'Aftershock kits' deployed in wake of April 5 earthquake

A team of scientists and technicians from the United States Geological Survey and partner research institutions this week deployed five suitcase-size portable sensors in New Jersey to measure the aftershocks of the 4.8-magnitude earthquake that shook the region April 5.

A permanent network of about 200 instruments as close as 50 miles to the mainshock epicenter in Whitehouse Station, New Jersey, and as far away as Antarctica registered that event and at least 50 of its stronger aftershocks, which have ranged in magnitude from 1.3 to 3.8. The portable sensors — which the USGS described in a news release as “aftershock kits” — will “detect and locate even smaller quakes,” said David Shelly, a USGS research geophysicist based in Golden, Colorado.

“We can’t predict earthquakes, but people spend a lot of time mapping out the fault locations,” said Shelly. “The more we know about where the faults are, the more we know where quakes are likely to occur.”

The portable sensors will send back more accurate information because they can be placed in key locations near the earthquake epicenters, said John Armbruster, senior staff associate at Columbia University's Lamont-Doherty Earth Observatory, one of the partner institutions.

“If the seismic wave travels 20 kilometers to reach the seismic station, there’s some uncertainty on how fast the rock transmits the wave,” he said. “If you’re right on top of the earthquake, you’re seeing very short paths, that uncertainty and the speed of the seismic wave becomes less and less relevant.”

Armbruster said that the lack of nearby monitoring stations meant that “some information was lost” in the days before placement of the aftershock kits.

Those kits could collect important data improving our understanding of earthquakes in an area that has had very few in recent history. Some researchers, however, said they had already lost valuable data because funding cuts to a seismic monitoring program meant sensors near the mainshock’s epicenter were not fully operable when the earthquake occurred.

Scientists study aftershocks to better understand the network of faults, or fractures in blocks of rock in the earth’s crust where earthquakes occur. Some faults are expressed at the earth’s surface, but many are buried miles below.

Aftershock data is important because only a handful of earthquakes of the magnitude of the April 5 mainshock have been registered in the region since the 1700s. “If you can record smaller earthquakes, you get a lot more earthquakes to work with,” Shelly said.

An earthquake is the ground shaking caused by sudden release of energy when two blocks of rock overcome friction to slip past each other. Mainshocks can trigger aftershocks, minor readjustments to the earth’s crust that occur for days or even years along nearby faults.

Multiple readings of the aftershocks will help researchers map “the geometry of the zone of seismicity,” said Stony Brook University geophysicist William Holt, and perhaps make inferences about the fault structure that was responsible for the mainshock.

But seismologist Won-Young Kim, a research professor at Columbia’s Lamont-Doherty Earth Observatory, said that 2020 funding cuts to the Advanced National Seismic System meant that five monitoring stations — including one about 5 miles from the mainshock epicenter — were not functional April 5. 

Had those stations been operating, he said, researchers could have located the epicenter with a high degree of accuracy. Also, Kim wrote in an email, “we could have sent out e-mail and text messages to NYC, NJ state police within [a] few minutes.” Notification took significantly longer, Kim wrote.

Because the strongest shaking occurred in an area away from a major population center, the public safety consequence was not dire, but “if it had occurred closer to Jersey City or Newark, there could have been substantial damage,” he said.

USGS did not comment Friday afternoon.

“Maybe the earthquakes aren’t so many in the New York City area,” Kim said, but monitoring was nonetheless important. “There is a lot to be damaged if there is an earthquake,” he said.