抄録
Detailed laboratory experiments have been performed on the stick-slip characteristics of friction of granite, particularly in relation to such environmental conditions as the stiffness of loading system, the velocity of ram advance in a testing machine and the normal load across sliding surfaces. It is found that the stick-slip amplitude Δμ=ΔF/N(ΔF: force drop and N: normal load) decreases at high stiffness, at high velocity and at high nomal load, and that there are the interre1ated effects of the stiffness, the velocity and the normal load on stick-slip. The somewhat conflicting observations so far on the effect of stiffness on stick-slip amplitude are explained system-atically considering the interrelated effects. Stiffness influences not only the slip amplitude, but the time of slipping, which corresponds to the rise time of the source time function of an earthquake. Frictional behavior is also investigated for various rock types in relation to roughness and bulk hardness of sliding surfaces. Stick-slip diminishes on rough fault surfaces. Hard rocks tend to increase stick-slip amplitude.
The in situ stiffness k for the unilaterally propagating fault of an earthquake was estimated in a previous paper as k=μ(υ/β)2W=ρυ2W, where μ is rigidity, υ is the propagating velocity of dislocation, β is shear wave velocity, W is fault width, and ρ is density. The in situ stiffness obtained from the above formula for a large shallow focus earthquake is 6 or 7 orders of magnitude more than the stiffness of a typical testing machine in a laboratory. It has been pointed out that the stress drop associated with earthquakes is remarkably small compared with that accompaning fracture or stick-slip in laboratory experiments. This difference may be partly due to the different stiffnesses of the two systems.
