Word: faulted
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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...
Still, there is a vast difference between suggesting that an earthquake is likely to happen and pinpointing when. For now, scientists cannot say whether a specific section of the San Andreas fault will snap in one year's time or in a hundred, but they are working on it. Seismic silence is one clue. Soundings taken along the San Andreas over the past 15 years showed that the small earthquakes that are a daily event along other parts of the system were not occurring in the Santa Cruz mountains. Scientists argued over the significance of this blank spot...
...earthquake prediction. Along a 20-mile section of the San Andreas, researchers have sunk strain gauges up to 1,000 ft. deep into the earth and laced the surface with "creep meters" that measure rock movement. "We're listening to the heartbeat of this section of the fault very, very closely," says the Geological Survey's Thatcher. The Parkfield section of the San Andreas is unusual in that it is the Old Faithful of earthquake zones, generating moderate tremors every 20 to 27 years. The last Parkfield earthquake occurred in 1966, which means that the next one should strike between...