ABSTRACT
A swarm of light to very minor earthquakes has been occurring since April 5, 2024 within a focused, 60-square mile area of Hunterdon, Morris, and Somerset Counties, NJ. An initial 4.8 magnitude event with an epicenter near Oldwick, NJ has been succeeded by hundreds of aftershocks over a months time. The initial earthquake is the second largest, historical event in New Jersey, although since 1950 there have been over 40 earthquakes in the region within 250 km that exceeded magnitude 3.0.  

The structural nature of the strongest events have provided unprecedented insights into the subtle, on-going mountain-building processes currently operating in the region stemming from stresses accompanying the slow, westward drift of the North American tectonic plate. The most probable faults for the two largest earthquakes (4.8 and 3.7 magnitudes) are blind, right-lateral reverse faults striking N8E to N11E degrees that dip moderately eastward at depths ranging between 2 and 10 km below ground surface within Proterozoic basement.

This talk will summarize the geospatial, structural, and temporal aspects of this unusual event swarm and explain how the physical dimensions of the associated faults are estimated. This swarm is compatible with having N-S striking neotectonic crustal arches and troughs running through the region west of the Ramapo seismic zone based on CORS GPS vertical crustal motions and the Sykes and others 2006 earthquake catalog for the Philadelphia and New York region.

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