Tuesday, October 19, 2021 – SHOULD WE BE READY FOR THE BIG ONE?
TUESDAY, OCTOBER 19, 2021
The 498th Edition
New York Earthquakes:
Is a Big One Coming?
Stephen Blank
Stephen Blank
Do you remember the 3.9 magnitude earthquake that shook the New York City region on November 30, 2010?
No reason you should, unless you’re a seismologist. The US Geological Survey reported that the tremor occurred in the Atlantic Ocean, about 80 miles off the coast of Southhampton. The earthquake wasn’t big enough to do any damage or hurt anyone, and the Coast guard said there was no threat of a tsunami. It was the biggest earthquake for our area in 18 years.
Not a danger, but the 2010 quake wasn’t unusual. Five earthquakes have occurred in the same area in the past 20 years, including a 4.7 magnitude quake in 1992. New York, which is riddled with faults, has a long history of earthquakes: On average, the region has witnessed a moderate quake (about a 5.0 on the Richter scale) every hundred years. The last one was in 1884 and had a magnitude of approximately 5. For this earthquake, observations of fallen bricks and cracked plaster were reported from eastern Pennsylvania to central Connecticut, and the maximum intensity reported was at two sites in western Long Island (Jamaica and Amityville). Two other earthquakes of approximately magnitude 5 occurred in this region in 1737 and 1783.
“Riddled with Faults”??!?!?
Some basic geology: At plate boundaries like the San Andreas Fault, scientists can often identify the specific fault on which an earthquake took place. In contrast, east of the Rocky Mountains this is rarely the case. The New York City area is far from the boundaries of the North American plate, which are in the center of the Atlantic Ocean, in the Caribbean, and along North America’s west coast.
But this doesn’t mean we are home free. The seismicity of the northeast is felt to be due to ancient zones of weakness that are being reactivated. In this model, pre-existing faults formed during ancient geological episodes persist in the intraplate crust, and earthquakes occur when present stress is released along these zones of weakness. The stress that causes the earthquakes is generally considered to be derived from rifting at the Mid-Atlantic ridge. Some experts feel that seismicity is scattered throughout most of the New York metropolitan area, particularly around Manhattan Island.
What about faults?
Map of geologic faults lines in NYC region
The Ramapo Fault is viewed by some as a major seismically active feature of our wider region. The Ramapo Fault zone spans more than 185 miles in New York, New Jersey and Pennsylvania.
A 2008 study argued that a magnitude 6 or 7 earthquake might originate from the Ramapo fault zone, which would almost definitely lead to many fatalities and billions of dollars in damage. And by the way, just off the northern terminus of the Ramapo fault is the Indian Point Nuclear Power Plant. You don’t have to worry about this one – the plant was closed down in April.
Earthquake Likely?
By looking at the City’s past earthquakes, experts point to the likelihood of 5.0 or greater hitting the city soon. “Researchers say New York City is susceptible to at least a magnitude 5 earthquake once every 100 years, a 6 about every 670 years, and 7 about every 3,400 years,” writes one. “It’s been 134 years since New York was last hit by at least a magnitude 5.”
Damage worse?
As quakes go, a 5 would not be a big one. But earthquake damage could be worse here than out west. Why? One reason is the nature of our geology. The cooler rocks in the northeast contribute to the seismic energy propagating as much as ten times further than in the warmer rocks of California. A magnitude 4.0 eastern earthquake typically can be felt as far as 60 miles from its epicenter. A magnitude 5.5 eastern earthquake, although uncommon, can be felt as far as 300 miles from its epicenter.
But not just geology. “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.”
Only is 1995 were seismic provisions included in the Building Code, meaning that relatively few buildings currently located throughout the city were erected with earthquake protections in mind.
200,000 buildings in NYC are unreinforced brick, with the most located in Brooklyn. These are most vulnerable to an earthquake because the walls in these buildings are prone to collapse outward.
Also, much of New York City’s waterfront is built on fill that will be unstable in a quake. Other areas that rest on artificial fill vulnerable to soil liquefaction are JFK Airport and the World’s Fair site in Queens. The UES and Chinatown are the same and they also have many unreinforced masonry buildings.
Earthquake scene from the film San Andreas 2015
But that’s not all. Experts wonder how our City’s ancient infrastructure would hold up in the event of an earthquake. Rubble of crumbled brick and stone buildings will clog already congested roads, blocking first responders and public transportation. Tunnels? Construction on the Steinway tunnel began around the time of the last earthquake, long before seismic codes or even modern engineering practices. In the event of a quake, holes where the tunnel walls no longer reach the surrounding mud will cause the tunnel to rattle around. And because the tunnel runs through both the soft mud of the riverbed and the hard bedrock on either side, different segments are going to rattle around at different speeds and frequencies. More than a dozen tunnels like the Steinway connect Manhattan to New Jersey and Long Island. All are at risk of serious damage in the event of a quake. Yikes.
Fact is that the City is doing better. Since the first seismic building codes for NYC were passed in 1995, additional steps have been taken to mandate earthquake protections into NYC structures. The Department of Building’s City Construction Codes in 2008 aim to make buildings stronger, more flexible, and more ductile – able to absorb energy without breaking in a brittle manner. The Codes have sections on soil types and building foundations. Seismic detailing is required to enable a building’s joints, structural connections and piping to hold up during an earthquake. Critical facilities such as firehouses and hospitals were required to be designed to both survive an earthquake event and to also remain open and functional following one. In 2014, the DOB revised the Construction Codes to follow the model of American Civil Engineers Standard for designing and constructing seismic-resistant structures, which requires “that new buildings in New York City are designed so it is less likely they will collapse or sustain significant damage during an earthquake.” To account for the inherent vulnerabilities posed by the prevalence of soft soil that structures all across New York are erected upon, “building designs must account for site-specific soil conditions and building foundations, and must ensure that joints and structural connections are flexible. Special detailing for electrical and mechanical systems, building contents, and architectural components are also specified.”
Still, unless we are too comfortable, did you see the piece in a recent Sunday Times that only three of New York’s 25 tallest residential buildings — and none of the towers on Billionaires’ Row — have completed building safety tasks required by the city?
And while new buildings may be built to the new codes, the vast majority of buildings in Manhattan were built long before these codes were introduced. Retrofitting these structures to make them more earthquake resistant – not to mention our abovementioned infrastructure – would be quite a task.
But I’m not going to worry about earthquakes here. Except, perhaps, about the fault on our Island.
Stephen Blank
RIHS
October 16, 2021
TUESDAY PHOTO OF THE DAY
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ROOSEVELTISLANDHISTORY@GMAIL.COM
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MONDAY PHOTO OF THE DAY
NEW ART INSTALLATION AT L TRAIN STATION
LAURA HUSSEY GOT IT!!
Subway art by Marcel Dzama at the Bedford Ave Station on the L line.
STEPHEN BLANK
Sources
https://www.wnyc.org/story/102699-biggest-earthquake-18-years-shakes-lond-island/
http://nesec.org/new-york-earthquakes/
https://www.earth.columbia.edu/articles/view/2235
New Supertalls Test the Limits, as the City Consults an Aging Playbook, New York Times, October 1, 2021
Text by Judith Berdy
Thanks to Bobbie Slonevsky for her dedication to Blackwell’s Almanac and the RIHS
Thanks to Deborah Dorff for maintaining our website
Edited by Melanie Colter and Deborah Dorff
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TUESDAY, OCTOBER 19TH, 6:30 P.M.
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