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Boston's Earthquake Problem - The Boston Globe
Boston's Earthquake Problem
By Jeremy Miller
May 28, 2006
ON NOVEMBER, 18, 1755, THE EARTH beneath the waters off Cape Ann heaved. Within seconds, the
seismic waves generated there traveled to the twisting lanes and wharves of pre-Revolutionary Boston.
According to historical accounts, chimneys toppled from roofs, steeples parted from churches, and gables
crumbled from building fronts and shattered on the lanes below. The weather vane atop Faneuil Hall
snapped. Vibrations were felt from Halifax, Nova Scotia, to Chesapeake Bay. Estimated at a magnitude 6.2,
the Cape Ann earthquake is one of New England's strongest in recorded history.
But it's not the aberration you might think. In an average year, 30 to 40 earthquakes strike New England.
Only a small fraction are strong enough to detect without instruments, yet a few have been large enough to
cause damage. Big quakes outside New England can be felt here, too. Four years ago, a magnitude 5.2
tremor that jolted a remote region in the Adirondack Mountains, causing roads to collapse and foundations
to crack, was felt as far south as Maryland. In 1929, a magnitude 7.2 quake centered off the southern coast
of Newfoundland generated a tsunami that killed at least two dozen people; the quake was felt as far away
as New York City.
A study by Boston College seismologist John Ebel, published earlier this year, zeroes in on the epicenter of
the 1755 Cape Ann earthquake. Ebel, who has spent the last 25 years studying local quakes, also proposes a
new idea: that all New England earthquakes -- including the 1755 one and a 1638 magnitude 7 quake
probably centered in New Hampshire -- might be the aftershocks of an even larger historical quake. He says
another large one may be looming.
Our earthquake threat is made more pressing by what distinguishes Boston among American cities: its
elegant brick-and-mortar architecture, which in many cases sits on loose, unstable soil. Experts also warn
that the city's aging infrastructure and utilities -- sewer mains, gas lines, bridges, and overpasses -- are rife
with vulnerabilities. The length of time since the last significant quake seems to have dulled -- and, in some
cases, erased -- our perception of the threat. Yet earthquakes do happen here. Why, then, isn't Boston ready
for the next one?
TO UNDERSTAND BOSTON'S COMPLEX SET OF risks, we must first understand the ground beneath our
feet. Most quakes, says Ebel, who directs BC's Weston Observatory, occur at the boundaries of tectonic
plates, great continent-carrying masses of land. But Boston sits more than 1,000 miles from the edge of the
North American plate. Using seismic data collected over the last 75 years at the observatory and historical
records, including church logs and newspapers, Ebel and his colleagues estimate that moderate (magnitude
5) quakes happen every 50 to 90 years in New England. He extrapolates that magnitude 6 quakes, like the
one in 1755, occur in the region every 500 to 900 years.
Scientists once believed that New England earthquakes were caused by the slow, and occasionally jarring,
upward movement of the region after the retreat of the glaciers 10,000 years ago. But current data suggest
that our quakes result from the collision of the North American and Pacific plates, which puts unrelenting
pressure on the continent. And, of course, Ebel has added a new wrinkle - that New England's quakes might
be aftershocks of a larger historical event. "It's a very new idea," he says. "But the largest quakes that are
possible in New England may still be on the horizon."
Whatever the size of the quake, says Nano Seeber, a seismologist at Columbia University's Lamont Doherty
Earth Observatory, its effects are magnified by the way that earthquakes travel through the rocks of the
Northeast. Rock formations here tend to be more dense, rigid, and cold and less fractured than rocks in,
say, California. So seismic waves generally travel farther. It also appears that a greater proportion of
Northeast quakes happen near the surface, so smaller tremors have the potential to do greater damage. "In
California, damage happens at 5.5," Seeber says. "Here, it can happen at 4.5."
"Amplification" and "liquefaction" are two words often used by specialists to describe Boston's earthquake
vulnerability. Amplification -- when seismic waves hit a region of loose soil and become stronger -- was
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demonstrated to horrific effect in the Mexico City quake of 1985; a strong earthquake centered hundreds of
miles away was strengthened at the surface by the soft soils beneath the city. Thousands of unreinforced
buildings were leveled, and 9,500 people were killed.
Liquefaction happens when saturated sand or gravel deposits are shaken, increasing the water pressure
between the grains and causing the soil to flow freely. When soil liquefies, buildings may sink as though
into quicksand and can buckle as their foundations shimmy and shift; that's what happened in the Loma
Prieta quake of 1989, which killed at least 63 people in the San Francisco Bay area. A 2004 study of Boston
by researchers Charles Brankman of Harvard University and Laurie Baise of Tufts University shows the
greatest threat of liquefaction to areas built on fill, such as Logan Airport, Back Bay, South Boston, and the
Cambridge waterfront.
THE FILLING OF MARSHES and shallow waters helped Boston prosper. "It's hard to conceive of Boston
and, in fact, almost any big city in the United States, without the process of land making," says Nancy
Seasholes, a research fellow at Boston University and author of Gaining Ground: A History of Landmaking
in Boston. However, land making is a fundamental reason why many of Boston's buildings are not as stable
as they look. The stately row houses that line Tremont Street in the South End, Charles Street at the foot of
Beacon Hill, and Commonwealth Avenue in Back Bay are anchored by wooden pilings driven into the soil
like candles into a moist birthday cake.
And the cake is getting stale.
Paul Finnegan awoke in his Beacon Hill bedroom on December 18, 1986, to a crash of brick and mortar
next door. "It was the middle of the night," he recalls. "My head was right against the adjoining wall, and I
heard this massive crash. I bolted upright to see if it was an earthquake." It was no earthquake but his
neighbors' home buckling above its rotted foundation piles. "They were locked inside. They couldn't get
their doors and windows open. It was a real mess." The level of water in the soil had fallen, and the wooden
pilings, exposed to air, had rotted and failed, causing the building to settle nearly half a foot. (Most pilings
in that area reach about 30 feet into the ground.)
With Boston's complex history of construction, large volumes of water have either leaked or been pumped
out of the ground. Yet this ground water is crucial in preventing dry rot and insect infestation of the wooden
pilings that hold up many of the city's older buildings. The falling water table has left the foundations of
many of Boston's historic buildings compromised and susceptible to earthquakes and other disturbances.
These landfill problems -- amplification, liquefaction, and dry rot -- are compounded by the fact that
Boston's grand old stock of wood-frame row houses, red-brick Victorians, and other unreinforced masonry
buildings are, by almost every measure, structurally defenseless against the ground movement experienced
in a large earthquake. Old buildings in Boston's suburbs face less risk, since fewer are built on landfill.
WE CAN GUESS THE TOLL AN EARTHQUAKE would exact on Boston. In 1990, researchers predicted
that a magnitude 6.2 quake would cause $2 billion to $10 billion in damage in the Boston area, along with
"hundreds of deaths and thousands of major and minor injuries." An unpublished 1997 study of Boston
forecast similar results. (The Loma Prieta quake caused about $10 billion in damage.) And in 1997, a
Stanford University researcher concluded that -- given the high population density, large proportion of
fragile buildings, and precarious soil conditions -- the risk of a quake causing catastrophic damage was
greater in Boston than in San Francisco or Mexico City.
The city's most fragile buildings went up before seismic building codes were introduced to the city in 1973
and adopted statewide in 1975. Rolf Goetze, a researcher at the Boston Redevelopment Authority, estimates
that about three-quarters of the city's 100,000 buildings were constructed before 1973. He adds that the
city doesn't track how many of these older structures have been brought up to at least 1973 building
standards.
While many of Boston's dwellings and low-rise brick structures lack strong lateral systems that compensate
for forces like a quake that move a building from side to side, the modern skyscrapers that punctuate the
city skyline are equipped with these key systems. "Lateral force requirements came into effect in
Massachusetts with the seismic code changes in the 1970s," says Dominic Kelly, a structural engineer at the
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Waltham offices of Simpson, Gumpertz and Heger who specializes in earthquake retrofitting and seismic
design. For one example of a building representing the leading edge of seismic engineering, Kelly points to
Cambridge. There you'll find Simmons Hall, an MIT dormitory that looks like a giant Lego building.
Throughout the concrete structure are shear walls -- reinforced barriers placed to prevent a building from
being pulled apart, or sheared, internally by side-to-side movement.
If only Boston's underground displayed such revolutionary design. Many of the aging gas, sewer, and water
mains beneath the city were built long before there were seismic provisions in the building code. "There you
have a real problem," says John Christian, an engineering consultant in Boston. "To lose water for a few
days is one kind of dilemma, but if you need that water to put out fires, like they did in San Francisco in
1906, you could have a real problem." And the city's roads, tunnels, and bridges? "The good news is that the
majority of these structures have been built up to seismic codes," Christian says. "The bad news is that these
things have, by all accounts, not been properly maintained and therefore are more vulnerable to
disturbances." One benefit of the Big Dig, says Christian -- who worked as a consultant on the highway
project after water was found leaking into the tunnels -- is that outdated utilities and infrastructure have
been replaced with the most current, earthquake-resistant designs. "The Dig is certainly one project in the
city where the latest seismic provisions have been incorporated."
EARTHQUAKES COME WITH LITTLE warning. In most cases, mere seconds. Seismologists are working
to develop a system that would alert vulnerable areas days or months before. Nascent alarm systems can do
such things as detect seismic waves and shut off gas lines, but good building design is the best defense
against quakes, authorities say.
Yet Boston has been slow to turn the evidence and predictions of engineers and seismologists into action.
While Massachusetts's building codes are adapted from California's -- the gold standard -- the effort to
protect the city's historic landmarks and provide incentives to property owners to retrofit vulnerable
buildings is embryonic, at best.
California planners and seismologists are not surprised that New Englanders have ignored earthquake
preparedness. Susan Tubbesing, executive director of the Earthquake Engineering Research Institute in
Oakland, says that even in earthquake-prone California, retrofitting is a hard sell. "We are most concerned
with the large number of unreinforced masonry buildings, offices, and apartments that remain in
California," she says. "These are the kind of buildings that 'pancaked' in the 1989 Loma Prieta and 1994
Northridge earthquakes."
While San Franciscans have spent billions in retrofitting over the last 20 years, 5.8 percent of San Francisco
County's single-family housing stock and 8.7 percent of its multi-family stock are built of unreinforced
masonry, according to the Association of Bay Area Governments. "San Francisco has lots of these buildings,
but there is no way to force businesses and homeowners to come into compliance," Tubbesing says. Ken
Topping, former director of city planning for Los Angeles, says that retrofitting an old building can cost
more than $100 per square foot. "Owners of larger buildings and retail space often find it difficult to make
the changes," he says. In 1999, city planners abandoned a retrofitting mandate in San Bernardino because
they were afraid it would hurt small-business owners and stunt economic growth.
The insurance picture also shows public apathy. Despite predictions that there is a 62 percent chance of San
Francisco experiencing a serious tremor in the next 30 years, only 13 percent of Californians own
earthquake insurance. "In New England, the percentage of earthquake insured is surely far lower," says
Jeanne Salvatore, a spokeswoman for the Insurance Information Institute in New York City.
Certainly, retrofitting every seismically deficient building in Boston would be a logistically Herculean and
financially crippling task. At current rates of retrofitting and new construction, says Ebel of the Weston
Observatory, half of the city's buildings will meet seismic standards by 2036. Only time and geology will tell
whether this is fast enough. However, a more focused push could be made to coordinate a citywide response
and bring Boston's landmark buildings into compliance. If cost and time will not allow the city's vulnerable
buildings to be retrofitted, then the people inside should be made aware by collecting structural
information in a central database that is easily accessible to renters and home buyers. Owners can reduce
their risk by having their homes inspected for major structural weaknesses like rotting piles and foundation
cracks. The first step in preparing for an earthquake is to acknowledge the temblors' tremendous,
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transformative power -- as well as their place in history -- even in spots where the ground appears
deceptively firm.
Jeremy Miller is a freelance writer in Boston. E-mail him at jeremy.j.miller@rcn.com.
© Copyright 2011 Globe Newspaper Company.
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