President Bush's call to lift restrictions on offshore drilling, including off the San Diego County coast, is raising the specter that a powerful earthquake might trigger an oil spill on the order of the 1969 Santa Barbara disaster.

Neal Driscoll, a geology professor at UC San Diego's Scripps Institution of Oceanography and an Escondido resident, said in an interview this week that perhaps the biggest threat is that a quake would set in motion a fast-moving landslide along the sea floor -- essentially, an underwater avalanche -- that would rip up wells and drilling equipment.

"There is great concern for underwater infrastructure if a landslide were to occur," Driscoll said.

The Santa Barbara quake of four decades ago left an 800-square-mile oil slick on the Pacific Ocean, fouling 35 miles of beaches, clogging the blowholes of dolphins and soaking diving birds with tar.

The spill of 200,000 gallons of crude wasn't the result of an earthquake, but rather a buildup of natural gas pressure that caused an oil well on the sea floor to burst.

However, the presence of three fault zones in an underwater basin stretching from La Jolla to Dana Point means offshore drilling would introduce at least the threat of an earthquake-induced spill, scientists say.

Industry representatives say the threat would be minor because drilling technology has advanced much in a generation and wells shut down immediately when there are accidents, blocking potential spills.

They also stress that oil companies have managed to operate in earthquake country for decades without a shaker triggering an offshore spill in Southern California.

Driscoll said the 1929 Grand Banks earthquake along the Atlantic coast of Canada provided a vivid picture of what can happen. In that magnitude-7.2 temblor, a submarine landslide knocked out many miles of telephone and telegraph cables.

Driscoll said that drilling also would invoke the potential for a shaker to sever an underwater pipeline at a place where it crosses a fault.

It's automatic

On the other hand, Iraj Ershaghi, professor of petroleum engineering at the University of Southern California, said technology has improved since 1969, and that oil-drilling facilities, much like Southern California buildings, are designed to withstand the force of earthquakes.

Ershaghi said the modern well is designed to halt release of oil in the event of a quake or accident.

"If something goes wrong, it shuts down automatically," he said.

According to the U.S. Interior Department's Minerals Management Service, about 11 billion barrels of oil could be mined from the sea along the West Coast, including 1 billion barrels off the coast of North County. To place that in perspective, the federal Energy Information Administration estimates that the United States consumes 7.5 billion barrels a year.

Three faults cross the North County offshore basin, including the Rose Canyon fault that is nearest the coastline. Rose Canyon runs in a northwestward track parallel to the coast at Oceanside, Carlsbad and Encinitas, migrating offshore at La Jolla and swinging back onshore at Newport Beach.

Running parallel to the Rose Canyon, the Coronado Bank fault is a little farther out and the San Diego Trough fault is farther still. Just beyond the oil basin lies the San Clemente fault that runs to the west of Santa Catalina Island.

The faults are capable of generating an earthquake of greater than magnitude 7. That is a huge amount of shaking capable of toppling buildings and freeways, and killing hundreds of people. The 1994 Northridge earthquake that rocked Los Angeles was measured at magnitude 6.7.

Faults a magnet for drilling

But while capable of producing the kind of quake that could destroy drilling equipment, the faults off North County are relatively quiet. They are far less active than the San Andreas and other faults well to the east in inland San Diego County and Riverside County.

Driscoll said along the San Andreas fault, the Pacific plate under the ocean and the North American plate under the continental shelf grind past each other at an average rate of 50 millimeters a year, and about 90 percent of that movement is accommodated along the San Andreas, San Jacinto and Elsinore faults.

Tom Rockwell, a San Diego State University geologist, said, "The likelihood of an earthquake is not high."

At the same time, it is not terribly unusual to find faults in oil drilling areas. Indeed, the prevailing trend is just the opposite.

"The entire coast of California has active faults along it," said Chris Wills, supervising engineering geologist for the California Geological Survey in Sacramento.

"Active tectonic plates and oil go together," Wills said, saying many of the best oil deposits tend to occur in fault zones.

Consequently, the industry prefers to drill in earthquake-prone regions and is familiar with the challenges of doing so.

"There are existing platforms in California offshore that have been there for many years and have great service records, even during earthquakes," said Andy Radford, policy adviser for the American Petroleum Institute in Washington, D.C.

Radford said offshore platforms are designed to weather earthquakes. And, if they don't, subsurface valves are designed to shut off the oil flow, he said.

Radford said that is what happened when rigs in the Gulf of Mexico were destroyed by Hurricane Katrina as it slammed into New Orleans. As a result, no major oil spills occurred during that enormous storm, Radford said.

A matter of when

Driscoll, Ershaghi and others said they were unaware of offshore spills in California having been triggered by earthquakes.

Still, earthquakes have triggered a few oil spills around the world in recent years.

In a March 2001 earthquake in Washington state, pipes sprung a leak of 600 gallons of gasoline and 700 gallons of diesel fuel on an island in the Seattle area and threatened to spill into Puget Sound, according to the Seattle Post-Intelligencer.

In August 1999, a massive 7.4 quake flattened major pieces of Turkey's largest refinery, along the shore, and spilled oil into Izmit Bay.

And the shaking of the Northridge quake of January 1994 ruptured a pipeline, spilling 190,000 gallons of oil -- nearly as much as in the Santa Barbara event -- along a 16-mile stretch of the Santa Clara River and killing fish, birds and other wildlife.

"Pipelines fail all the time," said Richard Charter, government relations consultant for the environmental group Defenders of Wildlife in Northern California.

And just because the drilling industry employs advanced technology does not mean an offshore oil rig won't fail, either, Charter said by telephone recently.

"The newer rigs tend to be pretty stringently engineered to withstand the maximum credible earthquake," he said.

But, he said, eventually a quake occurs on a scale that scientists had not counted on. And Charter said accidents plague even the most sophisticated equipment.

"It just seems like anything human beings build will, sooner or later, have some kind of failure," Charter said. "So, if we're going to play Russian roulette with the California coast, as some people in Congress seem to want to do, we might want to think twice because there inevitably are going to be adverse impacts. It is not a matter of if, it is a matter of when."

Contact staff writer Dave Downey at (760) 745-6611, Ext. 2623, or ddowney@nctimes.com.