California's hidden earthquake faults may be capable of producing events of even greater magnitude - and even greater destruction - than previously thought, according to Jonathan Stewart, assistant professor of civil and environmental engineering.

Stewart, who specializes in earthquake and foundation engineering, based his comments on findings he made while surveying damage from the Jan. 26 earthquake in India.

The 7.7-magnitude quake, the worst in that country's history, killed an estimated 20,000 people. Stewart and other members of the Earthquake Engineering Research Institute/National Science Foundation reconnaissance team visited the cities of Bhuj and Bachau, as well as several ports, and reported that damage was extensive, from thousands of collapsed homes to failed reservoirs.

Of local significance, Stewart said, is the fact that the fault that caused the India quake was a "blind thrust" fault. The same kind of fault can be found in Southern California, including one that runs directly beneath downtown Los Angeles.

Much is still to be understood about blind thrust faults, he explained.

What is known is that they are buried deep within the Earth - the Indian quake ruptured at a depth of about 12 miles. And because they are buried, they are very difficult to map.

What is also not known is how powerful an earthquake such a fault could trigger.

"Up to now, blind thrust faults had been assumed to produce no more than magnitude 7.3 earthquakes," Stewart said. A 7.7 quake like the one in India releases about four times more energy, he said.

"We're not sure yet whether that earthquake is something that could actually happen in Southern California," he said, because of geological differences between the two regions.

Added the scientist: "It's a little bit alarming. It needs to be looked into very carefully because it may hold important lessons for Southern California."