Getting Ready for The Big One
The City by the Bay minds history's lessons, sort of
Nevertheless, the flaws in the city's landscape could still prove disastrous. Large swaths of San Francisco are built on sandy, uncompacted soils--or in some cases, ashes from 1906 and decomposing remnants of gold rush ships--that would turn into runny, liquidlike jelly when exposed to heavy shaking, a phenomenon called liquefaction. Among the plausible scenarios, says Mary Lou Zoback, a seismologist with USGS's Menlo Park office, are streets disappearing into 10-foot sinkholes. Earthquake waves in these zones could be magnified anywhere from three to 10 times in strength. Buildings not anchored in deep bedrock might tip on their foundations or sink into sludge during the shaking, sparking fires. The area's main highways run through valleys silted with weak soils. Those roads would crack like eggshells.
In the crazy-quilt patchwork of faults, there would be almost no safe haven. San Francisco's downtown core, filled with skyscrapers likely to shatter in a major earthquake, is equidistant from the San Andreas fault and the Hayward fault, a roughly 60-mile line that jogs through the Oakland hills, famously bisecting the University of California-Berkeley's Memorial Stadium. The Hayward is considered ripe for a quake: The past four were about 130 years apart, but it's now been 137 years since it last shuddered. "We have a gallows humor," says Mary Comerio, a Berkeley architecture professor and author of Disaster Hits Home. "When it comes, it's either us or Stanford."
"Sword of Damocles." Some of the area's problems, of course, are man-made. After a 50-foot chunk of the upper deck of the Bay Bridge collapsed in 1989, state officials waited until 1997 to deliver a blueprint for a safer design. Years of political squabbling ensued. Now the new structure won't be ready until 2013, although the bridge has been strengthened somewhat. "None of us," Zoback says of the current bridge, "believe the [Bay Bridge] will still be standing after the next earthquake."
For the Bay Area Rapid Transit subway system, the picture is equally grim. A 2002 study showed that in the event of a moderately strong quake, the Transbay Tube, the 3.6-mile subway tunnel under the San Francisco Bay, would come unhinged from its cocoon inside the bay mud and potentially crack and fill with water. In that scenario, the first four stations in San Francisco proper--all below sea level--might also be flooded.
More troubling still is a possible series of related calamities that could turn a Northern California earthquake into a pan-California nightmare. Oil refineries, some built before modern building codes, ring fault-crossed hills in the East Bay, where a temblor could also trigger mudslides down the Oakland hills. Residents of Silicon Valley, says author Fradkin, "probably aren't aware the Sword of Damocles is hovering above their heads." Earthen dams hold back the Lower Crystal Springs reservoir from the valley's northern rim; Fradkin says they probably withstood the Loma Prieta quake only because a drought lessened the pressure on their walls.
Most frightening is the prospect of breaks in the Delta levee system, a 1,600-mile network that provides water to 22 million Californians. An earthquake on the Hayward fault would most likely liquefy the levees, and the results, says Jeffrey Mount, the head of the Center for Watershed Sciences at the University of California-Davis, would be "diabolical." Floodwaters could surge into eroded basins of farmland, making it almost impossible to reverse the damage.