic markers indicate the Hayward Fault has experienced a major earthquake roughly once every 220 years. The last one, however, occurred more than 300 years ago -- meaning a big shake-up is long overdue. If the full length of the fault were to rupture, at least 150,000 homes would be red-tagged, or made uninhabitable. That would leave more than 300,000 people temporarily homeless, with at least 100,000 of those needing immediate public shelter.
As many as 1,600 roads, including major traffic arteries, could be shut by a major quake, and there are concerns that key services including electricity, water and medical facilities could be jolted off line, in some cases indefinitely.
In 1989, most of the deaths were caused by the partial collapse of the double-decker Cypress Freeway in Oakland, which crushed rush hour commuters in a deadly "concrete sandwich" as the quake struck at 5:04 p.m.
If the same quake were to hit now, the freeway deaths would not occur. A massive program of seismic retrofitting has been undertaken on freeways throughout the Bay Area and officials are fairly confident that most could withstand a 7.0 quake.
Yet serious problems remain, and while public agencies have made headway in their retrofitting programmes funding has not always been sufficient to get all of the job done.
One major concern is the San Francisco-Oakland Bay Bridge, the main traffic link across the bay, which carries an estimated 280,000 commuters every day. The Bay Bridge is vulnerable to earthquakes from at least six different faults.
In 1989, one section of its eastern span collapsed, leading to weeks of traffic chaos. While the bridge was pasted back together, plans to retrofit or replace the entire eastern span are still at least three years from completion.
A $15.6 million interim retrofit designed to help the bridge withstand a magnitude 6.5 earthquake should be finished by mid-2000. But political squabbling among government agencies has kept a fuller safety plan off the table.
San Francisco's landmark Golden Gate Bridge is seen as more seismically stable. But it, too, should be retrofitted -- and the city is at least $171 million short on the $297 million needed to complete the job.
Another focus of worry is water supply. While San Francisco was badly damaged by the huge 1906 quake, what really leveled the city was the firestorm that followed as blazes swept through entire neighbourhoods that had no water to fight them.
San Francisco now gets most of its water piped in from the Hetch Hetchy reservoir hundreds of miles away in the Sierra mountains. After the 1989 quake, engineers identified at least $2.3 billion in necessary retrofitting to the piping system, but so far little appears to have been done.
April 23, 1999 -
San Franciscans shrug off talk of the coming "shake, rattle and roll". Or they joke about it, explaining that because earthquake insurance is prohibitively expensive, the top priority in the event of an emergency is to ensure that the house, covered by fire insurance, goes up in flames.
Is another Big One on the way? For some years geologists have been warning of a 30% chance that a Big One will hit San Francisco before 2015. New paleo-seismic research into movements along the Hayward Fault, one of many running up and down the Californian coast, suggests the risk is much higher. A new probability study comes out in October.
Each Friday, the San Francisco Chronicle plots earthquakes on a map. So far this month, the US Geological Survey has recorded 25 tremors in Northern California alone. None of this month's Californian quakes caused damage: the largest measured just 3.0 on the Richter scale. But as recently as 1994, the 6.7 Northridge quake rocked Los Angeles, killing 57 people and causing damage valued at $40billion, while in 1989, the 7.1 Loma Prieta quake killed 63 and caused widespread damage in and around San Francisco. A section of the 12km-long Bay Bridge collapsed, hundreds of homes built on landfill in the Marina district were razed, and the Embarcadero Freeway was levelled. Ten years later, city halls on either side of the Bay Bridge still argue over a proper, seismically sound bridge replacement, Marina house prices are booming again, and fears over the safety of approaches to the Golden Gate Bridge are forgotten.
