The destruction in Haiti has as much to do with the poverty of the country and its politics as it does its geology.

The earthquake in Haiti and its devastating human toll has once again focused the attention of the world on the natural hazards we face daily as we live on this planet. Thankfully, natural disasters such as earthquakes, volcanic eruptions, hurricanes, and wild fires happen infrequently enough and in isolated enough areas that most people will never experience them. Nevertheless, they do occur with some regularity and predictability.

Many can be avoided if one has the ability and will to move. One could choose not to live at (or below) sea level on the Gulf coast, next to an active volcano, or near to a major fault. The recent geological record, if not the historical record, will likely warn of the possibility of disaster in these regions: there will be records of previous hurricanes and floods, volcanic eruptions, and earthquakes. The catch is that it is not always possible to move, or there may be other good reasons to live in that place: the coast might be an excellent fishing ground or port, the volcanic soil might be very fertile, or the fault might form a bountiful valley. Or perhaps there is nowhere else to go, and no means to leave even if one wanted.

The latter situation is largely the fate of the Haitian people, descended mainly from slaves imported from Africa to work colonial sugar plantations and subsequently trapped in a disastrous political and economic morass since its independence from France in 1804. It is now the poorest country in the western hemisphere and also one of the most overpopulated. As Jared Diamond notes in his book Collapse, “Haiti is so poor, and so deficient in natural resources and trained or educated human resources, that it is really difficult to see what might bring about an improvement.” These words were written in 2005; in the wake of the earthquake, Haiti's future looks even bleaker.

Haiti's capital, Port-au-Prince, is built near a major fault line between the Caribbean and North American plates. It is a similar type of fault to the well known and highly dangerous San Andreas fault in California. These types of faults, called strike-slip faults, represent the vertical boundary between two plates of the Earth's crust that are slipping horizontally past each other.

Such plates can be thousands of kilometers across, as in the case of the North American plate, or only a few hundred kilometers across, as in the case of the small fragment of the Caribbean plate, the Gonave microplate, which Haiti and its island neighbour, the Dominican Republic, sit on. This plate fragment is located on the northern margin of the larger Caribbean plate, which is moving eastwards relative to the North American plate at about two centimetres per year. As such, it is in a very vulnerable location, and major earthquakes have occurred there in recent history.

Generally speaking, earthquakes happen infrequently, despite the constant relative motion of the plates, because faults are “sticky.” Friction stops the faults from sliding smoothly, resulting in a progressive build-up of stress, until the fault finally ruptures, causing a quake. The stickier the fault, the greater the build-up of stress, and consequently the greater the magnitude of the earthquake when the fault finally slips. Strike-slip faults tend to be particularly sticky, and therefore undergo less frequent but more catastrophic motions.

Another factor in the severity of damage from earthquakes is the depth at which the fault movement, or the “focus,” occurs (the “epicentre” of an earthquake is the surface location directly above the focus). Deeper earthquakes will cause less surface damage than shallow earthquakes of the same magnitude.

With a magnitude of 7.0, the earthquake in Haiti was not a particularly large one by global standards (there are about 10 such earthquakes each year around the world). And although the focus was relatively shallow (about 13 km below the surface), most buildings in modern cities would have comfortably ridden out such ground motions. Especially in earthquake-prone regions, modern building codes in wealthy countries typically require the extensive use of steel reinforcement in concrete structures, giving the otherwise brittle concrete strength and sufficient flexibility to withstand the wobbling and shaking motions caused by earthquakes.

But in a country as desperately poor and densely populated as Haiti, its buildings were not constructed to withstand even minor earthquakes. The cheaply built low-rise structures and slums of Port-au-Prince consequently crumbled instantly to dust.

This explains the very high casualty rate: because the buildings collapsed so suddenly and so completely, people had no time to escape. Properly constructed buildings, even if damaged, would not have collapsed in this way. I personally experienced an earthquake with a magnitute of 8.1 near the city of Antofagasta, Chile, in 1995. Although a number of buildings were slightly damaged, none collapsed, and there were no fatalities except from a heart attack.

Thus, the tragedy of Haiti is not geological so much as political and economic.