Thursday, March 4, 2010

Why Haiti's Quake Toll Higher Than Chile's

In the aftermath of last Saturday's earthquake in Chile, many people have been asking why the 8.8 earthquake, releasing 500 times more energy than the 7.0 in Haiti, caused significantly less damage. In a recent CNN article, Columbia University geophysicist Colin Stark speculated on why Haiti's quake toll is higher than Chile's.

Poverty is what ultimately kills most people during an earthquake. Poverty means that little or no evaluation is made of seismic risk in constructing buildings and no zoning takes place. It means that building codes are not written, and even if they do exist they are difficult, or impossible, to enforce. It means the choice between building robustly or building cheaply is not a choice at all.

Haiti is a tragic illustration of this. Weak building materials and poor construction standards share much of the blame for the grotesque number of fatalities, injured and internally displaced people.

Of course it's complicated. Earthquake shaking is a complex process and the chain of causation from earthquake source magnitude through infrastructural damage to human harm involves factors like the type of earthquake fault, its orientation, the hardness of bedrock or presence of wet soil, and so on. A lot also depends on the time of day the earthquake strikes in terms of how many people are inside the buildings that could collapse. Population density, distance from the epicenter, and the depth of the rupture are the most important factors of all.

Nevertheless, those countries most at risk of seismic tragedy are not simply those on tectonic plate boundaries, but also those with the least money to spend on protecting themselves.