Faultline under Los Angeles could cause huge earthquake

A recently discovered earthquake fault directly beneath downtown Los Angeles could devastate the city with a tremor 15 times as strong as the big quake in 1994, a study by the US Geological Survey shows.

A recently discovered earthquake fault directly beneath downtown Los Angeles could devastate the city with a tremor 15 times as strong as the big quake in 1994, a study by the US Geological Survey shows.

The most disturbing finding, published yesterday in the magazine Science, is that the so-called Puente Hills fault has a habit of triggering earthquakes measuring about 7.5 on the Richter scale, easily powerful enough to topple skyscrapers designed to withstand magnitudes of only 5.

The consolation is that such earthquakes have hit the Los Angeles basin only four times in 11,000 years. But LA is a city forever teetering on the brink of disaster, at least in its own imagination.

Fear of "the Big One" is in the city's lifeblood, although for most of the 20th century the assumption was that the villain would be the San Andreas fault, which runs the length of California but steers 50 miles east of downtown LA.

The Puente Hills fault, a so-called "blind thrust" fault because it is hidden by enveloping layers of rock that might one day be pushed up as much as eight feet, was discovered in 1999. The study establishes its history and shows that, unlike other faults, Puente Hills does not release its energy in small, frequent bursts but saves it up for massive tremors every 2,000 to 3,000 years.

The scientists who made the survey described the results as "very, very disturbing". LA's civic leaders may need to reconsider earthquake standards for downtown buildings, which house corporate and public offices employing hundreds of thousands of people. The 1994 earthquake, centred on Northridge in the northern LA suburbs, measured 6.7 on the Richter scale, an energy release roughly 15 times lower than a 7.5 quake. It killed 57 people, most of them trapped in a high-rise apartment complex, and caused $40bn of damage.