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
caribbeannetnews
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Showing posts with label shallow earthquake. Show all posts
Showing posts with label shallow earthquake. Show all posts
Saturday, January 16, 2010
Thursday, January 14, 2010
Haiti quake was nightmare waiting to happen say scientists
By Richard Ingham:
PARIS, France (AFP) -- The quake that hit Haiti on Tuesday was a killer that had massed its forces for a century and a half before unleashing them against a wretchedly poor country, turning buildings into death traps, experts said on Wednesday.
Scientists painted a tableau of horror, where natural forces, ignorance and grinding poverty had conspired to wreak a death toll tentatively estimated by Haitian Prime Minister Jean-Max Bellerive at more than 100,000.
The 7.0-magnitude quake occurred very close to the surface near the Haitian capital of Port-au-Prince, leaving almost no natural buffer to soften the powerful shockwave, these experts said.
"It was a very shallow earthquake, occurring at a depth of around 10 kilometers (6.2 miles)," seismologist Yann Klinger of the Institute of the Physics of the Globe (IPG) in Paris told AFP.
"Because the shock was so big and occurred at such a shallow depth, just below the city, the damage is bound to be very extensive," he said.
The US Geological Survey (USGS) said the quake occurred at 2153 GMT on Tuesday 15 kms (9.4 miles) southwest of Port-au-Prince.
It happened at a boundary where two mighty chunks of the Earth's crust, the Caribbean plate and the North America plate, rub and jostle in a sideways, east-west movement.
The USGS said the rupture occurred on the "Enriquillo-Plaintain Garden fault system," a slow-moving fault that last unleashed a large quake in 1860. Prior major events to that were in 1770, 1761, 1751, 1684, 1673 and 1618.
Sandy Steacey, director of the Environmental Science Research Institute at the University of Ulster in Northern Ireland, said the high death toll could be pinned overwhelmingly to construction.
"It's a very, very poor country without the building codes. Probably the fact that earthquakes (there) are very infrequent contributes in a way, because it's not a country that is focussed on seismic safety.
"Looking at the pictures, essentially it looks as if (the buildings are of) breeze-block or cinder-block construction, and what you need in an earthquake zone is metal bars that connect the blocks so that they stay together when they get shaken," said Steacey.
"In a wealthy country with good seismic building codes that are enforced, you would have some damage, but not very much."
French seismologist Pascal Bernard, also at the IPG, said that, given the nature of the fault, there was a "sizeable probability" that another large quake could occur in the same region within a matter of years.
Like other faults around the world, the Haitian crack is well known for domino activity, in which the release of pressure on one stretch piles on pressure in an adjoining stretch, bringing it closer to rupture.
In Haiti's case, the likeliest spot of a bust would be to the east of Tuesday's quake, Bernard said.
Asked whether another big quake was in the offing, Roger Searle, a professor of geophysics at Durham University, northeast England, said, "In the coming years, almost surely."
"We know pretty much where earthquakes occur, they've been mapped themselves and we can map faults and so on.
"The difficulty is it's very, very hard to predict when they will occur, because the network is so complex.
"It's a bit like making a pile of stones. You put more on the pile and it gets steeper and steeper and sooner or later the thing is going to collapse but you never which stone is going to do it and just where it's going to start to fail."
January 14, 2010
caribbeannetnews
PARIS, France (AFP) -- The quake that hit Haiti on Tuesday was a killer that had massed its forces for a century and a half before unleashing them against a wretchedly poor country, turning buildings into death traps, experts said on Wednesday.
Scientists painted a tableau of horror, where natural forces, ignorance and grinding poverty had conspired to wreak a death toll tentatively estimated by Haitian Prime Minister Jean-Max Bellerive at more than 100,000.
The 7.0-magnitude quake occurred very close to the surface near the Haitian capital of Port-au-Prince, leaving almost no natural buffer to soften the powerful shockwave, these experts said.
"It was a very shallow earthquake, occurring at a depth of around 10 kilometers (6.2 miles)," seismologist Yann Klinger of the Institute of the Physics of the Globe (IPG) in Paris told AFP.
"Because the shock was so big and occurred at such a shallow depth, just below the city, the damage is bound to be very extensive," he said.
The US Geological Survey (USGS) said the quake occurred at 2153 GMT on Tuesday 15 kms (9.4 miles) southwest of Port-au-Prince.
It happened at a boundary where two mighty chunks of the Earth's crust, the Caribbean plate and the North America plate, rub and jostle in a sideways, east-west movement.
The USGS said the rupture occurred on the "Enriquillo-Plaintain Garden fault system," a slow-moving fault that last unleashed a large quake in 1860. Prior major events to that were in 1770, 1761, 1751, 1684, 1673 and 1618.
Sandy Steacey, director of the Environmental Science Research Institute at the University of Ulster in Northern Ireland, said the high death toll could be pinned overwhelmingly to construction.
"It's a very, very poor country without the building codes. Probably the fact that earthquakes (there) are very infrequent contributes in a way, because it's not a country that is focussed on seismic safety.
"Looking at the pictures, essentially it looks as if (the buildings are of) breeze-block or cinder-block construction, and what you need in an earthquake zone is metal bars that connect the blocks so that they stay together when they get shaken," said Steacey.
"In a wealthy country with good seismic building codes that are enforced, you would have some damage, but not very much."
French seismologist Pascal Bernard, also at the IPG, said that, given the nature of the fault, there was a "sizeable probability" that another large quake could occur in the same region within a matter of years.
Like other faults around the world, the Haitian crack is well known for domino activity, in which the release of pressure on one stretch piles on pressure in an adjoining stretch, bringing it closer to rupture.
In Haiti's case, the likeliest spot of a bust would be to the east of Tuesday's quake, Bernard said.
Asked whether another big quake was in the offing, Roger Searle, a professor of geophysics at Durham University, northeast England, said, "In the coming years, almost surely."
"We know pretty much where earthquakes occur, they've been mapped themselves and we can map faults and so on.
"The difficulty is it's very, very hard to predict when they will occur, because the network is so complex.
"It's a bit like making a pile of stones. You put more on the pile and it gets steeper and steeper and sooner or later the thing is going to collapse but you never which stone is going to do it and just where it's going to start to fail."
January 14, 2010
caribbeannetnews
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