Main part of the stress results from the relative motion of the plates. Over the course of millions of years, the lithosphere plates have moved considerably. Plates either move apart from one another, collide with or slide past one another. The annual movement of the plates ranges from a couple of centimetres to almost twenty centimetres. The generated stresses and the energy is partly released as earthquakes.
Tectonic earthquakes occur due to the release of the stress caused by relative plate motion.
The most destructive earthquakes are always tectonic. Volcanic tremors are associated with volcanic eruptions, when magma penetrates the crust and ruptures it. Volcanic earthquakes are minor or at most moderate in magnitude. Collapse earthquakes are weak and usually occur in smallish caves, cavities or mines. A cave may collapse by itself or is triggered by human activity such as explosions.