Professor Allan Rubin on the April 5 New Jersey Earthquakes

April 5, 2024
Accelerogram from the Whitehouse Station earthquake recorded at Princeton University Guyot Hall, Department of Geosciences.

Vertical-component seismogram of the April 5th 2024 Whitehouse Station M4.8 earthquake, recorded by a seismometer in the basement of Guyot Hall at the Department of Geosciences. Data and graphic contributed by Frederik J. Simons.

The magnitude 4.8 earthquake that we felt on campus was one of only a handful this large to have struck New Jersey in the last 300 years. Probably the largest of these occurred in 1783, with a magnitude estimated to be 5.3 (this was before seismometers were available). There were large ones off the coast of New York City and Asbury Park in 1884 and 1927, and another M4.8 in 1938, which until today was "officially" New Jersey's largest earthquake (meaning well-recorded by seismometers). 

Allan Rubin profile pic

Allan M. Rubin, Professor of Geosciences

The April 5, 2024 earthquake with an epicenter in Whitehouse Station, NJ, occurred on or close to the Ramapo fault, New Jersey's most active fault zone, producing a felt earthquake every 2-3 years, typically M2-3. Where the fault crosses into New York it runs very close to the Indian Point nuclear power plant, which was shut down in 2021, largely due to earthquake hazard concerns. The Ramapo fault zone is left over from when North American and European continents started separating about 280 million years ago, forming the North Atlantic ocean, and remains a weak zone in the Earth's crust even though the style of faulting has changed (from roughly east-west extension when it formed, to east-west compression today).

The US east coast is tectonically much less active than the western US, so fractures in the bedrock tend to be healed, and there is less attenuation (energy loss) as seismic waves propagate.  California sees roughly one M5 earthquake per year, but they are felt over a much smaller region.

Some more context: there is roughly a factor of 10 reduction in earthquake recurrence rate for each unit increase in magnitude, so ~100 M3's for each M5.  And a 30-fold increase in energy release, so an M5 is nearly 1000 times stronger than n M3 and twice as strong as a M4.8.

Seismometer in the basement showing the slab that it rests on and a close-up of the seismometer itself
The seismometers located in the basement of Guyot Hall, maintained by the Department of Geosciences. (left) Both seismometers sit on a slab that is not attached to the building in order to record ground motion directly. (right) Close-up of the instruments. One of the instruments records three components (two horizontal and one vertical) of ground motion, while the other has six channels, two pairs of three with a different frequency response. Photos by Danielle Schmitt