NORTH COUNTY -- Although it is highly unlikely, a smaller, locally generated version of the tsunami that devastated South Asian countries Sunday could occur along coastal San Diego County, geologists say.

An earthquake with a magnitude above seven in the San Clemente fault zone 50 miles southwest of Point Loma could produce a rapid 5- to 10-foot rise in sea level, according to Mark Legg, a geologist in Huntington Beach. The wave would take just 20 minutes to arrive at the coast from its origin, too fast for an official warning from the state Office of Emergency Services.

"It wouldn't be like 5-foot surf," Legg said Monday. "It's a 6-foot surge that would sweep away cars and debris."

The historical record of tsunamis hitting Southern California is sketchy. A 1927 earthquake near Lompoc produced a 5- to 6-foot tsunami that hit the coast near San Luis Obispo, and an earthquake near Santa Barbara in 1812 also caused a tsunami, according to a University of California, Santa Barbara website.

The largest sudden rise in sea level ever recorded in the San Diego area was 3.5 feet at Scripps Institution of Oceanography pier in 1960, caused by a magnitude 9.5 earthquake in Chile, the strongest ever recorded. Sunday's earthquake caused the sea level to fluctuate almost a foot in San Diego and nearly 9 feet in one city on the Mexican west coast, according to the Pacific Tsunami Warning Center.

To protect against such surges, the National Oceanic and Atmospheric Administration of the National Weather Service placed buoys attached to sensors on the ocean floor in the early 1990s to track tsunami activity off the west coasts of North and South America.

There are three buoys off the Aleutian Islands and one each off Oregon, Washington and South America, the areas most likely to have tsunami activity first, said Willard Lewis, assistant director of the San Diego County Office of Emergency Services.

The state Department of Water Resources and the Office of Emergency Services developed dam inundation maps showing where tsunami waters would flow as they followed local water ways.

In the event of a tsunami, residents would be alerted and warned by the county through the Emergency Alert System on radio and television, Lewis said. The county would staff its emergency operations center in Clairemont Mesa to help cities affected, he said.

But anything as massive as the Asian tsunami would have lifeguards doing all they could to save themselves, said Chief Ray Duncan of the Oceanside Lifeguard Service.

"We would be most vulnerable at the San Luis Rey River, Loma Alta Creek at Buccaneer Beach, and Buena Vista Lagoon leading to the large (Westfield Shoppingtown) mall," said Ray. "We have houses (rather than) bluffs (along the beach). If something was big enough, it would go right over Pacific Street (just above the beach), possibly (up to two miles) to Interstate 5."

The lifeguards have had indoor drills aimed at dealing with the effects of tsunamis. Coastal fire officials also said they have plans to try to cope with tsunamis.

There have been tsunami watches along the county's coast infrequently in the past, but nothing significant has happened in recent memory, authorities said.

The problem in this county, officials said, is trying to convince people to stay away from the beach when big waves are expected because everyone wants to see them, officials said.

"We actually had people expecting the big one, and we had people going out on surfboards and down to the beach to watch this," said Encinitas Fire Chief Don Heiser. "We can evacuate people. We can warn people. Bottom line is people need to be responsible for their own safety."

The bluffs in the Encinitas area will provide some protection, but people need to have an emergency preparedness kit with them that will allow them to survive for 72 hours without help from authorities, Heiser said.

"At times we have gone out into the low-lying areas and tried to get people out of (the way of high waves)," said Carlsbad Battalion Chief Rick Fisher. "They don't pay any attention."

Three lagoons -- Buena Vista, Agua Hedionda and Batiquitos -- would be the low-lying danger points for tsunamis along the Carlsbad coast, Fisher said.

He said two of the city's fire stations might be threatened in the coastal area. After warning residents, firefighters would have to get their rigs to higher ground.

"We can't help anybody if we lose our equipment," Fisher said.

When it comes to tsunamis along the San Diego County coast, the San Clemente and San Diego Trough fault systems are the nearest active earthquake sources. They are strike-slip faults, where the two plates move past each other mostly horizontally.

Geologists have classified subduction zones -- places where one plate dives down below another -- as more dangerous for generating tsunamis than strike-slip faults. The massive earthquake Sunday came from a spot in the middle of the Indian Ocean where the India plate plunges under the Burma plate.

"You need the up and down motion of the sea floor to generate the tsunami," Legg said.

In a 2002 report to the United States Geological Survey, Legg argued that bends in the faults along the Southern California coast that restrain the plates from moving horizontally could generate seafloor uplift. Investigation of the seafloor in the San Clemente fault zone with the scientific submarine Alvin shows scarps, or cliffs, that are probably less than 1,000 years old that came after earthquakes, said Legg, an adjunct professor at San Diego State.

In a worst-case scenario, an earthquake could trigger an underwater landslide that would amplify the tsunami generated by the original earthquake, said Chris Goldfinger, a marine geologist at Oregon State University.

New York Times news services contributed to this article.

Contact staff writer Quinn Eastman at (760) 740-5412 or qeastman@nctimes.com. Contact staff writer Jo Moreland at (760) 740-3524 or jmoreland@nctimes.com.