MadSci Network: Earth Sciences

Re: Why don't Earth Quakes happen in the Northern and Southern partsofthe world

Date: Tue Jan 19 13:18:25 1999
Posted By: David Smith, Faculty Geology, Environmental Science
Area of science: Earth Sciences
ID: 915768364.Es

I'm not sure what exactly you mean by "Northern and Southern parts of the world." Earthquakes may occur nearly anywhere in the world, although they tend to be concentrated along the boundaries between plates. A quick view of recent earthquakes, such as the one available from:

will outline some of those boundaries. The most active earthquake zones are the subduction zones that ring much of the Pacific Ocean and transform faults such as the San Andreas fault.

Both the Artic and Antarctic are areas where there is currently only a small amount of activity. In the case of Antarctica, the whole continent sits on a single plate and the nearest plate boundaries are at 30-70 degrees latitude. There is a rift zone that cuts partway across the Antarctic continent that will have occasional earthquakes, but they are not common. The Artic is cut by the northern part of the mid-Atlantic ridge, which is a source of earthquakes, however, there are not very many quakes there.

To understand why, you need to look at how plates move. All plates move away from each other by rotating around on the surface of the earth. They rotate around a common point called a pole. To see how this works, place your hands on a basketball or other large ball so that they are side by side, then twist both hands around on the surface of the ball so that they move apart, except at one point at the tips of your index fingers. They should always touch there. Now, compare two points at the base of your thumbs with two points near the tips of your index fingers. You should see that the points on your thumbs move much farther in the same amount of time than the points near your fingertips.

In the earth, faster moving means more earthquakes in a certain time period. The artic is near the pivot point for the mid-Atlantic ridge, so the two sides move apart very slowly and there are few if any earthquakes there.

-David Smith
La Salle University, Philadelphia, PA,

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