Northern New Jersey and New York City were shaken by an April 5 shallow magnitude 4.8 earthquake. While no large earthquakes like the 1886 magnitude 7.0 Summerville-Charleston earthquake have been recorded in the New York City area, small to medium earthquakes have been felt in the New Jersey-New York area since colonial times. Like Charleston, the northeast corridor is underlain by numerous faults formed when the Appalachian mountains were formed and then later when Africa rifted away from North America and stretched the continental crust in the process. Most of the reported earthquakes occur in this area of the stretched crust where old extensional faults are re-activated by the current compressional stress field. Very much a case where the continental crust was weakened as it was stretched and now it is being pushed together.
Generally, a magnitude 4.8 earthquake will cause a decent amount of shaking (you will know what it is when you feel it), but generally little to no damage. The April 5 earthquake in New Jersey also occurred in an area of low population density and relatively far from the coastal area reducing the chance of damage. During the Charleston 1886 earthquake, there was a much higher percentage of damage done to houses that were built on ‘fill’, old marsh or ocean that was filled with dirt, than to houses built on true land. Thus, we would expect that if we were to have a magnitude 4.8 earthquake near Charleston we would have a higher risk of minor damage than New Jersey because of the number of buildings built on fill. This can be seen in the reports from the 1974 Charleston magnitude 4.7 earthquake indicating minor damage like cracked plaster and bricks from 3 isolated areas associated with weak fill soils.
East Coast earthquakes may be felt over a larger area because the bedrock here is stronger than on the West Coast (East Coast bedrock is like a bell with a couple of little cracks, West Coast bedrock is like a bell with lots of big cracks) there is no chance that an earthquake in the New Jersey area could ‘trigger’ an earthquake here.
Please contact Dr. Erin Beutel—beutele@cofc.edu; 843 478-5200 with questions.
