We developed a mechanical subducting plate model and re-examined the
crustal deformation history in the Sagami Trough subduction zone,
central Japan, the northernmost convergence boundary of the Philippine
Sea Plate. The elevation distributions and formation ages of the
Holocene marine terraces, representing past coseismic and long-term
coastal uplifts, have been thoroughly investigated in this region.
However, no physically consistent formation scenario to explain them has
been demonstrated. Surface deformations within subduction zones are
typically calculated using kinematic elastic dislocation models, such as
the back-slip model. However, these models cannot explain permanent
deformation after an earthquake sequence. This study develops a
mechanical subducting plate model that balances the slips of interplate
shear stress and can produce permanent deformations caused by a local
bump geometry. We modeled earthquake recurrences by shear stress
accumulation and coupling patches. As a result, we successfully
reproduced the averaged uplift rate distribution estimated from the
Holocene marine terraces. The findings suggest that the subducted
seamount significantly affects long-term deformation patterns. In
addition, the discrepancy between the elevation distributions and
formation ages of Holocene marine terraces, which previous geological
studies have indicated, can be interpreted by the rupture delay of
coupling patches. This study also demonstrates that the traditional
assumption of the back-slip model on the plate boundary for long-term
subduction possibly results in an oversimplified model.