<P> Although the eastern United States is not as seismically active as regions near plate boundaries, large and damaging earthquakes do occur there . Furthermore, when these rare eastern U.S. earthquakes occur, the areas affected by them are much larger than for western U.S. earthquakes of the same magnitude . Thus, earthquakes represent at least a moderate hazard to East Coast cities, including New York City and adjacent areas of very high population density . </P> <P> As can be seen in the maps of earthquake activity in this region (shown in the figure on the right), seismicity is scattered throughout most of the New York metropolitan area, with some hint of a concentration of earthquakes in the area surrounding Manhattan Island . The largest known earthquake in this region occurred in 1884 and had a magnitude of approximately 5 . For this earthquake, observations of fallen bricks and cracked plaster were reported from eastern Pennsylvania to central Connecticut, and the maximum intensity reported was at two sites in western Long Island (Jamaica, New York and Amityville, New York). Two other earthquakes of approximately magnitude 5 occurred in this region in 1737 and 1783 . The figure on the right shows maps of the distribution of earthquakes of magnitude 3 and greater that occurred in this region from 1924 to 2010, along with locations of the larger earthquakes that occurred in 1737, 1783 and 1884 . More recently, the 2011 Virginia earthquake, a 5.8 magnitude quake centered in northern Virginia that occurred on August 23, 2011, was felt by the occupants of some buildings in Manhattan, more than 200 miles north of the quake's epicenter and there was some actual physical building damage in Brooklyn . There were some disruptions, including building evacuations and delays at airports, while Amtrak train service at Penn Station was also delayed . </P> <P> 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 area's 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 New York 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 . </P>

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