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Earthquake ruptures with strongly rate-weakening friction and off-fault plasticity, 2: Nonplanar faults

Eric M. Dunham, David B. Belanger, Lin Cong, & Jeremy E. Kozdon

Published 2011, SCEC Contribution #1413

Observations demonstrate that faults are fractal surfaces, with deviations from planarity at all scales. Self-similar surfaces have local slope perturbations of order 10^{-3} to 10^{-2} that are independent of scale. We study dynamic rupture propagation on such faults using two-dimensional plane strain models, which feature strongly rate-weakening fault friction and off-fault plasticity. The latter is necessary to bound otherwise unreasonably large stress perturbations in the vicinity of bends, and furthermore prevents fault opening. A consequence of strongly rate-weakening friction is the existence of a critical background stress level at which self-sustaining rupture propagation (in the form of self-healing slip-pulses) is just barely possible. Around this level, at which natural faults are expected to operate, ruptures become extremely sensitive to fault roughness and exhibit substantial fluctuations in rupture velocity. Under a wide range of conditions, the fluctuations are roughly correlated with the local fault slope; self-similarity of the surface thus implies that the fluctuations occur with equal amplitude at all scales. These accelerations and decelerations excite waves of all wavelengths, resulting in ground acceleration spectra that are flat at high frequency, consistent with observed strong motion records.

Key Words
strong motion, ground motion, friction, propagation, tectonics, algorithms, plasticity, earthquakes, seismotectonics, faults

Dunham, E. M., Belanger, D. B., Cong, L., & Kozdon, J. E. (2011). Earthquake ruptures with strongly rate-weakening friction and off-fault plasticity, 2: Nonplanar faults. Bulletin of the Seismological Society of America, 101(5), 2308-2322. doi: 10.1785/0120100076.