May 13, 2005— Faults hidden beneath the waves of one of the world's deepest lakes may occasionally trigger large quakes that could set 30-foot tsunamis sloshing mercilessly back and forth, according to a new study.

The tsunamis could happen without warning, flooding the shores of Lake Tahoe, with the largest wave-making quakes recurring every 3,000 years or so.

The discovery is part of an experiment, published in the current issue of Geology, that uses the latest technology to study signs of past earthquakes in submerged landscapes.

Normally to study faults or old landslides, researchers dig a trench through the area.

"The problem is that underwater you can't use your backhoe," said Graham Kent of the Scripps Institution of Oceanography at the University of California in San Diego.

Instead, the team took a three-pronged approach to analyze Lake Tahoe's history.

The latest high-tech maps of the lake's underwater landscape were combined with seismic imagery of what lies under the lake bottom and analysis of sediments cores brought up from suspicious features around the steep banks of the 1,645-foot-deep lake.

The oceanographers found evidence that the faults under the lake have jerked loose and created quakes of at least magnitude 7 — greater than that which caused havoc in the San Francisco Bay Area in 1989.

"A large earthquake could happen up there today or it could be a thousand years," said seismologist John Anderson of the nearby University of Nevada in Reno, where Tahoe tsunami modeling has been done in the past.

"On the list of things people have to worry about, I don't think it would be very high." But it is a concern, he said.

No one has yet calculated how a tsunami would behave along Tahoe's shores, Anderson said. But about 75 percent of the lake shore is very steep, which would probably minimize damage to structures.

On the other hand, many lake-level homes in places like the Tahoe Keys Marina on the south shore are particularly vulnerable, he said.

Geologists have found ample evidence on land in northern Nevada of massive earthquakes. Two big earthquakes — magnitudes 7.2 and 6.8 — happened just minutes apart on Dec. 16, 1954 in Dixie Valley, Nev. They pushed up land on one side of a fault line by 10 to 15 feet in just seconds.

Such an event underwater would certainly cause lake waters to slosh and take time to settle down, Anderson explained.