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Monday, January 25, 2010

Deadly Haitian Quake in the Seismically Active Caribbean - NYTimes.com

Where's the next big quake going to be ? Not far from the last one:
But about 100 miles to the northeast is a long segment of a similar fault, the Septentrional, that has not had a quake in 800 years. Researchers have estimated that a rupture along that segment — and again, they have no idea when one might occur — could result in a magnitude 7.5 quake that could cause severe damage in the Dominican Republic’s second-largest city, Santiago, and the surrounding Cibao Valley, together home to several million people.

“You can imagine the strain that has accumulated there,” said Paul Mann, a senior research scientist at the University of Texas, referring to the Septentrional fault. “It’s been going on for longer and accumulating faster. Therefore it’s going to produce a stronger earthquake.” [...]

The recent quake on the Enriquillo fault and the forecast for the Septentrional are bleak reminders that the Caribbean is an active seismic zone, one with many hazards. Major earthquakes have regularly devastated the region’s cities, including the Jamaican capital, Kingston, which was destroyed twice in three centuries. An eruption of Mount PelĂ©e killed 30,000 people in Martinique in the Lesser Antilles in 1902, and it and other volcanoes are currently active along that island arc on the Caribbean’s north and eastern reaches. Earthquakes and landslides along the Puerto Rico Trench, an undersea fault zone, have the potential to cause tsunamis. [...]

Of some concern, researchers said, was that none of the aftershocks have occurred in the area of increased stress nearer to Port-au-Prince, where ordinarily some might have been expected.

“One possibility is that these are simply calculations, and they may be wrong,” Dr. Stein said. “The other possibility is, O.K., this fault is fundamentally locked in some fashion, on pretty much all scales, and might be capable of popping off something large.”

In its statement, the geological survey cautioned that near the capital, “the fault still stores sufficient strain to be released as a large, damaging earthquake during the lifetime of structures built during the reconstruction effort.” [...]

Dr. ten Brink’s main area of research is the Puerto Rico Trench, north of Puerto Rico and the United States Virgin Islands. This is a subduction zone — where the North American plate is sliding under the Caribbean, creating the potential for earthquakes and undersea landslides that can set off tsunamis.

“We’re trying to see if it’s a similar situation to the Sumatra fault,” Dr. ten Brink said, referring to the Indonesian subduction zone where a large earthquake in December 2004 created a tsunami that killed a quarter of a million people. Scientists have not yet found evidence of large subduction earthquakes on the Puerto Rican Trench, he said, “but that’s the $64,000 question.”

Because of the proximity of the trench to American territory, Dr. ten Brink and others have been able to obtain financing for their studies. But in other places around the Caribbean, research money has been hard to come by. [...]

Much of what is known about the seismic activity around Port-au-Prince has been gleaned from historical accounts of previous quakes. While far from precise, these accounts suggest a century-long, westward-marching sequence of quakes along the fault, beginning with one in 1751 in the Dominican Republic at the fault’s eastern end and including the 1770 earthquake that destroyed Port-au-Prince.

That raises the possibility that the Jan. 12 earthquake could be the beginning of a new sequence occurring over decades, with each successive quake redistributing stresses along the fault. “It’s certainly possible and it’s really something we’re very concerned about,” said Carol S. Prentice, a geologist with the geological survey in Menlo Park. Such sequences have been observed on other faults, including the North Anatolian in Turkey.

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