Scientists from Columbia University’s Earth Institute and Lamont-Doherty Earth Observatory have provided some photographs and commented analysis of the earthquake in Haiti.
–Photo from the scene. Preparing to move the injured from the UN Development Program compound. Uploaded from cell phone. Marc Levy, The Earth Institute, Columbia University.
MINUSTAH HQ building, Haiti. Photo by Marc Levy.
From Arthur Lerner-Lam Lamont, Doherty Senior Research Scientist, Seismology Geology and Tectonophysics:
There are several global plate tectonic models in common use for global earthquake hazard. Recent earthquakes are used to delineate the boundary between the Caribbean Plate and North American plate, which runs through Hispaniola. The boundary is characterized in these models as a simple strike-slip (lateral) fault system, extending west from the Puerto Rican trench and running to the north of Hispaniola. It’s not that simple.
In a Nature paper published in 1985, three Lamonters (students of Lynn Sykes) postulated that the boundary was twinned, with a second, active segment running parallel along the southern margin of Hispaniola, along the Cayman Trough. This segment does not have a lot of earthquakes relative to the northern branch, but their analysis suggested that this is because it may be “locked” between the occurrence of larger events. The global plate models took the lack of earthquakes as an indication that most of the relative plate motion is occurring along the northern segment. However, using this as the basis for the calculation of hazard potential is incomplete; a locked fault is very dangerous. Sykes et al. have been proven right (unfortunately).
The implications for future hazard are these: The fault that ruptured yesterday is a major component of a complex fault system – comprised of intertwined branches, not unlike the San Andreas in California or the Northern Anatolian Fault in northern Turkey. The release of stress yesterday has most likely loaded segments of this fault east and west of the segment that ruptured, and advanced the time to the next rupture. The segment that ruptured is probably only a 100 km long (or less), but the southern part of the system is probably 1000 km long or more. The western segments run through Jamaica, the eastern through the DR and Puerto Rico. In the next several days, I expect that calculations will give us a better idea of the excess loading on these segments.
From Dr. Geoffrey Abers, Doherty Senior Research Scientist:
I quickly made these 2 maps as an alternative to the USGS maps, to show a somewhat larger regional context around Haiti. These are generated with (LDEO-supported) GeoMapApp software.
Hispanola1.jpg shows M>5.5 earthquakes since 1970 through some time in 2009
haiti1day.jpg shows the last 24h of earthquakes/aftershocks.
– -this fault system (Enriquillo or Enriquillo-Plantain Garden FZ?) has been dead quiet for the instrumental record, despite large earthquakes in 1700’s
– -this aftershock zone is much smaller than the several hundred km length of the fault zone; loading of adjacent segments seems worth considering/evaluating. There’s a paper by Ali et al. (2008 GJI 174, 904-918) evaluating Coulomb stress buildup & interactions between this and the parallel fault system to the north, that I’m sure will be discussed in this context.
From Steve Cohen, executive director of The Earth Institute, writing in the Huffington Post that the crisis is “a critical test” for the Obama administration:
“Haiti is connected to our country by geography, family and history. We need to demonstrate American capacity and compassion in equal measure in the following weeks and months, and especially in the next 24 hours. … [But] there is a broader lesson to be taken from this disaster for both the United States and what we sometimes optimistically call the “community of nations.” As the world becomes more crowded and urbanized, the impact of natural disasters will only grow. It is not that we are seeing more hurricanes, earthquakes and floods than we used to, but rather that more people are in harm’s way than ever before. The lesson here is that we must build a global network of emergency response capacity that is far greater than the one we have now.