Intraplate earthquake
Encyclopedia
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
that occurs in the interior of a tectonic plate, whereas an interplate earthquake
Interplate earthquake
An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates. If one plate is trying to move past the other, they will be locked until sufficient stress builds up to cause the plates to slip relative to each other...
is one that occurs at a plate boundary.
Intraplate earthquakes are very rare and interplate earthquakes, ones that occur on a plate boundary are quite normal. Nonetheless, very large intraplate earthquakes can inflict heavy damage, particularly because such areas are not accustomed to earthquakes and buildings are usually not seismically retrofitted. Notable examples of damaging intraplate earthquakes are the devastating Gujarat earthquake
2001 Gujarat earthquake
The 2001 Gujarat earthquake occurred on January 26, 2001, India's 52nd Republic Day, at 08:46 AM local time and lasted for over two minutes. The epicentre was about 9 km south-southwest of the village of Chobari in Bhachau Taluka of Kutch District of Gujarat, India...
in 2001, the 1811-1812 earthquakes in New Madrid, Missouri
New Madrid, Missouri
New Madrid is a city in New Madrid County, Missouri, 42 miles south by west of Cairo, Illinois, on the Mississippi River. New Madrid was founded in 1788 by American frontiersmen. In 1900, 1,489 people lived in New Madrid, Missouri; in 1910, the population was 1,882. The population was 3,334 at...
, and the 1886 earthquake in Charleston, South Carolina
Charleston, South Carolina
Charleston is the second largest city in the U.S. state of South Carolina. It was made the county seat of Charleston County in 1901 when Charleston County was founded. The city's original name was Charles Towne in 1670, and it moved to its present location from a location on the west bank of the...
.
Fault zones within tectonic plates
According to the theory of plate tectonicsPlate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
, the surface of the Earth is made up of about a dozen large tectonic plates. These plates move very slowly, owing to convection currents within the mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
below the crust. Because they do not all move in the same direction, plates often directly collide
Convergent boundary
In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...
or move laterally along each other, a tectonic environment that makes earthquakes frequent. Relatively few earthquakes occur in intraplate environments; most occur on faults near plate margins. By definition, intraplate earthquakes do not occur near plate boundaries, but along faults in the normally stable interior of plates. These earthquakes often occur at the location of ancient failed rift
Rift
In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
s, because such old structures may present a weakness in the crust where it can easily slip to accommodate regional tectonic strain.
Compared to earthquakes near plate boundaries, intraplate earthquakes are not well understood, and the hazards associated with them may be difficult to quantify.
Historic examples
Historic examples of intraplate earthquakes include those in Mineral, VirginiaMineral, Virginia
Mineral is a town in Louisa County, Virginia, United States. The population was 424 at the 2000 census.-History:Mineral was originally known as Tolersville, but adopted its current name when it incorporated in 1902 due to the mining industry that supported the community...
in 2011
2011 Virginia earthquake
The 2011 Virginia earthquake occurred on August 23, 2011, at 1:51 pm EDT in the Piedmont region of the U.S. state of Virginia. The epicenter, in Louisa County, was northwest of Richmond and south-southwest of the town of Mineral...
(estimated magnitude 5.8), New Madrid
New Madrid Seismic Zone
The New Madrid Seismic Zone , sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes in the southern and midwestern United States, stretching to the southwest from New Madrid, Missouri.The New Madrid fault system was responsible for the...
in 1811 and 1812
New Madrid earthquake
The 1811-1812 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial pair of very large earthquakes on December 16, 1811. These earthquakes remain the most powerful earthquakes ever to hit the eastern United States in recorded history...
(estimated magnitude as high as 8.1), the Boston (Cape Ann) earthquake of 1755
1755 Cape Ann Earthquake
The Cape Ann Earthquake took place off the coast of the British Province of Massachusetts Bay on November 18, 1755. At between 6.0 and 6.3 on the Richter scale, it remains the largest earthquake in the history of Massachusetts...
(estimated magnitude 6.0 to 6.3), earthquakes felt in New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...
in 1737 and 1884 (both quakes estimated at about 5.5 magnitude), and the Charleston earthquake
Charleston earthquake
The Charleston Earthquake of 1886 was a powerful intraplate earthquake that hit the area of Charleston, South Carolina. After the 1811 and 1812 quakes in New Madrid, Missouri, it is one of the most powerful and damaging quakes to hit the southeastern United States. The shaking occurred at 9:50 p.m....
in South Carolina
South Carolina
South Carolina is a state in the Deep South of the United States that borders Georgia to the south, North Carolina to the north, and the Atlantic Ocean to the east. Originally part of the Province of Carolina, the Province of South Carolina was one of the 13 colonies that declared independence...
in 1886 (estimated magnitude 6.5 to 7.3). The Charleston quake was particularly surprising because, unlike Boston and New York, the area had almost no history of even minor earthquakes.
In 2001, a large intraplate earthquake
2001 Gujarat earthquake
The 2001 Gujarat earthquake occurred on January 26, 2001, India's 52nd Republic Day, at 08:46 AM local time and lasted for over two minutes. The epicentre was about 9 km south-southwest of the village of Chobari in Bhachau Taluka of Kutch District of Gujarat, India...
devastated the region of Gujarat, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
. The earthquake occurred far from any plate boundaries, which meant the region above the epicenter was unprepared for earthquakes. In particular, the Kutch district suffered tremendous damage, where the death toll was over 12,000.
Causes
Many cities live with the seismic riskSeismic risk
Seismic risk uses the results of a seismic hazard analysis, and includes both consequence and probability. Seismic risk has been defined, for most management purposes, as the potential economic, social and environmental consequences of hazardous events that may occur in a specified period of time...
of a rare, large intraplate earthquake. The cause of these earthquakes is often uncertain. In many cases, the causative fault is deeply buried, and sometimes cannot even be found. Under these circumstances it is difficult to calculate the exact seismic hazard
Seismic hazard
Seismic hazard refers to the study of expected earthquake ground motions at the earth's surface, and its likely effects on existing natural conditions and man-made structures for public safety considerations; the results of such studies are published as seismic hazard maps, which identify the...
for a given city, especially if there was only one earthquake in historical times. Some progress is being made in understanding the fault mechanics
Fault mechanics
Fault mechanics is a field of study that investigates the behavior of geologic faults.Behind every good earthquake is some weak rock. Whether the rock remains weak becomes an important point in determining the potential for bigger earthquakes....
driving these earthquakes.
Prediction
Scientists continue to search for the causes of these earthquakes, and especially for some indication of how often they recur. The best success has come with detailed micro-seismic monitoring, involving dense arrays of seismometerSeismometer
Seismometers are instruments that measure motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources...
s. In this manner, very small earthquakes associated with a causative fault can be located with great accuracy, and in most cases these line up in patterns consistent with faulting. Cryoseism
Cryoseism
A cryoseism, also known as a frost quake, may be caused by a sudden cracking action in frozen soil or rock saturated with water or ice. As water seeps down into the rock, it freezes and expands, putting stress on surrounding rock...
s can sometimes be mistaken for intraplate earthquakes.
See also
- New Madrid earthquakeNew Madrid earthquakeThe 1811-1812 New Madrid earthquakes were an intense intraplate earthquake series beginning with an initial pair of very large earthquakes on December 16, 1811. These earthquakes remain the most powerful earthquakes ever to hit the eastern United States in recorded history...
- New Madrid Seismic ZoneNew Madrid Seismic ZoneThe New Madrid Seismic Zone , sometimes called the New Madrid Fault Line, is a major seismic zone and a prolific source of intraplate earthquakes in the southern and midwestern United States, stretching to the southwest from New Madrid, Missouri.The New Madrid fault system was responsible for the...
- Saint Lawrence rift systemSaint Lawrence rift systemThe Saint Lawrence rift system is a seismically active zone paralleling the Saint Lawrence River. The rift system trends northeast and southwest and forms a half-graben that links the Ottawa-Bonnechere and the Saguenay grabens. The rift system extends more than 1000 km along the Saint Lawrence...
- 2011 Virginia earthquake2011 Virginia earthquakeThe 2011 Virginia earthquake occurred on August 23, 2011, at 1:51 pm EDT in the Piedmont region of the U.S. state of Virginia. The epicenter, in Louisa County, was northwest of Richmond and south-southwest of the town of Mineral...
Further reading
- Stein, S., and S. Mazzotti (2007). "Continental Intraplate Earthquakes: Science and Policy Issues", Geological Society of America, Special Paper 425.