Tahoe has had many earthquakes over the years | TahoeDailyTribune.com

Tahoe has had many earthquakes over the years

Joelle Babula, Tribune News Service

There are active fault lines lining the bottom of Lake Tahoe.

But that doesn’t necessarily mean a massive earthquake will shake the lake anytime soon.

“Earthquake prediction is not a very robust science right now, but you’re always better off knowing if there’s an active fault in your area,” said Graham Kent, with the Scripps Institute of Oceanography in San Diego. “There is clearly ongoing activity present (in Lake Tahoe).”

Last week Kent, a former South Lake Tahoe resident and 1980 graduate of South Tahoe High School, returned to Tahoe to spend five days on Lake Tahoe, taking images of the lake bottom and plotting the sedimentary layers and fault lines. The research was done only on a small portion of the lake starting at the Tahoe City Marina and heading east.

“We’re trying to learn the history of the lake and what’s developing,” Kent said. “All we can pretty much say is that in the geologic recent past, there’s been a lot of activity just near the Tahoe City Marina.”

And recent in geological terms can mean anywhere from several hundred to a few thousand years ago.

Kent says his research is preliminary.

“The more we can go and image the sub-bottom, the better chance we have of learning how the Basin was formed,” he said. “And, the more you know, the better idea you have of what type of hazards exist.”

According to Kent, the Lake Tahoe Basin was formed through a series of faulting and landslides. The floor of the lake is made up of sediment and volcanic rock.

“There are roughly flat layers (of sediment) and then suddenly, layers are at a high angle. This marks a fault line,” Kent said. “Sometimes it’s just a small displacement and sometimes it’s a mess. There are quite a number of faults.”

These sudden, steep angles in the basin floor are the result of basin formation and block sliding.

“You need some kind of tectonic force to get these flat beds to dip,” he said.

If the faulting on the lake bottom was really old, geologically speaking, than lake sediment would have filled in the dips and curves in the floor to make a more even basin bottom.

“You’d get present-day sediment filling in the holes,” Kent said. “It’s very recent and ongoing stuff down there.”

The technology Kent used to explore the lake bottom and plot up to 25 meters deep of subterranean earth is similar to a sonogram. A sonogram is a visual image of a pregnant woman’s fetus produced by reflected sound waves during an ultrasound examination.

“It sends out a chirp signal. We record the seismic waves and then plot it up,” Kent said. “It’s a broad-ban chirp which is a super, duper high resolution system.”

This high-resolution research will help scientists further understand the development of the Basin and will allow engineers to factor in the faulting and landslide pattern for mitigation purposes during building construction.

“This is just preliminary stuff,” Kent said. “We’re not in the business of predicting earthquakes. How big or how often is something we just don’t know yet.”

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