Discrete fault models: the dynamical role of asperities and their interaction

The present thesis focuses on the mechanics of the seismic source, in the framework of asperity models of faults. Thanks to the major role played by asperities in the dynamics of the seismic source, faults have been treated as dynamical systems made of a small number of asperities, weak regions or fault segments. The state of the system is described by the slip deficits or Coulomb stresses associated with the regions of the fault. Five cases are illustrated, differing for the number of asperities, weak regions or fault segments and for the mechanical processes investigated. In a model of a fault with a single asperity, the dynamics is described by two dynamic modes, corresponding to asperity loading and asperity failure, respectively. In a model of a fault with an asperity and a weak region, the dynamics is studied in terms of three dynamic modes, corresponding to interseismic intervals, seismic slip of the asperity and afterslip in the weak region. In a model of a two-asperity fault with purely elastic coupling, the dynamics is described by a sticking mode, associated with stationary asperities, and three slipping modes, corresponding to the slip of one or both asperities at a time. If viscoelastic coupling between the asperities is assumed, the model allows to highlight the role of rock rheology in the duration of the interseismic intervals of the fault and in the response to stress perturbations from neighbouring faults. In a model of a system of n faults generating a seismic sequence, it is possible to retrieve the state of the system at any time during the sequence. Also, the order of fault activation is described by a permutation of the first n natural numbers. In each case, applications to real faults are presented.