Although the eastern United States is not as seismically active as regions near

plate boundaries Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

, 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.http://gallery.usgs.gov/audios/?a=279 Why should people in the Eastern United States be concerned about earthquakes? Thus, earthquakes represent at least a moderate hazard to East Coast cities, including

New York City New York, often called New York City or NYC, is the most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the most densely populated major city in the Un ...

and adjacent areas of very high population density. Seismicity is scattered throughout most of the

New York metropolitan area The New York metropolitan area, also commonly referred to as the Tri-State area, is the largest metropolitan area in the world by urban landmass, at , and one of the most populous urban agglomerations in the world. The vast metropolitan area ...

, with some hint of a concentration of earthquakes in the area surrounding

Manhattan Manhattan (), known regionally as the City, is the most densely populated and geographically smallest of the five boroughs of New York City. The borough is also coextensive with New York County, one of the original counties of the U.S. state ...

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 Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

to central

Connecticut Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York to the west, and Long Island Sound to the south. Its capita ...

, and the maximum intensity reported was at two sites in western Long Island (

Jamaica, New York Jamaica is a neighborhood in the New York City borough of Queens. It is mainly composed of a large commercial and retail area, though part of the neighborhood is also residential. Jamaica is bordered by Hollis to the east; St. Albans, Springf ...

and

Amityville, New York Amityville () is a village near the Town of Babylon in Suffolk County, on the South Shore of Long Island, in New York. The population was 9,523 at the 2010 census. History Huntington settlers first visited the Amityville area in 1653 du ...

). Two other earthquakes of approximately magnitude 5 occurred in this region in 1737 and 1783. The map shows 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 On August 23, 2011, a magnitude 5.8 earthquake hit the Piedmont region of the U.S. state of Virginia at 1:51:04 p.m. EDT. The epicenter, in Louisa County, was northwest of Richmond and south-southwest of the town of Mineral. It was an ...

, a 5.8 magnitude quake centered in northern

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

that occurred on August 23, 2011, was felt by the occupants of some buildings in

, more than north of the quake's epicenter and caused minor physical building damage in

Brooklyn Brooklyn () is a borough of New York City, coextensive with Kings County, in the U.S. state of New York. Kings County is the most populous county in the State of New York, and the second-most densely populated county in the United States, be ...

. There were some disruptions, including building evacuations and delays at airports, while

Amtrak The National Railroad Passenger Corporation, doing business as Amtrak () , is the national passenger railroad company of the United States. It operates inter-city rail service in 46 of the 48 contiguous U.S. States and nine cities in Canada ...

train service at

Penn Station Pennsylvania Station is a name applied by the Pennsylvania Railroad to several of its grand passenger terminals. Pennsylvania Station or Penn Station may also refer to Current train stations * Baltimore Penn Station * Pennsylvania Station (Cinc ...

was also delayed.

Background

The New York City area is part of the geologically complex structure of the northern

Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...

. 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.http://3dparks.wr.usgs.gov/nyc/highlands/highlands.html USGS, Geology of the NYC Region, The Highlands Province 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 In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...

. Beginning about 200 million years ago, the present-day Atlantic Ocean began to form as plate tectonic forces began to

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

apart the continent of

. 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 The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

formed the Hartford and

Newark Newark most commonly refers to: * Newark, New Jersey, city in the United States * Newark Liberty International Airport, New Jersey; a major air hub in the New York metropolitan area Newark may also refer to: Places Canada * Niagara-on-the ...

Mesozoic rift basins. Earthquake rates in the northeastern United States are about 50 to 200 times lower than in

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

, but the earthquakes that do occur in the northeastern U.S. are typically felt over a much broader region than earthquakes of the same magnitude in the western U.S. This means the area of damage from an earthquake in the northeastern U.S. could be larger than the area of damage caused by an earthquake of the same magnitude in the western U.S. The cooler rocks in the northeastern U.S. contribute to the seismic energy propagating as much as ten times further than in the warmer rocks of California. A magnitude 4.0 eastern U.S. earthquake typically can be felt as far as 100 km (60 mi) from its

epicenter The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Surface damage Before the instrumental pe ...

, but it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake, although uncommon, can be felt as far as 500 km (300 mi) from its epicenter, and can cause damage as far away as 40 km (25 mi) from its epicenter. Earthquakes stronger than about magnitude 5.0 generate ground motions that are strong enough to be damaging in the epicentral area. At well-studied plate boundaries like the

San Andreas fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizonta ...

system in California, scientists can often make observations that allow them to identify the specific fault on which an earthquake took place. In contrast, east of the Rocky Mountains this is rarely the case. The New York City area is far from the boundaries of the North American plate, which are in the center of the Atlantic Ocean, in the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

, and along the west coast of North America. The seismicity of the northeastern U.S. is generally considered to be due to ancient zones of weakness that are being reactivated in the present-day stress field. In this model, pre-existing faults that were formed during ancient geological episodes persist in the intraplate crust, and the earthquakes occur when the present-day stress is released along these zones of weakness. The stress that causes the earthquakes is generally considered to be derived from present-day rifting at the

Mid-Atlantic ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North ...

Faults in the Northeastern U.S.

The northeastern United States has many known faults, but virtually all of the known faults have not been active for perhaps 90 million years or more. Also, the locations of the known faults are not well determined at earthquake depths. Accordingly, few (if any) earthquakes in the region can be unambiguously linked to known faults. Given the current geological and seismological data, it is difficult to determine whether a known fault in this region is still active today and could produce a modern earthquake. As in most other areas east of the Rocky Mountains, the best guide to earthquake hazard in the northeastern U.S. is probably the locations of the past earthquakes themselves.

New York City-area faults

The

Ramapo Fault The Ramapo Fault zone is a system of faults between the northern Appalachian Mountains and Piedmont areas to the east.New York,

New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...

, and

. It is a system of faults between the northern

and Piedmont areas to the east.Earthquakes and the Ramapo Fault System in Southeastern New York State
Earth Institute News Archive, Columbia University, 2004. Accessed October 24, 2009. 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. There is insufficient evidence to demonstrate unequivocally any strong correlation of earthquakes in the New York City area with specific faults or other geologic structures in this region. The damaging earthquake affecting New York City in 1884 was probably not associated with the Ramapo fault because the strongest shaking from that earthquake occurred on Long Island (quite far from the trace of the Ramapo fault). The relationship between faults and earthquakes in the New York City area is currently understood to be more complex than any simple association of a specific earthquake with a specific mapped fault. A 2008 study argued that a magnitude 6 or 7 earthquake might originate from the Ramapo fault zone, which would almost definitely spawn hundreds or even thousands of fatalities and billions of dollars in damage. Studying around 400 earthquakes over the past 300 years, the study also argued that there was an additional fault zone extending from the Ramapo Fault zone into southwestern Connecticut. As can be seen in the above figure of seismicity, earthquakes are scattered throughout this region, with no particular concentration of activity along the Ramapo fault, or along the hypothesized fault zone extending into southwestern Connecticut.Kafka, A.L. M.A. Winslow, and N.L. Barstow (1989), Earthquake Activity in the Greater New York City Area: A Fault Finder's Guide, in Field Trip Guidebook (D. Weiss,Editor), 61st Annual Meeting, New York State Geological Association, 177–204 Just off the northern terminus of the Ramapo fault is the Indian Point Nuclear Power Plant, built between 1956 and 1960 by Consolidated Edison Company. The plant operated from 1963 until 2021, and it has been the subject of a controversy over concerns that an earthquake from the Ramapo fault will affect the power plant. Whether the Ramapo fault actually does pose a threat to this nuclear power plant remains an open question.

References

{{Faults * Geology of New York (state) Geology of New Jersey Geology of Pennsylvania Earthquakes in the United States Seismic faults of the United States