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.