On a quiet April morning last week, people across parts of New York State, New Jersey, Connecticut and some nearby areas got a rare jolt: a magnitude 4.8 earthquake centered near Lebanon, N.J. The shallow temblor produced a robust amount of shaking that was widely felt—including by plenty of the eight million residents of New York City, many of whom immediately flooded social media to ask variations of the same stunned question: Did I actually just feel an earthquake?
Though the significant wobbling took many by surprise, seismologists and natural hazard researchers have known for some time that it isn’t just the western U.S. that experiences potent earthquakes. A recent analysis by a U.S. Geological Survey team found that almost 75 percent of the country has the potential to experience damaging quakes within the next century. That includes, among many other locations, the major Eastern cities of Washington D.C., Philadelphia, Boston and New York City, which is by far the most populous of the group.
Nobody can predict when or exactly where a major earthquake will occur. But based on historical data and the known locations and behaviors of geological faults, last Friday’s earthquake—which fortunately caused only a smattering of light damage—isn’t that surprising at all. The question, then, is: Could the event have been worse? To put it another way: How likely is it that a major quake will strike New York City—and is everyone there ready for one?
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“We know that there have been moderate and strong earthquakes in this region in the past, which means there will likely be moderate or strong earthquakes in the future,” says Wendy Bohon, an independent earthquake geologist. “The amount of damage those quakes cause depends on how prepared we are for them.”
Preparedness depends on understanding what causes seemingly “out-of-place” earthquakes. Major quakes tend to occur along or very close to tectonic plate boundaries. That is, in part, why the West Coast gets so much attention: From California’s San Andreas Fault, where plates slide past one another, to the Pacific Northwest’s Cascadia subduction zone, where one plate plunges below another, deleterious earthquakes of very high magnitude are inevitable in this region.
Crucially, though, faults can exist far from plate boundaries—and earthquakes can happen along such faults. Plates can be stretched and compressed by large-scale tectonic shuffling, squashing and stretching, causing myriad faults within the interior of those plates to snap and slip. Last Friday’s temblor was one of these “intraplate” events, and it serves as a reminder as to why the involved region is capable of some shaking. “Although there is not an active plate boundary in New Jersey today, this region was along an active margin millions of years ago,” says Alexandra Hatem, a USGS research geologist. The faults created by that ancient motion remain to this day, and although they are typically locked up, they can occasionally jolt.
Such fault reactivations usually happen without incident. “Earthquakes on the East Coast are not uncommon, but most of them are too small to feel,” Bohon says. But if enough stress from the plate margins gets transmitted through the plates into their interiors, and if that stress reaches a fault primed to make a hefty slip, it can trigger a larger quake. According to the USGS, since 1950, 13 earthquakes of magnitude 4.5 and above have happened within 300 miles of the April 5 convulsion. (Don’t be fooled by seemingly slight changes in magnitude: the earthquake scale is logarithmic, so a magnitude 4.0 quake releases 32 times more energy than a magnitude 3.0 one.)
Although not fully unexpected, the April 5 quake was indeed notable—on a geologically “short” timescale. “This was the largest earthquake in probably 140 years for this area,” says Judith Hubbard, a Cornell University earthquake scientist. The last one like it happened way back in 1884. “For people, that might seem like a long time,” Hubbard adds. “For faults, that’s pretty normal.”
Hazard researchers don’t expect a cataclysmically strong quake, akin to what West Coast faults can produce, to strike the eastern U.S. Nevertheless, it’s possible that an intense quake could one day produce destructive levels of shaking. A magnitude 5.8 quake violently shook central Virginia in 2011, causing up to $300 million in property damage. With that in mind, is New York City ready?
The answer is not an emphatic yes—but it’s not a no, either. “New York City is not completely unprepared for a more damaging earthquake,” says Samantha Montano, an emergency management expert at Massachusetts Maritime Academy. Communication systems, urban search-and-rescue protocols and other emergency management protocols that the city uses to respond to nonquake hazards, such as flooding or terrorist attacks, would be relevant in an earthquake scenario.
The infrequency of even modest temblors in the city, though, means many buildings and other infrastructure may not be particularly resistant to geological judders. “There are certainly a lot of old buildings in New York City that predate modern building codes,” Hubbard says. “Those kinds of legacy buildings can be especially vulnerable.” The skyscrapers that dominate the Manhattan skyline could be retrofitted with various quake-resistant features (or designed that way during initial construction). Such features can include motion dampers, which prevent buildings from violently swaying and ultimately breaking apart.
For most residents, preparedness is also probably lacking. “As people posted their reactions online, very few people seemed to immediately recognize it as an earthquake,” Montano says. She didn't see anyone say or demonstrate that they used the appropriate protective action: drop, cover and hold on. “In a bigger earthquake, that lack of reaction could lead to greater physical harm.”
There are national educational efforts such as the Great ShakeOut, but not unexpectedly, “participation certainly leans toward the West Coast,” Montano says. And changing awareness is often not as simple as telling people the facts. “It can be hard to talk about earthquakes in areas where people have very little living memory of these,” says Sara McBride, a social scientist at the USGS. “These conversations can be uncomfortable to have, and no one likes to hear bad news. But we need to find ways to have these uncomfortable conversations.”
Fortunately, last Friday’s temblor could provide some fuel for efforts to enhance awareness. McBride hopes that it will prompt emergency managers—not just in New York City and the rest of the Northeast but also in other parts of the country that are not known for large quakes—to reassess their earthquake planning and public education programs.
And though a tremendous quake hitting New York City isn’t especially likely, it’s not impossible. So McBride urges people to take some time to read authoritative sources on how best to prepare for that eventuality. “Have a plan, drill it and know what you’re going to do,” she says.
