February 2, 2010

Engineers: ‘Waves’ of Issues for Haiti

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In light of the earthquake in Haiti, resulting in an estimated 200,000 dead and $10 Billlion in damage, many have questioned why damage from this earthquake, magnitude 7.0, was so high. Earthquakes of similar magnitude in West Java, Indonesia in 2009 and San Francisco in 1989 neither took as many lives nor caused as much infrastructure damage.

“The Earth presents many hazards,” said Prof. Larry Brown, earth and atmospheric sciences, “It requires interventions from humans to make it into a disaster.”

In a lecture by Cornell scientists and engineers on Jan. 25, Brown asserted, there was a “… lack of appropriate action and attention to science, which could have averted this.” According to Brown, Prof. Rick Allmendinger, earth and atmospheric sciences, and Prof. Tom O’Rourke, civil and environmental engineering, scientists and engineers informed the Haitian government of possible earthquakes in the near future.

“People don’t have a long memory when it comes to natural disasters,” explained Allmendinger in an interview. Scientists can only give a range of years within which the earthquake may occur. Corrupt governments and poor people resist this information to avoid the choice of immediate comfort or protection from disasters.

Plate tectonics explains the cause for these disasters. The Earth’s outer layer is a mosaic of crust pieces, called plates. Hispaniola, the island containing Haiti and the Dominican Republic, lies on the Caribbean plate, a small section wedged between the large North and South American plates. The Caribbean plate moves eastward in a shearing motion past the North and South American plates, creating two fault lines in Hispaniola, including the Enriquillo fault, notorious for earthquakes.

According to Elastic Rebound Theory, as the plates move past each other in opposite directions, rock connecting the shifting plates is slowly stretched and pulled in opposite directions until it cannot sustain the strain. At that point, the rock breaks across the fault line and snaps back to place. This motion creates underground waves and surface waves, which generate earthquakes.

Earthquakes happen in sets, separated by “interseismic phases”, when strain builds up along the fault. “Ominously”, Allmendinger explained, there have been no large earthquakes from the Enriquillo fault since 1750.

According to Allmendinger and Prof. Rowena Lohman, earth and atmospheric sciences, the moderately-sized earthquake caused catastrophe because the earthquake was only eight meters below the surface.

O’Rourke stated that the damage caused by the earthquake would not have been nearly as severe “if there was a reasonable amount of engineering.”

Many unreinforced buildings collapse from the up-and-down motion and the shearing motion of surface waves. Earthquakes that happen closer to the surface are more dangerous because the waves dissipate less energy.

In the absence of wood and other materials, as Prof. Ken Hover, civil and environmental engineering, commented during a lecture on Jan. 29, Haitian buildings are generally made out of cement. This brittle material needs to be reinforced with steel in the vertical and horizontal directions, so the building becomes flexible enough to withstand pressure. Many buildings in Haiti are not reinforced.

Building codes, which provide guidelines for constructing earthquake-safe buildings, do not exist in Haiti, or the codes are unenforced, according to O’Rourke. Poor building construction affected poor people in Haiti, who could not afford to build homes with reinforced concrete, explained Prof. Chris Andronicos, earth and atmospheric sciences.

O’Rourke demonstrated by using before-and-after satellite images, that “soil liquefaction” was detrimental to buildings along the bay of Port-au-Prince, which sunk into the sea or were floated out to sea on liquid-like soil. This occurs when particles of sand in water-saturated soil loose the friction between one another due to earthquake shaking. The lack of friction causes the soil to flow as a liquid would. According to Hover, Port-Au-Prince’s bay was originally much deeper and was probably filled in over time “with a very soft and liquefiable soil” that contributed to the damage.

The damage may not be over.

“We tend to see the earth as very rigid, but on a large scale, rock can be flexible,” said Allmendinger. The movement and subsequent snapping of certain areas of a fault increases stress on other areas that have not slipped, changing the “stress field”. The fields 10’s or 100’s of meters away from the fault may change. Areas under stress are more likely to slip, creating the springing motion that causes earthquakes. Therefore, Hispaniola likely faces future earthquakes.

In addition, the approaching rainy season may bring landslides, health and sanitation issues to Haiti, especially to refugees in camps. The “first wave” of health issues, which includes injuries from the earthquake, is being treated, stated Hover. The “second wave”, infection, and the “third wave”, infectious diseases such as typhoid and diphtheria, are the challenges of the near future.

“There are mountains after mountains,” affirms a popular Haitian saying, summarizing the current predicament.

Original Author: Usha Rao