Poster #197, Ground Motions

Deterministic ground motion simulations with shallow crust nonlinearity

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Poster Presentation

2020 SCEC Annual Meeting, Poster #197, SCEC Contribution #10718
We perform a series of large-scale nonlinear ground motion simulations that account for the cyclic plastic behavior of sediments in the shallow crust. Our goal is to understand and quantitatively assess (1) how idealized models of sediment nonlinearity influence the amplitude, frequency content, and duration of ground motion in broadband earthquake simulations; and (2) how predictions of the hybrid 3D anelastic – 1D nonlinear site response analysis compare to the 3D nonlinear ground response analysis. We use the Garner Valley region in southern California as a test case where near-surface nonlinearity has been reported for peak ground accelerations (PGAs) as small as 0.05-0.2g. We model th...e sediment cyclic response using a multi-axial constitutive model formulated within the framework of bounding surface plasticity in terms of total stress and implemented in a high-performance computing finite element code. In all simulations, we extract the small-strain material properties from the Southern California Earthquake Center (SCEC) Community Velocity Model CVM-S4.26 (using its optional geotechnical layer) and constrain the nonlinear soil model parameters using empirical modulus reduction curves and ultimate shear strength. Our nonlinear simulations suggest that peak ground displacements within the valley increase relative to the linear case, while peak ground accelerations can increase or decrease, depending on the frequency content of the excitation. The comparisons of our simulations against hybrid 3D-1D site response analyses suggest the inadequacy of the latter to capture the complexity of fully 3D simulations.