Seismometers are popping up all over North Jersey. What are they for?

A group of Rutgers University seismologists has installed more than 100 seismometers around North Jersey to gather data on ground vibrations and better understand the subsurface faults that likely caused a magnitude 4.8 earthquake that shook the Garden State this spring.

The quake, one of the strongest ever recorded in New Jersey, rattled tables and shook windows. People felt it from Washington to Boston. And it gave scientists who study New Jersey’s geologic history a chance to gather new data in real time as aftershocks reverberated through the Garden State’s bedrock.

“By analyzing this earthquake and the aftershocks, we have the opportunity to explore in more detail the Ramapo Fault," said Roberto Masis Arce, a lead researcher on the team and a doctoral candidate at Rutgers' earth and planetary sciences department. "By using further seismic techniques, we can determine the type of fault and expected motion for future events.”

Another member of the Rutgers research team is James Bourke, a post-doctoral assistant. Right after the earthquake, Bourke rushed to his office on the Rutgers Busch Campus to activate an unused seismometer he had stored there, hoping to record aftershocks, which it did soon after.

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Now, Masis Arce and Bourke’s team is motivated to find what lies beneath New Jersey. "We hope to help produce a precise catalog of relocated seismicity near the fault region that is active,” said Bourke. 

More:NJ earthquake shook local geologists into action, sending them to precarious places

The installed seismometers will record data for some time, before a second stage in the project that involves installing more seismic stations. “This is an opportunity to characterize the region from a seismologic perspective, but we will be able to address other scientific inquiries that would not be addressed without this project,” said Masis Arce. 

Besides addressing scientific questions, the Rutgers team believes its work will provide a better understanding of the seismic hazards the Ramapo Fault zone represents.

How was the Ramapo Fault created?

North America, Europe and Africa were once part of a single giant tectonic plate, called Pangea. Pangea was formed about 400 million years ago as plates crashed together, creating massive mountains that scientists believe were as high as the Himalayas are today.

Those mountains eroded over time, giving us the Appalachians. The force of the collisions and resulting waves of mountain building also created ancient faults beneath the earth’s crust. One of those is the Ramapo Fault beneath New Jersey.

The stress from Pangea separating caused the Ramapo Fault system to become active again, according to Kenneth Miller, a professor in the Earth and planetary sciences department at Rutgers University.

The fault runs for about 185 miles from New York, through New Jersey — beneath Passaic, Morris, Somerset and Hunterdon counties — and on into Pennsylvania in a northeast-southwest orientation.

It’s not a simple line. The system is at least five to 10 miles wide.

In New Jersey, it runs beneath Pompton Lakes, Riverdale and Pequannock, just to the south of Lake Valhalla in Montville, on under Boonton, down beneath Bernardsville and Far Hills, and on into Hunterdon County, near the epicenter of the April 5 quake.

The Ramapo Fault system includes several smaller, secondary faults, such as the Rockaway Valley, Flemington, Longwood Valley, Spruce Run and others.

“Currently, we do not know the exact extent of the Ramapo Fault, but this sequence of events might illuminate new zones where the Ramapo Fault is located,” said Masis Arce. “If we can identify these new areas, we can act and be prepared as future earthquakes might occur in these new areas that, as of today, might not be considered as exposed to a seismic event.”

According to Masis Arce, the last event of this magnitude in the area was about 100 years ago. It's hard to predict the exact timing of earthquakes in the Ramapo Fault zone. “However, each earthquake is valuable to build a catalog and determine this time cycle to hopefully constrain time gaps where seismic events are more likely to occur than others,” said Masis Arce. 

It is still too early to provide decisive results, since data is still being gathered. But, Masis Arce said, "This data is very valuable and I’m sure it will be used for years to come in the scientific community.”