The mechanism of deep earthquakes



Most earthquakes occur within a few tens of kilometers below the Earth's surface by the familiar processes of brittle fracture and frictional sliding along preexisting faults [Scholz, 1990]. However, about 20% of all earthquakes occur at great depth (up to 680 km) where the high pressure prohibits conventional faulting. At these pressures, rock should flow rather than break, hence deep earthquakes would appear to be impossible. This paradox was recognized shortly after the discovery of deep earthquakes in the 1920s and it has remained unresolved since then.