What made the earth shake?

For the millions of survivors of last week’s earthquake in Haiti, answers do not come easily.

I can only imagine that many of these survivors are confused about why the earth shook so intensely that their family members were killed, their homes fell to the ground and their struggling country crumbled.  

Actually, earthquakes happen all the time, all over the world. If you go to the United States Geological Society Web site, you can find a list of the locations and magnitudes of over 20 earthquakes that occurred just yesterday.

The theory of plate tectonics suggests that Earth’s outer shell (what lies below the oceans and land masses) is covered by a layer of rigid plates of rocky material that are 30 to 90 miles thick. There are seven major plates that cover the earth, and they move a few centimeters every year on another, more fluid layer of earth.

Energy builds up between the plates when they move too close together, resulting in them sticking to each other. Earthquakes can happen when the tension between the plates snaps: the plates move suddenly and the energy is released. The release of energy causes the ground above to shake and tremble.

Last week’s earthquake in Haiti, however, was much more intense and destructive than your everyday tremble.

The Enriquillo-Plantain Garden Fault is a borderline between two tectonic plates that runs from Jamaica to the Dominican Republic. Since the last earthquake about 200 years ago, tension has been building up at this fault as the Caribbean Plate moves eastward relative to the North American Plate to the north.

On Tuesday, 10 miles away from Haiti’s capital, Port-au-Prince, and six miles underground, pressure was suddenly released due to the east-west movement of the plates at the fault. This kind of side-to-side motion defines what is known as a strike-slip fault, a term that describes both the Enriquillo-Plantain Garden Fault and the San Andreas Fault in California.

This earthquake was especially strong because the slippage occurred so close to the surface. Six miles of earth was not enough to absorb the energy released from the fault.

The Richter Scale is a mathematical formula that determines the magnitude of seismic activity during an earthquake. Haiti’s earthquake scored a 7.0, indicating a major disturbance (most everyday quakes score less than 5.0). The Richter Scale is a logarithmic scale, which means a quake with a score of 7.0 is 10 times stronger than a quake with a score of 6.0 and 100 times stronger than a quake that scores 5.0.

Finally, this earthquake was so destructive because it happened in a densely populated city with a poor infrastructure. Port-au-Prince was not prepared to withstand this much shock.

The force of human compassion is all Haiti’s survivors have to rebuild their lives after natural forces have devastated them. Please do what you can to contribute to the cause.