Geologists expected Haiti quake

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Geologists were not surprised by yesterday's earthquake in Haiti. The quake occurred on a well-known fault, and some seismologists had predicted that a large temblor was likely. The World's Science Correspondent Rhitu Chatterjee reports.

MS. JEB SHARP: Haiti has seen more than its share of natural disasters. It's usually hurricanes, not earthquakes that threaten the country. But if you talk to geologists, they'll tell you that yesterday's quake should not have been a surprise. The World's science correspondent, Rhitu Chatterjee, explains.

MS. RHITU CHATTERJEE: Eric Calais had warned the Haitian government that an earthquake was coming. He is a geophysicist at Purdue University in Indiana and he has been studying the fault zones on the island of Hispaniola for 20 years.

MR. ERIC CALAIS: Haiti and the whole island of Hispaniola and so the Dominican Republic to the east as well lie exactly on the plate boundary between Caribbean and North America.

MS. CHATTERJEE: The North American tectonic plate is moving west. The Caribbean plate is moving east. The two slide past each other at about an inch a year. And Calais says that movement in this fault zone has caused major earthquakes in the past.

MR. CALAIS: The last major earthquake on this fault occurred in 1751 and there was followed, about 20 years later by another event in 1770.

MS. CHATTERJEE: But since then, things have been relatively quiet. So for the people of Haiti the threat of an earthquake seemed remote.

MR. CALAIS: When you tell someone that there was a large event 300 years ago, it doesn't really resonate. They don't know, they don't realize physically what it means to them if it were to happen right now.

MS. CHATTERJEE: But for geologists, the quiet period was a sign of impending trouble. Jian Lin is a geologist at the Woods Hole Oceanographic Institution in Massachusetts. He says the plate had become stuck along the boundary on Hispaniola. The fault had become locked building up a lot of pressure.

MR. JIAN LIN: The longer it's locked, the more likely you have a larger earthquake. So that's exactly what happened in Haiti.

MS. CHATTERJEE: Two hundred years of built up pressure was released in about 45 seconds. Now that the plates are moving again, geologists say there are likely to be many aftershocks in the coming months. Geophysicist Eric Calais says that those aftershocks could worsen the impact of yesterday's quake.

MR. CALAIS: They will hit areas that have already been damaged to some degree by the main shock and therefore they will make structures that were significantly weakened collapse. So the population should move away from any building that shows any sign of structural damage because those aftershocks could make those buildings collapse.

MS. CHATTERJEE: Now that most of the pressure on this fault has been released, geologists say another major earthquake in this part of Haiti is probably many years off. But that doesn't mean the country is safe from seismic dangers. There is another major fault zone in the Northern part of Haiti and it's still building up pressure since it's last quake. That was 150 years ago. For The World, I'm Rhitu Chatterjee.

MS. SHARP: We have pictures from Haiti along with a list of aid organizations accepting donations at the world dot org.