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Earthquakes can occur above magma chambers and along the vents of volcanoes.
Earthquakes typically occur along the subduction boundary as the two plates rub against one another.
Shallow
100
200
300
400
Waves sent out from an earthquake.
0
Medium
Deep
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intermediate, or deep. The mountains around the Pacific Ocean are on this kind of boundary.
Seismic gaps
Earthquakes are part of long-term movement of the crust. Stresses do not often build up to be very big. In many places they are relieved by the multitudes of small earthquakes and aftershocks that happen every day. Through these small, often unnoticed quakes blocks of land creep past one another, and the tectonic plates drift over the earth’s surface.
A large earthquake often represents a stress that has been building up in the crust for a long time without being relieved. In effect it is a place where rocks have become jammed and unable to move. A part of a long fault where no earthquakes have occurred for a long time is called a seismic gap.
When the rocks do finally shift in a seismic gap, much more movement occurs than normal as the rocks ‘catch up’ on movements that have already occurred in the fault nearby.
For example, the total movements from earthquakes and creep along the San Andreas Fault are over 500
(Above) This diagram shows a place where two plates meet, forcing one into the earth. It
is called a subduction zone. Earthquakes are generated along the whole face, where
the two slabs scrape against one another. As a result, shallow, intermediate, and deep earthquakes are produced. This explains why subduction zones (such as those that occur along the western side
of the Pacific Ocean) are the most earthquake-prone places on earth.