Studies show increased quake hazard in Reno-Carson region

Nevada Appeal News Service

New research suggests earthquake hazard at Lake Tahoe and in the Reno-Carson area is much higher than previous studies have shown.

"The Reno-Carson region has some of the most active faults in Nevada," said Feng Su of the University of Nevada, Reno Seismological Laboratory.

Feng, along with seismologists and geologists from around the world, presented her findings about earthquake hazard at the Seismological Society of America's annual meeting at the Hyatt Regency Resort, Spa and Casino in Incline Village this week.

Researchers who have spent the last five years studying seismological events at Lake Tahoe say new data shows evidence of three prehistoric magnitude 7 or higher earthquakes in the basin. This new evidence can help researchers present a more complete picture of seismic hazard in the region, said Gordon Seitz of San Diego State University.

Seitz and his colleague, Graham Kent of the Scripps Institution of Oceanography, spent last summer excavating the Incline Village fault, which runs straight through the village and behind the old Incline Elementary School.

In the past, the level of earthquake hazard in the Tahoe Basin has been underestimated because active faults are covered by the lake. Because the Incline Village fault also runs offshore, researchers were able to examine it for evidence of past earthquakes.

"I guess the mantra today is we're getting real numbers," Kent said. "By and large people still have the faults in the basin wrong."

Kent said it's possible that the three Lake Tahoe faults - the West Tahoe, North Tahoe/Stateline and Incline Village faults - are connected, and movement at one fault could trigger movement in another.

But an earthquake might be the least of Lake Tahoe residents' concerns, Kent said. If an earthquake hit the basin, current models predict that a 10 meter tsunami-like wave, or seiche, could form in the lake. The largest waves in the Indian Ocean Tsunami in December reached a height of 14 meters off the shore of Banda Ache, Indonesia, Kent said.

"(At Lake Tahoe) what will happen is you'd feel a long shaking event ... you'd see the water go out, then come back," Kent said. "It's not always one of those Hawaii Five-0 waves."

Robert Karlin, a professor of geology and geophysics at UNR, said Lake Washington in Seattle also has the potential for tsunami-like waves, but that the lake is not nearly as deep as Lake Tahoe. He said it's also difficult to tell whether a tsunami-like wave has ever occurred in the basin because storms and floods have washed away deposits that would have been left by a large wave.

Although Seitz said the Incline Village fault is probably not large enough to cause a tsunami-like wave, other faults in the basin are, and Incline would be in danger.

"If you live in Incline Village, the Incline Village fault is pretty small potatoes because it doesn't extend far enough offshore to get the tsunami event," Seitz said.

Though Kent and Seitz make no predictions about when earthquakes or tsunami-like waves might occur, they said they're hoping to continue researching other faults in the basin to fine-tune current earthquake hazard documents. Their data will be integrated into regional planning guidelines, Seitz said.

"The thing that will change is state agencies will have to consider rezoning," he said. "The state has a hazard plan, but it doesn't include this current data. It's happening, but the lag time could go on forever if the work isn't published."