Re: Were there ever any earthquakes that hit New Jersey?

I do not know of any earthquakes in New Jersey, but this is not to say 
that they do not happen.  Most earthquakes occur along the boundaries of 
the Earth’s tectonic plates.  California is a good example, for here the 
San Andreas Fault is the boundary between the North American and Pacific 
plates, which are moving past one another.  Their relative movement is not 
smooth, as the fault locks up allowing strain the build up until it is 
released in a sudden movement that causes an earthquake.

New Jersey is located on a passive continental margin.  Passive margins 
are very stable geologically because all the tectonic action is happening 
elsewhere.  The North American continent is moving west, away from 
Europe.  The nearest plate boundary is a constructive boundary called the 
Mid-Atlantic Ridge, a chain of mountains and rift valleys that runs along 
the ocean floor down the centre of the Atlantic Ocean.  It is along the 
Mid-Atlantic Ridge that the European and North American plates are moving 
apart.  Although there are earthquakes all the time on the Mid-Atlantic 
Ridge, these do not affect the eastern edge of the North American 
continent because it is too far away.  New Jersey, and the entire Atlantic 
coast of North America, are located within the North American plate, 
facing the trailing edge of the continent, and are in a very quiet 
location as far as earthquakes are concerned.  The same can be said of the 
British Isles, on the opposite passive margin.

Having said this, earthquakes can still happen in such intraplate 
locations.  A huge earthquake hit Charleston, South Carolina in 1886.  
Such events are not well understood, but may be related to the 
transmission of stress from the boundary of a tectonic plate into other 
areas, or alternatively to stress applied from beneath the crust in the 
geologically early stages of the development of a rift system in a 
continent.  Much smaller earthquakes are actually quite common in 
continental interiors, usually along ancient faults that may remain 
susceptible to movement.

In the geological past, large earthquakes probably frequently affected the 
area we now call New Jersey.  In the Permian Period of the Palaeozoic Era, 
about 250 million years ago, the continents were all joined together into 
a supercontinent called Pangea.  North America and Africa were joined 
together as part of Pangea.  Pangea began to break up during the Triassic 
Period, and about 210 million years ago a great rift valley system formed 
that ran down what is now the eastern seaboard of the U.S.A. from New 
England to the Carolinas.  It was formed as the continental blocks that 
were to become Africa and North America began to pull apart. In a rift 
system the Earth’s crust is stretched apart and subsides in the middle, 
with the movement being taken up by faults along the edges of the 
subsiding area.  Subsidence along these faults causes earthquakes.

This ancient rift system would have been very similar to the great East 
African Rift Valley today, where the African continent is splitting 
apart.  The recent news coverage of the volcanic eruption in the Congo 
made mention of frequent earthquakes, and it is likely that some of these 
were caused by movement on the faults of the East African Rift (some of 
them were directly related to the movement of magma in the volcano).  New 
Jersey is in the middle of the ancient American rift system.  In the 
Triassic and Jurassic periods, when the continental crust of North America 
was actively subsiding, there would surely have been frequent earthquakes.

I hope this answers your question.

Best wishes,

David Scarboro