Mechanics of motion along plate boundaries

Plate boundaries are intensely deformed and fractured belts, across which the relative plate motion is accommodated. Boundary zones show a marked heterogeneity in mechanical and rheological properties and a spatially-variable behaviour in response to tectonic stresses. The major contrast is between slow, aseismic slip of weaker zones and abrupt, seismic slip of asperities. The subject is reviewed with particular emphasis on models describing the evolution of deformation and stress during the interseismic periods and the setting of conditions which produce great shallow earthquakes.