The Ramapo Fault and the Sixth Seal (Revelation 6:12)

ramapo fault line eastern united states | ... Madrid Fault Line experiences an earthquake, so may the east coast

Living on the Fault Line

Posted June 15, 2010 by Wayne J. Guglielmo

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.”

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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 Mahwah, near the Ramapo Fault.

History Warns New York Is The Sixth Seal (Revelation 6:12)

 New York Earthquake 1884

Friday, 18 March 2011 – 9:23pm IST | Place: NEW YORK | Agency: ANI

If the past is any indication, New York can be hit by an earthquake, claims John Armbruster, a seismologist at Columbia University’s Lamont-Doherty Earth Observatory. 

If the past is any indication, New York can be hit by an earthquake, claims John Armbruster, a seismologist at Columbia University’s Lamont-Doherty Earth Observatory.

According to the New York Daily News, Lynn Skyes, lead author of a recent study by seismologists at the Lamont-Doherty Earth Observatory adds that a magnitude-6 quake hits the area about every 670 years, and magnitude-7 every 3,400 years.

A 5.2-magnitude quake shook New York City in 1737 and another of the same severity hit in 1884.

Tremors were felt from Maine to Virginia.

„The problem here comes from many subtle faults,“ explained Skyes after the study was published.

He adds: „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.“

Armbruster says a 5.0-magnitude earthquake today likely would result in casualties and hundreds of millions of dollars in damage.

„I would expect some people to be killed,“ he notes.

Brace Yourselves for the Sixth Seal (Revelation 6)

http://www.ldeo.columbia.edu/news/images/nj-quake-030201.gif

Brace Yourselves, New Yorkers, You’re Due for a Major Quake

A couple of hundred thousand years ago, an M 7.2 earthquake shook what is now New Hampshire. Just a few thousand years ago, an M 7.5 quake ruptured just off the coast of Massachusetts. And then there’s New York.

Since the first western settlers arrived there, the state has witnessed 200 quakes of magnitude 2.0 or greater, making it the third most seismically active state east of the Mississippi (Tennessee and South Carolina are ranked numbers one and two, respectively). About once a century, New York has also experienced an M 5.0 quake capable of doing real damage.

The most recent one near New York City occurred in August of 1884. Centered off Long Island’s Rockaway Beach, it was felt over 70,000 square miles. It also opened enormous crevices near the Brooklyn reservoir and knocked down chimneys and cracked walls in Pennsylvania and Connecticut. Police on the Brooklyn Bridge said it swayed “as if struck by a hurricane” and worried the bridge’s towers would collapse. Meanwhile, residents throughout New York and New Jersey reported sounds that varied from explosions to loud rumblings, sometimes to comic effect. At the funeral of Lewis Ingler, a small group of mourners were watching as the priest began to pray. The quake cracked an enormous mirror behind the casket and knocked off a display of flowers that had been resting on top of it. When it began to shake the casket’s silver handles, the mourners decided the unholy return of Lewis Ingler was more than they could take and began flinging themselves out windows and doors.

Not all stories were so light. Two people died during the quake, both allegedly of fright. Out at sea, the captain of the brig Alice felt a heavy lurch that threw him and his crew, followed by a shaking that lasted nearly a minute. He was certain he had hit a wreck and was taking on water.

A day after the quake, the editors of The New York Times sought to allay readers’ fear. The quake, they said, was an unexpected fluke never to be repeated and not worth anyone’s attention: “History and the researches of scientific men indicate that great seismic disturbances occur only within geographical limits that are now well defined,” they wrote in an editorial. “The northeastern portion of the United States . . . is not within those limits.” The editors then went on to scoff at the histrionics displayed by New York residents when confronted by the quake: “They do not stop to reason or to recall the fact that earthquakes here are harmless phenomena. They only know that the solid earth, to whose immovability they have always turned with confidence when everything else seemed transitory, uncertain, and deceptive, is trembling and in motion, and the tremor ceases long before their disturbed minds become tranquil.”

That’s the kind of thing that drives Columbia’s Heather Savage nuts.

New York, she says, is positively vivisected by faults. Most of them fall into two groups—those running northeast and those running northwest. Combined they create a brittle grid underlying much of Manhattan.

Across town, Charles Merguerian has been studying these faults the old‐fashioned way: by getting down and dirty underground. He’s spent the past forty years sloshing through some of the city’s muckiest places: basements and foundations, sewers and tunnels, sometimes as deep as 750 feet belowground. His tools down there consist primarily of a pair of muck boots, a bright blue hard hat, and a pickax. In public presentations, he claims he is also ably abetted by an assistant hamster named Hammie, who maintains his own website, which includes, among other things, photos of the rodent taking down Godzilla.

That’s just one example why, if you were going to cast a sitcom starring two geophysicists, you’d want Savage and Merguerian to play the leading roles. Merguerian is as eccentric and flamboyant as Savage is earnest and understated. In his press materials, the former promises to arrive at lectures “fully clothed.” Photos of his “lab” depict a dingy porta‐john in an abandoned subway tunnel. He actively maintains an archive of vintage Chinese fireworks labels at least as extensive as his list of publications, and his professional website includes a discography of blues tunes particularly suitable for earthquakes. He calls female science writers “sweetheart” and somehow manages to do so in a way that kind of makes them like it (although they remain nevertheless somewhat embarrassed to admit it).

It’s Merguerian’s boots‐on‐the‐ground approach that has provided much of the information we need to understand just what’s going on underneath Gotham. By his count, Merguerian has walked the entire island of Manhattan: every street, every alley. He’s been in most of the tunnels there, too. His favorite one by far is the newest water tunnel in western Queens. Over the course of 150 days, Merguerian mapped all five miles of it. And that mapping has done much to inform what we know about seismicity in New York.

Most importantly, he says, it provided the first definitive proof of just how many faults really lie below the surface there. And as the city continues to excavate its subterranean limits, Merguerian is committed to following closely behind. It’s a messy business.

Down below the city, Merguerian encounters muck of every flavor and variety. He power‐washes what he can and relies upon a diver’s halogen flashlight and a digital camera with a very, very good flash to make up the difference. And through this process, Merguerian has found thousands of faults, some of which were big enough to alter the course of the Bronx River after the last ice age.

His is a tricky kind of detective work. The center of a fault is primarily pulverized rock. For these New York faults, that gouge was the very first thing to be swept away by passing glaciers. To do his work, then, he’s primarily looking for what geologists call “offsets”—places where the types of rock don’t line up with one another. That kind of irregularity shows signs of movement over time—clear evidence of a fault.

Merguerian has found a lot of them underneath New York City.

These faults, he says, do a lot to explain the geological history of Manhattan and the surrounding area. They were created millions of years ago, when what is now the East Coast was the site of a violent subduction zone not unlike those present now in the Pacific’s Ring of Fire.

Each time that occurred, the land currently known as the Mid‐Atlantic underwent an accordion effect as it was violently folded into itself again and again. The process created immense mountains that have eroded over time and been further scoured by glaciers. What remains is a hodgepodge of geological conditions ranging from solid bedrock to glacial till to brittle rock still bearing the cracks of the collision. And, says Merguerian, any one of them could cause an earthquake.

You don’t have to follow him belowground to find these fractures. Even with all the development in our most built‐up metropolis, evidence of these faults can be found everywhere—from 42nd Street to Greenwich Village. But if you want the starkest example of all, hop the 1 train at Times Square and head uptown to Harlem. Not far from where the Columbia University bus collects people for the trip to the Lamont‐Doherty Earth Observatory, the subway tracks seem to pop out of the ground onto a trestle bridge before dropping back down to earth. That, however, is just an illusion. What actually happens there is that the ground drops out below the train at the site of one of New York’s largest faults. It’s known by geologists in the region as the Manhattanville or 125th Street Fault, and it runs all the way across the top of Central Park and, eventually, underneath Long Island City. Geologists have known about the fault since 1939, when the city undertook a massive subway mapping project, but it wasn’t until recently that they confirmed its potential for a significant quake.

In our lifetimes, a series of small earthquakes have been recorded on the Manhattanville Fault including, most recently, one on October 27, 2001. Its epicenter was located around 55th and 8th—directly beneath the original Original Soupman restaurant, owned by restaurateur Ali Yeganeh, the inspiration for Seinfeld’s Soup Nazi. That fact delighted sitcom fans across the country, though few Manhattanites were in any mood to appreciate it.

The October 2001 quake itself was small—about M 2.6—but the effect on residents there was significant. Just six weeks prior, the city had been rocked by the 9/11 terrorist attacks that brought down the World Trade Center towers. The team at Lamont‐Doherty has maintained a seismic network in the region since the ’70s. They registered the collapse of the first tower at M 2.1. Half an hour later, the second tower crumbled with even more force and registered M 2.3. In a city still shocked by that catastrophe, the early‐morning October quake—several times greater than the collapse of either tower—jolted millions of residents awake with both reminders of the tragedy and fear of yet another attack. 9‐1‐1 calls overwhelmed dispatchers and first responders with reports of shaking buildings and questions about safety in the city. For seismologists, though, that little quake was less about foreign threats to our soil and more about the possibility of larger tremors to come.

Remember: The Big Apple has experienced an M 5.0 quake about every hundred years. The last one was that 1884 event. And that, says Merguerian, means the city is overdue. Just how overdue?

“Gee whiz!” He laughs when I pose this question. “That’s the holy grail of seismicity, isn’t it?”

He says all we can do to answer that question is “take the pulse of what’s gone on in recorded history.” To really have an answer, we’d need to have about ten times as much data as we do today. But from what he’s seen, the faults below New York are very much alive.

“These guys are loaded,” he tells me.

He says he is also concerned about new studies of a previously unknown fault zone known as the Ramapo that runs not far from the city. Savage shares his concerns. They both think it’s capable of an M 6.0 quake or even higher—maybe even a 7.0. If and when, though, is really anybody’s guess.

“We literally have no idea what’s happening in our backyard,” says Savage.

What we do know is that these quakes have the potential to do more damage than similar ones out West, mostly because they are occurring on far harder rock capable of propagating waves much farther. And because these quakes occur in places with higher population densities, these eastern events can affect a lot more people. Take the 2011 Virginia quake: Although it was only a moderate one, more Americans felt it than any other one in our nation’s history.

That’s the thing about the East Coast: Its earthquake hazard may be lower than that of the West Coast, but the total effect of any given quake is much higher. Disaster specialists talk about this in terms of risk, and they make sense of it with an equation that multiplies the potential hazard of an event by the cost of damage and the number of people harmed. When you take all of those factors into account, the earthquake risk in New York is much greater than, say, that in Alaska or Hawaii or even a lot of the area around the San Andreas Fault.

Merguerian has been sounding the alarm about earthquake risk in the city since the ’90s. He admits he hasn’t gotten much of a response. He says that when he first proposed the idea of seismic risk in New York City, his fellow scientists “booed and threw vegetables” at him. He volunteered his services to the city’s Office of Emergency Management but says his original offer also fell on deaf ears.

“So I backed away gently and went back to academia.”

Today, he says, the city isn’t much more responsive, but he’s getting a much better response from his peers.

He’s glad for that, he says, but it’s not enough. If anything, the events of 9/11, along with the devastation caused in 2012 by Superstorm Sandy, should tell us just how bad it could be there.

He and Savage agree that what makes the risk most troubling is just how little we know about it. When it comes right down to it, intraplate faults are the least understood. Some scientists think they might be caused by mantle flow deep below the earth’s crust. Others think they might be related to gravitational energy. Still others think quakes occurring there might be caused by the force of the Atlantic ridge as it pushes outward. Then again, it could be because the land is springing back after being compressed thousands of years ago by glaciers (a phenomenon geologists refer to as seismic rebound).

“We just have no consciousness towards earthquakes in the eastern United States,” says Merguerian. “And that’s a big mistake.”

Adapted from Quakeland: On the Road to America’s Next Devastating Earthquake by Kathryn Miles, published by Dutton, an imprint of Penguin Publishing Group, a division of Penguin Random House, LLC. Copyright © 2017 by Kathryn Miles.

New York Quake Overdue (The Sixth Seal) (Revelation 6:12)

http://www.gothamgazette.com/graphics/2008/09/skyesfig3_cropped.gif

New York City could start shaking any minute now.

Won-Young Kim, who runs the seismographic network for the Northeast at Columbia University’s Lamont-Doherty Earth Observatory, said the city is well overdue for a big earthquake.

From Metro New York:

The last big quake to hit New York City was a 5.3-magnitude tremor in 1884 that happened at sea in between Brooklyn and Sandy Hook. While no one was killed, buildings were damaged.

Kim said the city is likely to experience a big earthquake every 100 years or so.

“It can happen anytime soon,” Kim said. “We can expect it any minute, we just don’t know when and where.”

New York has never experienced a magnitude 6 or 7 earthquake, which are the most dangerous. But magnitude 5 quakes could topple brick buildings and chimneys.

Seismologist John Armbruster said a magnitude 5 quake that happened now would be more devastating than the one that happened in 1884.

“Today, with so many more buildings and people … we’d see billions in damage,” Armbruster said. “People would probably be killed.”

Quakeland: New York and the Sixth Seal

Quakeland: On the Road to America’s Next Devastating Earthquake

Roger Bilham

Given recent seismic activity — political as well as geological — it’s perhaps unsurprising that two books on earthquakes have arrived this season. One is as elegant as the score of a Beethoven symphony; the other resembles a diary of conversations overheard during a rock concert. Both are interesting, and both relate recent history to a shaky future.

Journalist Kathryn Miles’s Quakeland is a litany of bad things that happen when you provoke Earth to release its invisible but ubiquitous store of seismic-strain energy, either by removing fluids (oil, water, gas) or by adding them in copious quantities (when extracting shale gas in hydraulic fracturing, also known as fracking, or when injecting contaminated water or building reservoirs). To complete the picture, she describes at length the bad things that happen during unprovoked natural earthquakes. As its subtitle hints, the book takes the form of a road trip to visit seismic disasters both past and potential, and seismologists and earthquake engineers who have first-hand knowledge of them. Their colourful personalities, opinions and prejudices tell a story of scientific discovery and engineering remedy.

Miles poses some important societal questions. Aside from human intervention potentially triggering a really damaging earthquake, what is it actually like to live in neighbourhoods jolted daily by magnitude 1–3 earthquakes, or the occasional magnitude 5? Are these bumps in the night acceptable? And how can industries that perturb the highly stressed rocks beneath our feet deny obvious cause and effect? In 2015, the Oklahoma Geological Survey conceded that a quadrupling of the rate of magnitude-3 or more earthquakes in recent years, coinciding with a rise in fracking, was unlikely to represent a natural process. Miles does not take sides, but it’s difficult for the reader not to.

She visits New York City, marvelling at subway tunnels and unreinforced masonry almost certainly scheduled for destruction by the next moderate earthquake in the vicinity. She considers the perils of nuclear-waste storage in Nevada and Texas, and ponders the risks to Idaho miners of rock bursts — spontaneous fracture of the working face when the restraints of many million years of confinement are mined away. She contemplates the ups and downs of the Yellowstone Caldera — North America’s very own mid-continent supervolcano — and its magnificently uncertain future. Miles also touches on geothermal power plants in southern California’s Salton Sea and elsewhere; the vast US network of crumbling bridges, dams and oil-storage farms; and the magnitude 7–9 earthquakes that could hit California and the Cascadia coastline of Oregon and Washington state this century. Amid all this doom, a new elementary school on the coast near Westport, Washington, vulnerable to inbound tsunamis, is offered as a note of optimism. With foresight and much persuasion from its head teacher, it was engineered to become an elevated safe haven.

Miles briefly discusses earthquake prediction and the perils of getting it wrong (embarrassment in New Madrid, Missouri, where a quake was predicted but never materialized; prison in L’Aquila, Italy, where scientists failed to foresee a devastating seismic event) and the successes of early-warning systems, with which electronic alerts can be issued ahead of damaging seismic waves. Yes, it’s a lot to digest, but most of the book obeys the laws of physics, and it is a engaging read. One just can’t help wishing that Miles’s road trips had taken her somewhere that wasn’t a disaster waiting to happen.

Catastrophic damage in Anchorage, Alaska, in 1964, caused by the second-largest earthquake in the global instrumental record.

In The Great Quake, journalist Henry Fountain provides us with a forthright and timely reminder of the startling historical consequences of North America’s largest known earthquake, which more than half a century ago devastated southern Alaska. With its epicentre in Prince William Sound, the 1964 quake reached magnitude 9.2, the second largest in the global instrumental record. It released more energy than either the 2004 Sumatra–Andaman earthquake or the 2011 Tohoku earthquake off Japan; and it generated almost as many pages of scientific commentary and description as aftershocks. Yet it has been forgotten by many.

The quake was scientifically important because it occurred at a time when plate tectonics was in transition from hypothesis to theory. Fountain expertly traces the theory’s historical development, and how the Alaska earthquake was pivotal in nailing down one of the most important predictions. The earthquake caused a fjordland region larger than England to subside, and a similarly huge region of islands offshore to rise by many metres; but its scientific implications were not obvious at the time. Eminent seismologists thought that a vertical fault had slipped, drowning forests and coastlines to its north and raising beaches and islands to its south. But this kind of fault should have reached the surface, and extended deep into Earth’s mantle. There was no geological evidence of a monster surface fault separating these two regions, nor any evidence for excessively deep aftershocks. The landslides and liquefied soils that collapsed houses, and the tsunami that severely damaged ports and infrastructure, offered no clues to the cause.

“Previous earthquakes provide clear guidance about present-day vulnerability.” The hero of The Great Quake is the geologist George Plafker, who painstakingly mapped the height reached by barnacles lifted out of the intertidal zone along shorelines raised by the earthquake, and documented the depths of drowned forests. He deduced that the region of subsidence was the surface manifestation of previously compressed rocks springing apart, driving parts of Alaska up and southwards over the Pacific Plate. His finding confirmed a prediction of plate tectonics, that the leading edge of the Pacific Plate plunged beneath the southern edge of Alaska along a gently dipping thrust fault. That observation, once fully appreciated, was applauded by the geophysics community.

Fountain tells this story through the testimony of survivors, engineers and scientists, interweaving it with the fascinating history of Alaska, from early discovery by Europeans to purchase from Russia by the United States in 1867, and its recent development. Were the quake to occur now, it is not difficult to envisage that with increased infrastructure and larger populations, the death toll and price tag would be two orders of magnitude larger than the 139 fatalities and US$300-million economic cost recorded in 1964.

What is clear from these two books is that seismicity on the North American continent is guaranteed to deliver surprises, along with unprecedented economic and human losses.Previous earthquakes provide clear guidance about the present-day vulnerability of US infrastructure and populations. Engineers and seismologists know how to mitigate the effects of future earthquakes (and, in mid-continent, would advise against the reckless injection of waste fluids known to trigger earthquakes). It is merely a matter of persuading city planners and politicians that if they are tempted to ignore the certainty of the continent’s seismic past, they should err on the side of caution when considering its seismic future.

The Ramapo: The Sixth Seal Fault Line (Revelation 6:12)

Image result for ramapo fault lineThe Ramapo fault and other New York City area faults 

 Map depicting the extent of the Ramapo Fault System in New York, New Jersey, and Pennsylvania

The Ramapo Fault, which marks the western boundary of the Newark rift basin, has been argued to be a major seismically active feature of this region, but it is difficult to discern the extent to which the Ramapo fault (or any other specific mapped fault in the area) might be any more of a source of future earthquakes than any other parts of the region. The Ramapo Fault zone spans more than 185 miles (300 kilometers) in New York, New Jersey, and Pennsylvania. It is a system of faults between the northern Appalachian Mountains and Piedmont areas to the east. This fault is perhaps the best known fault zone in the Mid-Atlantic region, and some small earthquakes have been known to occur in its vicinity. Recently, public knowledge about the fault has increased – especially after the 1970s, when the fault’s proximity to the Indian Point nuclear plant in New York was noticed.

There is insufficient evidence to unequivocally demonstrate any strong correlation of earthquakes in the New York City area with specific faults or other geologic structures in this region. The damaging earthquake affecting New York City in 1884 was probably not associated with the Ramapo fault because the strongest shaking from that earthquake occurred on Long Island (quite far from the trace of the Ramapo fault). The relationship between faults and earthquakes in the New York City area is currently understood to be more complex than any simple association of a specific earthquake with a specific mapped fault.

A 2008 study argued that a magnitude 6 or 7 earthquake might originate from the Ramapo fault zone, which would almost definitely spawn hundreds or even thousands of fatalities and billions of dollars in damage.Studying around 400 earthquakes over the past 300 years, the study also argued that there was an additional fault zone extending from the Ramapo Fault zone into southwestern Connecticut. As can be seen in the above figure of seismicity, earthquakes are scattered throughout this region, with no particular concentration of activity along the Ramapo fault, or along the hypothesized fault zone extending into southwestern Connecticut.

Just off the northern terminus of the Ramapo fault is the Indian Point Nuclear Power Plant, built between 1956 and 1960 by Consolidated Edison Company. The plant began operating in 1963, and it has been the subject of a controversy over concerns that an earthquake from the Ramapo fault will affect the power plant. Whether or not the Ramapo fault actually does pose a threat to this nuclear power plant remains an open question.

Two Centuries Before The Sixth Seal (Revelation 6:12)

Image result for 1755 massachusetts earthquake

The worst earthquake in Massachusetts history 260 years ago

It happened before, and it could happen again.

By Hilary Sargent @lilsarg

Boston.com Staff | 11.19.15 | 5:53 AM

On November 18, 1755, Massachusetts experienced its largest recorded earthquake.

The earthquake occurred in the waters off Cape Ann, and was felt within seconds in Boston, and as far away as Nova Scotia, the Chesapeake Bay, and upstate New York, according to the U.S. Geological Survey.

Seismologists have since estimated the quake to have been between 6.0 and 6.3 on the Richter scale, according to the Massachusetts Historical Society.

While there were no fatalities, the damage was extensive.

According to the USGS, approximately 100 chimneys and roofs collapsed, and over a thousand were damaged.

The worst damage occurred north of Boston, but the city was not unscathed.

A 1755 report in The Philadelphia Gazette described the quake’s impact on Boston:

“There was at first a rumbling noise like low thunder, which was immediately followed with such a violent shaking of the earth and buildings, as threw every into the greatest amazement, expecting every moment to be buried in the ruins of their houses. In a word, the instances of damage done to our houses and chimnies are so many, that it would be endless to recount them.”

The quake sent the grasshopper weathervane atop Faneuil Hall tumbling to the ground, according to the Massachusetts Historical Society.

An account of the earthquake, published in The Pennsylvania Gazette on December 4, 1755.

The earthquake struck at 4:30 in the morning, and the shaking lasted “near four minutes,” according to an entry John Adams, then 20, wrote in his diary that day.

The brief diary entry described the damage he witnessed.

“I was then at my Fathers in Braintree, and awoke out of my sleep in the midst of it,” he wrote. “The house seemed to rock and reel and crack as if it would fall in ruins about us. 7 Chimnies were shatter’d by it within one mile of my Fathers house.”

The shaking was so intense that the crew of one ship off the Boston coast became convinced the vessel had run aground, and did not learn about the earthquake until they reached land, according to the Massachusetts Historical Society.

In 1832, a writer for the Hampshire (Northampton) Gazette wrote about one woman’s memories from the quake upon her death.

“It was between 4 and 5 in the morning, and the moon shone brightly. She and the rest of the family were suddenly awaked from sleep by a noise like that of the trampling of many horses; the house trembled and the pewter rattled on the shelves. They all sprang out of bed, and the affrightted children clung to their parents. “I cannot help you dear children,” said the good mother, “we must look to God for help.

The Cape Ann earthquake came just 17 days after an earthquake estimated to have been 8.5-9.0 on the Richter scale struck in Lisbon, Portugal, killing at least 60,000 and causing untold damage.

There was no shortage of people sure they knew the impretus for the Cape Ann earthquake.

According to many ministers in and around Boston, “God’s wrath had brought this earthquake upon Boston,” according to the Massachusetts Historical Society.

In “Verses Occasioned by the Earthquakes in the Month of November, 1755,” Jeremiah Newland, a Taunton resident who was active in religious activities in the Colony, wrote that the earthquake was a reminder of the importance of obedience to God.

“It is becaufe we broke thy Laws,

that thou didst shake the Earth.

O what a Day the Scriptures say,

the EARTHQUAKE doth foretell;

O turn to God; lest by his Rod,

he cast thee down to Hell.”

Boston Pastor Jonathan Mayhew warned in a sermon that the 1755 earthquakes in Massachusetts and Portugal were “judgments of heaven, at least as intimations of God’s righteous displeasure, and warnings from him.”

There were some, though, who attempted to put forth a scientific explanation for the earthquake.

Well, sort of.

In a lecture delivered just a week after the earthquake, Harvard mathematics professor John Winthrop said the quake was the result of a reaction between “vapors” and “the heat within the bowels of the earth.” But even Winthrop made sure to state that his scientific theory “does not in the least detract from the majesty … of God.”

It has been 260 years since the Cape Ann earthquake. Some experts, including Boston College seismologist John Ebel, think New England could be due for another significant quake.

In a recent Boston Globe report, Ebel said the New England region “can expect a 4 to 5 magnitude quake every decade, a 5 to 6 every century, and a magnitude 6 or above every thousand years.”

If the Cape Ann earthquake occurred today, “the City of Boston could sustain billions of dollars of earthquake damage, with many thousands injured or killed,” according to a 1997 study by the US Army Corps of Engineers.

Why New York City Will Be Shut Down At The Sixth Seal

Indian Point tritium leak 80% worse than originally reported

Published time: 10 Feb, 2016 22:12Edited time: 11 Feb, 2016 01:51

New measurements at the Indian Point nuclear power plant in upstate New York show levels of radioactive tritium 80 percent higher than reported last week. Plant operator insists the spill is not dangerous, as state officials call for a safety probe.

Entergy, which operates the facility 25 miles (40 km) north of New York City, says the increased levels of tritium represent “fluctuations that can be expected as the material migrates.”

“Even with the new readings, there is no impact to public health or safety, and although these values remain less than one-tenth of one percent of federal reporting guidelines,” Entergy said in a statement.

New York governor Andrew Cuomo raised an alarm last Saturday over the reports of groundwater contamination at Indian Point, noting that the company reported “alarming levels of radioactivity” at three monitoring wells, with “radioactivity increasing nearly 65,000 percent” at one of them.

The groundwater wells have no contact with any drinking water supplies, and the spill will dissipate before it reaches the Hudson River, a senior Entergy executive argued Tuesday, suggesting the increased state scrutiny was driven by the company’s decision to shut down another nuclear power plant.

“There are a number of stakeholders, including the governor, who do not like the fact that we are having to close Fitzpatrick,” Michael Twomey, Entergy’s vice president of external affairs, said during an appearance on ‘The Capitol Pressroom,’ a show on WCNY public radio.

The James A. Fitzpatrick plant is located on the southern shore of Lake Ontario, near Oswego, New York. Entergy said it intended to close the plant once it runs out of fuel sometime this year, citing its continued operations as unprofitable.

Indian Point Nuclear Power Plant on the Hudson river © wikipedia.org

‘65,000% radioactivity spike’: New York Gov. orders probe into water leak at Indian Point

“We’re not satisfied with this event. This was not up to our expectations,” Twomey said, adding that the Indian Point spill should be seen in context.

Though it has never reported a reactor problem, the Indian Point facility has been plagued by issues with transformers, cooling systems, and other electrical components over the years. It currently operates two reactors, both brought on-line in the 1970s.

In December, the federal Nuclear Regulatory Commission allowed Entergy to continue operating the reactors, pending license renewal. The facility’s initial 40-year license was set to expire on December 12, but the regulators are reportedly leaning towards recommending a 20-year extension.

By contrast, Reactor 4 at the Chernobyl Nuclear Power Plant in Pripyat, Ukraine was only three years old when it exploded in April 1986. To this day, an area of 1000 square miles around the power plant remains the “exclusion zone,” where human habitation is prohibited.

The tritium leak at Indian Point most likely took place in January, during the preparations to shut down Reactor 2 for refueling, according to Entergy. Water containing high levels of the hydrogen isotope reportedly overfilled the drains and spilled into the ground.

According to Entergy, tritium is a “low hazard radionuclide” because it emits low-energy beta particles, which do not penetrate the skin. “People could be harmed by tritium only through internal exposure caused by drinking water with high levels of tritium over many years,” an Entergy fact sheet says.

Environmentalist critics are not convinced, however.

“This plant isn’t safe anymore,” Paul Gallay, president of environmental watchdog group

Riverkeeper, told the New York Daily News. “Everybody knows it and only Entergy and the Nuclear Regulatory Commission refuse to admit it.”

The Sixth Seal Is Long Overdue (Revelation 6:12)

ON THE MAP; Exploring the Fault Where the Next Big One May Be Waiting

By MARGO NASH

Published: March 25, 2001

Alexander Gates, a geology professor at Rutgers-Newark, is co-author of ”The Encyclopedia of Earthquakes and Volcanoes,” which will be published by Facts on File in July. He has been leading a four-year effort to remap an area known as the Sloatsburg Quadrangle, a 5-by-7-mile tract near Mahwah that crosses into New York State. The Ramapo Fault, which runs through it, was responsible for a big earthquake in 1884, and Dr. Gates warns that a recurrence is overdue. He recently talked about his findings.

Q. What have you found?

A. We’re basically looking at a lot more rock, and we’re looking at the fracturing and jointing in the bedrock and putting it on the maps. Any break in the rock is a fracture. If it has movement, then it’s a fault. There are a lot of faults that are offshoots of the Ramapo. Basically when there are faults, it means you had an earthquake that made it. So there was a lot of earthquake activity to produce these features. We are basically not in a period of earthquake activity along the Ramapo Fault now, but we can see that about six or seven times in history, about 250 million years ago, it had major earthquake activity. And because it’s such a fundamental zone of weakness, anytime anything happens, the Ramapo Fault goes.

Q. Where is the Ramapo Fault?

A. The fault line is in western New Jersey and goes through a good chunk of the state, all the way down to Flemington. It goes right along where they put in the new 287. It continues northeast across the Hudson River right under the Indian Point power plant up into Westchester County. There are a lot of earthquakes rumbling around it every year, but not a big one for a while.

Q. Did you find anything that surprised you?

A. I found a lot of faults, splays that offshoot from the Ramapo that go 5 to 10 miles away from the fault. I have looked at the Ramapo Fault in other places too. I have seen splays 5 to 10 miles up into the Hudson Highlands. And you can see them right along the roadsides on 287. There’s been a lot of damage to those rocks, and obviously it was produced by fault activities. All of these faults have earthquake potential.

Q. Describe the 1884 earthquake.

A. It was in the northern part of the state near the Sloatsburg area. They didn’t have precise ways of describing the location then. There was lots of damage. Chimneys toppled over. But in 1884, it was a farming community, and there were not many people to be injured. Nobody appears to have written an account of the numbers who were injured.

Q. What lessons we can learn from previous earthquakes?

A. In 1960, the city of Agadir in Morocco had a 6.2 earthquake that killed 12,000 people, a third of the population, and injured a third more. I think it was because the city was unprepared.There had been an earthquake in the area 200 years before. But people discounted the possibility of a recurrence. Here in New Jersey, we should not make the same mistake. We should not forget that we had a 5.4 earthquake 117 years ago. The recurrence interval for an earthquake of that magnitude is every 50 years, and we are overdue. The Agadir was a 6.2, and a 5.4 to a 6.2 isn’t that big a jump.

Q. What are the dangers of a quake that size?

A. When you’re in a flat area in a wooden house it’s obviously not as dangerous, although it could cut off a gas line that could explode. There’s a real problem with infrastructure that is crumbling, like the bridges with crumbling cement. There’s a real danger we could wind up with our water supplies and electricity cut off if a sizable earthquake goes off. The best thing is to have regular upkeep and keep up new building codes. The new buildings will be O.K. But there is a sense of complacency.

MARGO NASH

Authorities Expecting The Sixth Seal? (Rev 6:12)

US Raises Threat of Quake but Lowers Risk for Towers

New York Times

By SAM ROBERTS

JULY 17, 2014

Here is another reason to buy a mega-million-dollar apartment in a Manhattan high-rise: Earthquake forecast maps for New York City that a federal agency issued on Thursday indicate “a slightly lower hazard for tall buildings than previously thought.”

The agency, the United States Geodetic Survey, tempered its latest quake prediction with a big caveat.

“The eastern U.S. has the potential for larger and more damaging earthquakes than considered in previous maps and assessments,” the agency said, citing the magnitude 5.8 quake that struck Virginia in 2011.

Federal seismologists based their projections of a lower hazard for tall buildings — “but still a hazard nonetheless,” they cautioned — on a lower likelihood of slow shaking from an earthquake occurring near the city, the type of shaking that typically causes more damage to taller structures.

“The tall buildings in Manhattan are not where you should be focusing,” said John Armbruster, a seismologist with the Lamont-Doherty Earth Observatory of Columbia University. “They resonate with long period waves. They are designed and engineered to ride out an earthquake. Where you should really be worried in New York City is the common brownstone and apartment building and buildings that are poorly maintained.”

Mr. Armbruster was not involved in the federal forecast, but was an author of an earlier study that suggested that “a pattern of subtle but active faults makes the risk of earthquakes to the New York City area substantially greater than formerly believed.”

He noted that barely a day goes by without a New York City building’s being declared unsafe, without an earthquake. “If you had 30, 40, 50 at one time, responders would be overloaded,” he said.

The city does have an earthquake building code that went into effect in 1996, and that applies primarily to new construction.

A well-maintained building would probably survive a magnitude 5 earthquake fairly well, he said. The last magnitude 5 earthquake in the city struck in 1884. Another is not necessarily inevitable; faults are more random and move more slowly than they do in, say, California. But he said the latest federal estimate was probably raised because of the magnitude of the Virginia quake.

“Could there be a magnitude 6 in New York?” Mr. Armbruster said. “In Virginia, in a 300 year history, 4.8 was the biggest, and then you have a 5.8. So in New York, I wouldn’t say a 6 is impossible.”

Mr. Armbruster said the Geodetic Survey forecast would not affect his daily lifestyle. “I live in a wood-frame building with a brick chimney and I’m not alarmed sitting up at night worried about it,” he said. “But society’s leaders need to take some responsibility.”