1884 A Forewarning Of The Sixth Seal (Revelation 6:12)

The Coney Island earthquake of 1884

Seismograph of New York Earthquake 1884

Seismograph of New York Earthquake 1884

January 20, 2010

New York City isn’t immune to earthquakes; a couple of small tremors measuring about 2.5 on the Richter scale even struck back in 2001 and 2002.

But on August 10, 1884, a more powerful earthquake hit. Estimated from 4.9 to 5.5 in magnitude, the tremor made houses shake, chimneys fall, and residents wonder what the heck was going on, according to a New York Times article two days later.

The quake was subsequently thought to have been centered off Far Rockaway or Coney Island.

It wasn’t the first moderate quake, and it won’t be the last. In a 2008 Columbia University study, seismologists reported that the city is crisscrossed with several fault lines, one along 125th Street. 

[Headline of The New York Times, August 12, 1884]

With that in mind, New Yorkers should expect a 5.0 or higher earthquake centered here every 100 years, the seismologists say.

Translation: We’re about 30 years overdue. Lucky for us the city adopted earthquake-resistant building codes in 1995.

USGS Evidence Shows Power of the Sixth Seal (Revelation 6:12)

New Evidence Shows Power of East Coast Earthquakes
Virginia Earthquake Triggered Landslides at Great Distances

Did You Feel the Virginia 2011 Earthquake?

Did You Feel the Virginia 2011 Earthquake?

Released: 11/6/2012 8:30:00 AM

USGS.gov

Earthquake shaking in the eastern United States can travel much farther and cause damage over larger areas than previously thought.

U.S. Geological Survey scientists found that last year’s magnitude 5.8 earthquake in Virginia triggered landslides at distances four times farther—and over an area 20 times larger—than previous research has shown.

“We used landslides as an example and direct physical evidence to see how far-reaching shaking from east coast earthquakes could be,” said Randall Jibson, USGS scientist and lead author of this study. “Not every earthquake will trigger landslides, but we can use landslide distributions to estimate characteristics of earthquake energy and how far regional ground shaking could occur.”

“Scientists are confirming with empirical data what more than 50 million people in the eastern U.S. experienced firsthand: this was one powerful earthquake,” said USGS Director Marcia McNutt. “Calibrating the distance over which landslides occur may also help us reach back into the geologic record to look for evidence of past history of major earthquakes from the Virginia seismic zone.”

This study will help inform earthquake hazard and risk assessments as well as emergency preparedness, whether for landslides or other earthquake effects.

This study also supports existing research showing that although earthquakes are less frequent in the East, their damaging effects can extend over a much larger area as compared to the western United States.

The research is being presented today at the Geological Society of America conference, and will be published in the December 2012 issue of the Bulletin of the Seismological Society of America.

The USGS found that the farthest landslide from the 2011 Virginia earthquake was 245 km (150 miles) from the epicenter. This is by far the greatest landslide distance recorded from any other earthquake of similar magnitude. Previous studies of worldwide earthquakes indicated that landslides occurred no farther than 60 km (36 miles) from the epicenter of a magnitude 5.8 earthquake.

“What makes this new study so unique is that it provides direct observational evidence from the largest earthquake to occur in more than 100 years in the eastern U.S,” said Jibson. “Now that we know more about the power of East Coast earthquakes, equations that predict ground shaking might need to be revised.”

It is estimated that approximately one-third of the U.S. population could have felt last year’s earthquake in Virginia, more than any earthquake in U.S. history. About 148,000 people reported their ground-shaking experiences caused by the earthquake on the USGS “Did You Feel It?” website. Shaking reports came from southeastern Canada to Florida and as far west as Texas.

In addition to the great landslide distances recorded, the landslides from the 2011 Virginia earthquake occurred in an area 20 times larger than expected from studies of worldwide earthquakes. Scientists plotted the landslide locations that were farthest out and then calculated the area enclosed by those landslides. The observed landslides from last year’s Virginia earthquake enclose an area of about 33,400 km2, while previous studies indicated an expected area of about 1,500 km2 from an earthquake of similar magnitude.

“The landslide distances from last year’s Virginia earthquake are remarkable compared to historical landslides across the world and represent the largest distance limit ever recorded,” said Edwin Harp, USGS scientist and co-author of this study. “There are limitations to our research, but the bottom line is that we now have a better understanding of the power of East Coast earthquakes and potential damage scenarios.”

The difference between seismic shaking in the East versus the West is due in part to the geologic structure and rock properties that allow seismic waves to travel farther without weakening.

Learn more about the 2011 central Virginia earthquake.

 

The History Of New York Earthquakes: Before The Sixth Seal (Rev 6:12)

 

The Historic Earthquakes
Near New York City, New York
1884 08 10 19:07 UTC
Magnitude 5.5
Intensity VII

New York historic earthquakes

USGS.gov

This severe earthquake affected an area roughly extending along the Atlantic Coast from southern Maine to central Virginia and westward to Cleveland, Ohio. Chimneys were knocked down and walls were cracked in several States, including Connecticut, New Jersey, New York, and Pennsylvania. Many towns from Hartford, Connecticut, to West Chester,Pennsylvania.

Property damage was severe at Amityville and Jamaica, New York, where several chimneys were “overturned” and large cracks formed in walls. Two chimneys were thrown down and bricks were shaken from other chimneys at Stratford (Fairfield County), Conn.; water in the Housatonic River was agitated violently. At Bloomfield, N.J., and Chester, Pa., several chimneys were downed and crockery was broken. Chimneys also were damaged at Mount Vernon, N.Y., and Allentown, Easton, and Philadelphia, Pa. Three shocks occurred, the second of which was most violent. This earthquake also was reported felt in Vermont, Virginia, and Washington, D.C. Several slight aftershocks were reported on August 11.

The Sixth Seal Is Past Due (Revelation 6:12)

New York City is Past Due for an Earthquake

by , 03/22/11

filed under: Newsnyc earthquake, new york city earthquake risk, nyc earthquake threat, earthquake

New York City may appear to be an unlikely place for a major earthquake, but according to history, we’re past due for a serious shake. Seismologists at Columbia University’s Lamont-Doherty Earth Observatory say that about once every 100 years, an earthquake of at least a magnitude of 5.0 rocks the Big Apple. The last one was a 5.3 tremor that hit in 1884 — no one was killed, but buildings were damaged.

Any tremor above a 6.0 magnitude can be catastrophic, but it is extremely unlikely that New York would ever experience a quake like the recent 8.9 earthquake in Japan. A study by the Earth Observatory found that a 6.0 quake hits the area about every 670 years, and a 7.0 magnitude hits about every 3,400 years.

There are several fault lines in New York’s metro area, including one along 125th Street, which may have caused two small tremors in 1981 and a 5.2 magnitude quake in 1737. There is also a fault line on Dyckman Street in Inwood, and another in Dobbs Ferry in Westchester County. The New York City Area Consortium for Earthquake Loss Mitigation rates the chance of an earthquake hitting the city as moderate.

John Armbruster, a seismologist at the Earth Observatory, said that if a 5.0 magnitude quake struck New York today, it would result in hundreds of millions, possibly billions of dollars in damages. The city’s skyscrapers would not collapse, but older brick buildings and chimneys would topple, likely resulting in casualities.

The Earth Observatory is expanding its studies of potential earthquake damage to the city. They currently have six seismometers at different landmarks throughout the five boroughs, and this summer, they plan to place one at the arch in Washington Square Park and another in Bryant Park.

Won-Young Kim, who works alongside Armbuster, says his biggest concern is that we can’t predict when an earthquake might hit. “It can happen anytime soon,” Kim told the Metro. If it happened tomorrow, he added, “I would not be surprised. We can expect it any minute, we just don’t know when and where.”

Armbuster voiced similar concerns to the Daily News. “Will there be one in my lifetime or your lifetime? I don’t know,” he said. “But this is the longest period we’ve gone without one.”

Via Metro and NY Daily News

Images © Ed Yourdon

Earthquake Assessment For The Sixth Seal (Revelation 6:12)

Earthquake Risk in New Jersey

by Daniel R. Dombroski, Jr.

by Daniel R. Dombroski, Jr.

A 10–fold increase in amplitude represents about a 32–fold increase in energy released for the same duration of shaking. The best known magnitude scale is one designed by C.F. Richter in 1935 for
west coast earthquakes.

In New Jersey, earthquakes are measured with seismographs operated by the Lamont–Doherty Earth Observatory of Columbia University and the Delaware Geological Survey.

An earthquake’s intensity is determined by observing its effects at a particular place on the Earth’s surface. Intensity depends on the earthquake’s magnitude, the distance from the epicenter, and local geology. These scales are based on reports of people awakening, felt movements, sounds, and visible effects on structures and landscapes. The most commonly used scale in the United States is the Modified Mercalli Intensity Scale, and its values are usually reported in Roman numerals to distinguish them from magnitudes.

Past damage in New Jersey

New Jersey doesn’t get many earthquakes, but it does get some. Fortunately most are small. A few New Jersey earthquakes, as well as a few originating outside the state, have produced enough damage to warrant the concern of planners and emergency managers.

Damage in New Jersey from earthquakes has been minor: items knocked off shelves, cracked plaster and masonry, and fallen chimneys. Perhaps because no one was standing under a chimney when it fell, there are no recorded earthquake–related deaths in New Jersey. We will probably not be so fortunate in the future.

Area Affected by Eastern Earthquakes

 

Although the United States east of the Rocky Mountains has fewer and generally smaller earthquakes than the West, at least two factors  increase the earthquake risk in New Jersey and the East. Due to geologic differences, eastern earthquakes effect areas ten times larger than western ones of the same magnitude. Also, the eastern United States is more densely populated, and New Jersey is the most densely populated state in the nation.

Geologic Faults and Earthquakes in New Jersey

Although there are many faults in New Jersey, the Ramapo Fault, which separates the Piedmont and Highlands Physiographic Provinces, is the best known. In 1884 it was blamed for a damaging New York City earthquake simply because it was the only large fault mapped at the time. Subsequent investigations have shown the 1884 earthquake epicenter was actually located in Brooklyn, New York, at least 25 miles from the Ramapo Fault.

However, numerous minor earthquakes have been recorded in the Ramapo Fault Zone, a 10 to 20 mile wide area lying adjacent to, and west of, the actual fault.

More recently, in the 1970’s and early 1980’s, earthquake risk along the Ramapo Fault received attention because of its proximity to the Indian Point, New York, Nuclear Power Generating Station. East of the Rocky Mountains (including New Jersey), earthquakes do not break the ground surface. Their focuses lie at least a few miles below the Earth’s surface, and their locations are determined by interpreting seismographic records. Geologic fault lines seen on the surface today are evidence of ancient events. The presence or absence of mapped faults (fault lines) does not denote either a seismic hazard or the lack of one, and earthquakes can occur anywhere in New Jersey.

Frequency of Damaging Earthquakes in New Jersey

Records for the New York City area, which have been kept for 300 years, provide good information
for estimating the frequency of earthquakes in New Jersey.

Earthquakes with a maximum intensity of VII (see table DamagingEarthquakes Felt in New Jersey )have occurred in the New York City area in 1737, 1783, and 1884. One intensity VI, four intensity V’s, and at least three intensity III shocks have also occurred in the New York area over the last 300 years.

The time–spans between the intensity VII earthquakes were 46 and 101 years. This, and data for the smaller–intensity quakes, implies a return period of 100 years or less, and suggests New Jersey is overdue for a moderate earthquake like the one of 1884.

Buildings and Earthquakes

The 1995 earthquake in Kobe, Japan, is an example of what might happen in New Jersey in a similar quake. It registered a magnitude 7.2 on the Richter scale and produced widespread destruction. But it was the age of construction, soil and foundation condition, proximity to the fault, and type of structure that were the major determining factors in the performance of each building. Newer structures, built to the latest construction standards, appeared to perform relatively well, generally ensuring the life safety of occupants.

New Jersey’s building code has some provisions for earthquake–resistant design. But there are no requirements for retrofitting existing buildings — not even for unreinforced masonry structures that are most vulnerable to earthquake damage. Housing of this type is common in New Jersey’s crowded urban areas. If an earthquake the size of New York City’s 1884 quake (magnitude 5.5) were to occur today, severe damage would result. Fatalities would be likely.

Structures have collapsed in New Jersey without earthquakes; an earthquake would trigger many more. Building and housing codes need to be updated and strictly enforced to properly prepare for inevitable future earthquakes.

The Sixth Seal: More Than Just Manhattan (Revelation 6:12)


New York, NY – In a Quake, Brooklyn Would Shake More Than Manhattan

The Sixth Seal

The Sixth Seal

By Brooklyn Eagle

New York, NY – The last big earthquake in the New York City area, centered in New York Harbor just south of Rockaway, took place in 1884 and registered 5.2 on the Richter Scale. Another earthquake of this size can be expected and could be quite damaging, says Dr. Won-Young Kim, senior research scientist at the Lamont-Doherty Earth Observatory of Columbia University.

And Brooklyn, resting on sediment, would shake more than Manhattan, built on solid rock. “There would be more shaking and more damage,” Dr. Kim told the Brooklyn Eagle on Wednesday.

If an earthquake of a similar magnitude were to happen today near Brooklyn, “Many chimneys would topple. Poorly maintained buildings would fall down – some buildings are falling down now even without any shaking. People would not be hit by collapsing buildings, but they would be hit by falling debris. We need to get some of these buildings fixed,” he said.

But a 5.2 is “not comparable to Haiti,” he said. “That was huge.” Haiti’s devastating earthquake measured 7.0.

Brooklyn has a different environment than Haiti, and that makes all the difference, he said. Haiti is situated near tectonic plate boundaries, while Brooklyn is inside the North American plate, far from its boundary.

“The Caribbean plate is moving to the east, while the North American plate is moving towards the west. They move about 20 mm – slightly less than an inch – every year.” The plates are sliding past each other, and the movement is not smooth, leading to jolts, he said.

While we don’t have the opportunity for a large jolt in Brooklyn, we do have small, frequent quakes of a magnitude of 2 or 3 on the Richter Scale. In 2001 alone the city experienced two quakes: one in January, measuring 2.4, and one in October, measuring 2.6. The October quake, occurring soon after Sept. 11 terrorist attacks, “caused a lot of panic,” Dr. Kim said.

“People ask me, ‘Should I get earthquake insurance?’ I tell them no, earthquake insurance is expensive. Instead, use that money to fix chimneys and other things. Rather than panicky preparations, use common sense to make things better.”

Secure bookcases to the wall and make sure hanging furniture does not fall down, Dr. Kim said. “If you have antique porcelains or dishes, make sure they’re safely stored. In California, everything is anchored to the ground.”

While a small earthquake in Brooklyn may cause panic, “In California, a quake of magnitude 2 is called a micro-quake,” he added.

New Jersey #1 Disaster State: The Sixth Seal (Rev 6:12)

States of danger

Kiplinger News
New York Quake

The Sixth Seal: New York Quake

Disasters can happen anywhere and at any time. But some places experience more than their fair share of floods, tornadoes, hurricanes, winter storms and severe weather — so much so that certain locales earn frightening nicknames, such as Tornado Alley. No matter where you live, make sure you have the right kinds and necessary amounts of insurance coverage to protect your finances.

  • Estimated property damage (2006-2013): $26.4 billion
  • Most frequent disasters: damaging wind, winter storms, floods and flash floods
  • Weather-related fatalities (2006-2013): 87

New Jersey earns the top spot on this list, in large part due to damage wrought by Sandy — which had weakened from a hurricane to a post-tropical cyclone by the time it the Jersey Shore — in October 2012. The state was among the hardest hit by Sandy, which was the second-costliest storm in U.S. history, after Hurricane Katrina. Many homes and businesses were destroyed along the Jersey Shore, and a portion of the Atlantic City Boardwalk washed away. Shortly after Sandy hit, another storm brought wet snow that caused more power outages and damage.

Homeowners who live along the coast or in areas where there are frequent storms should take steps before hurricane season begins to protect their homes and finances from damage.

A Lack Of Vigilance Before The Sixth Seal (Revelation 6)

Faults Underlying Exercise Vigilant Guard

Story by: (Author NameStaff Sgt. Raymond Drumsta – 138th Public Affairs Detachment
Dated: Thu, Nov 5, 2009

Faults Underlying Exercise Vigilant Guard
This map illustrates the earthquake fault lines in Western New York. An earthquake in the region is a likely event, says University of Buffalo Professor Dr. Robert Jacobi.

TONAWANDA, NY — An earthquake in western New York, the scenario that Exercise Vigilant Guard is built around, is not that far-fetched, according to University of Buffalo geology professor Dr. Robert Jacobi.

When asked about earthquakes in the area, Jacobi pulls out a computer-generated state map, cross-hatched with diagonal lines representing geological faults.

The faults show that past earthquakes in the state were not random, and could occur again on the same fault systems, he said.

“In western New York, 6.5 magnitude earthquakes are possible,” he said.

This possibility underlies Exercise Vigilant Guard, a joint training opportunity for National Guard and emergency response organizations to build relationships with local, state, regional and federal partners against a variety of different homeland security threats including natural disasters and potential terrorist attacks.

The exercise was based on an earthquake scenario, and a rubble pile at the Spaulding Fibre site here was used to simulate a collapsed building. The scenario was chosen as a result of extensive consultations with the earthquake experts at the University of Buffalo’s Multidisciplinary Center for Earthquake Engineering Research (MCEER), said Brig. Gen. Mike Swezey, commander of 53rd Troop Command, who visited the site on Monday.

Earthquakes of up to 7 magnitude have occurred in the Northeastern part of the continent, and this scenario was calibrated on the magnitude 5.9 earthquake which occurred in Saguenay, Quebec in 1988, said Jacobi and Professor Andre Filiatrault, MCEER director.

“A 5.9 magnitude earthquake in this area is not an unrealistic scenario,” said Filiatrault.

Closer to home, a 1.9 magnitude earthquake occurred about 2.5 miles from the Spaulding Fibre site within the last decade, Jacobi said. He and other earthquake experts impaneled by the Atomic Energy Control Board of Canada in 1997 found that there’s a 40 percent chance of 6.5 magnitude earthquake occurring along the Clareden-Linden fault system, which lies about halfway between Buffalo and Rochester, Jacobi added.

Jacobi and Filiatrault said the soft soil of western New York, especially in part of downtown Buffalo, would amplify tremors, causing more damage.

“It’s like jello in a bowl,” said Jacobi.

The area’s old infrastructure is vulnerable because it was built without reinforcing steel, said Filiatrault. Damage to industrial areas could release hazardous materials, he added.

“You’ll have significant damage,” Filiatrault said.

Exercise Vigilant Guard involved an earthquake’s aftermath, including infrastructure damage, injuries, deaths, displaced citizens and hazardous material incidents. All this week, more than 1,300 National Guard troops and hundreds of local and regional emergency response professionals have been training at several sites in western New York to respond these types of incidents.

Jacobi called Exercise Vigilant Guard “important and illuminating.”

“I’m proud of the National Guard for organizing and carrying out such an excellent exercise,” he said.

Training concluded Thursday.

Yes, Expect The Sixth Seal (Revelation 6:12)

Could an earthquake hit New York City? History says yes, but not like 9.0 magnitude Japan earthquake

A screengrab from 'The Day After Tomorrow.' Experts say an earthquake with at least a 5.0-magnitude affects New York City about every 100 years.

Could a major earthquake shake the Big Apple to its core?If the past is any indication, the answer is yes, says John Armbruster, a seismologist at Columbia University’s Lamont-Doherty Earth Observatory.Based on historical precedent, Armbruster says the New York City metro area is susceptible to an earthquake of at least a magnitude of 5.0 once a century.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.

There are several fault lines in the metro area, including one along Manhattan’s 125th St. – which may have generated two small tremors in 1981 and may have been the source of the major 1737 earthquake, says Armbruster. There’s another fault line on Dyckman St. and one in Dobbs Ferry in nearby Westchester County.

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

“While uncommon, the earthquake hazard of the New York City metropolitan area has been assessed as moderate,” the New York City Area Consortium for Earthquake Loss Mitigation writes on its website. “Considering population density and the condition of the region’s infrastructure and building stock, it is clear that even a moderate earthquake would have considerable consequences in terms of public safety and economic impact.”

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. “Enough chimneys, facades on buildings would fall and someone would be underneath.”

The scope and scale of damage would multiply exponentially with each additional tick on the Richter scale.

“Will there be one in my lifetime or your lifetime? I don’t know. But this is the longest period we’ve gone without one.”

ashahid@nydailynews.com

The Sixth Seal: Real Risk, Few Precautions (Revelation 6:12)

Eastern Quakes: Real Risk, Few Precautions

1989 San Francisco Earthquake

1989 San Francisco Earthquake

By WILLIAM K. STEVENS
Published: October 24, 1989

AN EARTHQUAKE as powerful as the one that struck northern California last week could occur almost anywhere along the East Coast, experts say. And if it did, it would probably cause far more destruction than the West Coast quake.

The chances of such an occurrence are much less in the East than on the West Coast. Geologic stresses in the East build up only a hundredth to a thousandth as fast as in California, and this means that big Eastern quakes are far less frequent. Scientists do not really know what the interval between them might be, nor are the deeper-lying geologic faults that cause them as accessible to study. So seismologists are at a loss to predict when or where they will strike.

But they do know that a temblor with a magnitude estimated at 7 on the Richter scale – about the same magnitude as last week’s California quake – devastated Charleston, S.C., in 1886. And after more than a decade of study, they also know that geologic structures similar to those that caused the Charleston quake exist all along the Eastern Seaboard.

For this reason, ”we can’t preclude that a Charleston-sized earthquake might occur anywhere along the East Coast,” said David Russ, the assistant chief geologist of the United States Geological Survey in Reston, Va. ”It could occur in Washington. It could occur in New York.”

If that happens, many experts agree, the impact will probably be much greater than in California. Easterners, unlike Californians, have paid very little attention to making buildings and other structures earthquake-proof or earthquake-resistant. ”We don’t have that mentality here on the East Coast,” said Robert Silman, a New York structural engineer whose firm has worked on 3,800 buildings in the metropolitan area.

Moreover, buildings, highways, bridges, water and sewer systems and communications networks in the East are all older than in the West and consequently more vulnerable to damage. Even under normal conditions, for instance, water mains routinely rupture in New York City.

The result, said Dr. John Ebel, a geophysicist who is the assistant director of Boston College’s Weston Observatory, is that damage in the East would probably be more widespread, more people could be hurt and killed, depending on circumstances like time of day, and ”it would probably take a lot longer to get these cities back to useful operating levels.”

On top of this, scientists say, an earthquake in the East can shake an area 100 times larger than a quake of the same magnitude in California. This is because the earth’s crust is older, colder and more brittle in the East and tends to transmit seismic energy more efficiently. ”If you had a magnitude 7 earthquake and you put it halfway between New York City and Boston,” Dr. Ebel said, ”you would have the potential of doing damage in both places,” not to mention cities like Hartford and Providence.

Few studies have been done of Eastern cities’ vulnerability to earthquakes. But one, published last June in The Annals of the New York Academy of Sciences, calculated the effects on New York City of a magnitude 6 earthquake. That is one-tenth the magnitude of last week’s California quake, but about the same as the Whittier, Calif., quake two years ago.

The study found that such an earthquake centered 17 miles southeast of City Hall, off Rockaway Beach, would cause $11 billion in damage to buildings and start 130 fires. By comparison, preliminary estimates place the damage in last week’s California disaster at $4 billion to $10 billion. If the quake’s epicenter were 11 miles southeast of City Hall, the study found, there would be about $18 billion in damage; if 5 miles, about $25 billion.

No estimates on injuries or loss of life were made. But a magnitude 6 earthquake ”would probably be a disaster unparalleled in New York history,” wrote the authors of the study, Charles Scawthorn and Stephen K. Harris of EQE Engineering in San Francisco.

The study was financed by the National Center for Earthquake Engineering Research at the State University of New York at Buffalo. The research and education center, supported by the National Science Foundation and New York State, was established in 1986 to help reduce damage and loss of life from earthquakes.

The study’s postulated epicenter of 17 miles southeast of City Hall was the location of the strongest quake to strike New York since it has been settled, a magnitude 5 temblor on Aug. 10, 1884. That 1884 quake rattled bottles and crockery in Manhattan and frightened New Yorkers, but caused little damage. Seismologists say a quake of that order is likely to occur within 50 miles of New York City every 300 years. Quakes of magnitude 5 are not rare in the East. The major earthquake zone in the eastern half of the country is the central Mississippi Valley, where a huge underground rift causes frequent geologic dislocations and small temblors. The most powerful quake ever known to strike the United States occurred at New Madrid, Mo., in 1812. It was later estimated at magnitude 8.7 and was one of three quakes to strike that area in 1811-12, all of them stronger than magnitude 8. They were felt as far away as Washington, where they rattled chandeliers, Boston and Quebec.

Because the New Madrid rift is so active, it has been well studied, and scientists have been able to come up with predictions for the central Mississippi valley, which includes St. Louis and Memphis. According to Dr. Russ, there is a 40 to 63 percent chance that a quake of magnitude 6 will strike that area between now and the year 2000, and an 86 to 97 percent chance that it will do so by 2035. The Federal geologists say there is a 1 percent chance or less of a quake greater than magnitude 7 by 2000, and a 4 percent chance or less by 2035.

Elsewhere in the East, scientists are limited in their knowledge of probabilities partly because faults that could cause big earthquakes are buried deeper in the earth’s crust. In contrast to California, where the boundary between two major tectonic plates creates the San Andreas and related faults, the eastern United States lies in the middle of a major tectonic plate. Its faults are far less obvious, their activity far more subtle, and their slippage far slower. 

Any large earthquake would be ”vastly more serious” in the older cities of the East than in California, said Dr. Tsu T. Soong, a professor of civil engineering at the State University of New York at Buffalo who is a researcher in earthquake-mitigation technology at the National Center for Earthquake Engineering Research. First, he said, many buildings are simply older, and therefore weaker and more vulnerable to collapse. Second, there is no seismic construction code in most of the East as there is in California, where such codes have been in place for decades.

The vulnerability is evident in many ways. ”I’m sitting here looking out my window,” said Mr. Silman, the structural engineer in New York, ”and I see a bunch of water tanks all over the place” on rooftops. ”They are not anchored down at all, and it’s very possible they would fall in an earthquake.”

Buildings of reinforced masonry, reinforced concrete and steel would hold up much better, engineers say, and wooden structures are considered intrinsically tough in ordinary circumstances. The best performers, they say, would probably be skyscrapers built in the last 20 years. As Mr. Silman explained, they have been built to withstand high winds, and the same structural features that enable them to do so also help them resist an earthquake’s force. But even these new towers have not been provided with the seismic protections required in California and so are more vulnerable than similar structures on the West Coast.

Buildings in New York are not generally constructed with such seismic protections as base-isolated structures, in which the building is allowed to shift with the ground movement; or with flexible frames that absorb and distribute energy through columns and beams so that floors can flex from side to side, or with reinforced frames that help resist distortion.

”If you’re trying to make a building ductile – able to absorb energy – we’re not geared to think that way,” said Mr. Silman.

New York buildings also contain a lot of decorative stonework, which can be dislodged and turned into lethal missiles by an earthquake. In California, building codes strictly regulate such architectural details.

Manhattan does, however, have at least one mitigating factor: ”We are blessed with this bedrock island,” said Mr. Silman. ”That should work to our benefit; we don’t have shifting soils. But there are plenty of places that are problem areas, particularly the shoreline areas,” where landfills make the ground soft and unstable.

As scientists have learned more about geologic faults in the Northeast, the nation’s uniform building code – the basic, minimum code followed throughout the country – has been revised accordingly. Until recently, the code required newly constructed buildings in New York City to withstand at least 19 percent of the side-to-side seismic force that a comparable building in the seismically active areas of California must handle. Now the threshold has been raised to 25 percent.

New York City, for the first time, is moving to adopt seismic standards as part of its own building code. Local and state building codes can and do go beyond the national code. Charles M. Smith Jr., the city Building Commissioner, last spring formed a committee of scientists, engineers, architects and government officials to recommend the changes.

”They all agree that New York City should anticipate an earthquake,” Mr. Smith said. As to how big an earthquake, ”I don’t think anybody would bet on a magnitude greater than 6.5,” he said. ”I don’t know,” he added, ”that our committee will go so far as to acknowledge” the damage levels in the Scawthorn-Harris study, characterizing it as ”not without controversy.”

For the most part, neither New York nor any other Eastern city has done a detailed survey of just how individual buildings and other structures would be affected, and how or whether to modify them.

”The thing I think is needed in the East is a program to investigate all the bridges” to see how they would stand up to various magnitudes of earthquake,” said Bill Geyer, the executive vice president of the New York engineering firm of Steinman, Boynton, Gronquist and Birdsall, which is rehabilitating the cable on the Williamsburg Bridge. ”No one has gone through and done any analysis of the existing bridges.”

In general, he said, the large suspension bridges, by their nature, ”are not susceptible to the magnitude of earthquake you’d expect in the East.” But the approaches and side spans of some of them might be, he said, and only a bridge-by-bridge analysis would tell. Nor, experts say, are some elevated highways in New York designed with the flexibility and ability to accommodate motion that would enable them to withstand a big temblor.

Tunnels Vulnerable

The underground tunnels that carry travelers under the rivers into Manhattan, those that contain the subways and those that carry water, sewers and natural gas would all be vulnerable to rupture, engineers say. The Lincoln, Holland, PATH and Amtrak tunnels, for instance, go from bedrock in Manhattan to soft soil under the Hudson River to bedrock again in New Jersey, said Mark Carter, a partner in Raamot Associates, geotechnical engineers specializing in soils and foundations.

Likewise, he said, subway tunnels between Manhattan and Queens go from hard rock to soft soil to hard rock on Roosevelt Island, to soft soil again and back to rock. The boundaries between soft soil and rock are points of weakness, he said.

”These structures are old,” he said, ”and as far as I know they have not been designed for earthquake loadings.”

Even if it is possible to survey all major buildings and facilities to determine what corrections can be made, cities like New York would then face a major decision: Is it worth spending the money to modify buildings and other structures to cope with a quake that might or might not come in 100, or 200 300 years or more?

”That is a classical problem” in risk-benefit analysis, said Dr. George Lee, the acting director of the Earthquake Engineering Research Center in Buffalo. As more is learned about Eastern earthquakes, he said, it should become ”possible to talk about decision-making.” But for now, he said, ”I think it’s premature for us to consider that question.”