Seismology Still not an Exact Science
By Edwin L. Aguirre
On Jan. 12, a powerful, magnitude 7.0 earthquake rocked the island of Hispaniola, just 15 miles from the Haitian capital of Port-au-Prince. This was followed eight days later by a magnitude 5.9 aftershock only 20 miles from the first epicenter. Images of the horrific devastation and carnage that gripped the impoverished Caribbean nation were splashed all across televisions, newspapers and the Internet for weeks.
Here in the United States, a magnitude 5.9 quake struck off the coast of Northern California on Feb. 4 and, six days later, a magnitude 3.8 tremor rattled residents in northern Illinois, including Chicago. Fortunately, no major damages or casualties were reported in both events.
What are the chances, one may ask, of an earthquake happening right here in New England?
“Nobody knows for sure,” says Prof. Arnold O’Brien, chair of the Environmental, Earth and Atmospheric Sciences Department. “Unlike on the West Coast, earthquakes happen so infrequently here in the Northeast that they are more difficult to predict. Our historical records date back only to the 1600s and they are very sketchy. It’s hard to derive any scientific conclusions based on scant historical reports.”
According to the U.S. Geological Survey, the last time the region experienced a series of major seismic events was in the 1700s. One happened on Nov. 10, 1727, on the northern Cape Ann region east of Newbury, and was followed by strong aftershocks.
Another quake occurred on June 14, 1744, this time on southern Cape Ann. It was felt not only in Newbury, Ipswich and Boston, but all the way from Maine to New York City.
The region’s most powerful temblor to date took place on Nov. 18, 1755, again on Cape Ann. In Boston, chimneys were leveled or heavily damaged, and stone fences were knocked down. New springs formed, and old springs dried up. Ground cracks were reported in Scituate, Pembroke and Lancaster, and the shaking was felt from Halifax, Nova Scotia, to Chesapeake Bay in Maryland.
“It’s hard to say when the next big one is coming,” says O’Brien. “There’s not enough data and not long enough records to go with so we cannot say for certain when the next one is going to be. Earthquakes do happen regularly in the region, but most of them are too weak or too remote to be felt.”
He did point out, however, that a fault zone - called the Clinton-Newbury fault - runs about a mile south of UMass Lowell’s North Campus close to Route 110 in Lowell, and continues through Drum Hill and Westford.
He explains it’s an ancient “suture” that was created during the Paleozoic era about 250 to 450 million years ago, when an island mass collided with the North American tectonic plate and was dragged down underneath the plate.
“You can’t see any evidence of the fault on the surface, just a lot of crushed, broken rocks,” he says.
Compared to the San Andreas fault in western North America, which is the most heavily studied and monitored fault on the continent and where ground movement is so evident, the Clinton-Newbury fault is not very well investigated. However, O’Brien says there has not been any significant seismic activity in the Clinton-Newbury fault and he doesn’t expect any in the foreseeable future.
He adds that there are also a series of faults around Boston, such as the Bloody Bluff fault near Lexington, but, like the Clinton-Newbury fault, they are also inactive.
Civil Engineering Prof. Samuel Paikowsky, director of UMass Lowell’s Geotechnical Engineering Research Laboratory, says major fault lines do exist but they are situated far from the coast.
“These faults are east of us under the ocean, along the North American/Eurasian/African tectonic plate boundaries,” he says. “They are far from us - about a thousand miles away. They are difficult to identify, but there is new research utilizing satellite imagery for that purpose.”
Paikowsky says modern buildings in Massachusetts were made to withstand earthquakes, but the level of design demand depends on the year the structures were built.
“The building codes are evolving and the newer ones are always more restrictive than the former,” he says.
So should we worry about earthquakes at all?
“Very much so,” says Paikowsky. “When it comes, it will be a big one.”
“The question is not if a devastating earthquake will happen but when,” says O’Brien. “So we should build and plan for it regardless of whether the earthquake will likely happen 50, 100 or even 500 years from now. It’s better to be prepared.”