Friction of faults is often unstable, and slip occurs rapidly as a rupture dynamically propagates over the fault surface. These sudden motions generate seismic waves and this is the mechanism of the most common and important type of earthquake. Seismicity is thus the short-timescale phenomenon of brittle tectonics. In this chapter we discuss the dynamics of faulting and review the most important attributes of earthquakes from the point of view of the rupture process.

Historical development

During most of human history, people's notion of the origin of earthquakes lay within the realm of mythology. Several of the schools of ancient Greek philosophy considered earthquakes to be natural phenomena, although their speculations on the matter relied heavily on imagination and do not bear much relationship with modern theories (see Adams (1938) for an excellent historical account of thinking on this topic from the Greeks up through the Renaissance). The idea that earthquakes represent an elastic reaction to geological phenomena was promulgated first by Hooke in his Discourse on Earthquakes, published in 1668. It was not until the middle and latter part of the nineteenth century that instrumental measurements began to be made and note taken of the geological associations of earthquakes. Lyell (1868) considered earthquakes to be an important agent in Earth dynamism, and was aware of both faulting and permanent changes in elevation brought about by them.