Spontaneous rupture processes with thermal pressurization: Spatial variation of rupture and effect of shear zone thickness and fault shap
We show thermal pressurization (TP) can affect spatial variation in stress/slip evolution of earthquake rupture processes, depending on shear zone thickness and fault shape, based on 3-D numerical simulations for spontaneous ruptures with TP. In this study, a rectangular fault is placed in an infinite, homogenous and elastic medium. The length of the fault is 8km and the width is 3km. The numerical algorithm is based on the finite- difference method of Kase and Kuge (2001). Rupture is initiated in a small patch at the center by decreasing shear stress to dynamic frictional stress, and proceeds spontaneously, governed by a slip-weakening law with the Coulomb failure criteria. We allow effective normal stress to vary with TP by the formulation of Bizzarri and Cocco (2006). We examine drained strike-slip fault (DS), undrained one (US), drained dip-slip fault (DD), and undrained one (UD), with shear-zone thickness w of 20cm, 2cm, and 2mm. Our numerical simulations show stress and slip distributions on the faults are not the same and depend on fault shape and shear zone thickness, although the rupture processes with w of 2cm and 2mm differ only slightly. On drained faults, tractions drop with increasing slip in the same way everywhere. On undrained faults, on the other hand, traction curves as function of slip and amount of stress drop depend on location on the faults. As a result, rupture length for attaining super- shear rupture in US is shorter than that in DS for the same S-value (Andrews, 1976), and nucleated rupture on US for w of 2cm quickly becomes super shear. Spatial variation of stress characterizing US includes a trough of stress drop in the ruptured zone for w of 20cm and short-wavelength variation for w of 2cm. In the case of UD, the stress variation is different from that in US because of an early arrival of a healing phase, and two peaks in the final slip distribution can arise from the combination of large slip due to TP and the early arrival of the phase. For the other three models, in contrast, rupture propagation is crack-like, and slip decreases with distance from the nucleation point. Therefore, the results suggest numerical simulations with TP are important and the results cannot be obtained by those simulations without it.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 7209 Earthquake dynamics (1242)