Haiti quake: why killed so many?

United Nations has described the last week’s earthquake in Haiti as the worst humanitarian crisis in decades, with the estimation of the number of dead ranging from 50,000 to 200,000. The Unitied Nations blames the fact that the quake hit a highly populated capital city, knocking out many of the agencies that would have dealt with disaster relief.

Geologists explained some of the other reasons why the quake was so bad, and warned that more quakes may come because not all the pent-up seismic energy was released in the earthquake.

First reason is, the quake was “shallow source” and it allowed less warning time to people to get out of buildings than deep quakes.The multi-storey concrete buildings that made up much of Port-au-Prince proved to be death traps when the earthquake struck. And “Port au Prince” was not built on solid rock but built on soil, which collapses more easily when shaken. Finally, building standards were not adequate enough for major earthquakes.

A tectonic geologist from the University of Wisconsin-Madison, Chuck DeMets says If a similar quake was occurred in California, the death rate would almost certainly have been much lower. “Better buildings would have saved lives.”

A seismologist at the University of Edinburgh, UK, Ian Main says “The buildings were brittle and had no flexibility, breaking catastrophically when the earthquake struck.”

2nd reason is the disaster was compounded by the earthquake’s shallow source. An expert on earthquakes in the Caribbean from the US Geological Survey in Woods Hole, Massachusetts, Uri ten Brink says “With deep earthquakes the primary waves arrive first, giving you a bit of warning before the shear waves, responsible for shaking the ground from side to side, arrive” . In Haiti the epicentre was so close to the surface that the primary and shear waves arrived almost at the same time with earthquake..

So what kind of buildings we need,which can withstand this kind of shake? Ian main says “Engineers use more flexible materials with a built-in capacity to absorb damage, much as car bonnets are now designed to crumple, leaving the interior intact.” Main explains “This might include base-isolation shock absorbers on the first floor, to help resist or minimise dynamic shear and twisting motions.”

Retrofitting conventional buildings to make them earthquake-proof is quite expensive but constructing new buildings to be shake-proof is not. Main says “Seismic-resistant buildings cost a few per cent more in building materials and need a little extra designer time, but they are not a great deal more expensive than ordinary buildings”.