Page last updated at 16:06 GMT, Monday, 1 March 2010

Why did fewer die in Chile's earthquake than in Haiti's?

Images from Haiti's earthquake (left) and Chile's earthquake (right)

By Anthony Reuben
BBC News

The death toll from Chile's 8.8 magnitude earthquake looks like being a fraction of the 220,000 people who were killed in Haiti in January.

This is despite the Chilean quake being 500 times stronger than the one in Haiti.

Clearly, Chile is a more prosperous country, with economic output per head of the population more than 10 times greater than Haiti.

That has meant that buildings in general are better built, but Chile was also better prepared.

People in Chile knew the safest places to go to when the earthquake struck.

Also, since an even stronger earthquake in 1960, Chile has developed a seismic design code for new buildings, which has made them better able to stay standing in an earthquake.

Graphic showing strong column weak beam system

One system that helps buildings stay up is called the "strong columns weak beams" system.

The idea is that buildings are held up by reinforced concrete columns, which are strengthened by a steel frame.

Reinforced concrete beams are joined onto the columns to make floors and the roof.

If there is an earthquake, the idea is that the concrete on the beams should break near the end, which dissipates a lot of the energy of the earthquake, but that the steel reinforcement should survive and the columns should stay standing, which means the building will stay upright.

The problem is that an 8.8 magnitude earthquake is "towards the top end of what you're designing for", according to Professor Colin Taylor, professor of earthquake engineering at Bristol University.

A mitigating factor in the Chilean quake was that its focus was 21 miles (34km) underground, off-shore and its epicentre was 70 miles (115km) from the nearest big city, Concepcion.

The energy from earthquakes falls the further away you are from the centre.

The Haitian quake on the other hand was only 8 miles (13km) underground and right on the edge of Port-au-Prince.

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