Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: Sean McCandless on 02/10/2011 22:30:02
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Sean McCandless asked the Naked Scientists:
Chris,
I was in the recent moderate earthquake in Washington DC and I'm puzzled at how an earthquake can happen where there isn't a plate boundary. How do they happen intra plate?
Sean
New Hampshire, USA
What do you think?
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Intraplate earthquakes are rare compared to those along plate margins- but their presence indicates that the crust can be strained in the middle of tectonic plates. Even though intraplate seismic zones are not well understood, they can be very active and produce large magnitude earthquakes. A couple of examples are the New Madrid seismic zone (1811-12) and the the Charleston seismic zone (1886).
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The area where the earthquake happened is a known earthquake zone. Its just that as time goes on memory of the last quake is lost. This one may be lost too, but since famous buildings and monuments where damage, chances are it will be slightly remembered 100 years from now.
If you goggle fault zones on the eastern North America, you may be quite surprised by what you find.
Also, as the earth continues to rebound from the last glaciation, there may be tremors here and there.
The earth is very much alive and never static, so surprises us when we least expect it.
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It works like an elastic rubber sheet. If you strain the rock even if it is far away from a boundary it can cause weakness and strain that must eventually be released. This can occur due to stress from other plate boundaries accumulating stress ex: The Mid-Atlantic Ridge, havy recent periods of glaciation, erosion, sudden disturbances of the upper crust such as drilling and mining, and other crustal activities. Many seismic zones exist today that have the potential to cause moderate to severe damage in populated areas. The New Madrid Seismic Zone which produced the 1811-1812 quake string, the Tennesee seismic zone, the Oklahoma seismic zone that destroyed 15 homes in 2011, the Ramapo seismic zone and neighboring faults that produced the 1884 NYC earthquake, the Mineral Valley seismic zone, and the Charelston Seismic Zone. These are just the most famous but there are plenty more. I live near the Ramapo Fault in Central Westchester so I know quite a bit about intraplate seismicity and constantly work on scenarios and movement patterns. Contact me if you want any information.
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Intraplate earthquakes are rare compared to those along plate margins- but their presence indicates that the crust can be strained in the middle of tectonic plates. Even though intraplate seismic zones are not well understood, they can be very active and produce large magnitude earthquakes. A couple of examples are the New Madrid seismic zone (1811-12) and the the Charleston seismic zone (1886).
New Madrid is an active rift zone. You take the amount it moves in one year and multiply by how old it is you get it's exact size. It is still rifting, only very, very slowly. It never stopped. Why it moves so slow is a mystery apparently, but it is still active. That is why it has earthquakes.