Kinematic Source Models for Earthquake Simulations with Fault-zone Plasticity

Zhifeng Hu, Daniel Roten, Kim B. Olsen, & Steven M. Day

Submitted August 14, 2018, SCEC Contribution #8541, 2018 SCEC Annual Meeting Poster #018

Fault slip and surface deformation patterns are essential factors in seismic hazard assessment. However, slip inversions reveal a widely observed shallow slip deficit (SSD) which has not yet been clearly explained. One possible cause of the SSD is distributed plastic deformation in the fault damage zone near the surface. Roten et al. (2017) performed 3D dynamic rupture simulations of the 1992 M7.3 Landers earthquake in a medium governed by Drucker-Prager plasticity. The study showed that while linear simulations tend to underpredict SSD and off-fault deformation (OFD), nonlinear simulations with moderately fractured rock mass can properly reproduce results that are consistent with the 30-60% SSD and around 46% OFD reported in geodetic observations. Analysis of the Roten et al. (2017) results shows that discrepancies between linear and nonlinear simulations are only significant in the top hundreds of meters of the surface-rupturing fault. Although inelastic responses in the fault damage zone provide more realistic representations of earthquake physics, it can be computationally expensive or numerically unfeasible (e.g., in adjoint methods) to include nonlinear effects in ground motion simulations. One solution proposed here is to use an equivalent kinematic source (EKS) model that mimics the fault-zone plastic effects. This method generates source-time-functions by modifying the slip rate time histories based on comparisons of linear and non-linear dynamic rupture models, which are then used as input to kinematic simulations. The EKS model is able to reproduce the reduction of ground motions observed in dynamic simulations with fault-zone plasticity compared against linear simulations. In spite of its simple formula, the EKS model is robust in the presence different stress drop, rock strength and rupture directions for a M7.8 earthquake scenario on the San Andreas Fault. Further verification of the method and comparison with the output from kinematic rupture generators are needed before the anticipated use in practical applications such as the SCEC CyberShake and Broadband platforms.

Key Words
plasticity, rupture generator, ground motions

Hu, Z., Roten, D., Olsen, K. B., & Day, S. M. (2018, 08). Kinematic Source Models for Earthquake Simulations with Fault-zone Plasticity. Poster Presentation at 2018 SCEC Annual Meeting.

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