REPORT RAISES DOUBTS PROPOSED AUBURN DAM WOULD WEATHER QUAKE.

Byline: Kimberly A. Moy Scripps-McClatchy Western Service

Just a week before an Auburn dam proposal is expected to be introduced in Congress, a U.S. Geological Survey report raises questions about whether a quake-proof dam can be built at the American River site.

The development Wednesday provides new fodder for environmentalists fighting to kill plans for a $1 billion project that could inundate miles of pristine American River canyons to provide regional flood protection and eventually water supply.

The new USGS report said a 17-year-old study of earthquake hazards at the proposed Auburn dam site should be updated - including recalculations of ground slippage estimates - before a final engineering design is approved.

The current Auburn dam plan calls for withstanding 9 inches of ground movement, but a new look at data may show that displacement could be greater, said geologist David Schwartz, lead author of the USGS report.

"We feel that in a re-evaluation, displacement could be larger," Schwartz said. "No one can say at this point in time how much. . . . We don't know if it's 10 inches, 12 inches or 20 inches."

An accurate estimate of maximum ground movement is vital to building a dam that won't crumble in an earthquake.

Auburn dam opponents plan to use the USGS report to lobby against the project in Congress, where legislation is expected to be introduced by Rep. John Doolittle, R-Calif., next week.

But Doolittle and other Auburn dam advocates continue to assert that a quake-proof dam can be built. They said an updated seismic study would simply help fine-tune dam designs, but shouldn't hurt the drive for a flood-control Auburn dam that could be expanded later into a multipurpose facility that permanently holds water.

"Congressman Doolittle wants to ensure that when we do construct a dam, we build a safe one," said Bill Mueller, Doolittle spokesman. He said the proposed one-year USGS study could run at the same time Sacramento-area representatives are seeking congressional approval for the dam.

A spokesman for Rep. Bob Matsui, D-Calif., agreed, saying the USGS report raises issues addressed previously and just asks for updated analysis.

Dam opponents, however, say Congress shouldn't authorize a dam until they have all the facts on its earthquake hazards.

"Congressman Doolittle has been telling us for years that seismic safety concerns were resolved 20 years ago," said Ron Stork, conservation director of Friends of the River. "That is clearly not the case."

David Conrad of the National Wildlife Federation said the USGS report weakens the dam's chances, because Congress is unlikely to support a $1 billion project "without having seismic issues well worked out in advance."

UC Berkeley Professor Gregory Fenves, an expert on earthquake behavior of concrete dams, said that a quake-proof dam can be built to handle ground slippage of up to 12 inches.

"Certainly if it's over 2 feet, you don't want a concrete structure," Fenves said. "Anything in between requires much more careful design. . . . It's not impossible, but it becomes more expensive and you need more careful validation."

Vern Perssons, state chief of dam safety, said that he thinks the Auburn dam design set in 1979 is adequate, but that a new USGS analysis would "set aside comments of people opposed to it."

Estimates of ground slippage from an earthquake have been controversial since a 6.5 magnitude earthquake hit Oroville in 1975 and halted construction of the original Auburn dam.

The proposed new Auburn dam site has been moved 800 feet downstream to avoid crossing an active fault line. That fault line has a 1-in-1,000 chance of a major quake in the next 50 to 100 years, according to Robert D. Brown, a former USGS geologist who studied the original Auburn dam site.

Earthquake theories have changed and new seismic data have been collected since design standards for an Auburn dam were set 17 years ago.

While estimates of maximum ground slippage could rise with a new study, USGS geologists expect the size of a maximum earthquake in the area would remain at 6.5 magnitude.

The theory that pressure from water stored behind a dam triggers earthquakes needs further study, Schwartz said. Engineers believe that reservoir-induced seismicity does not cause earthquakes, but just speeds up when they would occur naturally.

Auburn residents like Gary Estes, however, argue a dam that could trigger an earthquake shouldn't be built. Older buildings in Auburn need retrofitting to hold up during a temblor, he said.