Quote:
Originally Posted by FrancoRey
Just out of curiosity, what is the the minimum Richter Scale intensity for an earthquake that NYC buildings have to withstand to pass building code? Obviously before the modern era this was a non-issue but I imagine most buildings built in the last 40 years have to be re-enforced. Anyone know more about this subject? When did they begin retrofitting structures for earthquakes in NYC? Laws? Code?
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Here's what I was able to find.
http://www.columbia.edu/cu/record/archives/vol20/vol20_iss19/record2019.18.html
Scientist's Earthquake Codes Adopted
Photograph: Behind and to the right of Mayor Giuliani at the signing was Klaus Jacob, senior research scientist at Lamont-Doherty Earth Observatory, who helped write New York City's first earthquake codes.
Photo Credit: Edward Reed.
Photograph: Seismologists at Lamont-Doherty Earth Observatory, Noel Barstow, center, and John Armbruster, right, deploy portable seismometers on the Tappan Zee Bridge to evaluate how the Hudson Rover crossing would respond to an earthquake.
New York City Mayor Rudolph Giuliani last week signed into law the city's first earthquake building codes, requirements that Columbia seismologist Klaus Jacob long championed and helped write.
Jacob was at the Mayor's side last Tuesday for the official signing. The codes set minimum construction standards to make buildings resistant to earthquakes registering up to 5.5 on the Richter scale. They will apply to all new buildings more than three stories high.
"In cities, earthquakes by themselves don't cause the major loss of life; collapsing buildings do," Jacob said. "And New York City was built mostly without quakes in mind."
Jacob played a major role in alerting the public to the geological evidence that the U.S. East Coast--and New York City in particular--is not immune to earthquakes. As a member of the committee that drafted the new codes, Jacob also applied research on how different rock and soil types dramatically affect ground shaking caused by earthquakes.
"The historic record of earthquakes during the last three centuries in the eastern U.S. and in New York City, and geological findings elsewhere along Atlantic Coast, all provide solid reasons why one should take the eastern earthquake threat seriously," he said.
New York City's largest known quake, which registered between magnitude 5 and 6, occurred in 1884. It toppled chimneys, shattered windows and caused panic in the streets, but because it was centered about 15 miles offshore, no buildings collapsed and nobody was killed.
In 1985, a magnitude 4 quake centered in Ardsley in Westchester County was felt in New York City.
"Today, in high-rise New York, a magnitude 5, which is likely to strike the metropolitan area every 100 years, could cause $1 billion in damage and some loss of life," he said.
Chance Is Slim
"New York State has experienced four quakes of magnitudes 5 to 5.7 since 1884. Magnitudes 6 and 7 quakes, such as the one that devastated Kobe, have struck elsewhere along the East Coast and, based on geology, the possibility of such a strong quake in New York City is slim, but cannot be ruled out."
The probability of East Coast quakes is much lower than in the western U.S., where seismically active crustal plates collide, Jacob said, "but the older, harder rocks near New York transmit energy more efficiently over longer distances," producing the potential for a greater swath of destruction.
Unlike the West Coast, East Coast builders have largely ignored the threat of earthquakes, Jacob said. "Townhouses of unreinforced masonry, such as New York's Victorian-era brownstones, are especially vulnerable. Such buildings could crumble to rubble and dust in a quake, causing multiple injuries and asphyxiation."
Even high-rises are at risk if they are built on soft soils, which dramatically amplify ground shaking and often become liquid-like during earthquakes, he said. Unlike the World Trade Center and the Empire State Building, which are more safely anchored on rock, Battery Park City, Starrett City and Co-op City are all built on soft soils, he said.
The new seismic safety codes require that builders consider soil and rock conditions on which new structures are constructed. They require that masonry be reinforced to prevent it from falling during a quake and injuring people below.
In addition, new buildings will have to have reinforced foundations, strengthened joints, iron rods in walls, anchors connecting floors to exterior walls, and revised load factor formulas--all designed to keep buildings standing.
Jacob began his career studying earthquakes in Alaska, where large earthquakes frequently occur. But in the early 1980s he shifted his focus to the East Coast. "Though the frequency of earthquakes is not as great, we have tremendous risk here and a real need for the seismological knowledge we have accumulated to be applied right in our own backyard."
In 1986, Lamont-Doherty became a founding member of the National Center for Earthquake Engineering Research, a consortium of research institutions with a mission to apply seismological research to mitigating earthquake destruction.
Under NCEER auspices, Jacob organized conferences in the late 1980s attended by geologists, engineers, builders and government officials, which highlighted the East Coast earthquake risk and helped generate momentum to find ways to reduce it. Joining the committee to draft New York City's new code, he headed a subcommittee that focused on geotechnical issues.
"I sought to have an impact by providing the scientifically sound background to convince people of the need, " he said. "No city will ever be earthquake-proof. But we build our cities on an Earth that has its own agenda, which we ignore at our peril.
Race Against Time
Earthquake hazard mitigation is a constant race against time--human time against geologic time. The new building codes will have a real benefit in 50 to 100 years , as one by one, New York City structures are built to withstand earthquakes that will happen. It's only a matter of time."
Jacob said he will now focus on upgrading New York State's building code and on "the dilemma not dealt with yet--emergency preparedness." He said that police, fire, hospital, telecommunications, transportation and other officials should prepare plans to deal with the consequences of various earthquake scenarios.
Deploying portable seismometers on several New York City bridges, he and Lamont-Doherty colleagues are also evaluating how the bridges would respond to earthquake-induced shaking and recommending ways to retrofit the bridge to enhance public safety.
Columbia University Record -- March 3, 1995 -- Vol. 20,
No. 19
Scientist's Earthquake Codes Adopted
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