Published 30th April 2018
Researchers
believe that a powerful earthquake, magnitude 5 or greater, could cause
significant damage to large swathes of NYC, a densely populated area
dominated by tall buildings.
Some experts have suggested that NYC is susceptible to at least a magnitude 5 earthquake once every 100 years.
The
last major earthquake measuring over magnitude 5.0 struck NYC in 1884 –
meaning another one of equal size is “overdue” by 34 years, according
their prediction model.
Natural disaster researcher Simon Day, of University College London, agrees with the conclusion that NYC may be more at risk from earthquakes than is usually thought.
EARTHQUAKE RISK: New York is susceptible to seismic shaking from far-away tremors
But
the idea of NYC being “overdue” for an earthquake is “invalid”, not
least because the “very large number of faults” in the city have
individually low rates of activity, he said.
The
model that predicts strong earthquakes based on timescale and stress
build-up on a given fault has been “discredited”, he said.
What
scientists should be focusing on, he said, is the threat of large and
potentially destructive earthquakes from “much greater distances”.
The
dangerous effects of powerful earthquakes from further away should be
an “important feature” of any seismic risk assessment of NYC, Dr Day
said.
GETTY
THE BIG APPLE: An aerial view of Lower Manhattan at dusk in New York City
USGS
RISK: A seismic hazard map of New York produced by USGS
“New York is susceptible to seismic shaking from earthquakes at much greater distances” Dr Simon Day, natural disaster researcher
“An
important feature of the central and eastern United States is, because
the crust there is old and cold, and contains few recent fractures that
can absorb seismic waves, the rate of seismic reduction is low.
Central
regions of NYC, including Manhattan, are built upon solid granite
bedrock; therefore the amplification of seismic waves that can shake
buildings is low.
But
more peripheral areas, such as Staten Island and Long Island, are
formed by weak sediments, meaning seismic hazard in these areas is “very
likely to be higher”, Dr Day said.
“Thus,
like other cities in the eastern US, New York is susceptible to seismic
shaking from earthquakes at much greater distances than is the case for
cities on plate boundaries such as Tokyo or San Francisco, where the
crustal rocks are more fractured and absorb seismic waves more
efficiently over long distances,” Dr Day said.
In
the event of a large earthquake, dozens of skyscrapers, including
Chrysler Building, the Woolworth Building and 40 Wall Street, could be
at risk of shaking.
“The felt shaking in New York from the Virginia earthquake in 2011 is one example,” Dr Day said.
On
that occasion, a magnitude 5.8 earthquake centered 340 miles south of
New York sent thousands of people running out of swaying office
buildings.
USGS
FISSURES: Fault lines in New York City have low rates of activity, Dr Day said
NYC
Mayor Michael Bloomberg said the city was “lucky to avoid any major
harm” as a result of the quake, whose epicenter was near Louisa,
Virginia, about 40 miles from Richmond.
“But
an even more impressive one is the felt shaking from the 1811-1812 New
Madrid earthquakes in the central Mississippi valley, which was felt in
many places across a region, including cities as far apart as Detroit,
Washington DC and New Orleans, and in a few places even further afield
including,” Dr Day added.
“So, if one was to attempt to do a
proper seismic hazard assessment for NYC, one would have to include
potential earthquake sources over a wide region, including at least the
Appalachian mountains to the southwest and the St Lawrence valley to the
north and east.”