ABSTRACT
The global distribution of earthquake hypocenters maps the pattern of plate boundaries, and indeed this pattern was one part of the observational data that led to the theory of plate tectonics. Relative velocities between neighboring plates range from 0.001 m/year to 0.1 m/year. Plate boundaries separating oceanic lithosphere are sharp and clearly recognizable in the seafloor topography. On continents, plate boundaries manifest themselves in fault systems with widths of several 100 km. Most earthquakes occur in the upper crust, the schizosphere, which extends from near the surface to about 20 km depth, whereas some earthquakes follow subducting lithospheric slabs down to depths of around 600 km. Deformation during earthquakes may represent most of the total tectonic deformation, however segments of plate boundaries may also deform to a high percentage silently, i.e. by more or less steady creep.
