People reported to USGS today that they felt an aftershock from an earthquake that struck last spring in northern New Jersey. According to USGS, at 6:28 am this morning, a relatively weak magnitude 1.6 earthquake struck near Califon from a depth of only 1.8 km. The epicenter is close to where a stronger magnitude 4.8 earthquake struck last April. There have been more than 90 earthquakes in this area over the last 365 days. Today’s aftershock was too weak to create any damage nor injuries.

This earthquake sequence began in northern New Jersey on the morning of April 5, with a magnitude 4.8 earthquake striking near Tewksbury at 10:23 am. Since then, there have been more than 200 additional aftershocks, including two stronger ones.

Most of the aftershocks have been barely noticeable. But the initial earthquakes did so some damage. In Berkeley Heights, Union County, New Jersey, the Berkeley Heights Fire Department reported that the foundation of a home there failed and that the primary earthquake on April 5 was a contributing factor. A Brooklyn middle school gym was deemed unsafe after a Department of Buildings inspection found cracks inside; the rest of the school at 370 Fountain Avenue was determined to be safe. Dozens of gas and water leaks were reported in the region, leaving people without utilities like power or water.

According to USGS, the April 5, 2024 occurred as a result of oblique reverse and strike-slip faulting at shallow depths in the crust. Although this event did not occur near a plate boundary, such “intraplate” earthquakes can and do occur. “While this earthquake is relatively small globally, earthquakes of this magnitude are commonly widely felt in the eastern United States because of efficient seismic wave propagation in the region,” the USGS said.