Haiti warned to brace for another big quake

By Mica Rosenberg:


PORT-AU-PRINCE, Haiti (Reuters) -- Haiti should be preparing for another major earthquake that could be triggered by the catastrophic one last month which killed up to 200,000 people and left the capital Port-au-Prince in ruins, experts say.

Teams of geophysicists, who have been tracking movements in the fault line that slashes across Haiti and into the Dominican Republic, came to the nation last week to measure changes in the Earth's crust after the 7.0-magnitude quake on January 12.

Increased pressure on the fault after the quake could unleash another of the same size or bigger, although scientists acknowledge they have no way of knowing exactly when or where it will hit.

"Faults are always waiting for the right moment but if another earthquake gives them a little kick they go before their time," said Eric Calais, a professor of geophysics from Purdue University in Indiana, who is leading the seismology project in Haiti.

Preliminary calculations by his group show the January 12 quake could be the "little kick" that sets off another temblor along the 186 mile fault where two regional tectonic plates have been scraping together for millions of years.

More than 50 aftershocks, including one measuring 5.9 magnitude, have shaken Port-au-Prince after last month's quake. The US Geological Survey says the aftershock sequence will continue for months, "if not years", and "damaging earthquakes will remain possible in the coming months".

Calais was due to take his findings to a meeting on Monday with President Rene Preval and the head of the United Nations mission in Haiti, in which he would stress the urgent need to rebuild the city's critical infrastructure safely and quickly.

Haiti's government has announced plans to relocate up to half a million homeless quake victims -- many now camped out in rubble-strewn streets -- in temporary villages outside of Port-au-Prince. But some experts suggest the whole capital should be rebuilt away from the dangerous fault line.

Calais was part of a group of experts who warned Haitian officials in 2008 that there could be a 7.2 magnitude quake on the horizon.

But Haitian officials said there was not enough time or funds to shore up the impoverished Caribbean's country's shoddy construction or take precautions, and in last month's quake, many buildings pancaked, their bricks crumbling to dust.

"It's not too late. Now is the time to really get serious about this," Calais said.

Over 200 years ago, when Haiti saw its last major earthquake, there were actually several temblors in a row, two in 1751 and another in 1770, Calais said.

In one destroyed neighborhood in the Haitian capital, where people now live in tents made of bed sheets and sticks, curious children watched the scientists set up specialized global positioning systems. The devices, placed at different points along the fault, will gather data over three days and compare it to information gathered over the past five years.

But for all the precise measurements, there is no such thing as an exact science of earthquake prediction.

Haiti's national geological survey offices collapsed in the quake, killing some 30 people inside, including the institute's director. This complicates future research in a country that has no seismic network, except for Calais' GPS monitors.

"Scientists are blind when it comes to this earthquake ... We rely on data that is coming from stations that are far away," he said.

"It's like if you go to your doctor and the only thing we can do is look at you with binoculars -- so the diagnostic would be pretty poor."

February 2, 2010

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Bahamas Blog International

Haiti's fault rupture boosts long-term risk of Jamaica quake

By Tom Randall and Meg Tirrell:


NEW YORK, USA (Bloomberg) -- The magnitude 7 earthquake that killed as many as 100,000 people in Haiti this week may increase the likelihood of a future quake in Jamaica, according to seismologists who study geologic risk.

When aftershocks subside in the coming weeks, Haiti’s prospects of another earthquake will plummet, while areas west along the same fault line will see increased seismic pressure, said Stuart Sipkin, a seismologist at the US Geological Survey in Golden, Colorado.  It could take decades or a century for the pressure to rupture on the western edge of the fault in Jamaica.

A similar quake flattened the Haitian capital of Port-au- Prince 240 years ago, so long ago that most residents were unaware they were at risk, said Roger Musson, who advises engineers on regional dangers for the British Geological Survey.  The 1770 upheaval was part of a string of westward-moving temblors that culminated in Jamaica in 1907, he said.

“In Haiti, there’s not been earthquakes in living memory; now it’s likely that the stress will be increased on the next segment along,” Musson, the agency’s head of seismic hazard, said in a telephone interview.  However, he added, “You are constantly surprised by earthquakes doing things that they’re not supposed to do.”

Haiti lies near the eastern end of a fault line between the North American and Caribbean tectonic plates -- massive subterranean sections of the earth’s crust that move at about the speed that human fingernails grow, Sipkin said.

When the two passing tectonic plates get stuck together, pressure builds until it is relieved through a violent movement of earth, Sipkin said.

It probably took about 20 to 30 seconds for the fault to break, said Kate Hutton, a seismologist at the Seismological Laboratory at the California Institute of Technology in Pasadena.

“People probably felt it for longer,” Hutton said today in a telephone interview. “People’s perception of time slows down when they get really stressed.”

The Haiti earthquake was a “worst-case scenario,” a shallow rupture in the earth that ripped through a densely populated and poorly constructed city, said Pedro de Alba, professor of civil engineering at the University of New Hampshire in Durham.  The depth of the rupture is important, because if it occurs deep in the earth, much of the energy is absorbed by rock, he said.

“A shallow earthquake is the worst possible kind,” de Alba said in a telephone interview today.  “Pressure was building up for quite a long time.”

De Alba said the probability of a future quake west along the fault line has increased, “but to what extent we simply can’t predict.”

January 16, 2010

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