North County has all the natural elements needed to produce a tsunami -- unstable geology and miles and miles of low-lying, unprotected coastline.

But it has done little to prepare for the destructive wave.

"We have millions of people living next to the coastline, and the awareness is close to nil," said Richard Eisner, manager of the state's earthquake program for the Governor's Office of Emergency Services.

"In some ways," he said, "with the fear of terrorism, we have forgotten about natural disasters, like earthquakes and tsunamis, which are a real problem and pose a very significant threat."

Jose Borrero, a research professor at the Tsunami Research Group at the University of Southern California, agrees.

"Tsunamis may not be as significant a risk as earthquakes, but they are something we are completely unprepared for," Borrero said. "We have such a high population density along the coast that if something did happen, it could be very costly."

And just because there is no evidence of a major tsunami ever occurring from La Jolla to Oceanside doesn't mean it will never happen.

"There is no way to quantify the risk, because we have had records in California for only one 300-year period," said Borrero, who notes that historical research is helping scientists analyze the frequency of tsunamis and their relationship to large earthquakes.

"Turkey and Japan have thousands of years of records, but we have nothing like that here," he said. "We can't predict tsunamis any more than we can predict earthquakes, but we can say with certainty that it will happen. Like with earthquakes, it's not a matter of 'if,' but of 'when.' "

In fact, experts at the National Oceanic and Atmospheric Administration predict that sooner or later, a tsunami will strike every coastline in the Pacific. And since 1945, according to the Federal Emergency Management Association, more people have been killed around the world as a result of tsunamis than have died as a direct result of an earthquake's ground-shaking.

But whatever you do, don't call it a tidal wave.

A misnomer

"The term 'tidal wave' is a misnomer," Eisner said, because the tide does not affect it and tsunamis are not generated by the gravitational pull of the moon or sun, as with tides.

Tsunami means "harbor wave," and that is not really quite right, either, as they occur along the coastlines and not just in harbors. It is thought that the term may come from the fact that a tsunami can speed silently and undetected across the open ocean, then unexpectedly rise in shallow coastal areas.

"A better description would be a seismically generated extreme tide," Eisner said.

An earthquake occurring near or underneath the ocean usually produces a tsunami. Less frequently, they may also be triggered by a volcanic eruption, meteorite impact or underwater landslide.

For the last five years, a team of scientists from the world-renowned Scripps Institution of Oceanography in La Jolla has been working at Lake Tahoe. Using the latest underwater techniques and equipment, the scientists have been able to calculate the slip rate for the normal faults underneath the lake and conclude that a tsunami is likely to occur every 3,000 years on Lake Tahoe.

"You can model all you want, but until you have determined the slip rate (movement or displacement along the fault line), you cannot assess the hazard," said Graham Kent, a research geophysicist at Scripps and director of the Visualization Center.

Fresh from their success in Tahoe, Kent and his team are now focusing their efforts on the Southern California coastline -- to determine the likelihood of an underwater earthquake causing a tsunami here.

"We want to calculate the slip rates here like we did in Tahoe," Kent said. "We have been able to get beautiful underwater photos of the Rose Canyon fault that may help us date the offset layers. But since Rose Canyon is a strike-slip fault and runs through relatively shallow water, the likelihood is not great of it offsetting the seafloor and generating a large tsunami." With a strike-slip fault, one slab of the planet's crust slides past another slab.

"In Southern California," he said, "it would be more likely that an earthquake would trigger an underwater landslide that might, in turn, cause a tsunami or another fault further out at sea."

In any case, the Hollywood image of a massive wave, cresting at the horizon, curling and breaking over skyscrapers is completely wrong, Eisner insists.

"They are not unlike what you might call a 'sneaker wave,' " he explains. "Even in shallow water, they have a lot of power, and it is surprising how easy it is to lose your footing. The difference is the velocity of these waves. Like a swift flood, you can't outrun them."

Experts say that on the open ocean, a tsunami wave can travel faster than 500 mph, faster than many commercial jets.

Also telling is the reach of these waves. Tsunamis can cause destruction over a wide area -- particularly in low-lying areas. But unlike floods and hurricanes, tsunamis are not seasonal and do not occur regularly or frequently.

While nothing can be done to prevent them, experts say, loss of life and property can be reduced with proper planning.

A national effort

In 1965, the International Tsunami Information Center was established to develop relationships with research centers and improve preparedness for all Pacific Ocean nations. But it was not until 1992, Eisner said, that numerous factors converged at the national level to bring the message home.

There had been a tsunami in the Aleutian Islands (near Alaska), and a warning was issued in Hawaii. When no wave arrived, there were considerable business losses.

Then, in April 1992, a magnitude-7.1 earthquake at the southern end of the Cascadian subduction zone generated a small tsunami near Cape Mendocino in Northern California within 15 minutes of the quake. All of a sudden, the notion that a tsunami is an event that is six hours away and can be prepared for was scratched.

"We now know that we can have these near-shore events where we wouldn't have so much as a few minutes' warning," Eisner said. "Planning for such an event is much more problematic."

In the early 1990s, under the leadership of Sen. Mark Hatfield of Oregon, Congress passed legislation establishing the National Tsunami Hazard Mitigation Program, and all five Pacific states (Washington, Oregon, California, Hawaii and Alaska) set about completing inundation maps for every coastal community at risk -- that is about 3 million people in 512 U.S. cities and towns, according to the NOAA.

"The initial funding was about $2.3 million a year for five to six years," Eisner said. "Oregon got a mapping center, and a million dollars went to buoys which would confirm the generation of tsunamis in the mid-Pacific," he added. "Much of California's funding went to pay for the mapping effort."

Then, in 1997, the USC Tsunami research team, under the direction of Costas Synolakis, was selected to produce inundation projections for coastal areas in California, including San Diego County -- from Coronado to Camp Pendleton.

Mapping the threat

"In San Diego, where you have built in close proximity to the coastline, winter storms and storm surges are real problems," Eisner said. "A tsunami would replicate the same sort of hazards. You could have coastal inundations even with a small tsunami, if it were at high tide."

The maps show how far inland tsunami flooding might reach, and clarify the threat of tsunamis along the coast of California. North County has many lagoons and low-lying coastal areas that would be at risk from flooding.

At-risk communities are those within 1 kilometer, or six-tenths of a mile, from the coast. Starting with Oceanside and working south, much of Oceanside Harbor, the mouth of the San Luis Rey River, from the ocean to Interstate 5 and a small area just south of Oceanside Boulevard where the Loma Alta Creek opens at the ocean may be flooded in the event of a tsunami.

All the low-lying areas around the region's lagoons -- Buena Vista, Agua Hediona, Batiquitos and San Elijo -- also would be affected.

In Del Mar, the area around the racetrack and extending east of the freeway would be flooded, as would the low-lying lagoon from the ocean at Torrey Pines Reserve, just south of where Carmel Valley Road hits the beach, eastward to the freeway.

According to the NOAA, thousands of people are at risk in North County, including 8,936 people in south Camp Pendleton; 21,824 in Carlsbad; 7,710 in Del Mar; 19,593 in Encinitas; 25,242 in Oceanside; and 6,824 in Solana Beach.

"The mapping for San Diego County is complete," Borrero said. "It was one of the first ones we did. We still have to do the final line for Orange County, and then we are moving up to Northern California where tsunamis are a larger threat. But the population was greater in Southern California, so that is where we started."

Eisner said the inundation maps have been distributed to many coastal communities. State officials also have met with local communities to help them develop a tsunami response plan. Finally, he said, state and county offices of emergency services have worked to raise awareness of the risk by helping local populations learn the signs of impending tsunami hazards.

Tom Gallup, a management analyst with the Encinitas Fire Department, said that according to his city's maps, there are two areas in Encinitas that are particularly vulnerable to tsunamis: Moonlight Beach and Restaurant Row in Cardiff.

"A tsunami could potentially damage over 300 structures in the city based on a recent risk assessment," he said, "but with the new data by USC and OES, emergency planners in Encinitas have a greater understanding of where it will be necessary to evacuate residents, and luckily, both the locations mentioned are situated near major thoroughfares (Encinitas Boulevard and Coast Highway 101)."

Close to home

In the case of a remote tsunami, communities may have hours to prepare for evacuation. For example, a tsunami from northern Japan would take 10 hours to reach Neah Bay in Washington or Crescent City in California. It would take 10 to 12 hours from Peru or Chile to reach Los Angeles.

In those cases, the county's Office of Emergency Services would activate its emergency operations center and warnings would be issued, explained Susan Asturias, senior emergency services coordinator for San Diego County. Residents would receive orders to evacuate through the Emergency Alert System (television and radio) and from local law enforcement using bullhorns.

"We encourage residents and business owners next to the coast to purchase a NOAA weather radio that sounds an immediate alert when there is a tsunami watch or warning issued by the National Weather Service," Gallup said.

Asturias points out that if a warning were issued, local law enforcement agencies and the San Diego County Sheriff's Department would implement their evacuation plans as needed.

But when an underwater earthquake or submarine landslide occurs nearby, the first tsunami waves may reach coastal communities within a matter of minutes. In those cases, experts note, local residents must be able to recognize the signs of impending tsunami hazards.

"Every foot inland or upward can make a difference," Asturias said. "Especially if you are on the beach, and you feel an earthquake so strong it is hard to stand up. Get away from the area -- either 100 feet above sea level or 2 miles inland."

Tsunamis do's and don't's

1. Not all earthquakes cause tsunamis, but many do. When you hear that an earthquake has occurred, stand by for a tsunami emergency.

2. An earthquake in your area is a natural tsunami warning. Do not stay in low-lying coastal areas after a strong earthquake has been felt.

3. A tsunami is not a single wave, but a series of waves. Often, the first wave is not the largest, and later, waves may be more dangerous because of the debris in the water. Stay out of danger until a competent authority issues an "all clear."

4. Approaching tsunamis are sometimes preceded by a noticeable rise or fall of coastal water. This is nature's tsunami warning and should be heeded. They can occur day or night and any time of the year.

5. A small tsunami at one point on the shore can be extremely large a few miles away. Don't let the modest size of one make you lose respect for all.

6. The West Coast-Alaska Warning Center does not issue false alarms. When a warning is issued, a tsunami exists. The tsunami of May 1960 killed 61 people in Hilo, Hawaii, and they thought it was "just another false alarm."

7. All tsunamis, as with hurricanes, are potentially dangerous, though they may not damage every coastline when they strike.

8. Never go down to the shore to watch for a tsunami. When you can see the wave, you are too close to escape it. You cannot outrun a tsunami, and never try to surf one; tsunamis do not curl or break like surfing waves.

9. Tsunamis can travel up rivers and streams that lead to the ocean.

10. During a tsunami emergency, your local civil defense, police and other emergency organizations will try to save your life. Give them your fullest cooperation.

(Issued by the International Tsunami Information Center, Hawaii (revised October 2003))