Mark McMenamin on Earthquakes
In the wake of the devastating earthquake in Haiti, Questioning Authority asked Mount Holyoke professor of geology Mark A. McMenamin to talk about the significance of this quake, the likelihood it could happen again in Haiti or elsewhere, and how to improve the chance for survival in a quake.
QA: The Caribbean has a history of seismic activity, and scientists have said the January 12 earthquake was no surprise given the conditions of the Enriquillo fault. Did they—and you—expect there would be an earthquake of this magnitude?
MM: The Enriquillo fault system in Hispaniola and its extension as the Plantain Garden fault zone in Jamaica are known to generate historic earthquakes. There were a series of large quakes in the 1600s to 1800s that struck Kingston, Port Royal, Cap-Haïtien, and Port-au-Prince. So yes, a major earthquake in Haiti is no surprise.
QA: There are two faults that run through Hispaniola. Could the activity in the Enriquillo fault trigger a quake in the Septentrional fault that runs primarily through the northern portion of the Dominican Republic? Is Haiti still at risk for more quake activity in the near future?
MM: The short answer is yes. Similar tectonic forces control the Enriquillo and Septentrional fault systems. These fault systems converge to the west as they reach the Cayman Trench. As left-lateral strike slip faults (that is, land north of the fault moves west or “left” as you look north from the other side of the fault), they form a kind of mirror image to the right-lateral strike slip San Andreas Fault system in California. Both fault systems are an expression of the overall southwesterly motion of North America.
QA: As we all remember, the earthquake that occurred in December 2004 in Indonesia triggered a massive tsunami with tragic consequences. How is it that this quake did not cause a tsunami in the Atlantic Ocean?
MM: The December 26, 2004 Sumatra-Andaman earthquake, the second largest quake ever charted on a seismograph, was powerful enough to set off earthquakes in Alaska. Unlike that quake, the Haiti earthquake did not displace significant amounts of sea water.
QA: Given the relative proximity of Hispaniola to the continental United States, do the faults there pose a danger to Florida or the southern United States?
MM: There is some risk, yes, but keep in mind that a strike slip fault (where the halves of the fault slide past one another in a horizontal motion) does not have the vertical displacement required to generate a great tsunami. More worrisome is the possibility of a major sciorruck (underwater landslide that triggers a tsunami) from La Palma in the Canary Islands. A sciorruck there could send a wave racing across the Atlantic to devastate our eastern seaboard.
QA: Could we have an earthquake of equal magnitude to Haiti's in New England? California? Other parts of North America?
MM: The question is not if, but when. A 7.0 quake, similar in magnitude to the earthquake that recently struck Haiti, hit Québec on February 5, 1663, and caused masonry collapse in Massachusetts. The same spot generated a 6.2 quake on February 28, 1925. The 1755 quake off of Cape Ann, Massachusetts, estimated at magnitude 6.0, caused brick buildings to collapse and cracks to open up in the ground. There is a 62 percent chance of a major earthquake occurring on California’s San Andreas Fault system within the next 30 years. Most worrisome of all is the New Madrid fault system in Missouri. The fault system is associated with the Reelfoot Rift, an ancient subterranean crack in the North America that dates back to the times of supercontinent Rodinia. On February 7, 1812, the New Madrid fault cut loose with a truly massive earthquake and three great aftershocks that changed the course of the Mississippi River, forming what is now called the Kentucky Bend. Fortunately, the area was sparsely populated at the time.
My prediction is that the next large earthquake felt in South Hadley will be centered in Québec, near Charlevoix. And this is just a hunch, but perhaps during the month of February.
QA: What should governments do to prepare for such a catastrophe and improve the rate of survival among their populations? What can we do as individuals to improve our own odds?
MM: After a major earthquake, four things are required in short order: medical supplies, clean water/food, shelter, and money to rebuild. I recommend that every town in our area maintain a strategic cache of water, food, and emergency medical supplies. The financial impact of a major earthquake could be staggering, especially in times of economic recession. In 2000, after my public Millennium Lecture urging us to prepare, I passed around a hat and collected sufficient funds to start the Geological Event Recovery fund to rebuild Mount Holyoke College. The development office did not express any interest at the time in setting up an account, and the money is still languishing in a jar in my laboratory rather than gathering interest in a long-term account.
As individuals, we should each keep a week’s supply of water and food at home, plus a sleeping bag and tent to provide necessary outdoor shelter. Also, we need to educate ourselves about what to do the instant the quake strikes. For example, Doug Campbell and Fr. Tom Hagan, both working for our local Springfield relief agency in the Delmas neighborhood, Cite Soleil, Haiti, each saved their lives by crawling under a sturdy metal office table when the quake struck.