Word: faulting
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Dates: during 1980-1989
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...poles sway, then rushed to his seismographic station. "The instruments were off-scale!" he marveled. Within minutes the scientists on duty had pinpointed the epicenter of the quake in the rugged Santa Cruz mountains some 50 miles away. The spot was no surprise: it lay on the San Andreas fault, a great gash in the earth that extends nearly the length of the California coast. Even before the quake, the Santa Cruz area had been identified as a prime candidate for a big tremor. "We still can't predict when an earthquake will occur," says geologist Clarence Allen...
...aftershocks jolted the area, geologists fanned out into the mountains to look for changes wrought by the quake. They examined winding roads for fractures and shot laser beams across the fault to measure expected shifts in terrain...
Like a river with multiple tributaries, the San Andreas is associated with numerous lesser faults, among them the Hayward fault, which undercuts Berkeley and Oakland, and the San Jacinto fault, near San Bernardino. Some parts of the San Andreas are more dangerous than others. One segment that lies to the south of the Santa Cruz mountains does not appear prone to large jolts at all. "It just creeps along," says geophysicist Ross Stein of the USGS. "Probably & there's some remarkable material down there that, like talcum powder, acts as a lubricant...
...ancient pottery, is broken into 15 large pieces. These pieces of crust, called plates, restlessly roam about, driven by plumes of molten rock that roil up from the planet's superheated core. Many of the world's largest earthquakes occur at the boundaries of such plates. The San Andreas fault system divides the Pacific plate and the North American plate, which grind past each other at the pace of 2 in. a year. But this movement of the plates is not uniform. Along fault zones the plates tend to become "locked," resisting the overall motion. Explains Berkeley seismologist Robert Uhrhammer...
Even though the mechanics of earthquakes are understood, accurate prediction of their occurrence has remained beyond reach. Earthquake forecasting is mostly based on past history. If a fault once generated a big earthquake, it can be assumed that it will do so again. But just where and when will the next big break occur? Here scientists are beginning to make headway. Geophysicist Wayne Thatcher of the USGS notes that the 1906 quake ruptured a 260-mile-long section of the San Andreas, extending from Cape Mendocino to San Juan Bautista. But the plate movement along the southern portion...