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Deterministic ground motion simulations with shallow crust nonlinearity at Garner Valley in Southern California

Elnaz Seylabi, Doriam Restrepo, Ricardo Taborda, & Domniki Asimaki

Published October 28, 2020, SCEC Contribution #10063

We present deterministic ground motion simulations that account for cyclic multi-stress response of sediments in the shallow crust. The study estimates the extent to which nonlinear excursions of the near-surface deposits influence strong ground motions in deterministic broadband simulations. We use as test-case the GarnerValley strong motion downhole array site in Southern California. The multi-axialconstitutive model is based on the bounding surface plasticity theory in terms of total stress, and implemented in the high-performance finite element code Hercules.A major advantage of this model is the small number of free parameters that can be fully calibrated given a shear modulus reduction curve and soil strength. This, in turn, makes the model a suitable choice for regional-scale simulations where geotechnical data in the shallow crust are scarce. In this paper, we first describe a series of numerical experiments designed to verify the model implementation in Hercules. This is followed by a series of idealized regional simulations in a 35 x 26 x 4.5 km3 domain that encompasses the Garner Valley – an instrumented and well-characterized site inSouthern California. Material properties were extracted from the Southern CaliforniaEarthquake Center (SCEC) velocity model CVM-S4.26 with optional geotechnical layer, while the modulus reduction curves were selected empirically to constrain the nonlinear soil model parameters. Our nonlinear simulations so far 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.

Key Words
Nonlinear soil behavior, Bounding surface plasticity, Large-scale simulations

Seylabi, E., Restrepo, D., Taborda, R., & Asimaki, D. (2020). Deterministic ground motion simulations with shallow crust nonlinearity at Garner Valley in Southern California. Earthquake Engineering & Structural Dynamics, 50(1), 43-59. doi: 10.1002/eqe.3360.

Related Projects & Working Groups
Ground Motion