| | | 9 Dynamic Failure in a Homogeneous Half-Space |
We begin our examination of dynamic failure with simulations in a homogeneous half-space. We study the behavior of the rupture, including the role of fracture energy, the effects of the free surface on the rupture, and the effects of the various friction models on the ground motions. We also consider different variations in the effective normal stresses with depth and their implications on the parameters of the friction model.
We will use some of the basic features of ruptures observed in nature to judge the behavior of the simulated ruptures. Heaton (1990) examined the rupture behavior of seven earthquakes and found no systematic variations in the slip distributions with depth. On the other hand, we do expect some systematic variations in the slip distribution for theoretical, constant stress drop earthquakes (Heaton and Heaton 1989). When the fault reaches the free surface, for a uniform stress drop the largest slip occurs along the free surface due to the reduction in stiffness. Likewise, when we bury the fault, the largest slips occur near the center of the fault. Although difficult to resolve, Heaton (1990) did not find any clear variations in the duration of slip with depth. Consequently, we want relatively uniform maximum slip rates. We will also assume that the nominal tectonic tractions may be derived from application of relatively uniform stresses or uniform strains (the two are equivalent in homogeneous half-spaces).
| | | 9 Dynamic Failure in a Homogeneous Half-Space |