On the anniversary of the January 12th 2010 magnitude 7.0 earthquake in Haiti
it's important to reflect on the plate tectonic context and human impact of
that event. The Caribbean Plate moves eastward at about 2 centimeters per year
with respect to the North American and South American Plates. The boundary
between the North American and Caribbean Plates, in the Greater Antilles, is a
zone of distributed deformation broken into at least four microplates. These
microplates accommodate the transition of the North American Caribbean plate
boundary from strike-slip in the Cayman Trough between Cuba and Jamaica, to
oblique collision between Hispaniola and the Bahama Platform, to oblique
subduction at the Puerto Rico Trench, and then to subduction at the Lesser Antilles
Trench. The largest of these is the Gonave microplate that stretches from the
Cayman Spreading Center, to western Hispaniola in Haiti. The Gonave microplate
is bounded on the north by the Septentrional Fault, and on the south by
the Enriquillo Fault. These faults are predominantly left-lateral strike-slip
faults and both have rates of long-term motion of about one centimeter per year.
Major earthquakes on the Enriquillo Fault were documented in 1751 in 1770.
They were followed in 1842 and 1887 by major earthquakes on the Septentrional Fault.l
Over the following centuries the region around Port-au-Prince grew to
over three million people. Then, with little warning, the magnitude 7.0
earthquake occurred on the Leagone Fault just north of the Enriquillo Fault.
The epicenter was only 16 kilometers from Port-au-Prince. Rupture initiated at
12 kilometers depth and progressed upward and to the west reaching maximum
fault displacement of 5 meters at 5 kilometers depth. Resulting
ground-shaking in Port-au-Prince was strong to severe, with liquefaction
occurring in port areas and landslides affecting slopes. At least 52 felt
aftershocks greater than magnitude 4.5 were recorded in the next 12 days.
The human impact of the 2010 Haiti earthquake was horrendous with estimates
of at least a hundred thousand and possibly over 200,000 fatalities. Over
one million people were left homeless. This earthquake was the fourth most lethal
earthquake of any magnitude in the last 100 years and was five times more fatal
than any historical magnitude 7 earthquake. Why was this earthquake so deadly?
In a word? Construction. Typical concrete and
cinderblock buildings can survive hurricane-force winds but are extremely
vulnerable to earthquake ground shaking. Many structures collapse because the
lightly reinforced or unreinforced concrete columns or masonry-block walls
could not support the heavy concrete slabs of floors and roofs. The ability of
modern buildings, like this one across the street from the hospital, to
withstand ground shaking virtually undamaged, demonstrates the effectiveness
of earthquake resistant design and construction. In addition to overcrowding
Haiti is the most impoverished nation in the Western Hemisphere. This, and the
remoteness of the island made cleanup a monumental task, plus rebuilding using
the best thus most expensive construction materials and methods was
just not economically feasible. Nevertheless, important measures were
taken to increase earthquake resilience during the recovery and rebuilding major
efforts by the Haitian government and non-governmental agencies, such as Geo
Hazards International and Build Change included training local people to
incorporate cost-effective earthquake resistant design into the rebuilding and
new construction. The devastating losses in Haiti are a lesson to other
seismically active areas around the world. How buildings are constructed matters!
Engineering buildings and infrastructure to survive earthquake
shaking can save lives and property as well as help communities to recover more
quickly after disaster strikes.