Savage Disaster

Experts at the earthquake research center in Bensberg, near Cologne, are currently analysing the data provided by Tuesday's vast earthquake, which so savagely hit the Caribbean nation of Haiti. Among them is Professor Klaus Dieter Hinzen, who said he is not at all surprised about the earthquake.

"In the past there have always been earthquakes along the whole archipelago in the Caribbean," he said, adding the last earthquakes struck Haiti a long time ago. "We know that there was a large quake in 1860 and that earlier, between 1750 and 1770, the earth shook heavily there on three separate occasions."

In order to understand why Hinzen is not surprised Haiti has been hit again, it is necessary to understand why earthquakes occur.

Earth's surface consists of several different continental shelves which are in constant movement. These shelves thrust against each other, forming borders like the St. Andreas fault in California or one in Anatolia. Because of this, certain areas in the world are particularly prone to earthquakes. Haiti is one such pace, although the last quake took place there more than 240 years ago.

Haiti is on the Caribbean shelf, which is sandwiched between the North and South American shelves, according to Hinzen. The country was hit particularly hard because none of the plates shifted over and under one another, but rather shifted side-by-side.

Birger Luehr of the German Research Center for Geosciences in Potsdam explained two sideways displacements along the Western part of the fault – a northern and a southern one – form a shift of two centimeters (.79 inches) per year, which then becomes further divided. Latest measurements indicate a total movement of eight millimeters per year.

While that figure may not sound like much, it is multiplied by the 240 years since Haiti's last earthquake. The result is a huge crack of two meters.

"The epicenter of the Haiti earthquake was 10 kilometers deep and measured a seven on the Richter scale," Luehr said. "We can be fairly sure that the earth's crust burst through to the surface, which is why the effects were so devastating."

There are more than 300 seismographic measuring stations worldwide, but they can only measure an earthquake as it occurs. Scientists aren't capable of predicting the site, size or time of earthquakes, which left Haiti without warning. However, researchers are trying to become more precise about the probability of an earthquake, according to Luehr.

"For one, we observe the activity of small micro-quakes which can't be felt but only measured with very sensitive instruments," he said. "We measure expansions underground or check the water levels in wells, because variations can take place there before a big quake. We try to measure the electrical field of the earth, because in the past this has been observed to change before an earthquake. Still, none of these methods are true ways to predict an earthquake."

According to Luehr there was never a question if an earthquake would occur on Haiti: the question was when. And the fault is still emitting thousands of smaller earthquakes, which will continue for weeks or months.

Author: Wolfgang Dick/td/gps

Editor: Anke Rasper