Most earthquakes are caused by movement in narrow zones along plate boundaries. There are three types of plate boundaries that cause most seismic activity:

• Divergent boundaries: These occur where plates move apart from each other. As the plates move apart, hot magma rises from the mantle, pushing the plates apart. Earthquakes occur along the fractures that appear as the plates move apart. Divergent boundaries are associated with volcanic activity, and the earthquakes in these zones tend to be frequent and small.

• Convergent boundaries: These occur where two plates move towards each other. When one plate dives beneath the other, it is referred to as a subduction zone. As the oceanic plate descends, earthquakes are generated within the slab and at the interface between the plates. Convergent boundaries tend to produce most of the earthquakes that have magnitudes greater than 6.0. They are also associated with volcanic activity, and the earthquakes in these zones tend to be deep and powerful.

• Transform boundaries: These occur where two plates slide past each other. Earthquakes originate at shallow depths, and they tend to be very powerful.

In summary, all three types of plate boundaries can cause earthquakes, but the most powerful and destructive earthquakes tend to occur at convergent and transform boundaries.