EXPERIMENTAL ANALYSIS OF SLIP DISTRIBUTION ALONG A FAULT SEGMENT UNDER STICK-SLIP AND STABLE SLIDING CONDITIONS

Abstract

This paper presents the results of an experimental study of slip distribution along fault models with different sliding surface morphologies submitted to various orientations of fault and loading direction. Uniaxial compression tests were done on PMMA plates to measure the relative displacement of markers perpendicular to the sliding surfaces. Slip distribution profiles were then constructed for different stages of shortening of the samples.It was shown that fault morphology determines both the sliding regime and the slip distribution along the sliding surfaces. Along fault models with grounded surfaces (FMGS), stable sliding giving a symmetrical smooth distribution was observed. For fault models with natural fracture surfaces (FMNS), stick-slip was observed. In this case, the slip distribution exhibited significant irregularities in a generally symmetrical profile. Analysis of this profile enabled four types of local slip behaviour to be identified which may provide a physical basis for the interpretation of coseismic slip distributions. The local slip behaviours were interpreted in terms of interaction of irregular asperities, and helped understand the discrepancy observed between theoretical slip distributions and the displacement measured along the active faults. Analysis of the slip distribution profiles along the FMGS and the FMNS also showed that they evolved systematically after the appearance of branching.For a large amount of shortening, mode I branching was observed at the tips of the sliding surfaces. After its development, the global amount of slip along the faults increased, and the slip gradient between the centre and the tips of the faults decreased. This effect is consistent with numerical modelling studies.Finally, the observed profiles were compared with the linear, the tapered, and the elliptic theoretical models, using two different procedures. We conclude that, in the case of the FMNS, where the sliding surface topography is complex, no model could correctly describe the slip distribution, and that, in both cases of FMNS and FMGS, branching caused a change in the shape of the slip distribution profiles.