| Abstract: | The mechanism of thrust sheet motion and that of earthquake generation are two aspects of the same phenomenon. Studies of earthquake mechanisms show that only a part of the thrust fault, generally less than 10km in length, is in motion at any given instant; this part sweeps the length of the fault, moving at approximately 3 km/s. Since shear fracture propagation is inherently a dynamic phenomenon, it cannot be understood on the basis of the equations of static equilibrium. The previously proposed mechanisms all rest on such an equilibrium, which necessarily implies that the motion of a thrust sheet occurs simultaneously over its whole length; since the latter may exceed 100 km, the motion becomes a mechanical “enigma”. This enigma vanishes once the dynamic nature of the problem is recognized. The proposed mechanism also suggests that solution features on the fault result from the dissolution of barriers, thus explaining the motion of only part of a thrust sheet. |
