HOMOGENEOUS STRESS HYPOTHESIS AND ACTUAL FAULT SLIP - A DISTINCT ELEMENT ANALYSIS

The different inverse methods used in slip data analysis depend on the general validity of the mechanical model adopted by Carey and Brunier , and others. The mechanical scheme is based on the Wallace-Bott relat ionship assuming a faulted rock mass as a system of rigid blocks inter acting mechanically without friction. Until now the validity of this c onceptual model was supported by internally consistent results obtaine d by applying numerical inversion techniques to fault slip data. This paper presents the first results of a numerical modelling investigatio n of this simple mechanical model by a direct approach to the problem. The numerical method used here is a three-dimensional Distinct Elemen t Method which is suitable to study discontinuous media. First, by mod elling the behaviour of one fault, we propose an extrinsic verificatio n of the Wallace-Bott relation in three dimensions and considering roc k linear elasticity and friction effects on faults. According to the s mall discrepancy obtained (i.e. the deviation between the modelling re sults and the theoretical results), we conclude that the assumptions o f the basic model are justified i n the range of stress values that we study. Second, using a two-fault model, the effects of overlap in str ess perturbations around the faults results in particular fault slip i nteractions. The existence of such phenomena invalidates, in a general ly minor way taking into account practical uncertainties, the assumpti on of fault slip independence in the basic model. Finally, we discuss limits to inverse methodologies and the necessity for interactions bet ween data collection, interpretation of these data and the ability of the basic model to be used in microtectonic analyses.