Ramapo Fault

The Ramapo Fault zone, spanning more than 185 miles (300 kilometers) in New York, New Jersey, and Pennsylvania, is a system of faults between the northern Appalachian Mountains and Piedmont areas to the east. This fault is perhaps the best known fault zone in the Mid-Atlantic region, and some small earthquakes have been known to occur in its vicinity. Recently, public knowledge about the fault has increased, especially after the 1970s, when the fault's proximity to the Indian Point nuclear plant in New York was noticed.

Some seismologists have argued that this fault has the potential to produce a major earthquake, but earthquakes are scattered throughout this region, with no particular concentration of activity along the Ramapo fault (see Earthquake activity in the New York City area). Thus, others have argued that the Ramapo Fault has not been demonstrated to be any more active than any other fault zones in the greater New York City area.

The New York City area is part of the geologically complex structure of the Northern Appalachian Mountains. This complex structure was formed during the past half billion years when the Earth's crust underlying the Northern Appalachians was the site of two major geological episodes, each of which has left its imprint on the NYC area bedrock. Between about 450 million years ago and about 250 million years ago, the Northern Appalachian region was affected by a continental collision, in which the ancient African continent collided with the ancient North American continent to form the supercontinent Pangaea. Beginning about 200 million years ago, the present-day Atlantic Ocean began to form as plate tectonic forces began to rift apart the continent of Pangaea. The last major episode of geological activity to affect the bedrock in the NYC area occurred about 100 million years ago, during the Mesozoic era, when continental rifting that led to the opening of the present-day Atlantic Ocean formed the Hartford and Newark Mesozoic rift basins.

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