ABSTRACT:

The effect of accumulation of deformations on rock discontinuities due to low amplitude seismic vibrations has been investigated in laboratory and field experiments. A peculiar rheology of stressed faults and fractures leads to origination of relative residual displacements of discontinuity sides. A short-term disturbance in a stressed blocky medium can also trigger a slow slip, whose contribution to the integral amount of accumulated deformation may be appreciable.

1 INTRODUCTION

About 20–30 years ago the assumption was made that microseisms can play a constructive role in the evolution of deformation processes in the Earth's crust (Melosh 1979, Kocharyan & Rodionov 1989). Development of nonlinear models of the block medium has led to the idea that accumulation of small deformations in rock can occur similarly to metal fatigue and breaking (Hill & Prejean 2007). A well known example of the influence of a low amplitude dynamic effect on the regime of the Earth's crust deformation is the so-called trigger seismicity: a short-term variation in the seismic regime caused by propagation of seismic waves of a remote event (Hill& Prejean 2007). It seems, however, that the effect of continuous low-amplitude vibrations on a rock massif has wider consequences, than just stimulation of weak seismicity. We have performed lab and field observations, which show that the low-amplitude vibrations in a stressed rock massif or an engineering construction produce residual deformations localized at discontinuities. Accumulation of small displacements at discontinuities may turn to be an important factor in the evolution of stress-strain conditions.

2 LABORATORY EXPERIMENTS
2.1 Results

We have investigated the dynamic effect on an element of a blocky medium in laboratory experiments. In these tests the system of blocks (Fig. 1) loaded with a fixed static weight was subjected to the dynamic low-amplitude vibrations.

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