It’s been discovered that the quakes produced by the San Andreas Fault in California occur at regular intervals. This previously unnoticed cycle gives researchers hope that they’ll be able to predict them in the future.
Robert Sanders of U.C. Berkeley News writes that a new study by seismologists shows the frequency of tiny microquakes rises and falls over a three year period, and that quakes of the magnitude 4, 5 and 6 are six to seven times more likely to occur within a year of when this cycle is most active. Geophysicist Robert Nadeau says, “This has promise for forecasting larger quakes, though this is our first look and it needs to be refined more.”
Microquakes, which usually can’t be felt, were at their most frequent when the 7.1 Loma Prieta quake hit in 1989. If the three-year cycle is correct, microquakes should increase again in late 2004. About half of all microquakes occur repeatedly in the same spots, making it possible to install seismic monitors there to measure them. Nadeau thinks these areas are places where the San Andreas Fault is not lubricated by fluid or mud and doesn’t slide as easily as surrounding areas. Once the sensors pick up a surge in microquakes, we’ll know The Big One isn’t far behind.
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