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23 Small Aftershocks Reported By USGS In 23 Hours After New Jersey Earthquake

The USGS is reporting 23 aftershocks in the 23 hours since the New Jersey earthquake that rattled the Northeast.

Some of the aftershocks reported by the USGS between April 5 and 6.

Some of the aftershocks reported by the USGS between April 5 and 6.

 Photo Credit: USGS/Daily Voice
Cecilia Levine
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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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