Evaluate how plate tectonics theory helps our understanding of the distribution of seismic and volcanic events.

Paeleomagnetism suggests that the poles switch every several thousand years. Evidence of alternating polarity in the rocks in the ocean floor can be explained by plate tectonic theory. As two constructive plates diverge, new crust is gradually created over thousands of years, as polarity changes every 400,000 years, thus the different sections of this new crust are of alternating polarity. Knowledge of continental drift can thus explain why much of the sea floor is alternating polarity around mid-ocean ridges.

The discovery of destructive margins added more solidity to plate tectonic theory and also helped to show why volcanoes occur at these margins. Destructive margins occur when the plates converge, and the denser plate is then subducted and destroyed below the top plate. This usually means a continental plate subducts an oceanic plate, but oceanic-oceanic convergences do also occur. Earthquakes occur in these regions due to the friction caused during subduction, which can explain the distribution of such seismic events like the 2004 Indian Ocean Tsunami. Volcanic activity also occurs at these margins; as the subducting plate is destroyed, the rock melts, and this magma rises up through the surface, manifesting itself as a volcanic eruption. This means that tectonic theory is useful for understanding why volcanic arcs appear on islands like Japan, whose volcanoes make up one quadrant of the ring of fire. As well as this, plate tectonic theory can help us understand how volcanic arcs are formed, as these are created when oceanic plates collide, producing the same volcanic events, which is how Indonesia was created.

Constructive margins are also part of the theory. This is where no plate is created or destroyed, but the plates simply move past each other at varying speeds. This movement creates a build up of friction and energy, which is released as an earthquake, when the plates suddenly move. This means that plate tectonic theory can therefore explain the prevalence of earthquakes along the San Andreas fault line where the Pacific and North American plates move past each other, most notably the San Francisco earthquake in 1989. Additionally, the theory can help us to understand why volcanic activity does not occur in this area, but seismic activity does.

However there are flaws in this theory, which do not explain the appearance of volcanoes in the Pacific Ocean, some 3000km from any plate margin. These volcanoes are the result of hotspots, which are concentrations of radioactive elements in the mantle, which rise up through the lithosphere. Here there are active volcanoes, which are unassociated with plate convergence or divergence. Despite this flaw, hot spots can be explained by plate tectonic theory, as the hot spot is stationary, over time, the plate moves over this hotspot, creating an Island arc which includes an active volcano and other extinct own. This occurred on the Pacific plate, resulting in the Hawaiian island arc, which ends with active volcanoes, such as Mauna Loa the island currently above the hotspot. This means that despite its apparent irrelevance, which was first seen to refute plate tectonic theory; this demonstrates that plate tectonic theory can help to explain anomalous tectonic events.

There are also further seismic events whose distribution cannot be explained by plate tectonic theory, as they were of human creation. For instance, 200 small earthquakes were triggered when the Hoover Dam in the US was being filled; these earthquakes were not connected with any fault line or plate movement. Earthquakes in the UK have also been a result of fracking, where shale gas is extracted through drilling the crust, which has resulted in minor earthquakes in Blackpool of around 2.3 on the Richter scale. This demonstrates that although plate tectonic theory can explain the majority of seismic events, it cannot explain occurrences such as these.