Earthquakes May Endanger New York More Than Thought, Says Study
Indian Point Nuclear Power Plant Seen As Particular Risk
www.andrewtheprophet.com/11064
New York City and a few other parts of the eastern United States stand out on US Geological Survey seismic hazard maps
Courtesy USGS Earthquake Hazards Program
A study by a group of prominent seismologists suggests that a pattern
of subtle but active faults makes the risk of earthquakes to the New
York City area substantially greater than formerly believed. Among other
things, they say that the controversial Indian Point nuclear power
plants, 24 miles north of the city, sit astride the previously
unidentified intersection of two active seismic zones.
The paper appears in the current issue of the Bulletin of the Seismological Society of America.
Many faults and a few mostly modest quakes have long been known
around New York City, but the research casts them in a new light. The
scientists say the insight comes from sophisticated analysis of past
quakes, plus 34 years of new data on tremors, most of them perceptible
only by modern seismic instruments. The evidence charts unseen but
potentially powerful structures whose layout and dynamics are only now
coming clearer, say the scientists. All are based at
Columbia University’s Lamont-Doherty Earth Observatory, which runs the
network of seismometers that monitors most of the northeastern United States.
Lead author
Lynn R. Sykes
said the data show that large quakes are infrequent around New York
compared to more active areas like California and Japan, but that the
risk is high, because of the overwhelming concentration of people and
infrastructure. “The research raises the perception both of how common
these events are, and, specifically, where they may occur,” he said.
“It’s an extremely populated area with very large assets.” Sykes, who
has studied the region for four decades, is known for his early role in
establishing the global theory of plate tectonics.
The authors compiled a catalog of all 383 known earthquakes from 1677
to 2007 in a 15,000-square-mile area around New York City. Coauthor
John Armbruster estimated
sizes and locations of dozens of events before 1930 by combing
newspaper accounts and other records. The researchers say magnitude 5
quakes—strong enough to cause damage--occurred in 1737, 1783 and 1884.
There was little settlement around to be hurt by the first two quakes,
whose locations are vague due to a lack of good accounts; but the last,
thought to be centered under the seabed somewhere between Brooklyn and
Sandy Hook, toppled chimneys across the city and New Jersey, and
panicked bathers at Coney Island. Based on this, the researchers say
such quakes should be routinely expected, on average, about every 100
years. “Today, with so many more buildings and people, a magnitude 5
centered below the city would be extremely attention-getting,” said
Armbruster. “We’d see billions in damage, with some brick buildings
falling. People would probably be killed.”
Starting in the early 1970s Lamont began collecting data on quakes
from dozens of newly deployed seismometers; these have revealed further
potential, including distinct zones where earthquakes concentrate, and
where larger ones could come. The Lamont network, now led by coauthor
Won-Young Kim,
has located hundreds of small events, including a magnitude 3 every few
years, which can be felt by people at the surface, but is unlikely to
cause damage. These small quakes tend to cluster along a series of
small, old faults in harder rocks across the region. Many of the faults
were discovered decades ago when subways, water tunnels and other
excavations intersected them, but conventional wisdom said they were
inactive remnants of continental collisions and rifting hundreds of
millions of years ago. The results clearly show that they are active,
and quite capable of generating damaging quakes, said Sykes.
All known quakes, greater New York-Philadelphia
area, 1677-2004, graded by magnitude (M). Peekskill, N.Y., near Indian
Point nuclear power plant, is denoted as Pe.
Adapted from Sykes et al.
One major previously known feature, the
Ramapo Seismic Zone,
runs from eastern Pennsylvania to the mid-Hudson Valley, passing within
a mile or two northwest of Indian Point. The researchers found that
this system is not so much a single fracture as a braid of smaller ones,
where quakes emanate from a set of still ill-defined faults. East and
south of the Ramapo zone—and possibly more significant in terms of
hazard--is a set of nearly parallel northwest-southeast faults. These
include Manhattan’s 125th Street fault, which seems to have generated
two small 1981 quakes, and could have been the source of the big 1737
quake; the Dyckman Street fault, which carried a magnitude 2 in 1989;
the Mosholu Parkway fault; and the Dobbs Ferry fault in suburban
Westchester, which generated the largest recent shock, a surprising
magnitude 4.1, in 1985. Fortunately, it did no damage. Given the
pattern, Sykes says the big 1884 quake may have hit on a yet-undetected
member of this parallel family further south.
The researchers say that frequent small quakes occur in predictable
ratios to larger ones, and so can be used to project a rough time scale
for damaging events. Based on the lengths of the faults, the detected
tremors, and calculations of how stresses build in the crust, the
researchers say that magnitude 6 quakes, or even 7—respectively 10 and
100 times bigger than magnitude 5--are quite possible on the active
faults they describe. They calculate that magnitude 6 quakes take place
in the area about every 670 years, and sevens, every 3,400 years. The
corresponding probabilities of occurrence in any 50-year period would be
7% and 1.5%. After less specific hints of these possibilities appeared
in previous research, a 2003 analysis by
The New York City Area Consortium for Earthquake Loss Mitigation put the cost of quakes this size in the metro New York area at $39 billion to $197 billion. A separate
2001 analysis for northern New Jersey’s Bergen County
estimates that a magnitude 7 would destroy 14,000 buildings and damage
180,000 in that area alone. The researchers point out that no one knows
when the last such events occurred, and say no one can predict when they
next might come.
“We need to step backward from the simple old model, where you worry
about one large, obvious fault, like they do in California,” said
coauthor
Leonardo Seeber.
“The problem here comes from many subtle faults. We now see there is
earthquake activity on them. Each one is small, but when you add them
up, they are probably more dangerous than we thought. We need to take a
very close look.” Seeber says that because the faults are mostly
invisible at the surface and move infrequently, a big quake could easily
hit one not yet identified. “The probability is not zero, and the
damage could be great,” he said. “It could be like something out of a
Greek myth.”
The researchers found concrete evidence for one significant
previously unknown structure: an active seismic zone running at least 25
miles from Stamford, Conn., to the Hudson Valley town of Peekskill,
N.Y., where it passes less than a mile north of the Indian Point nuclear
power plant. The Stamford-Peekskill line stands out sharply on the
researchers’ earthquake map, with small events clustered along its
length, and to its immediate southwest. Just to the north, there are no
quakes, indicating that it represents some kind of underground boundary.
It is parallel to the other faults beginning at 125th Street, so the
researchers believe it is a fault in the same family. Like the others,
they say it is probably capable of producing at least a magnitude 6
quake. Furthermore, a mile or so on, it intersects the Ramapo seismic
zone.
Sykes said the existence of the Stamford-Peekskill line had been
suggested before, because the Hudson takes a sudden unexplained bend
just ot the north of Indian Point, and definite traces of an old fault
can be along the north side of the bend. The seismic evidence confirms
it, he said. “Indian Point is situated at the intersection of the two
most striking linear features marking the seismicity and also in the
midst of a large population that is at risk in case of an accident,”
says the paper. “This is clearly one of the least favorable sites in our
study area from an earthquake hazard and risk perspective.”
The findings comes at a time when Entergy, the owner of Indian Point,
is trying to relicense the two operating plants for an additional 20
years—a move being fought by surrounding communities and the New York
State Attorney General. Last fall the attorney general, alerted to the
then-unpublished Lamont data, told a Nuclear Regulatory Commission panel
in a filing: “New data developed in the last 20 years disclose a
substantially higher likelihood of significant earthquake activity in
the vicinity of [Indian Point] that could exceed the earthquake design
for the facility.” The state alleges that Entergy has not presented new
data on earthquakes past 1979. However, in a little-noticed decision
this July 31, the panel rejected the argument on procedural grounds. A
source at the attorney general’s office said the state is considering
its options.
Quakes located by instruments 1974-2007. Arrows
indivcate the Peekskill-Stamford seismic line and Ramapo seismic zone
(RSZ), which intersect near Indian Point. Purple numerals indicate
distance in kilometers.
Adapted from Sykes et al.
The characteristics of New York’s geology and human footprint may
increase the problem. Unlike in California, many New York quakes occur
near the surface—in the upper mile or so—and they occur not in the
broken-up, more malleable formations common where quakes are frequent,
but rather in the extremely hard, rigid rocks underlying Manhattan and
much of the lower Hudson Valley. Such rocks can build large stresses,
then suddenly and efficiently transmit energy over long distances. “It’s
like putting a hard rock in a vise,” said Seeber. “Nothing happens for a
while. Then it goes with a bang.” Earthquake-resistant building codes
were not introduced to New York City until 1995, and are not in effect
at all in many other communities. Sinuous skyscrapers and bridges might
get by with minimal damage, said Sykes, but many older, unreinforced
three- to six-story brick buildings could crumble.
Art Lerner-Lam,
associate director of Lamont for seismology, geology and
tectonophysics, pointed out that the region’s major highways including
the New York State Thruway, commuter and long-distance rail lines, and
the main gas, oil and power transmission lines all cross the parallel
active faults, making them particularly vulnerable to being cut.
Lerner-Lam, who was not involved in the research, said that the
identification of the seismic line near Indian Point “is a major
substantiation of a feature that bears on the long-term earthquake risk
of the northeastern United States.” He called for policymakers to
develop more information on the region’s vulnerability, to take a closer
look at land use and development, and to make investments to strengthen
critical infrastructure.
“This is a landmark study in many ways,” said Lerner-Lam. “It gives
us the best possible evidence that we have an earthquake hazard here
that should be a factor in any planning decision. It crystallizes the
argument that this hazard is not random. There is a structure to the
location and timing of the earthquakes. This enables us to contemplate
risk in an entirely different way. And since we are able to do that, we
should be required to do that.”
New York Earthquake Briefs and Quotes:
Existing
U.S. Geological Survey seismic hazard maps
show New York City as facing more hazard than many other eastern U.S.
areas. Three areas are somewhat more active—northernmost New York State,
New Hampshire and South Carolina—but they have much lower populations
and fewer structures. The wider forces at work include pressure exerted
from continuing expansion of the mid-Atlantic Ridge thousands of miles
to the east; slow westward migration of the North American continent;
and the area’s intricate labyrinth of old faults, sutures and zones of
weakness caused by past collisions and rifting.
Due to New York’s past history, population density and fragile,
interdependent infrastructure, a 2001 analysis by the Federal Emergency
Management Agency ranks it the 11th most at-risk U.S. city for
earthquake damage. Among those ahead: Los Angeles, San Francisco,
Seattle and Portland. Behind: Salt Lake City, Sacramento, Anchorage.
New York’s first seismic station was set up at Fordham University in
the 1920s. Lamont-Doherty Earth Observatory, in Palisades, N.Y., has
operated stations since 1949, and now coordinates a
network of about 40.
Front page, The New York Times, Aug. 11, 1884.
"Convulsion of the earth which shook buildings and drove people from
their homes, and caused much alarm."
New York Times
Dozens of small quakes have been felt in the New York area. A
Jan. 17, 2001 magnitude 2.4,
centered in the Upper East Side—the first ever detected in Manhattan
itself--may have originated on the 125th Street fault. Some people
thought it was an explosion, but no one was harmed.
The
most recent felt quake,
a magnitude 2.1 on July 28, 2008, was centered near Milford, N.J.
Houses shook and a woman at St. Edward’s Church said she felt the
building rise up under her feet—but no damage was done.
Questions about the seismic safety of the Indian Point nuclear power
plant, which lies amid a metropolitan area of more than 20 million
people, were raised in previous scientific papers in
1978 and
1985.
Because the hard rocks under much of New York can build up a lot strain
before breaking, researchers believe that modest faults as short as 1 to
10 kilometers can cause magnitude 5 or 6 quakes.
In general, magnitude 3 quakes occur about 10 times more often than
magnitude fours; 100 times more than magnitude fives; and so on. This
principle is called the Gutenberg-Richter relationship.
Lead Author Lynn Sykes
On the study and earthquake risk: “New York is not
as prone to earthquakes as California and Japan, but they do happen.
This study takes a more realistic look at the possibility of larger
ones, and why earthquakes concentrate in certain places. To understand
risk, you have to multiply hazard by assets, and vulnerability. When you
factor that in, our risk is high. Too much attention has been paid to
the level of hazard, and not enough to the risk. Earthquake hazard is
about the same today as in 1609 when Henry Hudson sailed up the River.
But earthquake risk is much, much higher today, since the number of
people, assets and their vulnerability are so much greater.”
On faults near Indian Point nuclear plant: “We think
that the intersection of these two features being so close to Indian
Point makes it a place of greater risk than most other points on the
map.”
Coauthor Leonardo Seeber
On estimating hazard: “Most people underestimate the
hazard here. Any conservative approach will look at geologically
similar environments. If you do that, we are similar to Bhuj, India
[where a 2001 magnitude 7 quake killed over 15,000 people]. There was no
obvious sign of strain there. There is a mystery here to be solved, and
we better step back and do our homework.”
On preparing: “Once you accept that one fault in a
family is active, you better consider that all the faults in that family
could be active. We need to adapt our structures with that in mind.”
Coauthor John Armbruster
On past and future quakes: “You could debate whether
a magnitude 6 or 7 is possible, but we’ve already had three magnitude
fives, so that is very realistic.
There is no one now alive now to remember that last one, so people
tend to forget. And having only a partial 300-year history, we may not
have seen everything we could see. There could be surprises—things
bigger than we have ever seen.”
