A 3-D numerical modelling approach for predicting the spatial distribution of cataclastic rocks along faults

The three-dimensional distribution of cataclastic rocks along faults deeply influences their mechanical and permeability properties. Despite their importance for seismic hazard and fluid flow, physical parameters controlling location of cataclastic rocks are still poorly constrained. We present results of three-dimensional numerical models specifically implemented for investigating the role of physical parameters enhancing the formation and location of cataclastic rocks along faults. Seven favourable conditions have been identified: failure under uniaxial stress conditions; failure by residual stress; failure by stress drop; interference of differently-oriented fracture populations, block rotation; fracturing of a previously fractured material, and rock anisotropy. Their weighted combination with boundary conditions including the geometry and kinematics of the fault surface, the overburden, the regional and kinematic stress fields, the rock rheology and strength, and pore fluid pressure, provide a scalar value proportional to the relative probability of cataclasis along the fault. Such a scalar value is named cataclasite generation function. The predictive capability of this numerical tool has been successfully tested in seven field sites in the Apennines, where fault zones in carbonate rocks are well exposed.