New California tremor map shows 50 new faults

Published 3 May 2010

California has an estimated 15,000 faults; many of those are short, and experts have found no evidence that they have generated sizable temblors; others, though, can produce major quakes; the state’s geological agency have placed fifty new faults — all of them surface faults that have been discovered over the last two decades — on one map which will help educate the public and aid in planning and quake readiness

More than fifty new surface earthquake faults have been discovered in California over the last two decades, according to a new state map that officials hope will help guide future development decisions and emergency planning. The state’s fault activity map, produced by the California Geological Survey, is the first in sixteen years and offers a sober reminder of California’s quake risks.

Los Angeles Times’s Hector Becerra writes that the new faults range from small ones that do not pose much threat for major temblors to very large ones, like that responsible for the 7.1 Hector Mine earthquake that shook Southern California in 1999.

Most of the faults have been known to researchers, and information on them is contained in scientific files. But state officials and quake experts hope that putting all the faults on one map will educate the state about quake risk zones and help residents grasp the geography of the fault lines.

I think every classroom in California should have these maps on the wall,” said Caltech seismologist Lucy Jones. “I don’t think we do enough to educate the general public about these features. We turn it into something for the specialists, as if science is only for scientists. But if you’re going to buy a house, would you like to know what fault is under your house?”

Becerra notes that about fifty new faults might not seem like a lot in a state with thousands of them, but experts say the new maps point to a basic fact of seismology: The more scientists study quakes in California, the more faults — and dangers — they find.

These maps are used to make a lot of other maps, to map landslides, areas where you have liquefaction because of earthquakes, for tsunami coastal mapping,” state geologist John Parrish said. “They can be used to make decisions on where to build schools and hospitals, where you need a higher standard of construction. They can tell you what kind of a surface you’re building on, and how close you are to a fault.”

The release of the map comes amid an increased interest in quakes in California and beyond. Last month’s 7.2 quake south of Mexicali produced thousands of aftershocks, including dozens registering above magnitude 4.0. As a result, officials said 2010 is shaping up to have significantly more quakes greater than 4.0 than any year in the last decade.

Parrish said the map represent the state’s