Numerical modelling of earthquake-induced large deformations in geomaterials presents significant challenges, requiring advanced constitutive models and reliable numerical methods. This study addresses these demands by introducing our recently developed SPH-based approach for seismic response analyses by incorporating SPH free-field boundary conditions. To accurately capture the cyclic response of geomaterials, a bounding surface plasticity model is implemented into the SPH framework. Following validation against seismic response observed at Sendai site, the proposed framework is applied to investigate earthquake-induced soil liquefaction and associated deformation mechanisms in an earth dam. The results offer valuable insights into the deformation processes and demonstrate the potential of SPH as a powerful tool for highly nonlinear seismic response analyses, contributing to improved seismic risk assessment and mitigation.