Intraplate earthquake

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, MO, and the 1886 earthquake in Charleston, SC.

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 your 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 creating transform faults. Earthquakes are usually not intraplate earthquakes, but are caused by the slips along plate boundaries (fault lines) created by stress and pressure. Intraplate earthquakes do not occur at plate boundaries, but at fault zones ('cracks') in the middle of a plate. These often occur at the location of ancient fault zones or failed rifts due to "adjustments" on an old rupture.

Historic examples

New Madrid Earthquakes 1811/1812

A series of famous intraplate earthquakes, culminating in the New Madrid Earthquake, occurred on the New Madrid fault zone in what is now Missouri, in the USA, in 1811 and 1812. These earthquakes were above magnitude 8 and were felt for hundreds of miles.

The earthquakes changed the course of the Mississippi River. Because of the change in the course of the Mississippi River land was cut off from counties by the river and wound up on the other side of the new riverbed of the Mississippi. The settlement of Reverie, Tennessee in Tipton County was cut off and placed on the western bank of the Mississippi River on the Arkansas side. [http://www.tnhistoryforkids.org/local/tipton www.tnhistoryforkids.org]

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 kutch region.

Other historic examples in the U.S.A.

Historic examples of intraplate earthquakes in North America 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 in North America and elsewhere 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 when they will strike next. 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.

ee also

* New Madrid earthquake
* New Madrid Seismic Zone
* Reverie, Tennessee

References

*wikicite|id=idStein2007|reference=Stein, S., and S. Mazzotti (2007). "Continental Intraplate Earthquakes: Science and Policy Issues", Geological Society of America, Special Paper 425.

External links

* [http://sprg.ssl.berkeley.edu/matt/seismo.html Intraplate Earthquakes: Possible Mechanisms for the New Madrid and Charleston Earthquakes]
* [http://scsn.seis.sc.edu/Publications/Paper1_082603_Revised.pdf "Symptomatic Features of Intraplate Earthquakes" - PDF]
* [http://www2.rcep.dpri.kyoto-u.ac.jp/members/iio/ronbun_list/eps2002_1001.pdf "A physical understanding of large intraplate earthquakes" - PDF]
* [http://earthquake.usgs.gov/eqcenter/eqinthenews/2006/usslav/ Earthquake Hazards Program, USGS]