Sometime within the last 60,000 years, scientists think an earthquake shattered the West Shore, sending humongous blocks of shoreline into the depths of Lake Tahoe.Photo:4266454,right;
"You can still see these city-block-sized chunks sitting at the bottom of the lake," said Glenn Biasi, a research seismologist at the University of Nevada, Reno, Seismological Laboratory.
Many of these chunks slid at least six miles out and 1,645 feet deep, coming to rest near the state line, which bisects the lake.
The chunks are visible in a detailed map of the lake's floor created in 1998 using sophisticated sonar technology. Until then, any clue of its bottom remained inaccessible to researchers.
Now, evidence of Tahoe's seismological past may provide clues to future activity.
Truckee's 4.8 earthquake on Sunday is the latest in recent activity over several years. Between August of 2003 and January 2004, an "earthquake swarm" rattled the Sierra with frequent, small temblors, then suddenly stopped. Turns out Slide Mountain under Mount Rose moved up and east about 3/8 of an inch.
Then, about a year ago on June 3, a similar-size earthquake struck northeast of Sunday's epicenter.
"It brings attention to the public that we do live in earthquake country," Biasi said.
The Sierra is moving half an inch a year relative to Central Nevada.
"Some of that half inch a year is distributed over a number of faults, or we'd have more earthquakes than we do," said Biasi.
At least one man said he saw it coming.
Jim Berkland says he's been predicting earthquakes since 1974 and predicted Sunday's quake would happen within an eight-day window.
A former geologist for the U.S. Geological Survey and Bureau of Land Reclamation, he says when the sun and moon line up - called a syzygy - it creates enough gravitational pull to trigger earthquakes.
The earthquake in Sumatra that triggered the devastating tsunami last December, the 1989 Loma Prieta earthquake and 1964 Southern Alaska earthquake, the largest recorded in North America, all happened on a full moon, he said.
But Biasi was a little skeptical, saying geologists are not trained to understand earthquakes, while seismology is a field of applied physics.
Science has yet to discover a proven method for predicting earthquakes.
"A lot of smart people have looked at this," said Biasi. "They've looked at the phases of the moon, and there seems to be a minor correlation with tides, but that's what it would be: minor. It's not a powerful predictor."
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