AGU Fall Meeting, San Francisco, USA, 5 - 9 December, 2011
Gaetano Festa, Jean-Pierre Vilotte
We discuss here the effects of rapid changes in the fault geometry on both the rupture dynamics and the strong ground motion. Faults are segmented at all scales, with rupture paths characterized by kinks, bends, jogs and jumps. Complexity in the geometry results into a rough profile for the initial stress even for a uniform remote charge and generates local stress concentration and off-fault dissipation as damage in the surrounding volume. It may also influence the high frequency radiation and the dynamic evolution of the rupture up to arrest it.
Tackling the geometrical complexity of the rupture with numerical methods is difficult. Rapid slope changes of the fault surface require adapted non Cartesian grids, with an accurate approximation of the energy balance between the elastodynamic flux and the dissipation in the process zone. Moreover, the kinematic incompatibility of the slip at the kinks results into an energy integrable singular static stress field which has to be taken into account by the numerical models.
We present here recent advances in numerical approximation of dynamic rupture using the non-smooth spectral element method that allows to model the geometrical complexity of the fault interface together with a spectral accuracy in the solution of the radiated wavefield. The non smooth contact and friction conditions are locally solved in terms of traction, slip and slip rate. We investigate the role of rapid variations in the fault geometry on the rupture velocity, the slip rate, the radiated energy, the wave amplitude and the stress distribution in the volume surrounding the fault as a function of the kinking angle, the initial conditions and the fracture energy. We discuss the radiated field provided by a segmented fault and the possibility to model it with a planar fault and a rough stress distribution. Numerical experiments will be discussed for both inplane and antiplane ruptures, on direct and conjugate faults. In conclusion, we draw on some ongoing extension toward the 3D case and the implication of rough interface geometry for the rupture energy radiation spectrum.