An aftershock of a preliminary magnitude 4.0 has struck just southwest of Gladstone, New Jersey, according to the United States Geological Survey.

 It happened at about 5:59 p.m. ET, USGS said.

 The aftershock comes nearly 8 hours after the main shock of 4.8 magnitude this morning. There have been at least 10 aftershocks, though most were in the 1.8 to 2.2 magnitude range