Quake forecasting has had its successes, like the 1989 Loma Prieta quake. Seismologists at the USGS publicly identified the Loma Prieta stretch of the San Andreas fault as a high-probability quake area in 1988. Then, in the summer of 1989, after two precursor tremblors, USGS warned that a much bigger quake could occur within days. They were wrong about the timing, but on Oct. 17, a violent tremor on the San Andreas fault destroyed much of Loma Prieto and, rippling northward, devastated parts of San Francisco and Oakland.
It stands to reason that southern California, with its huge population and nearly continuous seismic activity, is one of the most intensively studied earthquake zones within the United States. (Earthquake-risk predictions for the East Coast and the Mississippi Valley, by contrast, are far less credible.) And a new study by scientists at the Southern California Earthquake Center suggests the risk of a major quake in Los Angeles is extremely high. As the study reports, there is an 86 percent chance of an earthquake of at least magnitude 7 somewhere in Southern California within the next 30 years.
The crucial questions, if this study is accurate, are just where and when the earthquake will occur. Seismology cannot tell us. It could be anywhere, anytime – Santa Barbara in 2017 or Santa Ana in 1996. If that sounds vague, consider that an 86 percent probablility is nearly a guarantee – and to that one group of experts, anyway, the Big One is very real.
MAP: On Shaky Ground; Predicting earthquakes may be an inexact science, but seismologists across the United States are urging local governments to prepare. Among the most vulnerable areas:
Boston More than 50% chance of 6.3 quake in next 200 years New York Large quake unlikely. But city unprepared; buildings vulnerable to even moderate shaking Charleston, S.C. Repeat of major 1886 earthquake could kill more than 2,000 New Madrid, Mo. Unstable fault will likely rupture again. Could hit St. Louis hard. Salt Lake City 20% chance of large quake on Wasatch Fault in next 50 years. Los Angeles Quakes as large as 7.6 possible from smaller faults directly under the city. San Francisco 50-50 chance Hayward Fault produces 7.5 quake in next 30 years. Seattle Plates under ocean converging; quake could hit 9 or higher.
