Tahoe No Stranger to Quakes, Tsunamis

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The Lake Tahoe Basin is no stranger to fires, avalanches and snow, and a University of Nevada, Reno geology professor says earthquakes and tidal waves are not out of the question.

"The Lake Tahoe Basin is where the action is," according to Rich Schweikert.

Beneath the lake lie three active faults - a north-east one from along the north shore, another that stretches from north to west called the Tahoe-Sierra frontal fault zone, and a north-south fault that runs along the northwest shore north of Tahoe City.

Several earthquakes have been recorded in the Tahoe area. A 5.6 temblor shook Truckee in 1966 and a 4.9 quake hit north of Incline Village in 1998.

However, the three faults are capable of much stronger tremors. According to Schweikert, magnitude 7 seismic events occurred during the past 10,000 years in Tahoe, and could happen again.

"Scientists have a saying - if something happened in the past, it can happen in the future," he said in a talk to the Squaw Valley Institute.

The basin was formed 3.6 million years ago by fractures in the Earth's crust, causing blocks of land to move up or down.

Uplifted blocks created the Carson Range to the east and the Sierra Nevada to the west, while down-dropped blocks produced the great cavity in between. The basin was eventually filled by snow, rain and streams, forming a lake 120 feet deeper than its present level after lava eruptions dammed up the hole's outlets, Schweikert said. At the time, glaciers out of Alpine Meadows and Squaw Valley plugged up the Truckee River.

The effect of a strong quake on the lake would be enormous. Based on computer modeling done in Japan, Schweikert said that a magnitude 7 earthquake would produce tsunamis with waves up to 33 feet high with the largest waves hitting Sugar Pine Point, Rubicon Point, and the casinos in South Lake Tahoe.

Scientists have evidence of an even larger tsunami that struck McKinney Bay 7,000 years ago. The Blackwood Canyon glacier's 200-feet high moraines - accumulation of earth and stones deposited by a glacier - collapsed into the lake, generating giant waves that washed away the moraines and carved out a flat surface that is now Homewood and Tahoma.

However, Schweikert said that while the basin is sure to shake again some time in the future, in geological terms we are relatively safe.

"These are events that will happen in the future, but in our lifetimes or our grandchildren's the chances are relatively low."