By Dr. Robert Thorson
Philosopher Will Durant remarked on something that few people wish to dwell on: “Civilization exists by geological consent, subject to change without notice.”
Nowhere is his aphorism truer than in modern Haiti. This patch of dry land exists because of tectonic pressure. The veneer of Western civilization above it was changed without notice at 9:53 p.m. on Jan. 12 by a routine event originating at six miles’ depth at 18 degrees 27 minutes north latitude and 72 degrees 26 minutes west longitude.
The destruction that followed was staggering, even for scientists familiar with the physical setting, and who understood that disaster was waiting to strike.
Popular media outlets offered scant doses of the relevant science during the first few days after the quake. The coverage was focused almost entirely on the acute human tragedy, rather than on the geophysical reality, the back story behind the disaster.
Earthquakes don’t kill people by shaking them to death. Their secondary effects do. Falling buildings, tsunamis and landslides are the weapons of mass destruction involved. Luckily, these are manageable, given stable government, earth scienceeducation and sufficient funds for hazard mitigation.
The media script written for talking heads goes something like this. “It was business as usual in a poor, environmentally ravaged and politically unstable nation with uneasy diplomatic ties to the United States. Then came great rumbling noises, surface waves, hammer-like shocks, seismic rattles and the collapse of a known world. Striking next were fear, injury, death, despair, urgency, desperation, heroism, frustration, hunger, promises, anxiety, grief, anger, thirst and above all, suffering. Relief efforts are underway. Donations from celebrities, churches, governments, nonprofit organizations and coffee-can collections are pouring in. A nation destroyed will rise from the rubble.”
Though my heart grieves for those who suffer, my pre-frontal cortex grinds away on the more rational script, one based on excellent, carefully vetted and publicly available information from the U.S. Geological Survey.
The focus of the main shock took place along the Enriquillo-Plantain Garden fault zone. It is unequivocally active, with about 7 millimeters of average annual slip along the fault. Port au Prince, and the peninsula extending westward, lie directly above it. The historic record for strong and destructive earthquakes on or near this fault zone is also clear, based on accounts dating from the 17th century.
Human tragedies struck in 1618, 1673, 1684, 1751, 1761, 1770, and 1860. Since 1902, there have been eight earthquakes on or near the east-west trending fault (18 to 20 degrees latitude, 66 to 77 degrees longitude) with magnitudes equal to or larger than the event of Jan. 12. What is now being called “The Haiti Earthquake” is merely the latest in a series.
Studies of the aftershock sequence and the ground motion recorded on seismographs are entirely consistent with the tectonic geology: The lozenge-shaped island of Hispaniola was squeezed up between two large and gracefully curved fault zones that release part of that squeeze energy during frequent ruptures at unpredictable times.
Broadly speaking, the Jan. 12 rupture took place on a “California-style” strike slip fault. In California, the Pacific Plate slides northward relative to the North American Plate. In Haiti, the Caribbean Plate slides eastward relative to the same North American Plate at a rate of 20 millimeters per year, carrying Central America, the Yucatan Peninsula and parts of Columbia and Venezuela as if passengers on a great barge. Hispaniola is like a dinghy being squashed between these moving colossi while also being scraped on both sides.
The International Union of Geological Sciences said in its response to the tragedy: “The lack of education in and awareness of geological sciences worldwide tends to decrease awareness of the possibility of natural disasters and preparation for them and thus exacerbate their human and economic toll when they inevitably occur.”
I agree.