Big Quake "Guaranteed" to Hit California by 2037

Alicia Chang, AP Science Writer, in Los Angeles
Associated Press
April 14, 2008
California faces an almost certain risk of being rocked by a strong earthquake by 2037, according to the first statewide temblor forecast, released today.

New calculations reveal there is a 99.7 percent chance a magnitude 6.7 quake or larger will strike in the next 30 years.

The odds of such an event are higher in southern California than northern California—97 percent versus 93 percent.

(Related: "Major Quake May Strike Bay Area Next Year, Experts Say" [December 12, 2007].)

The last time a jolt this size rattled California was the 1994 Northridge disaster, which killed 72 people, injured more than 9,000, and caused $25 billion (U.S.) in damage.

The analysis, titled the "Uniform California Earthquake Rupture Forecast," took three years to complete.

It represents the first comprehensive effort by the U.S. Geological Survey (USGS), Southern California Earthquake Center (SCEC), and California Geological Survey to calculate quake probabilities for the entire state using newly available data.

The report "basically guarantees it's going to happen," said Ned Field, a USGS seismologist based in Pasadena and lead author of the study.

Wake-Up Call

California is one of the most seismically active regions in the world.

More than 300 faults crisscross the state, which sits atop the meeting of two of Earth's major tectonic plates, the Pacific and the North American.

About 10,000 quakes rattle southern California each year, although most of them are too small to be felt.

Previous quake probabilities focused on specific regions and used various methodologies that made it difficult to compare.

For example, a 2003 report found the San Francisco Bay Area faced a 62 percent chance of being struck by a magnitude 6.7 quake by 2032. The new study increases the likelihood to 63 percent by 2037.

For the Los Angeles Basin, the probability is higher at 67 percent. There is no past comparison for the Los Angeles area.

Scientists still cannot predict exactly where in the state such a quake will occur or when. But they say the analysis should be a wake-up call for residents to prepare for a natural disaster.

"A big earthquake can happen tomorrow or it can happen ten years from now," said Tom Jordan, director of SCEC headquartered at the University of Southern California, who was part of the research.

Knowing the likelihood of a strong earthquake is the first step in allowing scientists to draw up hazard maps that show the severity of ground shaking in a particular area.

The information can also help with updating building codes and emergency plans and setting earthquake insurance rates.

Fault Overdue

Of all the faults in the state, the southern part of the San Andreas—which runs from Parkfield to the Salton Sea—appears most primed to break, scientists found.

There is a 59 percent chance in the next three decades that a Northridge-size quake will occur on the fault, compared to a 21 percent chance for the northern section.

The northern San Andreas produced the 1906 San Francisco earthquake, a recent disaster compared to the southernmost segment, which has not popped in more than three centuries.

Scientists are also concerned about the Hayward and San Jacinto faults, which each have a 31 percent chance of producing a Northridge-size temblor in the next 30 years.

The Hayward fault runs through densely populated cities in the San Francisco Bay Area. The San Jacinto fault bisects the fast-growing city of San Bernardino.

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