| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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feature It's Everybody's Fault
Early one spring morning in 1906, a violent tremor shook G.K. Gilbert from his sleep. The wooden faculty club where he was staying at the University of California creaked and groaned, the ceiling light swung like a frantic pendulum, and he was tossed back and forth in his bed like a pinball. Instead of being terrified, Gilbert was thrilled. “It was with unalloyed pleasure that I became aware that a vigorous earthquake was in progress,” he wrote in a letter weeks later. Like most of his peers, he hoped to experience the triple crown of geology: a moving glacier, a volcanic eruption, and a major earthquake. The first two goals are relatively easy to attain, but a mountain of luck is needed to catch an earthquake. Gilbert had just hit the jackpot. The earthquake that struck San Francisco in 1906 was the largest to hit the continental United States during the twentieth century. The 7.8 magnitude quake ruptured almost 300 miles of the San Andreas fault from north of San Juan Bautista to Cape Mendocino, moving the ground more than 20 feet in some places. San Francisco suffered the worst damage. When the earthquake struck at 5:12 a.m. on Wednesday, April 18, buildings all over the city collapsed as the ground beneath them turned to mush. Thousands of people were killed in their beds, and many others were trapped in the rubble. Then the fire started. The blaze raged for three straight days, razed the financial district, devoured the heart of the city, and then spread westward. Tens of thousands were driven from their homes, the firefighters helpless to contain the inferno. The quake had fractured the water system, and hydrants soon ran dry. The army repeatedly dynamited buildings to create firebreaks, but each time the flames found their way across. When the conflagration finally abated, four square miles encompassing 508 city blocks and 28,000 buildings lay in ruins. Hundreds of millions of dollars worth of damage had been done. The city was left a smoldering skeleton, a black crater of debris. Today, nearly a hundred years after the Great San Francisco Earthquake, its effects have not been forgotten. “1906 is just burned into the psyches of San Franciscans,” says Lucien Canton, director of San Francisco Office of Emergency Services. Yet most people who live in the city, though well aware of the potential for earthquakes, are not prepared for the next Big One. What if the 1906 earthquake were to strike again today? “Death and destruction,” says David Schwartz, chief of the San Francisco Bay Earthquake Hazards Project for the U.S. Geological Survey. The population of San Francisco has almost doubled since 1906 to nearly 800,000, while the ten Bay Area counties, wild or rural in 1906, are now home to more than 6 million people. The potential for loss is tremendous. The 1906 earthquake brought San Francisco to its knees, but fire delivered the knockout blows. The two together became known as “the Great Fire.” In fact, citizens lived in denial that there had been an earthquake at all. Earthquakes were poorly understood, unpredictable events that insurance policies didn’t cover. Dependent on money from outside to rebuild, the city had no wish to become known as earthquake country. “Pains are taken to speak of the 1906 as a conflagration,” Gilbert said in a speech later that year to the American Association of Geographers, “and so far as possible the fact is ignored that the conflagration was caused, and its extinguishments prevented, by injuries due to the earthquake.” With the temblor safely relegated to a minor role in public consciousness, rebuilding began. To speed up the process, building codes already devoid of earthquake provisions were relaxed further. Within three short years, more than 20,000 buildings were erected. The new city that emerged from the frenzy of construction was even more vulnerable to earthquakes. Only when another major quake hit Long Beach in 1933 did Californians begin to accept them as a fact of life. Heavy damage to schools prompted laws that gave the state the power to approve public school construction plans. Another required most new buildings to be designed to withstand horizontal forces. However, this law was seldom enforced. During the ensuing years, incremental adjustments were made to the building codes, including one requiring wood buildings to be bolted to their foundations. But it wasn’t until after 1971 that major changes were made and enforced. In February of that year, a magnitude 6.4 earthquake jolted residents of the San Fernando Valley, causing 65 deaths and more than $500 million in damage. “The 1971 San Fernando Earthquake really made engineers, and the public in general, more aware of the kind of damage that can occur from an earthquake,” says Anne Kiremidjian, director of Stanford University’s John A. Blume Earthquake Engineering Center. It was the first one to do extensive damage to California’s mushrooming highways, toll bridges, and overpasses. The Lower San Fernando Dam nearly failed and the local Olive View Hospital, built to flex with earthquake shaking, collapsed instead. It also spurred Caltrans to retrofit overpasses and bridges. The project was well on its way in 1989 when the magnitude 6.9 Loma Prieta temblor hit. The disaster revealed spectacular weaknesses in the system: the Bay Bridge cracked, and an upper portion of Interstate 880 in Oakland pancaked on top of vehicles below when loosely connected columns were shaken out from under the road. The quake also collapsed buildings in San Francisco’s Marina district, 50 miles from the epicenter. Ironically, these were built on loose landfill largely gathered from 1906 quake rubble. When severely shaken, these sediments behave like a liquid, a process called liquefaction. Following the quake, engineers took to the streets to hunt for structure failure clues. They brought their findings back to their labs, where they subjected models of new reinforcement techniques to artificial earthquakes on shake tables. Five years later, a new, more stringent building code was born of their efforts. California now has the toughest earthquake building requirements in the country. Improvements to earthquake engineering have progressed hand in hand with our understanding of these events. Despite official attempts to sweep the 1906 earthquake under the rubble, some of the most prominent geologists of the time, including Gilbert, worked to document the event and its effects. The result was a landmark study known as the “Lawson Report,” and the discipline of seismology was born. But when the report was finished, it was largely ignored by Californians eager to forget. A subsequent geologic map of California published in 1916 by the State Mining Bureau didn’t have a single fault line on it. In the intervening years, the science of geology has come into its own. It underwent a major overhaul in the 1960s when the discovery of mid-ocean rifts led to the theory of plate tectonics. Geologists could finally confirm that the Earth’s surface is made up of discrete pieces of crust that fit together like a jigsaw puzzle. Moreover, the pieces grind by one another in constant motion. It soon became apparent that the San Andreas fault is the seam between two of the mightiest tectonic plates, the Pacific and the North American. The motion of these two plates scraping by one another builds up tension along the fault and causes most earthquakes in California. The advent of the Global Positioning System (GPS) has allowed geologists to determine that the Pacific plate is moving northward at an average rate of 1.5 inches per year relative to North America, building tension along the San Andreas. Geologists also began digging trenches across faults to search for evidence of past events and determine their frequency. They found that at least 32 earthquakes of magnitude 5.5 or higher shook the region between 1850 and 1906. Since 1906, however, California has experienced only eleven large quakes. “The twentieth century was a period of anomalously low earthquake activity,” says geologist Schwartz. He believes that the great 1906 temblor released most of the strain that had been built up in the area, creating an “earthquake shadow.” The question, of course, is when we will emerge from that shadow. Strain has been building, but hasn’t yet reached the levels of the 1850s. But as the magnitude 6.9 Loma Prieta earthquake demonstrated in 1989, that doesn’t mean the Bay Area is immune to suffering a major shaker in the meantime. Though the Loma Prieta quake was centered in an unpopulated area of the Santa Cruz mountains, it still killed 63 people, caused $7 billion in damage and ruptured 25 miles of the San Andreas fault. It started fires in San Francisco, and collapsed buildings in the city’s Marina district. If it had been centered in an urban area, the results would have been similar to the 1995 quake of the same magnitude that struck Kobe, Japan. That disaster killed more than 6,000 people and caused $100 billion in damage. By comparison, the 1906 earthquake was more than 30 times more powerful than the Loma Prieta and Kobe quakes. In 1997, the USGS brought together a group of more than 100 geologists, seismologists, geophysicists, and mathematicians led by Schwartz to determine the likelihood of another large Bay Area earthquake in the near future. By comparing how fast the plates are moving with how much slippage has occurred along faults, they made their best guess. The Pacific plate moves about 1.5 inches a year. So after ten earthquake-free years, 15 inches of movement will need to be accommodated. Using these principles, Schwartz and his colleagues came up with a 70 percent chance that the Bay Area will see a magnitude 6.7 or greater earthquake—that is, one that would affect the entire area—before 2030, a time frame that most people view as within their lifetime. “Pound for pound, the Bay Area has the highest density of active faults of any urban center in the world,” Schwartz says. The USGS group studied all the faults in the region, but focused on the major movers: the San Andreas, Hayward-Rodgers Creek, San Gregorio, Calaveras, Green Valley, Mount Diablo Thrust, and Greenville faults. A major rupture along any of these could affect the entire Bay Area. Most geologists put their money on the Hayward fault system in the East Bay to host the next major earthquake. But the worst-case scenario is another magnitude 7.8 event on the San Andreas near San Francisco. A recent study by Risk Management Solutions, Inc. (RMS) of Newark, CA, in conjunction with Stanford University, estimated that such an earthquake could cause as many as 8,000 deaths, 18,000 serious injuries, and $225 billion in damages. The good news is that the region is far better prepared than in 1906. “We have come a tremendously long way since 1989, and certainly light years from 1906,” says Canton. One of the biggest improvements has been in fire-fighting preparedness. “In 1906 it was almost as if they were ignoring the threat of fire,” Canton says. More than 80 percent of the quake’s total damage resulted from flame. RMS estimates that only 10 percent of the total damage caused by a repeat of the 1906 quake would be due to fire. But the total fire damage could cost up to $18 billion, compared to the $1 billion in damages from the Oakland Hills fire of 1991. One of the first buildings lost in the 1906 blaze was the fire department’s dispatch center, which made coordinating the fire-fighting efforts nearly impossible. Today, the dispatch center has been moved to a safer location near the Civic Center, and communication systems are no longer dependent on ground-based systems. Water delivery is more reliable, too. The water-delivery system failed in 1906 because damaged pipes left hydrants dry. For a city almost entirely surrounded by water, the supply was disastrously low where it was needed most. Today, high-pressure pumps can draw on water from a reservoir near Twin Peaks, maintained exclusively for emergencies, as well as from the bay. Throughout the city, underground cisterns that were largely empty or filled with debris in 1906 have been rebuilt and are now maintained, and more than 80 new ones have been added. Nevertheless, according to Richard Eisner of the Governor’s Office of Emergency Services in Oakland, “They still have a fire safety problem in San Francisco.” He points out that in 1989, liquefaction caused both the conventional and high-pressure systems to fail, and water had to be pumped from the bay. Today, stringent construction rules apply in areas prone to liquefaction. In 1906, a good portion of City Hall was shaken to the ground. Today’s recently renovated version sits atop rubber cushions that will absorb shock and allow the building to move without falling down during a quake. The building was designed to withstand a magnitude 8.2 earthquake, according to city building inspector Zan Turner. Another milestone in disaster preparedness was the “mutual aid” system set up throughout California. It allows resources from all over the state to be diverted wherever a disaster occurs. All emergency management systems and plans in the state have been standardized to make the process run smoothly. Federal responders are included as well. “We don’t look at this as we’re on our own,” says Canton. “We’re the first responders.” "Apart from York City, we probably have the most capable emergency management system in the country,” Eisner says. “But mitigation is an ongoing process. We could always do more.” Another great earthquake on the San Andreas fault could leave more than 240,000 Bay Area residents homeless, according to Jeanne Perkins, who leads the earthquake program for the Association of Bay Area Governments. “Logistically, it’s going to be a mess,” she says. And most of those who do become homeless won’t be prepared to rough it for a while. “In 1906, Bay Area folks had better survival skills, as they were only decades out of covered wagons,” says Eisner. “We have lost many of those skills.” The Bay Area Red Cross is working hard to prepare for the hordes of people that would be forced out of their homes by a high-magnitude quake, and their plan has become a model for the rest of the country. But they will almost certainly fall short of taking care of everyone. “At some point it’s not the Red Cross’s responsibility. It’s Mr. and Mrs. Smith’s,” says Perkins. “I don’t think the typical person in the Bay Area understands that they really could be in a shelter. It could be your house, folks.” Fewer than ten percent of the older houses in the region have been retrofit to meet earthquake building standards. Many of the row houses with living space above a garage so characteristic of San Francisco are unsafe. The large garage doors leave the front faces of the buildings unbraced, allowing side to side movement in an earthquake. Adding a steel brace to the garage is an easy fix, but few people have taken this step. Many other San Francisco structures are still vulnerable as well. “We have a big inventory of pre-1970 concrete buildings,” says Eisner. Many of them would collapse in a major earthquake. Today there are more than 500 high-rises in San Francisco. Newer buildings have sprinkler systems that are connected to on-site water supplies, but nearly 400 of these skyscrapers, filled with thousands of people during work hours, lack their own water reserves. When a single Los Angeles high-rise caught on fire in 1988, 383 firefighters were needed to put it out. To make matters worse, phone lines will go down and cell phone systems will be overloaded, making it difficult to even report a fire. Another fire hazard that looms is the potential for natural gas line ruptures. In 1906, 30 low-pressure gas lines in San Francisco broke, causing explosions that left craters up to 30 feet across. Today’s high-pressure gas delivery systems pose a greater threat. In a magnitude 5.9 earthquake in Los Angeles in 1987, 80 gas lines ruptured. Areas prone to liquefaction will always be hazards. This includes a large portion of the city, much of Highway 101, and many of the region’s airport runways. The isolation will be compounded by major bridge damage. And despite Caltrans’s efforts, hundreds of minor bridges and overpasses will become impassable. Emergency personnel and supplies brought in by boat may be met by damaged piers. Limited help could be flown in by helicopter, but once in the city, transportation and distribution will be next to impossible. For those first crucial days, San Francisco will be on its own. “The Bay Area is one of the riskiest places in the country. There’s no doubt about that,” says Guy Morrow, a geologist with RMS. But at least residents now know what to expect. “It’s part of the culture here that we have earthquakes,” says Eisner. And when Canton compares the region to other parts of the country prone to earthquakes such as Salt Lake City, Utah, and along the New Madrid fault in the Midwest, he says “I’d rather be in San Francisco. The Bay Area is one of the most prepared places in the country.” For geologists like G.K. Gilbert and David Schwartz, earthquakes are merely part of the state’s charm. “It’s really exciting living here, given what I do,” says Schwartz. Awareness and preparedness are important for people living in the Bay Area, but residents must accept some risk. “An earthquake can happen tomorrow, and if you’re in the wrong place at the wrong time, you’re going to get squashed. But that’s what you take on by living here.” Betsy Mason is a freelance science writer and geologist. |
