Magazine article Science News

Historical Clues from the San Andreas

Magazine article Science News

Historical Clues from the San Andreas

Article excerpt

The Loma Prieta earthquake of 1989 caused major damage in the San Francisco Bay area, but its force paled in comparison with the great 1906 shock in that region. Geologists have now uncovered signs that a comparable megashock struck the Bay area around 1650. The finding may help scientists predict when the next great quake will shake this segment of the San Andreas fault.

Trenches dug across the San Andreas fault in the Santa Cruz mountains reveal evidence of two earthquakes in this region: the 1906 event and one from the mid-1600s, reports David Schwartz of the U.S. Geological Survey in Menlo Park, Calif. A trenching study conducted at Point Arena, several hundred kilometers to the north, also shows signs of two quakes from the same periods. At both sites, scientists used carbon-dating techniques. The evidence from these two widely separated sites suggests that the entire length of the fault between the Santa Cruz mountains and Point Arena may have broken at once in a great earthquake around 1650, Schwartz says. …

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