Seismologists learn from Haiti

In the aftermath of the terrible Haitian earthquake, the priority is of course the relief effort. But seismologists are using data from the magnitude 7 tremor to increase their knowledge of the way stresses build up in the Earth’s crust as tectonic plates grind slowly together – and are released suddenly in an earthquake.

Although there is no way the Haiti quake could have need predicted, in terms of giving a useful warning of timing, some seismologists had been concerned about the risk of disaster there.

In a remarkable piece of timing, Robert Yeats, a geoscientist at Oregon State University in Corvallis, told Scientific American in an interview a week before the disaster that an imminent big earthquake on the US west coast concerned him far less than a “big one” that might occur in Haiti, due to the large fault near the capital city of Port-au-Prince — and the poverty-driven low level of earthquake-preparedness there.

“If they have an earthquake on this fault that runs through Port-au-Prince,” the death toll would be tremendous, he said — a prediction that turned out to be horribly true.

The Enriquillo-Plaintain Garden Fault passes within 16 kilometers of Port-au-Prince, at the intersection of the North American and Caribbean tectonic plates, which are sliding past one another at a rate of one or two centimetres a year. This movement creates a “strike-slip fault”, the same kind as the San Andreas Fault in California where the North American and Pacific plates are sliding in different directions. The Enriquillo-Plaintain Garden Fault had been building up pressure since the last serious earthquake under Haiti in the 19th century.

Current methods of assessing where quakes are most likely to occur are based mainly on the record of recorded historical events. Huilin Xing of the University of Queensland says these could be supplemented with new computational and observational technologies.

Very destructive recent earthquakes have occurred after long periods of inactivity, Xing points out. It was 600 years between the 2004 Boxing Day Sumatra earthquake/tsunami and a previous equally strong quake. The corresponding intervals were 5,000 years to the 2008 China Sichuan earthquake and 200 to the current Haiti earthquake.

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