The occurrence of earthquakes propagating at speeds not only exceeding the shear wave speed of the medium (~3 km/s in the Earth's crust), but even reaching compressional wave speeds of nearly 6 km/s is now well established. In this paper, the history of development of ideas since the early 1970s is given first. The topic is then discussed from the point of view of theoretical modelling. A brief description of a method for analysing seismic waveform records to obtain earthquake rupture speed

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... rmation is given. Examples of earthquakes known to have propagated at supershear speed are listed. Laboratory experiments in which such speeds have been measured, both in rocks as well as on man-made materials, are discussed. Finally, faults worldwide which have the potential to propagate for long distances (> about 100 km) at supershear speeds are identified ("fault superhighways").