Marine terraces have long been a subject of paleoseismology to reveal the rupture history of megathrust earthquakes. However, the mechanisms underlying their formation, in relation to crustal deformation, have not been adequately explained by kinematic models. A key challenge has been that the uplifted shoreline resulting from a megathrust earthquake tends to subside back to sea level during subsequent interseismic periods. This study focuses on the remaining permanent vertical deformation resulting from steady plate subduction and examines it quantitatively using three plate subduction models. Specifically, we pay attention to the effects of irregular geometries in the plate interface, such as subducted seamounts. Besides a simplified model examination, this study employs the plate geometry around the Sagami trough, central Japan, to compare with surface deformation observation. The subduction models employed are the kinematic subducting plate model, the elastic/viscoelastic fault model, and the mechanical subducting plate model (MSPM). The MSPM, introduced in this study, allows for more realistic simulations of crustal displacements by imposing net zero shear stress change on the plate boundary. Notably, the presence of a subducted seamount exerts a significant influence on surface deformation, resulting in a concentrated permanent uplift above it. The simulation of earthquake sequence demonstrates that coseismic uplifts can persist over time and contribute to the formation of marine terraces. The results demonstrated that the geological observations of coseismic and long-term deformations can be explained by the influence of a subducted seamount, previously identified in seismic surveys.