Frictional constraints on thrust, wrench and normal faults

Abstract

IT is generally true that in ancient fault zones, quartzofeldspathic mylonites which indicate partial plastic yield throughout a volume of rock1, are most extensively developed in association with thrust faults. They are less widespread along wrench faults (unless the finite displacement is very large) and are comparatively rare along normal faults2. The release of seismic energy at shallow depths follows the same general pattern. More than 90% is released in areas of compressive plate interaction, mostly where underthrusting is the dominant mechanism, whereas only 6% is derived from the midocean ridges, where tensional rifting is operative3.