University Experts Assess Seismic Hazard
By Edwin L. Aguirre
The magnitude 9.0 earthquake that rocked the northeastern coast of Japan on March 11 unleashed deadly tsunami waves that wiped out entire villages.
What are the chances of such a devastating earthquake happening right here in New England?
“Nobody knows for sure,” says Prof. Arnold O’Brien 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.”
Looking Into the Past for Clues
According to the U.S. Geological Survey, the last time New England 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.”
The Clinton–Newbury Fault
O’Brien does 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 million 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 is 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 Atlantic Ocean, along the North American/Eurasian/African tectonic plate boundaries,” says Paikowsky. “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.”
Says civil engineering Asst. Prof. Tzu-Yang Yu: “Here in New England, new buildings need only to meet the minimum level of seismic resistance in their design. This is based largely on the site’s characteristics and the seismic history of the region.”
He says hurricane-force winds, not earthquakes, are the major hazards that local builders usually consider when constructing high-rise buildings.
“If geologists do discover a new, potentially dangerous fault, then the building codes will have to be re-evaluated, and old constructions will need to be reinforced or retrofitted to meet the new requirement,” he says.
A Worst-Case Scenario
Although a strong earthquake in New England is very unlikely based on the current understanding of the geology of the region, if a severe earthquake does occur, Yu says the devastation would be “unimaginable.”
“If that ever happens, buildings 10 stories or higher that were built to the current standard would be subject to considerable structural damage,” he says. “Walls would crack and the buildings would sink or tilt, though not necessarily collapse.”
He says soil liquefaction — a condition wherein high pressure from underground water loosens the ground and makes it fluid — can be a major problem, especially in Boston’s Back Bay.
“This entire area was underwater before it was filled with dirt in the late 1800s,” he says.
Liquefaction can cause structures to collapse vertically or horizontally like a pancake, and electrical cables and gas/water pipelines to break or rupture.
“Without water pressure in the hydrants, a firestorm can engulf the city very quickly,” he says. “This is the worst-case scenario.”
Adds O’Brien: “The question is not if a devastating earthquake will happen, but when. 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.”