Investigating fault reactivation through mechanical and numerical modelling: an application to the Central- Northern Apennines of Italy

Inversion tectonics refers to regions that experience a switch in the stress regime. In these contexts, the reactivation of pre-existing discontinuities depends upon a wide number of structural, stratigraphic and mechanical factors. Among these, a fundamental aspect is represented by the orientation and attitude of pre-existing discontinuities with respect to the new stress field. Starting from some field example of positive and negative inversion tectonics from the Central-Northern Apennines fold-and-thrust belt (Italy), mechanical (slip tendency analysis) and numerical (using COULOMB 3.3 software) models have been developed with the aim to investigate how the orientation of fault planes influences their tendency to reactivation. Both field data and modelling results point to a strong influence exerted by the orientation and attitude of pre-existing discontinuities in inversion tectonic processes. During the positive inversion tectonic event, NNE-SSW/N-S high-angle faults, oblique to the shortening direction, were preferentially reactivated as thrusts (rather than NW-SE orthogonal planes) because they can take advantage of their orientation that allows a strike-slip component of movement. Also for the negative inversion tectonic phase, model results support our field observations highlighting, in this case, the major tendency to reactivation as normal faults of the NW-SE planes rather than of the oblique N-S discontinuities.