Haiti Earthquake: Why did it Happen?

The major earthquake that struck Haiti Tuesday may have shocked a region unaccustomed to such temblors, but the devastating quake was not unusual in that it was caused by the same forces that generate earthquakes the world over. In this case, the shaking was triggered by much the same mechanism that shakes cities along California's San Andreas fault.

The 7.0-magnitude Haiti earthquake would be a strong, potentially destructive earthquake anywhere, but it is an unusually strong event for Haiti, with even more potential destructive impact because of the weak infrastructure of the impoverished nation.

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Earthquakes typically occur along the jigsaw-puzzle pieces of Earth's crust, called plates, which move relative to one another, most of the time at an imperceptibly slow pace. In the case of the Haiti quake, the Caribbean and North American plates slide past one another in an east-west direction. This is known as a strike-slip boundary.

Stress builds up in points along the boundary and along its faults where parts of the crust stick; eventually that stress is released in a sudden, strong movement that causes the two sides of the fault to move and generate an earthquake. The fault system that ruptured to cause this quake is called the Enriquillo-Plantain Garden fault system.

Another factor in the damage that a quake can cause is it intensity. While magnitude is a measurement of how much energy is released by an earthquake, intensity is "simply an estimate or a measure of how strongly that earthquake was felt," said Don Blakeman, an earthquake analyst with the United States Geological Survey.

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