Haiti has been devastated. The already frail infrastructure of the struggling nation has collapsed, people are starving and gangs are overrunning the streets of the capital. Destruction and death have ruled the country for the past week, and many want answers as to why the earthquake occurred.
There are several factors that contributed to the gravity of the disaster. Part of the reason for the extent of the devastation was lack of preparation for any type of earthquake in Haiti. There have been no large earthquakes in the country in recent years, and the only accounts of large earthquakes in the region date back to 1860, 1770 and still further back to 1618. Yet even the accounts of these earthquakes cannot be confirmed as originating from the same place as the earthquake that occurred on Jan. 12.
The geological stability of past centuries may have been a contributing factor in the catastrophe that was the Haitian earthquake.
It's actually a good thing if there [are] a lot of low magnitude earthquakes, because then you're constantly relieving the stress," Anne Gardulski, head of the Tufts geology department, said. "It's when you get locked up like what happened along this fault in Haiti for 200 years, that's when you start really having big earthquakes. This is not unusual. It is unusual in a human time frame - we think of things in terms of decades, but geologically these are very common events; even earthquakes of this magnitude."
Research from the United States Geological Survey (USGS) has found that the Haitian earthquake originated from an area known as the Enriquillo-Plantain Garden fault zone (EPGFZ). This area is located in the southern part of Haiti and runs almost straight through Port-au-Prince, the nation's capital, from east to west. The fault system is active, which means that there is still movement along the faults.
The EPGFZ is the area where the Caribbean tectonic plate is moving east past North America towards the Atlantic Ocean. It is very similar to the San Andreas Fault in California, where the Pacific plate is moving north relative to the North American plate.
The friction as the plates move past each other is intense, and as they squeeze by each other in opposite directions and collide, the area in the middle - in this case, Haiti - is especially affected.
The earthquake on Jan. 12 measured a 7.0 on the Richter scale. The scale, which measures the magnitude of an earthquake, ranges from a low of one to a high of 10. A 7.0 is a major earthquake, but location, as well as magnitude, matters for the intensity of damage. The Haitian earthquake was very shallow - less than 10 miles underground.
"The amount of shaking of the rock decreases rather dramatically the further you get from the focus of the earthquake. So if it's deep in the earth, say 100 miles down, the earthquake energy will have been dispersed somewhat by the time it reaches the earth's surface. You can have a magnitude seven earthquake which, if it's a very deep earthquake, can still be very damaging, but probably not as damaging as one that is so close to the earth's surface," Gardulski explained.
Another significant factor in the destruction of Port-au-Prince was the underlying rock and soil. "Sediment can shake more than hard rock, and you can get amplification of waves. If you have a hard tough rock like granite, it will certainly shake, but you're not going to develop problems like liquefaction of sediment or landslide damage. And it sounds like in Haiti there were a lot of landslide problems because of the steep slopes there with unconsolidated, unlithified sediment on the slopes. And that just gave way. Whole villages were coming down and being buried," Gardulski said.
Many were concerned about whether or not there would be a tsunami in the area after the quake, bringing yet more destruction. While there have been a number of tsunamis that have resulted from earthquakes in recent history, there was little to no chance of one occurring in Haiti.
"To generate a tsunami you have to have some abrupt movement vertically on the sea floor - you have to have a block of rock move up or drop down, and that sends a shock wave into the overlying water. This fault - along which there was motion in Haiti - was one where there's only horizontal motion, and therefore even if this was underwater, it's not generating vertical motion up and down across the fault. They did put out a tsunami warning just after it happened because they didn't know yet what kind of earthquake it was," Gardulski said.
Places that are hit by earthquakes on a regular basis have learned to deal with the instability of the earth on which they live. Some densely populated countries, such as Japan, are constantly beset by earthquakes, but they suffer less damage because of strict regulations of building codes. Precautionary procedures such as the ones in these countries could serve as valuable examples as Haiti looks to rebuild in the future.
"One of the things I'm concerned about personally is the people that are going to try to rush in there and rebuild. If they don't take into account earthquake-mitigating construction guidelines, it doesn't do you any good to go in there and rebuild. It's not a question of if this is going to happen again. It is going to happen again, sometime. I'd just like to encourage people - ¦ [to not] put up more of the same types of buildings that were there," Gardulski said.
