Modeling shallow crustal nonlinearity in physics-based earthquake simulations: Beyond perfect plasticity

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

Published August 13, 2019, SCEC Contribution #9537, 2019 SCEC Annual Meeting Poster #004

In this project, we advance the current SCEC simulation capabilities in deterministic earthquake simulations by implementing an elastoplastic constitutive model in Hercules, one of the SCEC’s High-F simulation software. Our goal is to quantitatively assess the extent to which shallow crust nonlinearities influence strong ground motions in broad-band earthquake simulations. The multi-axial constitutive model is formulated within the framework of bounding surface plasticity in terms of total stress (i.e. cannot capture effective stress phenomena like liquefaction). A major advantage of this model is the small number of free parameters that can be fully calibrated given a shear modulus reduction curve. This, in turn, makes the model a suitable choice for regional-scale simulations where geotechnical data in the shallow crust are scarce. In Year 3 of SCEC5, we performed a catalog of experiments to verify the model implementation; then, we performed a series of synthetic experiments in a region of size 35 x 26 x 4.5 km3 that encompasses the Garner Valley – an instrumented and well-characterized site in Southern California. The velocity model was extracted from CVM-S4.26 with the optional geotechnical layer, while modulus reduction curves were selected empirically to constrain the nonlinear soil model parameters. We subjected the model to vertically propagating plane waves applied by means of the domain reduction method and studied the basin response for low and high-frequency content of the incoming waves. 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.

Citation
Esmaeilzadeh Seylabi, E., Restrepo, D., Asimaki, D., & Taborda, R. (2019, 08). Modeling shallow crustal nonlinearity in physics-based earthquake simulations: Beyond perfect plasticity. Poster Presentation at 2019 SCEC Annual Meeting.

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