EVENTUALLY the rock slabs' pent-up pressures prove too much. In a lethal letting-go -- probably within the next two decades -- it finally happens: California comes apart at the seams.
The Big One.
Two-thirds of the state convulses in a seizure of continental proportions. For two or three minutes, the earth shakes. Mountains heave. Highways buckle. One in every 100 buildings topples to the ground. Power plants shut down. Electric systems fail. Oil refineries explode in raging infernos. Pipelines shatter. Across the region, telephones fall silent. A major aqueduct cracks. Fires everywhere, but firefighters lack water to put them out.
Between 3,000 and 14,000 people die. Another 12,000 to 55,000 need hospital care. Up to 141,000 people are homeless. The population is paralyzed. Rescuers can't get through streets clogged with rubble. For at least 72 hours, people are in the dark and they are on their own. In the words of an official California planning scenario: "Circumstances will . . . overwhelm our institutional and personal capabilities to cope."
Seismologists describe last week's quake as mere prologue in the geological drama of California under seismic stress. The final act -- more than 60 percent likely within 25 years -- could be one of the most devastating natural disasters of our times.
Experts say the earth, in a quake rumbling at 8.3 magnitude, will release perhaps 100 times as much energy as last week's quake. Damage could be $200 billion to $300 billion -- numbers that horrify the insurance industry.
"We're going to have a disaster; we're getting very close," says Tom Henyey, director of the Southern California Earthquake Center. "It's going to be at least 10 to 20 times as bad as what happened last week, in every way."
Worse, the big California earthquake for which scientists, emergency planners and national insurance companies are bracing is only one of two "Big Ones" virtually certain to strike the western United States within the next century.
"A lot of people don't realize there's another Big One waiting to happen in the Pacific Northwest -- and that we have the potential for a more powerful one," says University of Oregon seismologist Gene Humphreys.
As California anticipates an earthquake of 8.3 on the Richter scale, off the coast of the Pacific Northwest -- where the huge slab of the earth's crust known as the continental plate is sliding beneath the Pacific plate -- the stage is set for perhaps an 8.5 to 9 quake.
Because the "fault" lies just off the coast, prospects are for high and powerful "tsunami" waves to spill onto the mainland, perhaps flooding coastal towns such as Tillamook, Ore., even as cities such as Portland endure heavy damage from the shaking.
Cities like Portland, which has only in the past few years awakened to the prospects of a severe earthquake, could sustain more physical damage on an average city block than would be the case near Los Angeles, engineers say.
One study in Portland estimated that perhaps as many as one in four of the city's buildings could collapse, compared with one in 100 in Southern California. This past September, the city decided to find ways to earthquake-proof its 158 bridges.
"We haven't been shaken like L.A. every 20 years, so most of their junk buildings and other structures are gone already. Ours aren't," explains Roger McGarrigle, chairman of a state advisory seismic safety commission.
In Southern California, improved building codes have been in place for years, but discussions among experts still often focus on limiting damage and casualties rather than avoiding them. In Los Angeles, an estimated 7,000 older buildings are almost certain candidates for collapse.
About the impending catastrophe, there is a certain fatalism.
As University of Southern California seismologist Keiiti Aki, chairman of a scientific review panel, says: "It's inevitable. A large area will suffer."
But he adds, "I'm not worried about my life at all, not compared with having a traffic accident on our highways on any other day."
The Big One, experts predict, will look like last week's quake multiplied many times: Major highway overpasses will crash down. Natural gas pipelines will explode in flames. Smaller buildings from two to 10 stories will collapse. Bridges such as the Golden Gate will sway, but stay.
"You can only build in as much protection as your pocketbook can afford," says Dario Gasparini, a civil engineer at Case Western Reserve University who specializes in earthquake engineering.
While nuclear plants, hospitals and other key facilities have added earthquake protection, "you can't safeguard every bridge, building and person -- the expense is too great. There will be hundreds and hundreds of deaths."
For more than a decade, insurance companies have been distressed at the likelihood of a giant natural disaster rivaling the great San Francisco quake of 1906. One insurance industry study estimates that, as in San Francisco then, fires will cause 80 percent of the damage in either Los Angeles or the Bay Area.
"When the Big One happens, things will be so chaotic fire departments will be overwhelmed, they won't have manpower and they won't be able to get through," says Don Segraves, executive director of the Insurance Research Council, an insurance industry think-tank. "Despite improvements, San Francisco and Los Angeles are still disasters waiting to happen."
In recent years, scientists have concluded that severe earthquakes strike California once every 100 years. And they've noted a cluster of stronger quakes during the last decade, suggesting a prelude to a major quake.
When will restless California settle down for sure? Scientists say not for at least another 50 million years.
Keith Epstein is a reporter for the Cleveland Plain Dealer.