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The initial earthquake had a magnitude of 4.8 and was reported in Whitehouse Station at 10:23 a.m. Friday, April 5. Tremors were felt by more than four million people from Maryland to New Hampshire.
The first aftershock was reported just under an hour later at 11:20 a.m. 6 km NNE of Whitehouse Station with a magnitude of 2.0. The largest aftershock had a 4.0 magnitude and happened just before 6 p.m. Friday, April 5.
Most of the aftershocks were not notable, with magnitudes between 1.7 and 2.0
Below are all of the aftershocks reported by the USGS as of 9 a.m. Saturday, April 6:
- M 1.9 - 6 km SW of Gladstone, New Jersey - 8:16 a.m.
- M 2.5 - 7 km WSW of Gladstone, New Jersey 6:46 a.m.
- M 1.9 - 4 km E of Califon, New Jersey - 4:18 a.m.
- M 1.7 - 6 km ESE of Califon, New Jersey - 4:09 a.m.
- M 1.7 - 4 km WSW of Bedminster, New Jersey 3:11 a.m.
- M 1.7 - 5 km SW of Gladstone, New Jersey 1:07 a.m.
The following aftershocks happened on Friday, April 5, according to the USGS:
- M 1.5 - 5 km WSW of Gladstone, New Jersey 8:51 p.m.
- M 1.8 - 4 km W of Bedminster, New Jersey 8:39 p.m.
- M 1.5 - 5 km NE of Whitehouse Station, New Jersey 7:39 p.m.
- M 1.9 - 3 km SW of Bedminster, New Jersey 7:10 p.m.
- M 1.9 - 5 km WSW of Bedminster, New Jersey 6:16 p.m.
- M 3.8 - 7 km SW of Gladstone, New Jersey 5:59 p.m.
- M 1.9 - 3 km ENE of Whitehouse Station, New Jersey 4:21 p.m.
- M 2.0 - 6 km NNE of Whitehouse Station, New Jersey 4:13 p.m.
- M 1.7 - 4 km NW of Bridgewater, New Jersey 3:58 p.m.
- M 1.8 - 6 km ESE of Califon, New Jersey 2:40 p.m.
- M 2.2 - 4 km NE of Whitehouse Station, New Jersey 1:32 p.m.
- M 2.0 - 5 km SSW of Chester, New Jersey 1:18 p.m.
- M 1.8 - 7 km W of Bedminster, New Jersey 12:31 p.m.
- M 2.0 - 5 km SSE of Long Valley, New Jersey 11:49 a.m.
- M 1.8 - 6 km ESE of Califon, New Jersey 11:37 a.m.
- M 1.9 - 6 km NNE of Whitehouse Station, New Jersey 11:27 a.m.
- M 2.0 - 6 km NNE of Whitehouse Station, New Jersey 11:20 a.m.
Aftershocks are smaller earthquakes that happen in the same general area during the days to years following a larger event or "mainshock," the USGS website says.
"They occur within 1-2 fault lengths away and during the period of time before the background seismicity level has resumed," the site says.
"As a general rule, aftershocks represent minor readjustments along the portion of a fault that slipped at the time of the mainshock. The frequency of these aftershocks decreases with time."
The USGS said aftershocks can happen in the week following an earthquake, with a 50 percent probability of earthquakes with magnitudes above 3.
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