Experts say another major earthquake in Haiti unlikely

MIAMI — Does another “Big One” loom over Haiti?

The question came up Wednesday after a magnitude 5.9 aftershock struck 35 miles outside of Port-au-Prince — eight days after a major earthquake shattered the city.

Another major quake is unlikely but possible, experts say.

“It’s really hard to predict,” said Brady Cox, assistant professor of civil engineering at University of Arkansas. “Any time there’s a large quake it causes significant stress redistribution along earthquake fault lines. It relieves stress in some areas and increases it in others.”

“There’s a natural progression of aftershocks,” says Dr. Paul Mann, a geologist with the Jackson School of Geosciences at the University of Texas. “The general trend is for them to become smaller over time.”

On the Richter scale, a magnitude 5.9 quake like Wednesday’s is considered “strong,” with light damage expected. Still, on the mathematically complex scale that measures earthquakes, even a 6.0-magnitude quake would have only 1/30th the destructive power of a 7.0 quake.

Wednesday’s aftershock was centered 6.2 miles below the Earth’s surface; the big quake a week ago was centered 8.1 miles down. Quakes closer to the surface do more damage, experts say.

“To a building already damaged by the earlier quake, it could be a very serious thing,” said Tim Dixon, professor of geophysics at the Rosenstiel School of Marine and Atmospheric Science in Miami.

Wednesday’s tremor wasn’t the first strong aftershock. Since the big quake, the area around Haiti has had 44 aftershocks measuring 4.1 to 5.9, according to the United States Geological Survey.

Wednesday’s 5.9-magnitude aftershock was bigger than expected, but not too far out of line, Dixon said.

In Haiti and the Caribbean, the original earthquake and the aftershocks are taking place along the Enriquillo Fault Zone that starts in Jamaica in the west and goes through Haiti and into the Enriquillo Valley in the Dominican Republic. It’s part of the ever-shifting boundary between the massive North American and Caribbean tectonic plates.

The Enriquillo zone is 600 miles long. Last week’s earthquake near Port-au-Prince ruptured only about 50 miles of that fault line, increasing the stress on the portions remaining unruptured, Dixon said.

Still, most of the current aftershocks are in the part of the Enriquillo line that slipped in last week’s big quake, not in areas outside it.

“They’re just stress being redistributed along the line that already slipped,” he said.

Most of the 44 aftershocks have taken place to the west of the original earthquake, he said, because the original quake was created by a slipping of the plates in a westerly direction.

The aftershocks may continue, but they’re unlikely to be as big as Wednesday’s, Dixon said.

He said the 5.8-magnitude quake that rattled the Cayman Islands on Tuesday was not directly related to the Port-au-Prince quake. It’s on the same North American/Caribbean tectonic plate boundary, but not on the same fault line, he said.

Still, another big quake is possible, Cox said. He said two major separate quakes struck Turkey, both within 100 miles of Istanbul, within three months of each other in 1999.

A 7.4-magnitude quake hit near Istanbul on Aug. 17, 1999, killing 17,000, followed by a 7.2-magnitude quake on Nov. 12 that killed 1,000.

Geologists said the second quake was not an aftershock, but a separate seismic event on the same Anatolian Fault Line.

“These things are unpredictable” Cox said.

This article originally appeared in The Miami Herald and was distributed by McClatchy-Tribune

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