Stick slip, stable sliding, and earthquakes-Effect of rock type, pressure, strain rate, and stiffness

Abstract

The magnitude of the stress drops that occur during frictional sliding on ground surfaces and on faults has been studied at confining pressures of as much as 5 kb. It was found that the stiffness of the loading system and the rate at which the load was applied had no effect on the magnitude of the sudden stress drops. Confining pressure and rock type were found to be the most important parameters. For example, sliding on fault surfaces in unaltered silicate rocks at confining pressure below 1 to 2 kb was stable; that is, stick slip was absent. At higher pressures, motion occurred by stick slip, and the magnitude of the stress drop during slip increased with pressure. Stick slip was absent at all pressures in gabbro, in dunite where the minerals are altered to serpentine, and in limestone and porous tuff. These results suggest that, if stick slip on a fault in the earth produces earthquakes, the earthquakes should become more abundant and increasingly severe with depth. Also, if a fault traverses various rock types, then over part of the fault elastic buildup of stress prior to sudden movement may occur at the same time as stable creeping motion elsewhere on the fault.