Long Island's 50-year quake forecast: slight chance, but with damage

Hazard maps released earlier this year found Long Island, along with most of New York State, faced a small but measurable risk of a damaging earthquake nearly the strength of the one that hit the region on Friday.

The United States Geological Survey National Seismic Hazard Model released in January gave Long Island a 10% chance in a 50-year period of experiencing a Modified Mercalli Intensity Scale Level 5 earthquake, and a 2% chance of experiencing a Level 7 earthquake. The intensity scale is based on observable earthquake damage at a particular location, unlike the Richter scale, which measures the motion of the ground to determine an earthquake’s magnitude.

A magnitude 4.8 earthquake shook Long Island and the New York City metro area Friday morning, a rare event felt by millions that had its epicenter in New Jersey. The quake hit at 10:23 a.m., the USGS said.

A Level 5 intensity could break windows and glassware. A Level 7 could damage foundations of one- and two-story wood-frame houses, damage larger buildings and shift furniture.

Nearly three-quarters of the United States could experience damaging earthquakes in a 100-year period, though the risk is highest on the West Coast, where more major fault lines lie. In fact, Jan. 17was the 30th anniversary of the 6.7 magnitude Northridge Earthquake at the north end of Los Angeles's San Fernando Valley.

For perspective, that quake, located in a region noted for its seismic activity, injured more than 9,000 people, killed 60 more, with up to $20 billion in property damage and total economic losses of $40 billion, according to the California Department of Conservation.

A paper on the map models noting Long Island's chances for a damaging earthquake was published online Dec. 29 in the scientific journal Earthquake Spectra.

'Best available science'

“These models that we make forecast where future earthquakes will occur,” said Mark Peterson, a USGS geophysicist and lead author of the paper.

“This is the best available science,” Peterson said. “Engineers will use it in their consideration of building codes and risk assessments.”

Changes to municipal building codes could filter down over the next six years, he said. While New Yorkers should “not forget that earthquakes can affect some of those structures,” risks from wind damage and flooding are probably more salient, he said.

While far from being a hotbed of tectonic shaking, Long Island has felt the earth move in the past. From Massapequa to Montauk, a 3.9-magnitude earthquake jolted Long Islanders in November 2010. It was centered nearly 100 miles southeast of the Island, according to the U.S. Geological Survey and there have been other small quakes since.

And hundreds of millions of years ago, this part of the world routinely had earthquakes powerful enough to shape hills into mountain peaks, according to geophysicists.

To build the model for the new hazard maps, scientists and engineers compiled data from 130,000 earthquakes, going back centuries, for which seismologic or geologic data exists. The finished product presents a slightly grimmer picture for parts of the eastern United States because it incorporates data from the New Madrid Seismic Zone near Missouri that shows past seismic activity there was more powerful than previously understood. It also incorporates data from the 2011 Mineral, Virginia, earthquake, the most widely felt in U.S. history, and from other soil studies that indicated “slightly higher ground-shaking potential” than was previously understood.

Minor seismologic activity

Folarin Kolawole, Columbia University assistant professor of structural geology, said the January hazard model affirmed recent research that suggests a pattern of mostly minor seismologic activity along the heavily populated Atlantic Coastal Corridor over the last 20 years.

“We have fault systems within the New York metro area that can accommodate up to magnitude 5 quakes, which is the minimum you need to create damage at the surface.”

He cited a minor earthquake in Queens several weeks ago. That and other “micro-quakes” appear to be related to a fault line running from New Jersey, across 125th Street and past Roosevelt Island before disappearing in Queens, he said.

The region also experienced a magnitude 5 earthquake in 1884, whose epicenter is believed to have been somewhere in the ocean south of Long Beach, Kolawole said. There will be a repeat, he said. “From a geoscience and seismology perspective, we know it will happen. We will have a minimum 5.0 at some point in time … the reason we know is, it has happened before.”

But William Holt, professor of geophysics at Stony Brook University, said the new model “doesn’t keep me awake at night … We’re in a plate, not in a plate boundary zone” that would yield earthquakes and volcanoes, with measures of strain smaller by orders of magnitude than they are on the West Coast, he said.

The last major plate tectonic activity in the area was about 240 million to 160 million years ago, during the breakup of the supercontinent Pangea, Holt said. “Hurricanes are a much more real hazard.”

Still, the chance of a significant earthquake does exist, and the hazard map can help manage risk, he said.

“The next step is transferring this knowledge to engineering practices” and balancing the benefits of earthquake resilience against the cost of design and implementation, he said.