Friday morning at round 10:30 native time, a magnitude 4.8 earthquake popped three miles under Whitehouse Station, New Jersey. Though nowhere close to the magnitude of the West Coast’s monster quakes, the seismic waves traveled a whole bunch of miles, jostling not simply close by New York City, however Philadelphia and Boston and Washington, DC. The United States Geological Survey is urging the area to organize for aftershocks of smaller magnitude.

For a area not accustomed to earthquakes, it was a jolt. Its wide-ranging affect seems to be not a quirk, however a byproduct of the East Coast’s distinctive geology of historic fault strains and rock composition.

“Earthquakes in this region are uncommon, but not unexpected,” stated seismologist Paul Earle, of the USGS National Earthquake Information Center, on a press name Friday. “Earthquakes on the East Coast are felt much farther—four or five times farther—than a similar earthquake on the West Coast.”

Back in 2011, for example, individuals felt the shock of a 5.8 quake in Virginia from as much as 600 miles away, whereas a 6.8 a couple of years later in Napa, California—which produced twice as a lot vitality—traveled less than half that distance. Given how rather more densely populated the East Coast is than the West Coast, meaning a complete lot of individuals over a a lot wider space will really feel not less than just a little shaking, even when the magnitude is considerably smaller than one thing like a Loma Prieta earthquake, which devastated the Bay Area in 1989.

Jostled East Coasters can blame the geology beneath their ft. On the West Coast, an unlimited internet of faults pop off on a regular basis alongside an lively plate boundary, sending shocks throughout the panorama. “We have new faults forming, we have old faults taking on strain and rupturing in big earthquakes,” says Columbia University structural geologist Folarin Kolawole.

But when an earthquake occurs in a given fault, there are neighboring faults by which the vitality is distributed. Basically, as a result of the western US has so many faults alongside an lively plate, it has a variety of channels to soak up earthquake vitality—subterranean shock-absorbers, of kinds.

While the USGS hasn’t but pinpointed the precise fault answerable for right now’s earthquake, it occurred in a area the place the fault system is extra static than on the West Coast. It seems an inactive fault was reactivated Friday morning underneath New Jersey, someplace within the Ramapo fault system.

The relative stability of the East Coast fault system is because of its geological age: Its rocks fashioned a whole bunch of hundreds of thousands of years earlier than rocks on the West Coast. Geologically talking, the East Coast is a quiet outdated man, whereas the West Coast is a rambunctious teenager.

“We don’t have that tectonic complexity on the East Coast,” says Gregory Mountain, a geophysicist at Rutgers University. “We had it in the geologic past, hundreds of millions of years ago, but things are pretty well solidified—is one way to call it—and stabilized. For that reason, on the East Coast, seismic energy could actually probably travel quite a bit farther and have less energy loss with distance.”