Haiti Earthquake — Looking for Lessons
UN Secretary General Ban Ki Moon made an appeal in February for $1.44 billion in humanitarian aid, of which about half had been funded as of mid-March. Reconstruction may cost as much as $14 billion, according to an estimate by the Inter-American Development Bank.
Extent of the Damage
Foreign teams of geologists, engineers, and architects have started making damage assessments in Haiti. As they conduct the slow work of deciding which buildings can be repaired and which must be torn down, crews of Haitian day laborers, paid through aid groups, have begun demolition in some areas.
While information on the full extent of destruction remains sketchy, a localized sample damage survey of 107 buildings in Port-au-Prince's downtown, carried out by the U.S. Geological Survey (USGS) and the nonprofit Earthquake Engineering Research Institute (EERI) of Oakland, California, found that 28 percent of the buildings had collapsed entirely and another 33 percent would require repair work.
The USGS/ EERI Advance Reconnaissance Team, a five-member team of seismology and earthquake engineering experts, visited the country about two weeks after the quake, and prepared a report based on their field reconnaissance.
In a sample survey area in Léogâne, west of Port-au-Price and even closer to the epicenter of the earthquake, 93 percent of 52 buildings inspected had either collapsed or sustained significant damage, according to the report.
Overall, single-story shanties with lightweight walls and roof, and single-story concrete or masonry buildings with light corrugated metal roofs, faired better proportionally than multi-story concrete apartment and office buildings, which were typically made vulnerable by the greater weight of concrete roofs, the report concluded.
Apparently, a larger proportion of more substantial, multi-story structures failed dangerously than of the most impoverished, less formal dwellings. Dozens of residential buildings of various types were observed to have collapsed due to earthquake-induced landslides.
Earthquake-induced soil liquefaction was also a major cause of dangerous building and structure failure in several areas. Liquefaction is considered the primary cause of collapse of port facilities, which caused deaths directly and has hampered relief efforts.
First Big Quake in a Century - More on the Way
In recent memory, concerns in Haiti about buildings' structural integrity have centered on whether they could withstand hurricanes — not earthquakes. The country is in a patch of Caribbean that each year sees a generous share of severe weather.
Ironically, a building culture that had been adapting to hurricane risk by moving toward heavier construction may have been creating grave new risks in the form of disproportionate seismic loadings from the very same weightiness.
In contrast, Haiti hadn't experienced a major earthquake since 1860, far too long ago to readily inform contemporary building practices. And the January 2010 quake more closely resembled one that struck the country even farther back, in 1770, according to Walter Mooney, a USGS earthquake expert who traveled to Haiti as part of the USGS/ EERI Advance Reconnaissance Team in late January and early February, then returned in mid-March.
"The future is not rosy. They have to be prepared for another event of equal magnitude" within the next 10 to 20 years, he says. "Historically, that's what happens."
Mooney explains that the 1770 event was the second of two earthquakes. The first occurred in 1751, pushing the eastern end of the fault toward the Dominican Republic. When the second quake struck 19 years later, it moved the fault line back toward the west.
This time around, Mooney says, the order is reversed in terms of directionality, but the one-two punch is likely to be repeated, as the compression created along the fault line in January eventually causes another quake — sort of like a spring being compressed and then releasing.
"The good news is, we have a very good understanding of what went on out there. The situation that they are facing is highly comparable to that of the San Francisco Bay Area," says Mooney.
Given the similarities to Northern California's earthquake vulnerability, Mooney says the USGS has formally recommended that Haiti adopt California state building codes. Now, it's up to the Haitian government to follow through with new legislation, he says. International aid funding for the code localization and adoption process a limiting factor in the past will likely be needed for it to be successful.
And, of course, that would just be an initial step, since evolving a building culture takes much more than just a change in the official rules.
Even if legislation isn't enacted, international donors, who are expected to pay for much of the country's reconstruction, may make the stricter rules a sort of de facto code by requiring that new construction they fund meet strong standards in major new construction projects, according to Mooney.
Factors That Lead to the High Death Toll
It's natural to compare the Haiti earthquake to other recent quakes, most immediately to Chile's February 27 earthquake, which registered 8.8 on the moment magnitude scale, and which officially killed just 452 people and displaced far fewer people, despite its much greater magnitude.
Many observers attribute the better outcome in Chile to a strict seismic building code, among a variety of factors.
However, the magnitude of an earthquake is just a single number representing the fundamental energy released geologically. Because of several other factors, the impact on buildings can vary widely for earthquakes of similar magnitude.
These factors include the depth of the quake, the horizontal distance from the quake zone to structures, the spatial concentration of the geological energy release, the duration of shaking, local geological amplification effects (often from alluvial soils), and even the distribution of ground accelerations between the horizontal and the vertical.
According to USGS reports, compared to the Chile event, the Haiti earthquake was shallower, much closer to a large population center, and highly concentrated relative to its magnitude value.
Each of these factors can serve to increase the actual level of acceleration to which buildings are subjected, relative to the basic earthquake magnitude. And much of Port-au-Prince, like many harbor towns, is built on alluvial soils, though the depth and distribution of those soils remains largely unknown.
In addition and as an alternative to the simple event magnitude, the USGS produces "shake maps" for major quakes around the world, using the Modified Mercalli Intensity scale. These maps show a closer approximation of the level of earthquake forces actually experienced by structures on the ground.
Comparing the Modified Mercalli Intensity maps for the Haiti and Chile events suggests that, despite the high underlying geological energy of the Chile event, vastly more structures in Haiti, occupied by as many more people, may have been subjected to the highest levels of shaking in the January earthquake. (Due to the scarcity of instrumentation for the Haiti event, these numbers are likely to continue to be adjusted.)
For instance, the Haiti event is estimated to have had 2,000 people in areas subjected to the highest Modified Mercalli Intensity level, X, and 2,387,000 people in areas subjected to the next intensity level, IX. In comparison, for the Chile event, current USGS estimates show the next level down, level VIII, as the highest level to which any significant population was subjected.
Discuss this article in the Architecture Forum...