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Map highlights new California earthquake faults

April 27, 2010 |  3:03 pm

Faultmap More than 50 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 16 years and offers a sober reminder of California quake risks.

The new faults range from small ones that don’t pose much threat for major temblors to very large ones, such as the one responsible for the 7.1 Hector Mine earthquake that shook Southern California in 1999. Most of the faults have been known to researchers and contained in scientific files.

But state officials and quake experts hope that pulling all the faults together onto 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?”

Roughly 50 new faults might not seem like a lot in a state with thousands of them. But experts said the new map points 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 map comes amid an increased interest in quakes in California and beyond. Last month’s 7.2 Mexicali quake produced thousands of aftershocks, including dozens registering more than magnitude 4.0. As a result, officials said 2010 is shaping up to have significantly more quakes greater than 4.0 than in the last decade.

Parrish said the map represents the state’s best efforts at compiling the faults across California and will hopefully be used to enhance earthquake preparedness.

Parrish and others stressed that residents should not necessarily be alarmed if they live or work near one of California’s estimated 15,000 faults. Many of the faults are fairly short, and experts have found no evidence they have produced sizable temblors. But others can produce major temblors.

Some of these faults were discovered after a large quake erupted in the area over the last two decades.

Scientists, however, found others through research and believe they have a history of major seismic activity that could date back thousands of years. The new faults are spread across the region, including some along the Santa Monica Bay and Orange County coast as well as some -- like Hector Mine -- in the Mojave desert.

One new fault of concern to seismologists is the Maacama fault, which runs along the coastal mountains of Northern California.

-- Hector Becerra

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