California forecast: large quake in next 30 years
A new study reports a 46% chance of a magnitude 7.5 or greater temblor striking in the next few decades. Researchers point to Southern California as the likely spot.

California is likely to experience an earthquake of 6.7 magnitude or greater in the next 30 years, according to a study released today. The study marks a rare effort to actually forecast the likelihood of a major temblor in a state known as “earthquake country.” The forecast is significant because such a large temblor could cause billions of dollars in damage as well as loss of life.

Study participants include the U.S. Geological Survey, the California Geological Survey and the Southern California Earthquake Center.

The researchers found that the chances of a magnitude 7.5 or greater temblor in the next 30 years is 46%. They determined such a quake would likely occur in Southern California.

According to a report from the researchers, the forecasts were made by combining "information from seismology, earthquake geology, and geodesy [measuring precise locations on the Earth's surface]. For the first time, probabilities for California having a large earthquake in the next 30 years can be forecast statewide."

"This new, comprehensive forecast advances our understanding of earthquakes and pulls together existing research with new techniques and data," explained USGS geophysicist and lead scientist Ned Field in a statement. "Planners, decision makers and California residents can use this information to improve public safety and mitigate damage before the next destructive earthquake occurs."

In 2006, seismologists met in San Francisco to discuss the 100th anniversary of the great San Francisco quake. Presentations suggested that California needed to do more to prepare for the next major temblor.

First, future quakes could easily do more damage than past ones because the population of California continues to increase and there are more buildings in areas near fault lines on soft ground susceptible to liquefaction. Second, the state must do more to retrofit vulnerable buildings.

A landmark study presented at the conference by noted structural engineer Charles Kircher found that 5% of buildings would cause 50% of the deaths in the event of a major temblor. Those buildings include unreinforced masonry, brittle concrete structures and buildings with open floor plans on the first floor, such as apartments with first-story garages or retail businesses. Seismologists and state officials have long warned of the danger of such buildings, but regulating them has been difficult. Though some retrofitting has occurred on old brick buildings, relatively little has been done about so-called "nonductile" concrete buildings and "soft" first-story buildings despite their proliferation across the state.

_{Bron: LA Times}