A major earthquake isn’t likely here, but if it comes, watch out.
This
chart shows the location of the Ramapo Fault System, the longest and
one of the oldest systems of cracks in the earth’s crust in the
Northeast. It also shows the location of all earthquakes of magnitude
2.5 or greater in New Jersey during the last 50 years. The circle in
blue indicates the largest known Jersey quake.
The
couple checked with Burns’s parents, who live in nearby Basking Ridge,
and they, too, had heard and felt something, which they thought might
have been an earthquake. A call by Burns some 20 minutes later to the
Bernardsville Police Department—one of many curious and occasionally
panicky inquiries that Sunday morning, according to the officer in
charge, Sergeant John Remian—confirmed their suspicion: A magnitude 2.6
earthquake, its epicenter in Peapack/Gladstone, about seven miles from
Bernardsville, had hit the area. A smaller aftershock followed about two
and a half hours later.
After this year’s epic earthquakes in
Haiti, Chile, Mexico, Indonesia, and China, the 2.6 quake and aftershock
that shook parts of New Jersey in February may seem minor league, even
to the Somerset County residents who experienced them. On the
exponential Richter Scale, a magnitude 7.0 quake like the one that hit
Haiti in January is almost 4 million times stronger than a quake of 2.6
magnitude. But comparisons of magnitude don’t tell the whole story.
Northern
New Jersey straddles the Ramapo Fault, a significant ancient crack in
the earth’s crust. The longest fault in the Northeast, it begins in
Pennsylvania and moves into New Jersey, trending northeast through
Hunterdon, Somerset, Morris, Passaic, and Bergen counties before
terminating in New York’s Westchester County, not far from the Indian
Point Energy Center, a nuclear power plant. And though scientists
dispute how active this roughly 200 million-year-old fault really is,
many earthquakes in the state’s surprisingly varied seismic history are
believed to have occurred on or near it. The fault line is visible at
ground level and likely extends as deep as nine miles below the surface.
During the past 230 years or so, New Jersey has been at the epicenter of nearly 170 earthquakes,
according to data compiled by the New Jersey Geological Survey, part of
the United States Department of Environmental Protection.
The
largest known quake struck in 1783, somewhere west of New York City,
perhaps in Sussex County. It’s typically listed as 5.3 in magnitude,
though that’s an estimate by seismologists who are quick to point out
that the concept of magnitude—measuring the relative size of an
earthquake—was not introduced until 1935 by Charles Richter and Beno
Gutenberg. Still, for quakes prior to that, scientists are not just
guessing.
“We can figure out the damage at the time by going back
to old records and newspaper accounts,” says Won-Young Kim, a senior
research scientist at Columbia University’s Lamont-Doherty Earth
Observatory in Palisades, New York, directly across the New Jersey
border. “Once the amount and extent of contemporary damage has been
established,” Kim says, “we’re then able to gauge the pattern of ground
shaking or intensity of the event—and from there extrapolate its
probable magnitude.”
Other earthquakes of magnitude 5 or higher have been felt in New Jersey, although their epicenters laying near New York City. One—which
took place in 1737 and was said to have been felt as far north as
Boston and as far south as northern Delaware—was probably in the 5 to
5.5 range. In 1884, an earthquake of similar magnitude occurred off New
York’s Rockaway Beach. This well-documented event pulled houses off
their foundations and caused steeples to topple as far west as Rahway.
The shock wave, scientists believe, was felt over 70,000 square miles,
from Vermont to Maryland.
Among the largest sub-5 magnitude
earthquakes with epicenters in New Jersey, two (a 3.8 and a 4.0) took
place on the same day in 1938 in the Lakehurst area in Ocean County. On
August 26, 2003, a 3.5 magnitude quake shook the Frenchtown/Milford area
in Hunterdon County. On February 3 of last year, a 3.0 magnitude quake
occurred in the Morris County town of Mendham. “A lot of people felt
this one because of the intense shaking, although the area of intensity
wasn’t very wide,” says Lamont-Doherty’s Kim, who visited the site after
the event.
After examining the known historical and geological
record, Kim and other seismologists have found no clear evidence that an
earthquake of greater than 5.3 to 5.5 magnitude has taken place in this
area going back to 1737. This doesn’t mean, of course, that one did not
take place in the more remote past or that one will not occur in the
future; it simply means that a very large quake is less likely to occur
here than in other places in the east where the seismic hazard is
greater, including areas in South Carolina and northeastern New York
State.
But
no area on the East Coast is as densely populated or as heavily
built-up as parts of New Jersey and its neighbors. For this reason,
scientists refer to the Greater New York City-Philadelphia area, which
includes New Jersey’s biggest cities, as one of “low earthquake hazard
but high vulnerability.” Put simply, the Big One isn’t likely here—but
if it comes, especially in certain locations, watch out.
Given
this low-hazard, high-vulnerability scenario, how far along are
scientists in their efforts to predict larger magnitude earthquakes in
the New Jersey area? The answer is complex, complicated by the state’s
geographical position, its unique geological history, the state of
seismology itself, and the continuing debate over the exact nature and
activity of the Ramapo Fault.
Over millions of years, New Jersey
developed four distinct physiographic provinces or regions, which divide
the state into a series of diagonal slices, each with its own terrain,
rock type, and geological landforms.
The northernmost slice is the
Valley and Ridge, comprising major portions of Sussex and Warren
counties. The southernmost slice is the Coastal Plain, a huge expanse
that covers some three-fifths of the state, including all of the Shore
counties. Dividing the rest of the state are the Highlands, an area for
the most part of solid but brittle rock right below the Valley and
Ridge, and the lower lands of the Piedmont, which occupy all of Essex,
Hudson, and Union counties, most of Bergen, Hunterdon, and Somerset, and
parts of Middlesex, Morris, and Passaic.
For earthquake monitors
and scientists, the formation of these last two provinces—the Highlands
and the Piedmont—are of special interest. To understand why, consider
that prior to the appearance of the Atlantic Ocean, today’s Africa was
snuggled cozily up against North America and surrounded by a single
enormous ocean. “At that point, you could have had exits off the New
Jersey Turnpike for Morocco,” says Alexander Gates, professor of geology
and chair of the department of Earth and Environmental Sciences at
Rutgers-Newark.
Under the pressure of circulating material within
the Earth’s super-hot middle layer, or mantle, what was once a single
continent—one that is thought to have included today’s other continents
as well—began to stretch and eventually break, producing numerous cracks
or faults and ultimately separating to form what became the Atlantic
Ocean. In our area, the longest and most active of these many cracks was
the Ramapo Fault, which, through a process known as normal faulting,
caused one side of the earth’s crust to slip lower—the Piedmont—relative
to the other side—the Highlands. “All this occurred about 225 million
years ago,” says Gates. “Back then, you were talking about thousands of
feet between the Highlands and the Piedmont and a very active Ramapo
Fault.”
The Earth’s crust, which is 20 to 25 miles thick, is not a
single, solid shell, but is broken into seven vast tectonic plates,
which drift atop the soft, underlying mantle. Although the
northeast-trending Ramapo Fault neatly divides two of New Jersey’s four
physiographic provinces, it does not form a so-called plate boundary, as
does California’s infamous San Andreas Fault. As many Californians know
all too well, this giant fault forms the boundary between two plates—to
the west, the Pacific Plate, and to the east, the North American Plate;
these rub up against each other, producing huge stresses and a
regularly repeating pattern of larger earthquakes.
The
Ramapo Fault sits on the North American Plate, which extends past the
East Coast to the middle of the Atlantic, where it meets the
Mid-Atlantic Ridge, an underwater mountain range in constant flux. The
consequences of this intraplate setting are huge: First, as Gates points
out, “The predictability of bigger earthquakes on…[such] settings is
exceedingly poor, because they don’t occur very often.” Second, the
intraplate setting makes it more difficult to link our earthquakes to a
major cause or fault, as monitors in California can often do.
This
second bit of uncertainty is especially troubling for some people,
including some in the media who want a neat story. To get around it,
they ignore the differences between plate settings and link all of New
Jersey’s earthquakes, either directly or implicitly, to the Ramapo
Fault. In effect, such people want the Ramapo Fault “to look like the
San Andreas Fault,” says Gates. “They want to be able to point to one
big fault that’s causing all of our earthquakes.”
Gates does not
think that’s the case, and he has been working with colleagues for a
number of years to prove it. “What we have found is that there are
smaller faults that generally cut from east to west across the
northeast-trending Ramapo Fault,” he explains. “These much smaller
faults are all over the place, and they’re actually the ones that are
the active faults in the area.”
But what mechanisms are
responsible for the formation of these apparently active auxiliary
faults? One such mechanism, say scientists, is the westward pressure the
Atlantic Ocean exerts on the North American Plate, which for the most
part resists any movement. “I think we are in an equilibrium state most
of the time,” says Lamont-Doherty’s Kim.
Still, that continuous
pressure on the plate we sit on causes stress, and when that stress
builds up sufficiently, the earth’s crust has a tendency to break around
any weak zones. In our area, the major weak zone is the Ramapo
Fault—“an ancient zone of weakness,” as Kim calls it. That zone of
weakness exacerbates the formation of auxiliary faults, and thereby the
series of minor earthquakes the state has experienced over the years.
All
this presupposes, of course, that any intraplate stress in this area
will continue to be released gradually, in a series of relatively minor
earthquakes or releases of energy. But what if that were not the case?
What if the stress continued to build up, and the release of large
amounts of energy came all at once? In crude terms, that’s part of the
story behind the giant earthquakes that rocked what is now New Madrid,
Missouri, between 1811 and 1812. Although estimates of their magnitude
have been revised downward in recent years to less than magnitude 8,
these earthquakes are generally regarded as among the largest intraplate
events to have occurred in the continental United States.
For a
number of reasons—including the relatively low odds that the kind of
stored energy that unleashed the New Madrid events could ever build up
here—earthquakes of plus-6 magnitude are probably not in our future.
Still,
says Kim, even a magnitude 6 earthquake in certain areas of the state
could do considerable damage, especially if its intensity or ground
shaking was of sufficient strength. In a state as geologically diverse
and densely populated as New Jersey, this is a crucial wild card.
Part
of the job of the experts at the New Jersey Geological Survey is to
assess the seismic hazards in different parts of the state. To do this,
they use a computer-simulation model developed under the direction of
the Federal Emergency Management Agency, known as HAZUS, for Hazards US.
To assess the amount of ground shaking likely to occur in a given
county during events ranging in magnitude from 5 to 7 on the Richter
Scale, NJGS scientists enter three features of a county’s surface
geology into their computer model. Two of these features relate to the
tendency of soil in a given area to lose strength, liquefy, or slide
downhill when shaken. The third and most crucial feature has to do with
the depth and density of the soil itself and the type of bedrock lying
below it; this is a key component in determining a region’s
susceptibility to ground shaking and, therefore, in estimating the
amount of building and structural damage that’s likely to occur in that
region. Estimates for the various counties—nine to date have been
studied—are sent to the New Jersey Office of Emergency Management, which
provided partial funding for the project.
To appreciate why this
element of ground geology is so crucial to earthquake modelers, consider
the following: An earthquake’s intensity—which is measured on something
called the Modified Mercalli Scale—is related to a number of factors.
The amount of energy released or the magnitude of an event is clearly a
big factor. But two earthquakes of the same magnitude can have very
different levels of intensity; in fact, it’s quite possible for a lower
magnitude event to generate more ground shaking than a higher magnitude
one.
In addition to magnitude, other factors that affect intensity
are the distance of the observer or structure from the epicenter, where
intensity is the greatest; the depth beneath the surface of the initial
rupture, with shallower ruptures producing more ground shaking than
deeper ones; and, most significantly, the ground geology or material
that the shock wave generated by the earthquake must pass through.
As
a rule, softer materials like sand and gravel shake much more intensely
than harder materials, because the softer materials are comparatively
inefficient energy conductors, so whatever energy is released by the
quake tends to be trapped, dispersing much more slowly. (Think of a bowl
of Jell-O on a table that’s shaking.)
In
contrast, harder materials, like the solid rock found widely in the
Highlands, are brittle and break under pressure, but conduct energy
well, so that even big shock waves disperse much more rapidly through
them, thereby weakening the amount of ground shaking. “If you’ve
read any stories about the 1906 earthquake in San Francisco, you know
the most intense damage was in those flat, low areas by the Bay, where
the soil is soft, and not in the hilly, rocky areas above,” says Karl
Muessig, state geologist and NJGS head.
The map that accompanies
the online version of the NJGS’s Earthquake Loss Estimation Study
divides the state’s surface geology into five seismic soil classes,
ranging from Class A, or hard rock, to Class E, or soft soil (
state.nj.us/dep/njgs/enviroed/hazus.htm).
Although
the weakest soils are scattered throughout the state, including the
Highlands, which besides harder rock also contains areas of glacial
lakes, clays, and wetlands, they are most evident in the Piedmont and
the Coastal Plain. “The largest expanses of them are in coastal areas
where you have salt marshes or large glacial lakes, as in parts of the
Passaic River basin,” says Scott Stanford, a research scientist with
NJGS and lead author of the estimate. Some of the very weakest soils,
Stanford adds, are in areas of filled marshland, including places along
the Hudson waterfront, around Newark Bay and the Meadowlands, and along
the Arthur Kill.
Faults in these areas—and in the coastal plain
generally—are far below the ground, perhaps several hundred to a
thousand feet down, making identification difficult. “There are numerous
faults upon which you might get earthquake movement that we can’t see,
because they’re covered by younger sediments,” Stanford says.
This
combination of hidden faults and weak soils worries scientists, who are
all too aware that parts of the coastal plain and Piedmont are among
the most densely populated and developed areas in the state. (The
HAZUS computer model also has a “built environment” component, which
summarizes, among other things, types of buildings in a given area.) For
this reason, such areas would be in the most jeopardy in the event of a
large earthquake.
“Any
vulnerable structure on these weak soils would have a higher failure
hazard,” Stanford says. And the scary truth is that many structures in
New Jersey’s largest cities, not to mention New York City, would be
vulnerable, since they’re older and built before anyone gave much
thought to earthquake-related engineering and construction codes.
For
example, in the study’s loss estimate for Essex County, which includes
Newark, the state’s largest city, a magnitude 6 event would result in
damage to 81,600 buildings, including almost 10,000 extensively or
completely; 36,000 people either displaced from their homes or forced to
seek short-term shelter; almost $9 million in economic losses from
property damage and business interruption; and close to 3,300 injuries
and 50 fatalities. (The New York City Area Consortium for Earthquake
Loss Mitigation has conducted a similar assessment for New York City, at
nycem.org.)
All
of this suggests the central irony of New Jersey geology: The upland
areas that are most prone to earthquakes—the counties in or around the
Ramapo Fault, which has spawned a network of splays, or auxiliary
faults—are much less densely populated and sit, for the most part, on
good bedrock. These areas are not invulnerable, certainly, but, by
almost all measures, they would not sustain very severe damage, even in
the event of a higher magnitude earthquake. The same can’t be said for
other parts of the state, where the earthquake hazard is lower but the
vulnerability far greater. Here, the best we can do is to prepare—both
in terms of better building codes and a constantly improving emergency
response.
Meanwhile, scientists like Rutgers’s Gates struggle to
understand the Earth’s quirky seismic timetable: “The big thing with
earthquakes is that you can commonly predict where they are going to
occur,” Gates says. “When they’re going to come, well, we’re nowhere
near being able to figure that out.”
***********************
Planning for the Big One
For
the men and women of the state police who manage and support the New
Jersey Office of Emergency Management (OEM), the response to some
events, like hurricanes, can be marshalled in advance. But an earthquake
is what responders call a no-notice event.
In New Jersey, even
minor earthquakes—like the one that shook parts of Somerset County in
February—attract the notice of local, county, and OEM officials, who
continuously monitor events around the state from their Regional
Operations and Intelligence Center (The ROIC) in West Trenton, a
multimillion dollar command-and-control facility that has been built to
withstand 125 mph winds and a 5.5 magnitude earthquake. In the event of a
very large earthquake, during which local and county resources are apt
to become quickly overwhelmed, command and control authority would
almost instantly pass to West Trenton.
Here, officials from the
state police, representatives of a galaxy of other state agencies, and a
variety of communications and other experts would assemble in the
cavernous and ultra-high tech Emergency Operations Center to oversee the
state’s response. “A high-level earthquake would definitely cause the
governor to declare a state of emergency,” says OEM public information
officer Nicholas J. Morici. “And once that takes place, our emergency
operations plan would be put in motion.”
Emergency officials have
modeled that plan—one that can be adapted to any no-notice event,
including a terrorist attack—on response methodologies developed by the
Federal Emergency Management Agency (FEMA), part of the U.S. Department
of Homeland Security. At its core is a series of seventeen emergency
support functions, ranging from transportation to firefighting, debris
removal, search and rescue, public health, and medical services. A
high-magnitude event would likely activate all of these functions, says
Morici, along with the human and physical resources needed to carry them
out—cranes and heavy trucks for debris removal, fire trucks and teams
for firefighting, doctors and EMTs for medical services, buses and
personnel carriers for transportation, and so on.
This is where an
expert like Tom Rafferty comes in. Rafferty is a Geographic Information
Systems Specialist attached to the OEM. His job during an emergency is
to keep track electronically of which resources are where in the state,
so they can be deployed quickly to where they are needed. “We have a
massive database called the Resource Directory Database in which we have
geolocated municipal, county, and state assets to a very detailed map
of New Jersey,” Rafferty says. “That way, if there is an emergency like
an earthquake going on in one area, the emergency managers can quickly
say to me, for instance, ‘We have major debris and damage on this spot
of the map. Show us the location of the nearest heavy hauler. Show us
the next closest location,’ and so on.”
A very large quake, Rafferty says, “could overwhelm resources that we have as a state.” In
that event, OEM has the authority to reach out to FEMA for additional
resources and assistance. It can also call upon the private sector—the
Resource Directory has been expanded to include non-government
assets—and to a network of volunteers. “No one has ever said, ‘We don’t
want to help,’” Rafferty says. New Jersey officials can also request
assistance through the Emergency Management Assistance Compact (EMAC),
an agreement among the states to help each other in times of extreme
crisis.
“You always plan for the worst,” Rafferty says, “and that
way when the worst doesn’t happen, you feel you can handle it if and
when it does.”
Contributing editor Wayne J. Guglielmo lives in M
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