Effect of off-fault plasticity on the dynamics of elongated earthquake ruptures

Ekaterina Bolotskaya, & Jean-Paul Ampuero

Published September 11, 2022, SCEC Contribution #11933, 2022 SCEC Annual Meeting Poster #128

Large earthquakes saturate the seismogenic width of the fault zone and propagate laterally, developing elongated pulse-like ruptures with large length‐to‐width ratios. Smaller earthquakes can also propagate in a width-bound regime due to heterogeneities of stress field or material properties. A large rupture aspect ratio affects the energy balance of the earthquake rupture: the energy release rate of elongated pulse-like ruptures is width‐limited rather than length‐dependent, unlike the energy release rate of conventional circular cracks. The presence of off-fault plasticity also affects the energy balance by providing an extra mechanism for energy dissipation into irreversible deformation of the material surrounding the fault. Besides, plastic dissipation allows earthquake ruptures to reach steady-state at velocities below the Rayleigh wave speed (c_R) (which is the limiting speed for subshear mode II ruptures in an elastic medium). Here, we carry a computational study of large earthquake ruptures with off-fault plasticity, with a particular focus on steady rupture speeds.
We combine a 2.5D (width‐averaged) modelling approach and Drucker-Prager plasticity to simulate width-bound earthquake ruptures propagating in inelastic medium. We observe steady state pulse-like ruptures propagating at velocities below the Rayleigh wave speed. We study the energy balance of these ruptures and measure the steady rupture velocity depending on the along‐strike distribution of fault stress, fracture energy, rupture width, and closeness to plastic failure. As expected, the presence of plastic dissipation affects the energy balance of the earthquake rupture and allows the rupture velocity to saturate at 0.6c_R – 0.95c_R, similar to the common range of speeds of real earthquakes. Our results indicate that off-fault dissipation is a viable mechanism to achieve realistic earthquake rupture speeds, even on planar faults with homogeneous stress and strength.

Key Words
model, earthquake rupture, plasticity, rupture velocity, energy balance

Citation
Bolotskaya, E., & Ampuero, J. (2022, 09). Effect of off-fault plasticity on the dynamics of elongated earthquake ruptures. Poster Presentation at 2022 SCEC Annual Meeting.

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