3D Numerical Modeling of Near Source Energy Spectra with Co-seismic Non-classical Nonlinear Damage

Dynamic perturbations reveal unconventional nonlinear behavior in rocks, as evidenced by field and laboratory studies. In Niu et al.(ArXiv, 2023), we analyze physical damage models in 1D and 2D, informed by acousto-elastic experimental measurements. By adopting the Adaptive Metropolis Markov Chain Monte Carlo method, we quantify the uncertainties of inferred parameters and find that damage variables can trade off with the stress-strain nonlinearity in discernible ways. During the rapid coseismic release of energy, rocks within fault zones are often subjected to stress changes exceeding 10 MPa. At such levels of stress perturbations, it may be insufficient to estimate the mechanical behavior of rocks with linear elastic models. Thus, prior studies employed different models of off-fault damage, including plasticity (e.g., Andrews, 2005), continuum damage models (e.g., Lyakvosky et al., 1997), diffuse interface and phase-field approaches (e.g., Gabriel et al., 2021; Fei et al., 2023; Hayek et al., ArXiv, 2023), and explicit representation of off-fault fractures (e.g., Okubo et al., 2019). Kurzon et al. (2019, 2021, 2022) show that a continuum damage-breakage model (CDBM) reproduces interesting observations, such as changes in near-fault wave speeds, damage-induced anisotropy, volumetric components of deformation, and enhanced high-frequency contents in the radiated energy. Here we investigate the effects of including the CDBM in dynamic rupture and seismic wave propagation simulations in a 3D framework and its coupled effect on changing elastic moduli in the fault zone region. We address the computational challenges by extension of SeisSol, a high-performance computing open-source software based on the arbitrary high-order derivative (ADER) discontinuous Galerkin (DG) Method. We implemented a version of CDBM in SeisSol. In the first step, we employ our new 3D implementation to study the frequency range, tensorial components, and the azimuthal dependence of the radiated energy from an earthquake source and compare it with linear elastic rheology.      «

Dynamic perturbations reveal unconventional nonlinear behavior in rocks, as evidenced by field and laboratory studies. In Niu et al.(ArXiv, 2023), we analyze physical damage models in 1D and 2D, informed by acousto-elastic experimental measurements. By adopting the Adaptive Metropolis Markov Chain Monte Carlo method, we quantify the uncertainties of inferred parameters and find that damage variables can trade off with the stress-strain nonlinearity in discernible ways. During the rapid coseismi...     »