Thaindian News

London, January 20 (ANI): Geologists have explained some of the reasons why the Haiti mega earthquake killed such a large number of people.

One of the reasons that the quake was so deadly was that it was “shallow source” and so allowed less warning time to get out of buildings than deep quakes.

Also, Port au Prince is built not on solid rock but on soil, which collapses when shaken.

Finally, building standards were not adequate for major earthquakes.

“Better buildings would have saved lives,” said Chuck DeMets, a tectonic geologist from the University of Wisconsin-Madison.

A comparison with two very similar earthquakes backs up this assertion.

In 1988, the Spitak magnitude-6.9 earthquake in Armenia took more than 25,000 lives. By contrast the magnitude-7.1 Loma Prieta earthquake in California in 1989 caused only 63 deaths.

Both occurred in densely populated regions, but they had very different outcomes.

“The difference in the numbers of fatalities illustrates the huge effect that high building standards can have in saving people’s lives,” said DeMets.

The multi-storey concrete buildings that made up much of Port-au-Prince in Haiti proved to be death traps when the earthquake struck.

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

The disaster was compounded by the earthquake’s shallow source.

“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,” said Uri ten Brink, an expert on earthquakes in the Caribbean from the US Geological Survey in Woods Hole, Massachusetts.

In Haiti, the epicentre was so close to the surface that the primary and shear waves arrived almost at the same time.

As to the type of buildings that can withstand this kind of shake, Main said, “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.”

“This might include base-isolation shock absorbers on the first floor, to help resist or minimise dynamic shear and twisting motions,” he said.

Retrofitting conventional buildings to make them earthquake-proof is expensive, but constructing new buildings to be shake-proof is not.

“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,” said Main. (ANI)