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's quake risks.
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?"
About 50 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 best efforts at compiling information on the faults across California and will hopefully be used to enhance earthquake preparedness.
With the new digital images as a base, The Times has produced its own map of Southern California's earthquake exposure, showing the potential magnitude of quakes. The Times map couples the surface faults on the state map with estimates in the 2007 Uniform California Earthquake Rupture Forecast, a study of the likelihood and probable magnitude of quakes.
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 those are fairly short, and experts have found no evidence that they have generated sizable temblors.
But others can produce major quakes. Some of the new faults were discovered after a large quake erupted there. Scientists, however, found others through research and say they have a history of major seismic activity that could date back thousands of years.
The new faults are spread across the region and include some along Santa Monica Bay and the Orange County coast as well as some — including Hector Mine — in the Mojave Desert. One new fault of concern to seismologists is the Maacama, which runs along the coastal mountains of Northern California.
Parrish said one goal of the new maps was to make them easier for the public to understand. The map uses color-shaded relief to better show the paths of fault lines and contours of the geology around them.
"The 1994 map was very good for the time," he said. "But there's been a lot of mapping done in the intervening years, with more details here and there. New areas have been mapped, with new interpretations."
The map shows only surface faults; those below the surface, such as the one that caused the Northridge quake, are not included. The California Geological Survey also released a new geology map, identifying the composition of rock and soil across the state — key to how earthquakes inflict damage — for the first time since 1977.
Formed because of the Gold Rush, the office that became the survey was initially created to provide detailed information about mining. Despite numerous devastating earthquakes over the years, it wasn't until a 7.3 magnitude quake struck Kern County in 1952 and killed a dozen people that the office got involved in public safety.
The fault activity map is the fourth the state has released.
Wally Lieu, engineering section manager for the Metropolitan Water District of Southern California, said his agency is eager to review the new map. He said that the MWD already uses seismic maps in planning projects but that the state map provides additional useful information.
"Anything they have is of interest to us, especially in electronic form," Lieu said. "We have a mapping team in engineering, and they have responsibility for updating our maps as we collect information."
Parrish said the digital version of the new maps should be updated far more rapidly than in the past. If a new fault is discovered, it could be only months before its location is reflected electronically, he said.
Times staff writer Doug Smith contributed to this report.