Distribution of seismicity associated with the New Madrid Seismic Zone (since 1974). This zone of intense earthquake activity is located deep within the interior of the North American plate.
Anintraplate earthquake is an earthquake that occurs in the interior of a tectonic plate, in contrast to an interplate earthquake on the boundary of a tectonic plate. It is also called an intraslab earthquake, especially when occurring in a microplate.[1][2]
The Earth's crust is made up of seven primary and eight secondary tectonic plates, plus dozens of tertiary microplates. The large plates move very slowly on top of convection currents in the underlying mantle. Because they do not all move in the same direction, plates often directly collide or slide laterally along each other, a tectonic environment that makes interplate earthquakes frequent.
By contrast, relatively few earthquakes occur in intraplate environments away from plate junctures.[4] These earthquakes often occur at the location of ancient failed rifts, partial fractures of existing plates, because they may leave a weakness in the crust vulnerable to regional tectonic strain.
Intraslab earthquakes radiate more seismic energy than interplate earthquakes (megathrust earthquakes) of a similar magnitude. This variation makes seismic energy a better measure for the potential macroseismic effects of an earthquake than the more common seismic moment used to calculate the magnitude Mw .[5]
Examples of intraplate earthquakes include those in Mineral, Virginia, in 2011 (estimated magnitude 5.8), Newcastle, New South Walesin1989, New Madridin1811 and 1812 (estimated magnitude as high as 8.6),[6] the Boston (Cape Ann) earthquake of 1755 (estimated magnitude 6.0 to 6.3), earthquakes felt in New York City in 1737 and 1884 (both quakes estimated at 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.
In 2001, a large intraplate earthquake devastated the region of Gujarat, India. 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 and the total death toll was higher than 20,000.
In 2017, the 24–29 km deep magnitude 6.5 Botswana earthquake that shook eastern Botswana occurred at over 300 km from the nearest active plate boundary.[7] The event occurred in an underpopulated area of Botswana.
The 1888 earthquakeinRío de la Plata was an intraplate quake,[8] from reactivated faults in the Quilmes Trough, far from the boundaries of the South American Plate. With a magnitude greater than 5.0 it was felt "in the cities of Buenos Aires, La Plata and other small towns and villages along the Rio de Plata coastal regions."[9] The towns of Punta del Este and Maldonado in Uruguay were hit by a tsunami generated by the quake.[9]
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[7] and sometimes cannot even be found. Some studies have shown that quakes can be caused by fluids moving up the crust along ancient fault zones.[7][10] In such circumstances, it is difficult to estimate the 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.
Intraplate earthquakes may be unrelated to ancient fault zones and instead caused by deglaciation or erosion.[11]
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.
^Iwata, Tomotaka; Asano, Kimiyuki (2011). "Characterization of the Heterogeneous Source Model of Intraslab Earthquakes Toward Strong Ground Motion Prediction". Pure and Applied Geophysics. 168 (1–2): 117–124. Bibcode:2011PApGe.168..117I. doi:10.1007/s00024-010-0128-7. S2CID140602323.
^Senoa, Tetsuzo; Yoshida, Masaki (2004). "Where and why do large shallow intraslab earthquakes occur?". Physics of the Earth and Planetary Interiors. 141 (3): 183–206. Bibcode:2004PEPI..141..183S. doi:10.1016/j.pepi.2003.11.002.
^Leyton, Felipe; Ruiz, Javier A.; Camposa, Jaime; Kausel, Edgar (2009). "Intraplate and interplate earthquakes in Chilean subduction zone: A theoretical and observational comparison". Physics of the Earth and Planetary Interiors. 175 (1): 37–46. Bibcode:2009PEPI..175...37L. doi:10.1016/j.pepi.2008.03.017. citing Choy, G.L.; Boatwright, J.; Kirby, S., 2002. The radiated seismic energy and apparent stress of interplate and intraslab earthquakes at subduction-zone environments: Implications for seismic hazard estimation, in The Cascadia subduction zone and related subduction systems–Seismic structure, intraslab earthquakes and processes, and earthquake hazards, Open-File Report 02–328, pp. 107–114, eds Kirby, S.H.; Wang, K.; Dunlop, S., US Geological Survey, Menlo Park, CA.
^Penick, James L. The New Madrid Earthquakes. Columbia, MO: University of Missouri Press, 1981. ISBN0-8262-0344-2
^ abcKolawole, F.; Atekwana, E. A.; Malloy, S.; Stamps, D. S.; Grandin, R.; Abdelsalam, M. G.; Leseane, K.; Shemang, E. M. (2017-09-09). "Aeromagnetic, gravity, and Differential Interferometric Synthetic Aperture Radar analyses reveal the causative fault of the 3 April 2017 Mw6.5 Moiyabana, Botswana, earthquake". Geophysical Research Letters. 44 (17): 8837–8846. Bibcode:2017GeoRL..44.8837K. doi:10.1002/2017gl074620. ISSN0094-8276. S2CID134584787.
