Two patterns of stick-slip observed in frictional experiments on rocks

Abstract

Stable slide and two stick-slip patterns could be observed in triaxial frictional experiment on the smooth surface of granite. Under low confining pressure, slip started in stick-slip oscillations with small amplitude (we called this the first pattern of stick-slip). After sliding for some distance stick-slip gradually transformed into stable slide and approached the maximum friction. Under high confining pressure, slip was stable at the beginning and then large amplitude of stick-slip occurred when the friction approached the maximum (we called this the second pattern of stick-slip). Under medium confining pressure, slip started in the first pattern of stick-slip and then transformed into stable slide. When the friction approached the maximum the second pattern of stick-slip occurred. The double shear frictional experiment on the smooth surface of granite showed that the first pattern of stick-slip occurred at the clean and smooth surface, the stick-slip did not reoccur if the smooth surface was roughened or had slipped. So it can be considered that the first pattern of stick-slip only occurs on clean and smooth surface under low normal stress, and the second pattern of stick-slip only occurs under high normal stress, whether the surface was smooth, rough or even had some gouge, as in natural faults. The two patterns of stick-slip are controlled by different physical mechanisms. The stick-slip oscillations (the first pattern of stick-slip) which were observed by Hoskins et al. (1968) during his double shear frictional experiments on smooth surfaces are essentially different from the stick-slip (the second pattern of stick-slip) which was observed by Byerlee (1967a,) during triaxial frictional experiments on faulted surfaces. The second pattern of stick-slip is more important for the behavior of natural faults. The frictional experiment in the laboratory is always carried out on smooth surface. In order to correctly understand the results obtained from laboratory it is also important to know the first pattern of stick-slip and its physical mechanism.