Plenary: Takeo

The Japanese archipelago is a tectonically active region, with crustal deformation driven by subduction of oceanic plates beneath the continental plate. High strain rates in coastal areas have traditionally been attributed to elastic deformation from plate locking. However, inelastic deformation processes, such as brittle and plastic deformation, play a critical role but remain understudied. This research adopts the inelastic deformation model by Barbot et al. (2017) and applies it to GNSS data to estimate inelastic strain structures in Southwest Japan. Using surface displacement data converted via Delaunay triangulation and Green's function for elastic deformation, an inversion method was developed to estimate subsurface inelastic strain. Validation tests with synthetic data confirmed the effectiveness of maximum principal strain and strain energy as indicators of inelastic deformation. Applying this method to filtered GNSS data from Southwest Japan revealed significant inelastic strain near the Izu Peninsula, attributed to the collision of the Izu Block. The results highlight pronounced inelastic deformation at depths exceeding 30 km, suggesting the presence of larger inelastic blocks. This study demonstrates that incorporating inelastic processes provides new insights into crustal deformation not explained by elastic models. These findings have implications for earthquake mechanisms and underscore the need for further studies to refine the approach and apply it to other tectonic regions.