Word: stress
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Dates: during 2000-2009
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...volume report published in 1908, Lawson and his team went on to elaborate a new model of earthquake formation--the elastic-rebound theory--that holds up to this day. For years, they correctly surmised, stress had been ratcheting up along the San Andreas until finally it became so overwhelming that the earth's crust snapped like an overextended rubber band. Moreover, the buildup and release of strain appeared to be recurrent, resulting over time in a succession of earthquakes "of greater or less violence." These pioneering researchers provided the first big clue that earthquakes occur in cycles--that...
...clues to its murky prehistory and to re-create in cyberspace the primordial violence of the 1906 quake. In addition to being the centennial of the last Big One, April 18, 2006, marks the approximate midway point in the countdown to the next Big One--100 years of stress accumulation in one of the world's most earthquake-prone regions. The more scientists learn about the ways in which that stress may be released, the more ominous the next earthquake cycle seems...
...speed at which the plates are traveling, in this case about 2 in. a year. The problem for the Bay Area boils down to this: except for one short section, the plates on either side of the San Andreas are tightly locked together. It's only when the stress becomes overwhelming that the San Andreas breaks apart, allowing the plates to lurch forward, 10 ft. to 20 ft. at a time...
...principle, this cycle of stress accumulation and release should be fairly regular, but scientists are finding it is not. Paleoseismologist Tina Niemi of the University of Missouri--Kansas City, for example, is studying a stream-fed marsh near Tomales Bay that has preserved evidence of past earthquakes in its sedimentary layers. By trenching through those layers to a depth of 15 ft., she has uncovered buried fissures formed by recurrent earth movements along the San Andreas. On average, that pattern repeats every 250 or so years, but "average" in this case covers a wide range. In one instance there appears...
Time, unfortunately, is not on the Bay Area's side. Scientists say the "shadow" of the 1906 earthquake--a kind of protective umbra generated by the enormous release of stress 10 decades ago--is already beginning to dissipate. That means the Bay Area will soon be rocked by the next cycle of seismic unrest, with smaller but still damaging earthquakes signaling the start of a new era of danger for a city that's had more than its share...