At 4:31 in the morning on January 17, 1994, the earth's crust snapped 11.4 miles beneath the community of Northridge in Los Angeles. An immense slab of rock began to thrust upward along an unknown buried fault, shifting the San Fernando Valley eight inches and releasing a surge of energy approaching in power the 1980 eruption of Mount St. Helens. At that moment, 15 miles south in Santa Monica, Rob Wirtz, a firefighter, was sound asleep in his station house. Within seconds a shock wave from Northridge knocked the wall phone above Wirtz's bed off its hook and onto his head. It was an unwelcome wake-up call, not only for Wirtz but for everyone in L.A.
The 38-year-old captain leaped up and into the trousers and boots he keeps at his bedside and ran toward the station's garage.
"Things were shaking so hard I could scarcely get my pants pulled up," he recalls. Reaching the garage, Wirtz saw a 38,000-pound fire engine bouncing up and down.
"I looked out the garage-door windows and saw the lights of L.A. blacking out," he says. "I knew something big-time was going on."
The Northridge earthquake--the most costly in the history of the United States--had struck. And L.A. residents were experiencing what geologists warn may be a new era of disastrous earthquakes throughout California.
Near the epicenter in Northridge, Rosemary Sato jolted upright in bed as tremors slammed through her house with the deafening sound of a sledgehammer. "Who has such wrath?" she recalls wondering as the quake blew open her front door, knocked down the wall around her house, and tossed furniture around like toys.
In a neighborhood west of downtown L.A., eight-year-old Carlos Bejarano woke up to the flashes of power transformers blowing outside his family's apartment.
"I thought monsters were flying into my room," he remembers.
Fate struck more violently at the three-story Northridge Meadows apartment complex. An early rising resident, Steve Langdon, was about to make coffee when his building lurched eight feet. The top two floors then crashed down onto his first-floor apartment.
"A wall fell on me," he says. "I couldn't move my head. I was pinned against a bed for five hours with a collapsed lung, five fractured ribs, and a broken collarbone."
Meanwhile, 16 other apartment residents died. Thirteen were crushed in bed by the joists of the upper floors. David and Cecilia Pressman, who had been married for 51 years, died embracing each other.
As aftershocks rumbled, L.A. residents assessed their losses. The magnitude 6.7 quake killed 60 people. It destroyed or left uninhabitable more than 3,000 homes. It toppled ten highway bridges, closing three major freeways. Its spasms demolished part of a huge shopping mall in Northridge and collapsed seven concrete parking structures. Damage estimates exceeded 20 billion dollars.
By comparison, the 1989 Loma Prieta quake in the San Francisco Bay area cost six billion dollars. Of all U.S. natural disasters, only Hurricane Andrew in 1992 cost more--about 30 billion dollars. Still, the city was lucky. Striking in the predawn hours, the quake claimed far fewer lives than if it had hit with rush-hour traffic on the freeways, children in school, and shopping malls crowded.
In the days of the aftermath I fly into L.A. to begin a survey of California's seismic future. I want to explore how its people, from San Diego to Eureka, live with the faults beneath their state, especially after being shaken by two big urban earthquakes in the past five years.
Californians grow up with earthquakes, typically experiencing small quakes less than magnitude 5 or the rumblings of something larger off the coast or in the desert.
"The small ones can be fun--like riding a roller coaster," says Paula Stewart of Rio Dell. "They don't hurt anyone, and you don't have to pick up after them."
Recent big quakes have been giving them a different ride.
"The earth didn't roll through," says Ken Torbert of Ferndale, recalling the 7.2 Petrolia quake of 1992, which hit near Eureka. "It went up and down like a piston."
Now, with Northridge fresh on people's minds, I find tension everywhere. In a Laguna Beach coffee shop, for instance, I overhear two women making small talk.
"What a day," says one. "Like heaven. So clear and hot."
"It scares me," replies the other. "It's earthquake weather."
Scientists reject any correlation between heat waves and earthquakes. Weather aside, there's good reason for Californians to be concerned.
"Something unusual is happening," one of the state's leading geologists, Kerry Sieh of Caltech, tells me. "We've never seen so many destructive earthquakes so close together."
For one thing, he says, the notorious San Andreas Fault system, which bisects California from the Mexican border to the northern coast, may have entered a period of high activity. The San Andreas drives most of California's seismic turmoil. It is a complex network. The main fault--or fracture in the earth's crust--is a line of connecting fault segments running through the state. However, the system also includes a zone of parallel, branching faults as much as 100 miles across. This zone forms the boundary between two great blocks of earth's crust. One is the tectonic plate that carries the Pacific Ocean, along with much of coastal California; the other is the North American continent.
Pulled and pushed by forces deep within the planet, the Pacific plate is sliding northwest past North America at an average of about two inches a year--roughly the same rate as fingernails grow. But movement along the fault usually occurs in bursts. Along most of the fault, the colder, more rigid rocks near the earth's surface resist the plate motions. Eventually enough strain develops along a segment of the fault to overcome that resistance. Then, in geologic terms, that stretch of the fault "breaks," "fails," or "ruptures," and a segment of the crust riding the Pacific plate surges north, creating an earthquake. In the magnitude 7.7 San Francisco earthquake of 1906, which killed more than 3,000 people, a 270-mile-long segment of the San Andreas from south of San Juan Bautista to Cape Mendocino surged northward as much as 21 feet in a few seconds. Half a century earlier in 1857, during a similar but little known 7.8 quake, much of coastal southern California shifted north.
Such great earthquakes--in the range of 8--released about 30 times the energy of Northridge's 6.7 magnitude quake. They probably dramatically lowered stress along their segments of the San Andreas, and indeed for most of this century Californians have experienced relatively few large earthquakes. That respite is probably over.
In the 75 years preceding the great San Francisco earthquake, notes Bob Simpson of the U.S. Geological Survey (USGS), 16 earthquakes with magnitudes greater than 6 struck the bay area. Then, for more than seven decades the area was hit by only one quake that large--a 6.5 in 1911. Now activity is increasing again in the region: Four quakes above magnitude 5.7 have hit since 1979. Likewise, southern California has been averaging one quake in that size range every year since 1986.
Moreover, the Northridge quake proved that southern California is particularly vulnerable to another, newly recognized seismic hazard--hidden faults. Called blind thrust faults, they move differently from the San Andreas, whose sides rip past each other horizontally, rupturing the ground with a visible scar. Blind thrust faults, by contrast, slope at shallow angles toward the surface. When they break, one side thrusts upward, and, as in the Northridge quake, the earth above them shudders with especially violent upward jolting. Blind thrust faults usually do not rupture the surface. Therefore, the only evidence of their existence may be mountain ranges that rise above them. During the Northridge quake, for instance, Oat Mountain, near its epicenter, was lifted up and northwest 18 inches. Yet the fault that created the havoc was unmapped, confirming a growing suspicion among geologists about the mountain-rimmed L.A. Basin.
"Northridge reminded us that there are unknown, obscure faults everywhere beneath L.A.," says Kerry Sieh. "We know now that just one of them can create a magnitude 6.7 quake. What if two or more break together? We would get a much larger earthquake--perhaps even a 7.5. We used to think the main danger to L.A. was a big one originating on the San Andreas Fault, which runs at least 30 miles from downtown. But the San Andreas is no longer the only source for a big one. We now have the enemy right beneath the city as well as on its margins."
Just one magnitude 7 quake under downtown L.A., says Ron Eguchi, a hazards-assessment specialist at the engineering firm EQE International, could kill 5,000 people in Los Angeles County if it struck during the day. Another 50,000 could be injured and 500,000 might be left homeless. Damage to buildings could run 50 billion dollars, with another 25 billion dollars in repairs to such regional infrastructure as roads and utility lines.
As damaging as blind thrust faults may be, the dominant quake maker remains the San Andreas system. The main fault begins about 90 miles northeast of San Diego. However, the system originates in Mexico as a series of faults coming out of the Gulf of California. One of these, the Imperial, feeds much of the Pacific plate's northward motion into the San Andreas.
Like many sediment-covered faults the Imperial is hard for untrained eyes to find. Tom Rockwell, a geologist at San Diego State University who specializes in southern California's faults, drives me into Mexico to see it. We find it crossing an east-west road outside the city of Mexicali. The only evidence, however, is an offset row of tamarisk trees along the road. Part of the row is 15 feet north of the other.
"Those trees were planted across the fault in a straight line," explains Rockwell. "But in 1940 a magnitude 7 earthquake moved all the trees west of the fault closer to California."
Across the border in the Imperial Valley farming town of Brawley, Millie Ralls, 80, remembers that moment well.
"It was a Saturday night," she recalls. "We'd come into town to get our groceries. We'd stopped in at Mel's Root Beer. Then, wham! My root-beer float went sailing down the counter. That quake just kept hitting us again and again. The Woodrow Hotel down the street collapsed. A drunk on the second floor didn't even know there'd been a quake. He just walked out the window into the street."
Few places in California get hammered by earthquakes as frequently as the fertile Imperial Valley, nicknamed America's Salad Bowl. More than a dozen major quakes have hit this century, the most recent in 1979 and 1987.
"We don't count 'em," says Ralls. "But you make a habit of looking at the clock every time you feel one."
"Fortunately, there's not a lot here to shake down," adds another longtime resident, George Wheeler. "You practically have to go out of the county to find an elevator."
At the north end of the Imperial Valley lies the Salton Sea, a tranquil saline lake whose peaceful appearance masks the seismic trouble brewing beneath it. Along its south coast we drive past small volcanic cones and steaming geothermal energy plants, indications of the heat being generated close to the surface.
"Just underground here," explains Rockwell, "the plate motions carried along the Imperial Fault are being shifted over to the San Andreas."
The San Andreas emerges full-blown on the northeast coast of the sea, beneath a tiny, fault-laced town of trailers and retirees called Bombay Beach. If the favorite scenario of many geologists is correct, Bombay Beach may become famous as the site that gave birth to the next big one.
"It's 12 months pregnant there," says Kerry Sieh, referring to the southernmost 60 miles of the fault.
Not until the late 1970s could scientists make such statements. Then, while still a graduate student, Sieh began applying a powerful new tool geologists were developing to look at a region's earthquake history. At a site called Pallett Creek, about 30 miles northeast of L.A., he began digging trenches across the San Andreas Fault.
Sieh takes me into one of his trenches. About ten feet deep, it is striated by dark layers of peat deposited during periods over the past 1,200 years in which Pallett Creek was a swamp. Because the peat contains carbon, radiocarbon dating has been able to determine the age of each layer to within a few decades.
"My feet are at A.D. 800, when Charlemagne ruled, and my head's up with Shakespeare," he says.
He points at one layer that abruptly breaks and drops a few inches.
"That offset was created by an earthquake about A.D. 1350," he says.
Such offsets let Sieh document past big ones along this segment of the San Andreas. The data were revolutionary. They helped inaugurate a new branch of geology called paleoseismology. Now scientists trench every fault they can, trying to understand how often faults generate earthquakes and the hazards they pose.
Some segments of the San Andreas seem primed to go. Sieh trenched the southernmost segment of the fault down near the Salton Sea. He found an alarming absence of earthquakes on that 60-mile segment, which runs past Palm Springs to the San Bernardino Mountains. "Our site there tells us we have major earthquakes on average every 220 years," he explains. "The last one was in 1680. That's why that segment seems past due."
New work by another team at a site 15 miles southeast of Pallett Creek, near the town of Wrightwood, underscores the threat along yet another stretch of the San Andreas.
"At Wrightwood we've found five major earthquakes since 1450," says the team's leader, Tom Fumal of USGS. "That averages one every hundred years. We think the fault is very close to failure. It's almost certainly going to happen in the lifetime of most people now living in southern California."
Just how big will that one be? The magnitude of an earthquake depends on the length of the rupture on the fault. If the system breaks from the Salton Sea through Palm Springs to the San Bernardino Mountains, for example, the quake would be about 7.4. If the rupture extended beyond Pallett Creek, the magnitude would grow to perhaps 7.9. Conceivably, the quake could exceed 8 if the rupture extended north into central California.
The fault probably cannot break along its entire 750-mile length, however. Near the town of Parkfield in central California, the rocks become less rigid, and for the next 90 miles the plates creep past each other without storing strain energy for a big quake. This stretch, known as the creep zone, buffers the northern and southern segments of the San Andreas from each other.
No matter where the southern San Andreas breaks, the city of San Bernardino, in the vast, densely populated suburban basin east of L.A., seems doomed to take the worst beating. This area is also threatened by the perhaps equally hazardous San Jacinto Fault, a splinter of the San Andreas that runs parallel to and about 25 miles west of the main fault.
"San Bernardino used to call itself City on the Move," says Kerry Sieh. "They never should have changed that motto."
"City on the Move? They should call it City of Liquefaction," says a local college student, improbably named Gavin Muck. "It's the worst place to build a city. It used to be a swamp."
Liquefaction is a devastating earthquake phenomenon that occurs where the water table is high and the soils are loose. The shaking turns the earth to quicksand, destroying its strength and amplifying the waves of energy shaking the ground.
Muck says most residents are aware of the hazard but "don't want to think about it."
Heading into L.A., I enter the newly recognized blind-thrust belt, where earthquake scenarios become as abundant as the boomtown dreams that built this brash metropolis.
"We've got six major fault systems in the metro area, excluding the San Andreas and San Jacinto," says Jim Dolan, an earthquake geologist at Caltech. "We're dividing those faults into potential sources for Northridge-size earthquakes. We've identified more than 50 so far."
"Our problem in Los Angeles is that we have this big kink in the plate boundary," says Lucile Jones of USGS in Pasadena. As the San Andreas approaches L.A., she explains, it takes a more westerly bend for about a hundred miles. That bend puts the North American plate in the path of most of southern California and Baja California, which are riding the Pacific plate north. Instead of grinding slowly past North America, southern California rocks collide with the continent around L.A. The collision contorts and squeezes the plate edges, building L.A.'s scenic mountain ranges higher and higher.
The collision is a fast one by geologic standards. The global positioning system (GPS), a network of navigation satellites, now lets geologists measure movements of the earth's crust with great precision. GPS data confirm that the Palos Verdes peninsula at the southern tip of L.A. is moving closer to Pasadena in the north by a third of an inch a year, squeezing the basin in between. Therefore, estimates Ross Stein of USGS, the L.A. Basin is losing about a quarter of an acre of land a year.
Given that rapid rate of collision, L.A. has not had enough earthquakes in historic times.
"We need 15 more Northridges to catch up with the strain that's built over the past 200 years," says Dolan. "Or else one big 7.5 event. It could be as high as an 8."
Much of that strain may be accumulating, Jones says, along a newly recognized hidden fault zone called the Elysian Park thrust-and-fold belt. It runs under the skyscrapers and crisscrossing freeways of downtown L.A.
From a mountaintop in Griffith Park, I gaze out with Jim Dolan at the glass towers of downtown L.A. On a mountain behind us rises the famous Hollywood sign. Below us Sunset Boulevard heads west toward Beverly Hills. The high-rise complex at Century City lies in the distance.
"This whole basin is a 25,000-foot-deep sea of sediments that have eroded off these mountains," he says. "Look at Century City. Those buildings are sitting on the tip of a buried mountain range. If you removed those sediments and stood at the bottom of the basin, it would be like looking up at the Himalaya."
We drive west along Sunset Boulevard, which is actually built along the Hollywood Fault. Until recently, this fault was considered inactive. Dolan, however, found that it breaks every few thousand years.
"If it broke, it would create an earthquake similar to Northridge," he says. "The Hollywood sign would go up and west a foot or two."
The Hollywood Fault also might fail in tandem with the adjacent Santa Monica Fault and the Elysian Park Fault system, generating a 7.5 disaster from east of downtown through Beverly Hills to Malibu.
Scientists can only speculate for now. More GPS receivers soon to be installed throughout the L.A. Basin will help them identify regions where stress may be building. But actually predicting earthquakes in L.A. remains a distant dream. What goes on beneath the surface of this city seems to grow ever more complex.
Meanwhile, survivors of the Northridge experience are having difficulty blocking out the possibility of another big earthquake.
"I hate earthquakes!" says seven-year-old Ryan Campbell. "I've hated them ever since I was one week old and came home from the hospital. I want to live in England."
In fact, Ryan's anxiety began in 1992 when a 7.3 quake near the Mojave Desert town of Landers shook his home in L.A. After the Northridge quake, he refused to be alone. A clinical psychologist who specializes in earthquake trauma, Robert T. Scott, helped Ryan find ways to cope. For one thing, the boy took down pictures in his room that he feared would fall on him and replaced them with posters.
"The most damnable things are the aftershocks," says his father, Dale, a psychiatrist. "They get Ryan so rattled. Now he's so acutely attuned that even the garbage truck making the windows shake can panic him."
Meanwhile, Ani Shakhverdyan, eight, daughter of Armenian immigrants, is conquering her trauma with a magic sword.
"Our fear was so strong," says her mother, Hasmik. "We had to sleep in our cars for two nights. Even now, as we talk, my heart is beating fast and my hands are shaking."
Weeks after the quake, Ani would still cling to her parents, was terrified of the dark, and would not even go to the bathroom unattended. Levon Jernazian, a clinical psychologist, asked her to draw a picture of her fears. She drew a big rat. After telling her he was giving her an imaginary sword she could keep in her heart to use whenever she needed, he told her to cut the picture of the rat in pieces, burn it, and then stomp on its ashes. Ani did what he suggested, and her fears subsided.
Other reactions after the quake varied.
"Now many people are coping actively," says Cheri Adrian, a clinical psychologist specializing in trauma at the UCLA Medical Center. "They are buying earthquake emergency supplies, bolting down their belongings, making specific plans for what they would do and how they would contact their loved ones. This gives them a sense of control."
Many take their fears out on the city.
"L.A. is getting ridiculous," complains Paul Warner, a 30-year-old film director who woke up that January morning to bookcases falling on him. "Riots. Murders. Fires. Mud slides. This city is an apocalyptic zone. It's like an absurd comedy act. I'm getting out."
The earthquake, in fact, tipped the balance for many residents. Fed up with catastrophes and the state's dismal economy, thousands fled to other western states.
Most are staying. "I'm in the music industry. I can't run anywhere," says Ron Fair, a senior vice president with RCA Records on Sunset Boulevard. Fair recently bought the house owned by 1950s TV stars Ozzie and Harriet Nelson. The Hollywood Fault runs right through his living room. Even though the Northridge quake did 150,000 dollars' worth of damage, he cites the estimates that the Hollywood Fault only breaks every few thousand years.
"I'll take my chances," he says.
Still, the cost of this earthquake--one insurance company lost 815 million dollars--creates fears about future catastrophes. It might have been worse. Stronger building codes, implemented after the 1971 San Fernando earthquake, prevented far greater damage to L.A.'s structures in the Northridge quake. Nevertheless, the tragic failure of the Northridge Meadows apartments underscores the need for better inspections.
And this wasn't the big one--not even close," says attorney Joel Castro as we climb through the debris of the most devastated building in the Northridge Meadows complex. The odor of rotting food surrounds us as we step over the rubble of wallboard, insulation, fallen joists, and twisted window frames.
"We haven't found any building in this project in which the interior partition walls were connected to the floors and ceilings," continues Castro, who represents earthquake victims and their survivors in pending litigation. "Plywood shear walls, or support panels, would have held this building up--if there had been enough of them. Whole lengths of some were actually removed to put in utility panels."
Among many other defects, Castro points out joist hangers that are only half the size called for in the building's design.
"I'm not sure how much insurance the defendants have," he says, "but I'm pretty sure we'll get all of it."
Defense attorney Allen Tharpe expects a settlement. "We maintain," he says, "that the shaking was so strong this building would have collapsed even if it were built perfectly."
In fact, the shaking was surprisingly intense. In some places the ground accelerated with a motion exceeding one g--the force of gravity. Most buildings are designed for much less than that. So the first news was good: Most structures performed well.
The bad news began emerging a few days after the quake. In more than a hundred steel-frame buildings--a common type of construction in buildings five stories and higher for the past 25 years--inspectors uncovered cracks in critical welds, flanges, columns, and beams. Even though some tests done in the 1970s showed steel welds could be unreliable, engineers had embraced welding technology, applying it to hundreds of billions of dollars of high-rise construction, not just in California but in downtowns and suburban business centers across the country.
Now every structural engineer I talk with tells me that even though no steel-frame building collapsed during the quake, the welds and connections between their beams and columns must be strengthened.
"Confidence in steel-frame buildings has eroded," says Tom Sabol, a member of a panel of southern California structural engineers studying the problem.
Engineers are still debating how to fix the buildings. Strengthening one connection costs $5,000 to $50,000. A major high-rise with a thousand connections would thus face staggering retrofitting costs.
"Most of those buildings will not collapse in a big earthquake," Sabol emphasizes. "But it's a risk, and people occupying those buildings should be aware of the risk."
Many experts believe that California should rethink the goals of its building codes.
"The codes were designed to prevent life-threatening collapses," says John Hall, an engineering professor at Caltech. "But now that we're discovering we have a lot more faults and increasing seismicity, it may make sense to spend a little more money and build stronger buildings. We don't want them so damaged we have to tear them down."
Earthquake anxiety diminishes as I leave the Los Angeles Basin and travel the San Andreas toward the San Francisco Bay area. Slicing its way through central California, the fault crosses dramatic but sparsely populated cattle country. Big earthquakes happen here, but not until the San Andreas approaches the bay area does it threaten another populous region.
The bay area has still not recovered fully from the 7.0 Loma Prieta quake of 1989--or from the awareness that most of the region was actually spared from that quake's fury. Loma Prieta's epicenter was 70 miles south of San Francisco. Also, the rupture spread out in two directions. Parts of San Francisco and Oakland were shaken only six seconds. Had the earthquake's full energy been directed north, the shaking would have lasted twice as long.
The brunt of Loma Prieta was felt in Santa Cruz, which lost 40 percent of its downtown buildings. Today cappuccino bars, bookstores, and art galleries line the city's rebuilt main streets. But vacant lots still remind residents of what used to be.
Recovery has been slow and painful, says Neal Coonerty, owner of Bookshop Santa Cruz, which partly collapsed. For three years, while he struggled to find loans and rebuild, Coonerty operated out of a tent in a nearby parking lot.
"You get emotionally worn-out," Coonerty says. "And the feelings of that moment never leave you. It was so sudden. You never forget that at any second it could happen again."
Earthquake stress may have triggered another emotional aftershock.
"Ten days after the earthquake we had an all-time high in rape calls," says Melyssa Jo Kelly, coordinator of Santa Cruz's Commission for the Prevention of Violence Against Women. "And there was a 300 percent increase in reports of sexual assault and domestic violence. Both are crimes of power and control. I remember how completely powerless and out of control we all felt."
Santa Cruz is famous for its alternative lifestyles, and some residents comforted themselves with more spiritual tactics.
Kelly recalls falling apart after an aftershock. A young woman tried to console her: "Don't worry. This is just mother earth's way of giving birth to the New Age."
Geologists have another explanation. Loma Prieta was triggered by horizontal and vertical thrust motion due to compression against a kink in the San Andreas Fault.
Thrust faults were the last thing bay area residents needed. They already had enough hazard with the San Andreas and several other faults that branch off it. Geologists now know that blind thrust faults lurk not only in the Santa Cruz Mountains, where Loma Prieta struck, but also to the east under San Jose and the Silicon Valley.
Still, the San Andreas and its affiliates dominate the hazard picture in the bay area.
"They aren't little puppies," says David Schwartz, a geologist at USGS in Menlo Park. "They are big biting dogs, and they each get unleashed every few hundred years."
The San Andreas runs up the San Francisco peninsula. But before it reaches the peninsula, it spins off side branches, the Calaveras and Hayward Faults, which cut through the cities of the populous east bay. Geologists divide the Hayward into northern and southern segments. Each segment ruptured in the 19th century. A fourth hazard, the Rodgers Creek Fault, bisects Sonoma County to the north but could direct a quake toward the bay area. Other worries include the poorly known San Gregorio Fault off the coast of the peninsula.
All those faults are loaded guns. USGS conservatively gives the bay area a 67 percent chance of being rocked by at least one 7 or higher quake from those faults in the next 30 years.
David Schwartz suggests that the odds are closer to 90 percent. No one would be surprised to see several big temblors within that period.
"Each one will be at least a 30-billion-dollar quake," estimates Bill Bakun of USGS.
The costs could go much higher. A repeat of the 1906 quake would today cost about 135 billion dollars.
Most scientists believe that a repeat of that quake, during which the San Andreas Fault ruptured well into northern California, is unlikely within the next century. They calculate that it takes 200 years for enough strain to build. Nevertheless, just the segment of the fault on the peninsula could unleash a major earthquake anytime. In fact Bob Simpson tells me the Loma Prieta quake could have added stress to the San Andreas north and south of its source.
"Those segments are more loaded now," adds Ross Stein. "Wouldn't that be cruel irony to the people of Santa Cruz, who think they've had their earthquake?"
The prime candidate for the next rupture, however, is the northern segment of the Hayward Fault, which cuts through Oakland and Berkeley. Most water, sewage, and power lines serving cities of the east bay cross the fault. Schools, hospitals, fire stations sit on its edges. Much of the housing in the area was built before stronger modern codes were established.
"People here have a false sense of what their homes will withstand," says Jerome Lenoir, owner of Quake Busters, an Oakland firm that reinforces houses to make them quake resistant.
Wood-frame homes can be made quite safe, he says, if they are bolted to their foundations and the walls strengthened with plywood.
Lenoir drives me up into the Oakland Hills, so ravaged by the fires of 1991. We pass an older brick home close to the fault.
"Unless they do some serious work, that house will be history," he says.
Farther uphill, in the area of the burn, the views of the bay below--the sailboats, the skyscrapers, the audacious bridges--grow spectacular. Construction crews crowd every street. Four-story houses that survived the fire perch on steep slopes. Scores of new ones near completion. Granted the view is grand, but considering the dangers, why would anyone move back here?
I ask the same question in San Francisco's bayside Marina district, which some geologists and structural engineers consider the most hazardous spot in the region. Built on an old marsh and filled in with rubble from the 1906 quake, the Marina's soil liquefied during the Loma Prieta earthquake. Many buildings collapsed, gas lines burst, and fires raged. Those devastated buildings have been replaced or seismically strengthened. No sign of disaster remains. Instead, youthful residents--the Marina is a mecca for single professionals in their 20s--jog past me or head for work in Jeeps and Porsches. Most are newcomers since the quake, and they pay some of the highest rents in the city. To live on the edge.
"Why did you move back here?" I ask Linda Lamb, a resident I meet in Bechelli's, a popular neighborhood coffee shop.
"This is my home. I wasn't ready to be pushed out," she says. "I survived the last one. I joined NERT Neighborhood Emergency Response Team and learned what to do. I'm not scared anymore. Also, it's similar to being in a plane crash. What are your chances of being in another?"
Here? At 90 percent in the next 30 years? Not bad.
One of the greatest hazards in San Francisco is its hundreds of older, unreinforced brick buildings. Chinatown, for example, is filled with these structures, which easily collapse. Unlike Los Angeles, which more than ten years ago began requiring that brick structures be strengthened, San Francisco and most other California communities have been slow to act. Poor people live in many of those buildings. Stricter rules would threaten their housing.
Officials are acting more urgently to retrofit the world-famous Golden Gate and San Francisco-Oakland Bay Bridges. Engineers warn that both must be extensively upgraded to safely withstand the big quakes expected. In the 1989 quake a small section of the Bay Bridge's upper deck collapsed onto the lower roadway, closing that vital artery for a month.
Much more destruction could occur in the more powerful shaking experts anticipate. The piers, which rest on timber pilings, could be damaged. Engineers say that while neither the Bay Bridge nor the Golden Gate is likely to collapse in their over-water sections, their approach ramps are vulnerable. Some trusses that support the roadways could also buckle.
"About 250,000 cars a day use the Bay Bridge. At any one time 4,000 people are on it," says Abolhassan Astaneh, a civil engineering professor at the University of California at Berkeley who led a recent, detailed analysis of that structure.
Beyond the obvious life-safety questions, Astaneh says closing the bridge for a year or more would be economically devastating.
"The state's policy now is that major bridges should be completely functional after an earthquake," says Astaneh, noting that the Bay Bridge is "the most complex structure I have ever seen. Strengthening it is going to be a very big challenge."
Work on both bridges is scheduled to begin this year and take several years to complete. The cost will run more than 100 million dollars for the Golden Gate and 350 million dollars for the Bay Bridge.
Seismic hazards persist north of San Francisco, especially in the wine country of Sonoma County. The city of Santa Rosa was leveled by the 1906 quake, but today the Rodgers Creek Fault worries David Schwartz more.
"We think we see three big earthquakes in the past thousand years," says Schwartz at a trench his team has dug across the fault. "They occur on average every 230 years. We think the last one was about 1650. This fault can create at least a 7. There'll be a lot of wine on the ground."
At the Kenwood Winery, one of nearly 150 in Sonoma County, I ask co-owner Mike Lee how he lives with the nearby fault.
"By hoping it won't happen," he says.
We enter a room filled with 12 huge stainless-steel tanks. "This is what really scares me," he says.
Each tank, he explains, holds more than 12,000 gallons, worth about $500,000 retail. Because he has no place else to store them, Lee has stacked 60-gallon wooden wine barrels along the walls, where they could easily fall and snap the valves that keep wine in the tanks.
Dennis Fagent, a structural engineer who helped Kenwood Winery retrofit its buildings, points out another problem: "The tanks are not designed to withstand earthquakes. In a big quake the steel tanks could buckle."
Thicker tanks might not buckle but would cost more, explains Lee's partner and sister, Elizabeth Sheela. Other wineries do not use them, and Kenwood cannot afford them either. The market is too competitive. "As always in business," she says, "it comes down to dollars."
North of San Francisco Bay the San Andreas runs mostly offshore, and its affiliates grow hard to locate. By the time I reach Eureka the dynamics driving California's earthquakes have changed.
"San Andreas land is finished," says Gary Carver, a geologist at Humboldt State University. "You have entered Cascadia."
Cascadia, named for the Cascade Range, encompasses the entire coast of the Pacific Northwest. It begins at a point geologists call a triple junction. Here, just south of Cape Mendocino, three plates--the Pacific, the North American, and a small oceanic slab called the Gorda plate--converge. The Gorda is subducting, or diving, east beneath North America while being butted from the south by the encroaching San Andreas system. Geologists consider this spot one of the most seismically tortured in California.
The greatest hazards here are subduction earthquakes, generated as the Gorda plate thrusts beneath the coast. Subduction quakes are the largest on earth. The 9.2 magnitude Alaska earthquake of 1964 was a subduction quake. On April 25, 1992, a smaller one--a mere 7.2--hit the coast near the triple junction.
On that day Bob Shinn, a local general-store owner, was diving for abalone with his brother-in-law, Ric LeGendre.
"We'd just come onto the beach," recalls Shinn. "I'd pulled off my hood, when...."
"The ground rushed up at us as if we were riding an elevator," finishes LeGendre. They take me to that same beach, where a cluster of rocks rises near the water's edge.
"It was like being on a bucking horse," says Shinn. "We were staggering around just trying to stay upright. Then I noticed that rock out there where I'd been swimming. It was about four feet higher out of the water. All the other rocks with mussels were way above water too. We took off. We thought we were going to have a tidal wave. But that water never did come back. All those mussels died off."
The two men had in fact ridden the coast skyward, witnesses to the process that has built mountains along the coast of California north of the triple junction: As the Gorda goes under, it jacks up the land above.
Although small by subduction-quake standards, this Petrolia earthquake--named for the town nearest its epicenter--traumatized residents of the sparsely populated region.
"I was upstairs at the computer when the rocking started," says Bonny Barnwell of Petrolia. "When the stereo flew past me, I panicked and went for the stairs. But our dresser jumped over and knocked me hard. It was probably a blessing. If I'd made it to the stairs, I think I'd have been thrown down them."
The quake triggered fires that burned down Petrolia's general store and post office. Some residents, says Barnwell, are still in emotional aftershock, easy to startle or subject to anxiety attacks. She herself broke a leg months after the quake in an accident she blames on a delayed stress reaction.
In nearby Ferndale, a touristic town of Victorian homes and bed-and-breakfasts, Dale Belvin recalls crawling out of a grocery store on his hands and knees as bricks fell around him. About 50 homes were thrown off their foundations. Although the town rebounded quickly, reports of earthquake damage devastated business for months.
"When I moved here 12 years ago from New York, I thought the earthquakes were all in Los Angeles," says local newspaper editor Elizabeth Poston McHarry. "Dumb me."
"The fact is we experience more earthquakes around the Eureka-Petrolia area than anywhere else in the state," says Gary Carver. "We feel a quake about once a month. There's a damaging one every three years on average."
The biggest concern, he says, is that "the Petrolia earthquake might be a precursor to a much more powerful subduction earthquake."
Until recently, scientists thought the Cascadia subduction zone was inactive. Now Carver is among several researchers finding evidence of huge subduction quakes in the recent past. In a saltwater marsh near Arcata he shows me stumps of trees that were killed and peat layers that formed from smothered vegetation after a major earthquake abruptly altered the tide line. Marshes in Washington and Oregon show similar evidence. Radiocarbon analyses date all this dead vegetation to about 1700. Does each site reflect the same monster quake? Striking along 400 miles of coastline, it would have been a magnitude 9 event. Or was there a series of smaller giants--8.3 or so--clustered over two or three decades? No one can say. Nor can they yet determine exactly how often big quakes recur.
"The estimates range from every 300 to 600 years," says Carver. "But the intervals aren't necessarily regular."
Since the last one apparently hit 300 years ago, how does he see the risk?
"Over the next 50 years, quite high."
So much uncertainty. I finish my journey feeling frustrated. Many critical questions will be answered only by earthquakes of the future. I have to hope they won't happen, yet I know they will, and I anticipate what they will teach us. Is the news too alarming? Consider the lives at stake if Californians don't heed what geologists are gleaning about the past.
As David Schwartz says: "My wife's a real estate agent. She hides me from her friends. We geologists may spread doom and gloom, but that's the way it is."
Copyright 1995 National Geographic Society. All rights reserved.
