Numerical simulations of stress variations with depth in a model for the San Jacinto fault zone

Niloufar Abolfathian, Christopher W. Johnson, & Yehuda Ben-Zion

Published August 8, 2019, SCEC Contribution #9394, 2019 SCEC Annual Meeting Poster #192

Depth dependent crustal stress orientations in strike-slip faulting environments are explored using quasi-static numerical simulations with variations of fault geometry and rheology of a layered substrate, to compare model predictions with stress inversion of focal mechanisms from the San Jacinto fault zone. We attempt to understand observed rotations up to ~30 ̊ of the principal stress axes below 10 km depth in this region. The simulations employ the finite element software package PyLith for solving the partial differential equations describing the tectonic deformation. The basic model consists of a vertical right-lateral frictional fault in a solid with horizontal crustal layers, constant tectonic loading, and gravitational forces. The model design incorporates different scenarios with a fault in an elastic upper crust atop a transition zone and a viscoelastic lower crust. Variations of stress orientations in relation to seismic velocities, rheology of the transition zone and fault dipping are analyzed. Temporal changes of stress parameters within an earthquake cycle are also compared with observations from the San Jacinto fault zone. Initial results indicate that the stress evolution is not sensitive to the velocity model, but the rheology plays a large role in the stress accumulation in the brittle-ductile transition layer. Allowing fault creep in the elastic transition zone produces rotation of the principal stresses and smaller earthquakes at the bottom of the seismogenic thickness seen in observed data.

Key Words
State of stress, Fault model

Citation
Abolfathian, N., Johnson, C. W., & Ben-Zion, Y. (2019, 08). Numerical simulations of stress variations with depth in a model for the San Jacinto fault zone. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)