Abstract
Marine terraces have long been a subject of paleoseismology, revealing 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 is 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 multiple sequences of megathrust earthquakes with plate subduction and examines it quantitatively using three plate subduction models. Specifically, we examine the effects of irregular geometries in the plate interface, such as subducted seamounts. The subduction models employed include the kinematic subducting plate model, the elastic/viscoelastic fault model, and the mechanical subducting plate model (MSPM). The MSPM, introduced in this study, considers more realistic boundary conditions and 3-D geometry of the plate-interface and the subducting slab. employing stress boundary conditions. A subducted seamount strongly influences surface deformation, resulting in a concentrated permanent uplift above it. We further examine the MSPM by employing the plate geometry around the Sagami Trough, central Japan, to compare with geomorphological observations. The simulation of earthquake sequences demonstrates that coseismic uplifts can persist over time and contribute to the formation of marine terraces. The results demonstrate that geological observations of coseismic and long-term deformations can be explained by the influence of a subducted seamount, previously identified in seismic surveys.