Seismic Risk in Haiti

A geological fault is a discontinuity in the earth’s outer layer, called crust. Every time a breakage occurs along a fault, energy is released and brings about an earthquake on the earth’s surface. For this reason, every area close to a fault has a seismic hazard to some extent. One area in the world which has a high seismic hazard is Haiti. In fact, Haiti is located in the Caribbean geological plate and it is crossed by two very active faults: the northern fault and the Enriquillo fault (or southern fault). The northern fault triggered an earthquake that killed about 5000 people in 1842 in the city of Cap-Haitien, whereas the Enriquillo fault generated three major earthquakes in 1751, in 1770 and more recently in 2010. The latter destroyed the capital Port-au-Prince, causing more than 200,000 casualties. The loss was not only in human life but also in the economy. Thousands of buildings were severely damaged, including the national palace. According to “Ministry of Transportation and Public Work” in Haiti this seism in 2010 was of magnitude 7 and had its epicenter (the vertical projection on surface where the fracture in the fault occurred) in a city close to Port-au-Prince and its hypocenter (the area underground where the fracture occurred) at about 30 km. This depth is considered as a shallow one by seismologists which makes the seism even more violent.

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So many buildings collapsed in Haiti in 2010 because they were not adequately designed to withstand earthquakes. Haitians did not take into consideration earthquake loads while designing structures partly because they were not fully aware of the seismic hazard. Only vertical loads were used in the designs, which led to a lack horizontal stability and bracings in the structures. When a structure is horizontally not stiff enough, it becomes very vulnerable to earthquakes because the seismic loads are merely horizontal. Moreover, the material used in the construction was not of good quality. Rubber collected from collapsed structures showed poor-quality concrete and insufficiency of steel reinforcement. In fact, this seism was not among the most violent one that ever happened, but due to Haiti’s vulnerability, it was among the deadliest one.

A seism can also have some induced effects, such as tsunami which is a huge water wave resulted from a fault fracture under sea. This can happen when a fault line is located in the ocean. Indeed, the northern fault in Haiti partly lines in the Caribbean Sea. As a result, this constitutes a massive earthquake and tsunami risk for the city of Cap-Haitien, the second most populated in the country. Specialists in seismology and earthquake engineering have warned the population that another seism is imminent along this fault since the last major fracture along it was registered in 1842. It was more than 150 years ago. During those years, stresses have accumulated along the fault and can likely release at any time. The more time it takes to release the stress, the more violent the earthquake or resulting tsunami will likely be. What is even worse, the magnitude of the seism expected in this fault is 8.0, which is 30 times stronger than a seism of magnitude 7; and very disconcerting to the people in the north department due to the vulnerability of their cities.

 

Author: marclaguerreblog

PhD Student in Civil Engineering at Rice University

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