Where does the overwhelming amount of seismic activity occur on Earth's surface?
Most of the seismic activity on Earth is found on (or near) the boundaries of tectonic plates. Earth's lithosphere is divided into a number of fragments, known as tectonic plates and these plates are in constant motion. The interaction of plates, with each other, gives rise to three types of boundaries: convergent (where plates are coming towards each other), divergent (where plates are moving away from each other) and transform (where plates are moving horizontally, past one another). Divergent boundaries (such as, mid-ocean ridges) are associated with small earthquakes, while convergent (such as, Nazca plate and South American plate) and transform (such as, Pacific plate and North American plate) boundaries are associated with large earthquakes. Some of the major earthquakes of recent human history, such as the one in Indian Ocean in December 2004 have taken place near plate boundaries. In fact, if one were to plot the location of major earthquakes in last few hundred years on Earth's map, most of them would coincide with plate boundaries.
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