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Haiti, Jamaica at greater tsunami risk than previously thought, study finds

Study finds that quakes occurring on faults not previously believed to often produce tsunamis can in fact do so, report says. Experts say coastal California needs to be better prepared.

October 12, 2010|By Rong-Gong Lin II, Los Angeles Times

Haiti and Jamaica are at greater risk for destructive tsunamis than previously believed, according to a new study of tsunamis generated during the catastrophic Haiti earthquake in January.

The study, published online Sunday in the journal Nature Geoscience, raises troubling questions about the possibility of high death tolls should Jamaica be hit by a large earthquake, which could cause populated coastal areas to collapse into the Caribbean Sea and trigger tsunamis that would rebound back to shore.

John Orcutt, geophysics professor at Scripps Institution of Oceanography at UC San Diego, who was not involved in the study, said the report is a reminder that people on beaches or living near the coastline during a quake should be aware of the dangers of tsunamis.

After a quake, "If you live along the coastline, you want to be thinking about the potential tsunami hazard and get a couple hundred yards — a couple football fields up — just to make sure you're not going to be in an area that's inundated," Orcutt said.

He said even a 3-foot-high tsunami could bring in a wall of water moving at 40 mph. "It's nothing to mess with," he said. "It's like being hit by a car."

Costas Synolakis, director of the Tsunami Research Center at USC, who also was not involved in the study, said Californians need to be better prepared. "The lesson here is, we really need to prepare for this," Synolakis said. "Even if they are rare events, they are high impact events."

Matthew Hornbach, a research associate at the University of Texas Institute for Geophysics, said the study helps explain what was observed during the magnitude 7 or 8 earthquake that hit Port Royal in Jamaica in 1692, destroying the hub of British colonial interests in the Caribbean. Jamaica and Haiti both lie on top of the Enriquillo-Plantain Garden fault.

"During that event, a large chunk of Port Royal sunk into the ocean, and it also experienced a couple of tsunamis," Hornbach said. "It basically devastated the British Empire in the Caribbean for a while.... A lot of people drowned," he said, some because their houses sank below sea level and others because tsunamis pushed walls of water inland.

"They found bodies floating in the water for days," Hornbach said.

Much of the city sank into the sea. Much of the city sank into the sea. The toll was placed at 2,000 dead, but authorities at the time did not include slaves in their count.

The study was conducted to explain a mystery that popped up after the Haiti earthquake: Why were there so many reports of tsunamis in a region that wasn't supposed to have many?

Hornbach said scientists had long expected tsunamis to occur from earthquakes generated from "subduction zones," in which one tectonic plate slides under another. Such earthquakes push up the seafloor, moving water up and resulting in tsunamis.

But the Haiti quake occurred on a fault where one plate pushes past the other and doesn't significantly push up the seafloor. Scientists had long believed those faults don't often cause tsunamis.

But what Hornbach's team found during a visit to Haiti in February and March was that the Jan. 12 quake caused the collapse of both coastal land and underwater sediment.

It was those landslides — both above and under water — that triggered tsunamis that rebounded onto sparsely populated coastal areas of Haiti, killing at least three people and wiping out several homes.

For example, near the town of Grand Goave, a chunk of shoreline the size of several football fields sank near where a tsunami roared ashore.

The study published Sunday was a collaboration of the University of Texas, the City University of New York, the U.S. Geological Survey, the University of Missouri, the Haitian Bureau of Mines and Energy, the Universite d'Etat de Haiti and UC Santa Barbara.

ron.lin@latimes.com

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