Stress heterogeneity at restraining double bends under multicycles and its effect on rupture propagation in 3D

Dunyu Liu, & Benchun Duan

Published August 15, 2016, SCEC Contribution #6812, 2016 SCEC Annual Meeting Poster #050

The conditions under which a rupture is able to propagate through geometrical complexity, such as restraining double bends, are crucial to the estimation of potential maximal event size on a fault system like the central Altyn Tagh Fault. Previous studies using 2D multicycle dynamic rupture models, including a viscoelastic model to represent off-fault deformation and inter-seismic loading and a spontaneous dynamic rupture for coseismic deformation, illustrate that heterogeneous stress builds up around restraining double bends under multiple earthquake cycles. The restraining double-bend stops or initiates rupturing in most cases but sometimes it may allow the rupture link through the bends, leading to a large event. With the slip-weakening friction law and uniform pre-stresses applied, stress heterogeneity concentrates around the double-bend and a stable rupture pattern develops after a number of cycles. However, the 2D models are assumed at a specific depth, at which depth the rupture is limited, whereas the depth dependency of stress states and of frictional property on fault may play a role in affecting the rupture propagation. In this study, we extend the 2D methodology to 3D case and apply it to the central Altyn Tagh Fault, whose trace is geodetically measured. Preliminary results show that ruptures tend to link through a double-bend at shallow depths if a constant slip-weakening distance were applied over the whole fault. However, frictional strengthening behavior at shallow fault significantly affects the jumping condition of ruptures at the double-bend and the consequent rupture behavior during multiple earthquake cycles. Besides, the stress heterogeneity observed over a large range of scales, is not well reproduced by the 2D methodology with slip-weakening law and uniform pre-stresses. Two ways have been proposed to be able to produce the stress heterogeneity by dynamic rupture models. One is to start from uniform pre-stresses and to include rate-weakening in the friction law, whereas the other one keeps using the slip-weakening law while directly replaces the uniform pre-stress to a heterogeneous one. Both schemes are able to generate healing phase during the rupture and resultant pulse-like rupture and stress heterogeneity observed. In the current stage, we will apply a self-similar pre-stress together with the simple slip-weakening law to examine whether or not multiple scales of stress heterogeneity can be reproduced and can be conserved during multiple earthquake cycles, as well as effect of the stress heterogeneity on rupture behavior around restraining double bends.

Key Words
stress heterogeneity, geometrical complexity, multiple earthquake cycles, dynamic rupture

Citation
Liu, D., & Duan, B. (2016, 08). Stress heterogeneity at restraining double bends under multicycles and its effect on rupture propagation in 3D. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)