Word: parkfield
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Dates: during 2000-2009
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...Andreas Fault, yet the quake to end all quakes has yet to occur. In 1980, a federal report declared the likelihood of a major earthquake striking California within the next 30 years to be "well in excess of 50%." Seismologists predicted a 1993 earthquake in the community of Parkfield - which lies along the San Andreas Fault - but the quake did not come until 2004. Earthquake prediction is a tricky practice, and one that, for all their gadgets, measurements and years of study, scientists have not yet mastered...
Reporting in the July 10 edition of the journal Nature, researchers used a high-tech equivalent of a stereo speaker lowered into a bore hole near Parkfield, Calif., a half-mile deep and five yards from a measuring device. For two months beginning in late 2005, researchers transmitted pulse signals three times per second, from the speaker to the measuring device, calculating travel time between the two stations. Surprised scientists learned the seismic waves slowed dramatically on only two occasions: two hours prior to a magnitude-1 temblor, and a startling 10 hours before a magnitude-3 quake...
...this point, Parkfield's seismic history seems suggestive. For more than a century, the area just south of the drill site produced magnitude-6 earthquakes on a roughly 22-year cycle--or so it seemed in the mid-1980s, when a USGS team threw a net of instruments over the area, hoping to catch the next iteration. The last quake occurred in 1966, so scientists figured the next would come around 1988. Instead, the 1966 quake was followed by a 38-year pause. Some speculate that another earthquake, which occurred on a nearby thrust fault in 1983, reset the seismic...
...scientists are trying to gauge how last year's Parkfield quake affected the broader San Andreas system. Stress has been off-loaded to the section of the fault directly south of the rupture, and that has at least the potential to set the stage for a larger upheaval. In 1857, for example, a moderate temblor at Parkfield was followed within hours by a major earthquake that started in the vicinity of Cholame, 15 miles away, and ripped south for 225 miles. In some places the ground moved more than...
...stress has accumulated along this section of the fault to power another 1857-style spasm. That one approached a magnitude of 7.9, making it even stronger than the 1906 quake that devastated San Francisco. Still, experts acknowledge, it's not inconceivable that the next moderately strong shake-up at Parkfield could lead to the unzipping of a longer section of the fault, spawning a quake of, say, magnitude 7. If that happens, SAFOD would provide scientists with more than they bargained for--a near ringside seat at the start of, if not the Big One, something pretty close...