Haiti Earthquake Science
Edit February 27, 2010: for information on the Chile and Japan earthquakes, please see this new post.
The day after the earthquake in Haiti I put up a post that talked a little about the devastation and then referred people to the excellent United States Geological Survey (USGS) site for general earthquake information. I’ve gotten a lot of hits on that post from people searching for “Haiti Earthquake Science” and the like, so let’s talk more specifically about the science behind the earthquake in Haiti.
Why did this earthquake happen in Haiti? First of all, this earthquake did not strike the people of Haiti because God hates them (thanks Newsweek), because they have a pact with the devil (thanks Pat Robertson), or because of their belief in voodoo (thanks, well, Pat Robertson again). The earthquake struck Haiti because Haiti sits on a fault and that fault slipped suddenly, releasing energy in the form of an earthquake. It’s the same reason all earthquakes happen; it’s just the way our planet works.
The Earth’s crust is not one solid mass. It’s a series of large (like, larger than continent size large) slabs called tectonic plates that float on the more molten middle part of the earth, called the mantle.
These plates move around on the upper mantle and interact with each other in a number of different ways. The areas where this interaction occurs are called plate boundaries or boundary environments. One of the more dramatic examples of this interaction is the formation of the Himalayas on the border between India and the Tibetan plateau. The Indo-Australian plate is pushing northward into the Eurasian plate, causing both plates to buckle upward, forming the mountain range. Geologists call this process orogeny, from the Greek for “mountain building.” What’s really cool is that this process is still going on. The Himalayas grow about a centimeter (just under half an inch) every year.
Tectonic plates can also interact by sliding past each other. The boundaries where this sliding occurs are commonly called fault lines or fault systems. The island of Hispaniola, shared by Haiti on the west and the Dominican Republic on the east, sits at the boundary between the North American plate and the Caribbean plate. Haiti has two major fault systems, the Septentrional fault system in the north, and the Enriquillo-Plantain Garden fault system to the south. The January 12th quake occurred when the North American plate moving westward and the Caribbean plate moving eastward moved suddenly past each other, slipping, effectively, and releasing tension building up in the Enriquillo-Plantain Garden fault zone in the form of a massive earthquake.
Some warning, but accurate predictions are not possible Geologists monitor the movement of the tectonic plates and activity at plate boundaries. They know how much each plate moves per year, which direction they are moving in, and how each plate interacts with it’s neighbors. Combining this information with historic records of past earthquakes, scientists can predict which fault systems are most likely to experience an earthquake in the near future and how large that earthquake could be. In fact, a team of scientists from the United States and Jamaica presented a talk in 2008 at the 18th Caribbean Geological Conference predicting a magnitude 7.2 earthquake along the Enriquillo-Plantain Garden fault zone. They warned that without adequate preparation, the earthquake could cause significant death and destruction in Haiti, the Dominican Republic and/or Jamaica.
The problem is, scientists have no way of knowing exactly when an earthquake will occur. It could be a year from now, it could be a hundred years from now. They also have no way of knowing exactly how powerful an earthquake will be, where it will be centered, or what other factors will influence the destructive power of the earthquake. Because scientists are necessarily vague in their predictions, the will to act is often lost among people living in earthquake zones, often to horrific ends.
How does the January 2010 Haiti earthquake relate to other recent quakes? The Haiti earthquake measured 7.0 on the Richter scale. This is not the name of the devise used to measure the shaking (that’s a seismograph). The Richter scale takes seismograph information and turns it into a number representing the magnitude of the earthquake. For every whole number increase on the scale, the magnitude increases by a factor of ten. This means an earthquake of magnitude 7.0 is ten times more powerful than one of magnitude 6.0. To put that into perspective, the earthquake that caused the December 2004 tsunami in southeast Asia had a magnitude of 9.1, over 100x more powerful than the 2010 Haiti quake. The 2008 quake in Sichuan Province, China measured a magnitude 7.9, nearly 10x more powerful than the Haiti quake. Both of these quakes were among the most destructive earthquakes in recorded history. The most powerful earthquake ever recorded occurred in Chile in 1960. That earthquake had a magnitude of 9.5.
Could Haiti have prevented the horrific loss of life caused by this earthquake? Yes, if the resources to build adequate infrastructure had been available to them. The 1989 Loma Preita earthquake that rocked San Francisco, famously collapsing a section of freeway and disrupting the 1989 World Series, was nearly the same magnitude (6.9) but resulted in only 62 deaths. Technology exists to prevent building collapse, rescue survivors from rubble and treat the injured in a timely way. Unfortunately, the Haitian people do not have access to that technology. The reasons why are complex and well beyond the scope of a science blog, but it’s a theme that runs throughout science, engineering and medicine (think HIV/AIDS treatment, accessibility of clean water, access to vaccination, disaster preparedness, famine prevention). Technology to prevent human suffering often exists, but access is limited, funding is limited, political will is limited, and on and on. What can we do to make sure that science and technology benefit everyone, not just a privileged few?
If we have learned nothing else from this earthquake, we need to learn that where and how natural disasters strike may be largely outside of human influence, but the amount of devastation they cause can be controlled with preparation and education.