Three minor earthquakes struck North Jersey last month. Yes, Jersey. Turns out the state known for its turnpikes and shopping malls also has a major geological landmark: the Ramapo Fault, which crosses into New York and Pennsylvania. “Earthquakes are not unexpected here,” seismologist Won-Young Kim told The New York Times. “It’s just an indication that Planet Earth is evolving.”
Kim studies earthquakes at Lamont-Doherty Earth Observatory and runs the Lamont-Doherty Cooperative Seismographic Network, which listens for earthquakes from Maryland to Maine. He grew up in Seoul, where as a teenager, he picked up rock climbing and an interest in geology. In 1977, he visited the northern Italian region of Friuli, where a magnitude 6 earthquake had killed a thousand people the year before. Struck by the devastation, Kim decided then to become a seismologist.
Q: Most Americans have heard of California’s San Andreas Fault. How does the Ramapo compare?
Kim: The Ramapo Fault is shorter–55 miles versus 800 miles—and also older–created about 200 million years ago when the continents of North America and Eurasia split apart, forming the Atlantic Ocean. The fault was active as the Appalachian Mountains were forming but today lies inactive. The recent earthquakes likely occurred on minor faults around the Ramapo.
Q: The earthquake that struck Randolph, N.J., on Feb. 2 measured 3.0. Two more struck nearby, a 2.4 on Feb. 14 and a 2.3 Feb. 18. Is this unusual?
Earthquakes greater than 3.0 are relatively rare in New Jersey but strong enough to cause substantial shaking and trigger aftershocks–a few hours to several weeks later. That’s what happened last month.
Q: If the earthquakes were so small, why did at least 1,000 people report feeling them?
The earthquakes were shallow– less than 3 kilometers below the surface. The rock on the East Coast is also more rigid, which helps to propagate ground motion further.
Q: When did the last big earthquake hit New Jersey?
Written records tell us that a 5.1 hit near Rockaway, Morris County, in 1783. It was felt from New Hampshire to Pennsylvania and toppled chimneys, but caused no major damage. Since the 1910s, we’ve been able to measure earthquakes more accurately using seismometers.
Q: Any idea when the next big one will hit?
That’s difficult to predict based on our limited statistics. But we can expect a 5.0 or greater about every 200 years, which means we may be overdue.