An intraplate earthquake is an earthquake that occurs in the interior of a tectonic plate, whereas an interplate earthquake is one that occurs at a plate boundary.
Intraplate earthquakes are rare compared to earthquakes at plate boundaries. Nonetheless, very large intraplate earthquakes can inflict heavy damage. Notable examples of damaging intraplate earthquake are the 1811-1812 earthquakes in New Madrid, Missouri, and the 1886 earthquake in Charleston, South Carolina.
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Fault zones within tectonic plates
According to the theory of plate tectonics, the surface of the Earth is modeled as being made up of about a dozen large tectonic plates. These plates move very slowly (about the rate that human fingernails grow), owing to convection currents within the mantle below the crust. Because they do not all move in the same direction, plates often directly 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 rifts, because such old structures may present a weakness in the crust that can easily slip and shorten 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
Gujarat Earthquake 2001
A similar large earthquake, the 2001 Gujarat Earthquake, devastated the region of Gujarat, India, in 2001, resulting in a large loss of life especially in the Kachchh region.
Other historic examples
Historic examples of intraplate earthquakes include those in Boston in 1755, New York City in 1737 and 1884 (both quakes estimated at about 5.5 magnitude), and the Charleston earthquake in South Carolina 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 (to put in perspective, in addition to the three northeastern U.S. events previously mentioned, a more moderate magnitude 4 earthquake was recorded just north of New York City in 1985).
Causes
Many cities live with the seismic risk 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 for a given city, especially if there was only one earthquake in historical times. Some progress is being made in understanding the fault mechanics 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 seismometers. 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. Cryoseisms can sometimes be mistaken for intraplate earthquakes.
See also
References
- Stein, S., and S. Mazzotti (2007). "Continental Intraplate Earthquakes: Science and Policy Issues", Geological Society of America, Special Paper 425.
External links
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