Hugh Pickens writes writes: "Newsweek reports that first there was a violent magnitude-8.8 event in Chile in 2010, then a horrifically destructive Pacific earthquake in New Zealand on February 22, and now the recent earthquake in Japan. All three phenomena involved more or less the same family of circum-Pacific fault lines and plate boundaries—and though there is still no hard scientific evidence to explain why, there is little doubt now that earthquakes do tend to occur in clusters: a significant event on one side of a major tectonic plate is often—not invariably, but often enough to be noticeable—followed some weeks or months later by another on the plate’s far side. "It is as though the earth becomes like a great brass bell, which when struck by an enormous hammer blow on one side sets to vibrating and ringing from all over. Now there have been catastrophic events at three corners of the Pacific Plate—one in the northwest, on Friday; one in the southwest, last month; one in the southeast, last year." That leaves just one corner unaffected—the northeast. And the fault line in the northeast of the Pacific Plate is the San Andreas Fault, underpinning the city of San Francisco. All know that the San Andreas Fault is due to rupture one day—it last did so in 1906, and strains have built beneath it to a barely tolerable level. Although geologists believe a 9.0 quake is virtually impossible along the San Andreas, a network of "strike-slip" faults smaller and more fragmented than the great chasm that exists where two continent-sized plates of the Earth's crust meet along the Japanese islands, USGS studies put the probability of California being hit by a quake measuring 7.5 or more in the next 30 years at 46 percent, and the likelihood of a 6.7 quake, comparable in size to the temblors that rocked San Francisco in 1989 and Los Angeles in 1994, at 99 percent statewide."
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