By MIKE MILIARD  |  February 27, 2008
THE WORST earthquake in Massachusetts to date was the 1755 disaster at Cape Ann. Estimated to have registered 6.3 on the yet-to-be-invented Richter scale, it caused damage as far north as Portland, Maine. Image courtesy of the National Information Service for Earthquake Engineering, EERC, University of California, Berkeley.

An uneven playing field
Ours is a city flush with new development. The $14.6 billion Central Artery/Third Harbor Tunnel Project (a/k/a the Big Dig) is, at long last, finished. So confident are city officials in the sturdiness and stability of our streets that they’ve spearheaded construction of a Biosafety Level-4 laboratory. Huge new high-rise residential buildings are being erected in the South End and the Fenway, their massive girths resting on soft and soggy fill.

All recent construction has been built to comply with — and in some cases exceed — Massachusetts building codes that address seismic concerns. But until an earthquake hits, it’s tough to predict how those buildings will hold up.

Even the sturdiest structures are full of heavy light fixtures and heating ducts. That’s to say nothing of the catastrophic fires that are often the by-products of major quakes. Or even the chance of a small seismic tsunami flooding the waterfront. The property damage would easily be in the billions.

It’s impossible to predict, of course. But let’s play “what if?” If a magnitude-6 quake happened today, with its epicenter in Boston, “then you’re probably talking somewhere in the order of $40 billion [in damage] throughout Massachusetts,” says Edward Fratto, executive director of the Northeast States Emergency Consortium, a nonprofit all-hazards emergency-management organization based in Wakefield.

Worse, Fratto could envision perhaps 1200 to 1300 people dead and 20,000 to 25,000 injured. “The numbers go up considerably if the earthquake happens in a populous area,” he says. “Certainly, a large earthquake would have a significant impact.”

A look at the lay of the land (so to speak) is helpful to understanding New England’s unique earthquake risk. The western edge of the North American tectonic plate runs more or less directly under Los Angeles and San Francisco and northwestward toward Alaska. The eastern edge lies beneath the Atlantic Ocean, a little more than halfway between the East Coast and Europe.

At that spot, the “sea floor is opening, basically on the order of one to two inches a year,” says BC’s Ebel. As it does, it’s “pushing the North American plate roughly from east to west; on the other side, the plate is running into the Pacific plate. When the two plates rub together we have a lot of earthquakes, as we do out West.”

Meanwhile, here in the Northeast, at roughly the center of the North American plate, “what’s happening is the plate is very slowly being squeezed. Think about it like putting a clay brick in a vice. You can’t squeeze forever before the brick breaks to try to relieve the pressure.” The vice, Ebel reminds us, has been cranking for 150 million years. “Occasionally, the rock just cracks; it seems to preferentially crack here along the Appalachian region, where you have old faults that formed millions of years ago during past plate collisions.”

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