The stick-slip phenomenon is used to explain a mechanism of earthquake recurrence. A number of stick-slip experiments have been performed to clarify the mechanism of recurring slip instabilities and slip weakening. Although the amplitude of sliding of most experiments is quite smaller than actual earthquakes, and the observed acceleration is larger. The authors have developed an experimental setup, in which blocks move on a conveyor belt and is restrained by the spring, and conducted stick-slip experiments. However, the amplitude of slippage and acceleration observed in these experiments were quite smaller than actual earthquakes. Therefore, a large-scale experimental device was improved to be able to experiment with a larger rock blocks, and the experiment which changed the size and the type of the rock blocks was conducted. In this study, the results of large-scale experimental device were compared with the results of previous experiments, and the scale effect of rock discontinuities on the stick-slip phenomenon was investigated.

1 Introduction

The stick-slip is a phenomenon that interfaces is repeated sticking (accumulation of stress) and slip (release of stress). In the field of rock engineering, it is very important to explain the periodic occurrence of earthquakes, and seismic moment and displacement accompanying the stress drop at the fault plane, as well as creep behavior of unstable zones of slope movement and large underground cavities. Brace & Byerlee (1966) conducted some laboratory experiments using rocks to explain the mechanism of occurrence of earthquakes, and proposed that the stick-slip phenomenon is associated with this mechanism. However, most were using the compression testing equipment in the past studies, amount of slippage was very small with lμm-lmm and the peak accelerations during slipping were very large with 102-105 m/s2 (Ohnaka 2003). These results are quite different from case of medium/large earthquakes, slip amount of 10cm-lm, peak acceleration of 1-10 m/s2.

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