AbstractA multiscale approach that couples the finite-element method (FEM) and the discrete-element method (DEM) is used to model and analyze the earthquake fault rupture–soil–foundation interaction (FR–SFI) problem. The approach obtains the soil constitutive responses from the DEM solutions of representative volume elements (RVEs) embedded at the FEM integration points, effectively bypassing the phenomenological hypotheses in conventional FEM simulations. The fault rupture surfaces and shear localization patterns under normal and reverse faults with or without foundation atop were adequately captured using the multiscale approach and verified with available centrifuge experimental and numerical results. An examination of the stress-strain responses and the microstructural evolutions of local RVEs revealed that the RVEs located in or immediately outside the shear bands behaved distinctly and might change their stress states from initially at rest to active under normal fault or passive under reverse fault. The micromechanics study also sheds light on the capability of heavy foundations to protect the superstructure due to rupture surface diversion under reverse fault and their possible detriment under normal fault.