by The fault that ruptured under New Jersey on Friday morning was likely an ancient dormant seam in the Earth, awakening geological forces in a region where earthquakes are rare and seismic risks are not fully understood.
The magnitude-4.8 earthquake was New Jersey’s strongest in more than 200 years.
The United States Geological Survey said in a news conference that more earthquakes are possible, with statistical modelers estimating a 3% chance of a magnitude 5 or greater earthquake in the coming weeks.
A 4.0 magnitude aftershock struck New Jersey on Friday evening. The USGS website has reported at least 11 former occupations in the area so far. Statistical models based on past earthquakes suggested there could be as many as 27 aftershocks of magnitude 2 or greater next week, the USGS said.
As the shaking subsided on Friday, scientists began working to determine exactly where the rupture occurred.
“This is a region with many older faults that could be reactivated at any time. At this time, the fault that caused the earthquake is still unknown,” said Jessica Jobe, USGS research geologist.
Scientists suspect that the earthquake probably originated in the area of the Ramapo fault zone in the Newark basin. There is a branching network of faults in the fault system. Some have been mapped but others are probably unknown, so the fault where Friday’s quake occurred may be unmapped.
“It’s probably an anonymous fault, but we don’t really know. It’s hard to figure that out in a place with such turbulence,” said Dara Goldberg, a USGS geophysicist. “It could be on a branch of the Ramapo fault. It could be nearby, we’re not entirely sure.”
The scientists said that the fault zone is old and complex. Determining exactly what happened will help researchers understand what to expect from the zone in the future and better manage seismic risk in the Northeast.
Unlike the West Coast, where tectonic plates meet at a boundary and create a seismic hazard that runs down the spine of the coast, the Northeast’s tectonic risk is rooted in ancient history: Faults still exist from inactive tectonic processes further, which leaves. scattered cracks and weaknesses.
Stress slowly accumulates on this network of faults and sometimes causes a slip, producing an earthquake, said Frederik J. Simons, professor of geosciences at Princeton University.
“Stress is always growing at very slow rates,” Simons said. “It’s like an old house creaking and groaning.”
Compared to the West Coast, earthquakes on the East Coast can be felt far away and can cause more significant shaking relative to their size because rocks in the region are often older, harder and denser.
“These are competent rocks that transmit energy well,” Simons said.
Friday’s earthquake was widely felt, from Washington, DC to Boston. It was also relatively shallow – the USGS said it probably ruptured less than 3 miles below the Earth’s surface.
“The shallower or closer it is, the more we as humans feel it,” Simons said.
However, the strength of earthquakes in the region is limited by the length of the faults.
“The magnitude of an earthquake is directly proportional to the distance the fault has moved,” Goldberg said. “In the North East, the faults are not very long.”
Felix Waldauser, a seismologist and research professor at the Lamont-Doherty Earth Observatory, said the earthquake highlighted the need to better understand the region’s earthquake risk.
“We don’t really understand the faults here. If we don’t understand the faults, it’s hard to assess the hazard,” Waldauser said.
He lamented the fact that the USGS in 2019 cut funding to the Lamont-Doherty Cooperative Seismographic Network, which he said had 45 stations collecting seismic data across the Northeast but is now down to about 20.
“In an ideal world, our network would be running and recording data and analyzing the data, finding out exactly where the event was,” he said.
Waldauser said Friday afternoon that he wanted to round up his colleagues to deploy seismometers around the epicenter of the quake, near Whitehouse Station, New Jersey, to record aftershocks, which could help the main fault identify
“We’re trying to bring people together. I’m not sure if it’s going to happen,” he said.
However, Goldberg said that a dense local network of equipment is very beneficial for monitoring smaller earthquakes and doing detailed science, but not necessary for understanding larger quakes like Friday’s.
“Anything in the size 4 range, we can determine in a global series of stations,” she said. “On the scale of earthquakes that are relevant to society and people’s daily lives, we can do a great job without that density.”
Simons, who grabbed his coat and hurried out of his Princeton office when the quake struck, said the 35 seconds of “violent, strong and prolonged” shaking made for an exciting morning and offered a reminder to the coast of a less seismically active country: “It’s like being a little out of shape and having a little warning – a mini-stroke, a heart attack,” he said.
“The Earth is giving us energy that we cannot control. We will continue to build good buildings and enforce building codes and prepare for disaster, so we can respond when the next one hits,” Simons said.
This article was originally published on NBCNews.com
