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Scientist: Myrtle Beach area tsunami likely not in the cards

Living near the ocean, and within 90 miles of a nuclear reactor, it's only natural to wonder if the area could face the devastation and nuclear danger now confronting Japan.

Good news, Grand Strand: The chances are slim.

Scientists who study earthquakes and tsunamis say the most likely worst-case scenario for the Grand Strand would be a 9.0 quake in the Puerto Rico Trench, a 500-mile long undersea gash in the earth that lies southeast of us. Its lowest point is 28,232 feet - nearly as deep as Mt. Everest is high.

If that were to happen, northeastern South Carolina would likely see a 6-foot tsunami within four to five hours.

"There wouldn't be mass evacuations," said Horry County Emergency Services Director Randy Webster, "but we would have to get everyone off the beach."

He said most of the Grand Strand is far enough above sea level that beachgoers would simply have to move 300 yards from the water line. In Myrtle Beach, that means crossing Ocean Boulevard.

Or people could go up to the second and third floors of oceanfront buildings, he said.

Much of Ocean Boulevard in Myrtle Beach is 10 to 11 feet above sea level, Webster said, and the Myrtle Beach International Airport is 22 to 27 feet above sea level, even though it's only a mile from shore. Low spots along the Grand Strand include Garden City Beach and Cherry Grove.

Of course if that worst-case tsunami happened in the middle of tourist season, Webster said, four or five hours' warning wouldn't seem long at all. Emergency personnel would have to go to the beaches and herd people off, because there are no audible tsunami sirens here.

"People wouldn't know what they were," he said. "How would you educate everyone who visits here what the tsunami alarm would be? It would just sound like a siren."

Tsunamis don't require a certain size to be so labeled. It's their origin that earns them the Japanese name "tsunami," which means "harbor wave." Tsunamis come from sudden displacements in the sea floor, landslides or volcanic activity.

Steven Jaume, an earthquake expert and associate professor at College of Charleston who works with the college's S.C. Earthquake Education and Preparedness Program, said the kinds of earthquakes that cause tsunamis happen much less often in the Atlantic Ocean than in the Pacific and Indian oceans, but they have happened.

In 1755, a quake off the coast of Portugal spawned a tidal wave that was recorded on tidal gauges from Canada to the Caribbean, Jaume said. It was less than a foot high on the East Coast.

Tsunami-spawning quakes are so much less common in the Atlantic than in the Pacific and Indian oceans that the Atlantic didn't even have the National Oceanic and Atmospheric Administration's Deep Ocean Assessment and Reporting of Tsunami buoys until after the devastating Indonesian quake and tidal wave in 2004, Jaume said. Now all oceans have them and they are monitored by Tsunami Warning Centers worldwide.

The other kind of earthquakes - the kind that do their damage mainly on land - don't happen often along the Grand Strand, either.

U.S. Geologic Survey maps for S.C. don't show any notable quakes centered here at all.

State Geologist C. W. Clendenin could not be reached for comment, but Jaume said there are not even any seismometers in Horry County, said, because quakes so rarely happen here. There are also no identified earthquake faults in this area that he is aware of, he said.

Jaume said some of the state's faults could be "blind," meaning they have been buried by sediment from the ocean and rivers. But that also means they are not as active as the faults in other states that can be seen and identified, because sediment fill-in takes a long time.

The Earthscope Project has been moving its U.S. Array of seismometers across the entire United States over a 10-year period, and Horry County is scheduled to receive one seismometer for 18 months in 2012 or 2013, and scientists will then have a better idea of how often the ground shakes here.

Charleston faced a huge quake in 1886, a 7.3 on the Richter scale that killed 60 people and was felt over 2.5 million square miles, from Cuba to New York, and Bermuda to the Mississippi. Structural damage extended several hundreds of miles to cities in Alabama, Ohio and Kentucky, according to the Earthquake Education and Preparedness Program. It was the biggest temblor ever recorded on the East Coast.

Jaume said scientists still do not know precisely which fault caused that quake.

That earthquake factored into the design of Progress Energy's nuclear power plant in Brunswick County, N.C., said company spokesman Ryan Mosier.

He couldn't say exactly how the design allows for the unlikely event of a major earthquake on or off the East Coast or a tsunami that could cause nuclear plant problems such as those now affecting some Japanese nuclear power plants.

But like the Japanese plants, Mosier said the Brunswick plant has redundant systems to keep it safe should its main power source be cut.

Even though a large tsunami or earthquake on the Grand Strand isn't a major concern, hurricanes are, and Mosier said the plant was designed to withstand very high winds. He didn't know the maximum wind tolerance, though.

He said flooding has not been a problem at the plant, which opened in 1975.

The plant's safety plan includes issuing iodine tablets to residents within a certain radius of the plant. A system of horns is placed near the plant to warn of any significant problems that might occur.

Webster said Horry County is considered "storm ready" and "tsunami-ready" by the National Oceanic and Atmospheric Administration. The county is updating its flooding inundation maps for hurricanes, but Webster said those likely won't apply in a tsunami.

"In a hurricane, you have the storm surge and wind-driven waves, which can reach astronomical heights," he said. "In a tsunami, it's just the rise in water without the wind driving it. But we just don't have any models that will show us what could happen in a tsunami."

Staff writer Steve Jones contributed to this report.

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