How do earthquakes occur?

Earthquakes are caused by the breakage of underground, crustal rock largely close to or near plate boundaries. It should also be noted that the breakage of rock occurs along a fault line, which is a long crack in the earth's surface. The reason that this breakage occurs is often due to tectonic plate movement. There are debates regarding how this tectonic plate movement occurs, but one of the most recognised theories is that of Arthur Holmes who suggested it was convection currents in the asthenosphere which cause friction on the base of the tectonic plates, allowing the plates to move in different directions. In an example where two continental plates are moving towards each other at a destructive boundary, a build in pressure occurs as the plates are forced against each other. Eventually, rock breakage will occur leading to an emission of seismic energy in the form of body waves, causing the primary hazard of ground shaking. Surface waves are the second set of waves to be released from the earthquake's focus (point of rock breakage), these are usually the most damaging due to their slower movement.Contrasting to the belief that earthquakes only occur along plate boundaries or faults, intraplate earthquakes occasionally occur too, which means that they happen away from a plate boundary. Often, these earthquakes are induced by human activity, like fracking. However, sometimes, they happen due to isostatic forces as rock is still moving, and trying to resettle after the previous Ice Age had its effect..