I Didn’t Know That

Q: Why was the highly destructive San Andreas fault named after a saint, of all things? And how many quakes have there been on it?

A: The fault was actually named after San Andreas Lake south of San Francisco, where the fault was first recognized. According to geologist Kerry Sieh of Caltech, there have been hundreds of thousands of small quakes on the fault over the millenniums, as well as many larger ones. Near Palmdale, for example, large temblors have occurred about every 130 years, the last being in 1857. Near Palm Springs and Indio, the last major earthquake was in about 1680 and the average time between quakes is about 250 years, so we are way overdue. West of Bakersfield, the average interval is about 160 years, with the most recent occurring in 1857. The fault is slipping at a rate of about 2 inches per year, bringing Los Angeles closer to San Francisco. For more information, visit: sepwww.stanford.edu/oldsep/joe/ fault_images/BayAreaSanAndreasFault.html.