11:15 AM - 11:30 AM
[SGD03-09] Estimation of Deformation Patterns Using GNSS-Based Inelastic Deformation Tomography Method
Keywords:GNSS, inelastic deformation, crustal strength structures
1. Introduction
Japan is located at the convergence of multiple tectonic plates, leading to highly active seismic and volcanic activity. Crustal deformation is caused by the interactions between subducting oceanic plates and the overriding continental plates, with high strain rates observed particularly along coastal regions. Traditionally, these strain distributions have been explained by interplate coupling; however, the influence of inelastic deformation related to brittle failure and plastic deformation within the crust has also been recognized as an important factor. In general, crustal strength increases with depth, reaching a maximum before decreasing due to temperature-induced plastic deformation. The distribution of crustal strength is crucial for understanding the boundary between brittle and plastic regions and serves as a fundamental framework for considering the depth of seismogenic layers and faulting mechanisms. This study aims to estimate the three-dimensional tomography-like spatial distribution of inelastic deformation, which is strongly related to crustal strength, and to examine its relationship with the crustal strength structure.
2. Methodology
In this study, we adopt the generalized strain representation of inelastic deformation proposed by Barbot et al. (2017) and develop an inversion method to estimate the three-dimensional distribution of inelastic strain rate using GNSS data. The estimated inelastic strain is represented as a six-component strain tensor in three-dimensional space. The observed displacement data are converted into strain data using Delaunay triangulation, and the inelastic block strain components are determined using a minimum-norm solution approach. To apply this method to actual GNSS data, we use velocity data obtained from GNSS observations in southwest Japan, after removing the influence of the subduction of the Philippine Sea Plate. Inelastic blocks are arranged at 10 km intervals horizontally, and a three-dimensional tomography-like analysis is performed with a 10 km vertical resolution, excluding the shallowest layers.
3. Results and Discussion
The analysis reveals a strong correlation between the spatial distribution of inelastic deformation and the distributions of active faults and earthquakes. The estimated inelastic strain values decrease with depth, and spatial heterogeneity also diminishes. In particular, inelastic deformation is concentrated at depths shallower than 30–40 km in the Niigata-Kobe deformation zone, where compressional and shear strain fields dominate. Additionally, significant inelastic deformation is observed along the Median Tectonic Line, with deformation concentrated at depths shallower than 20 km, where shear strain fields are predominant. These results suggest that the depth of inelastic deformation varies by region, indicating a significant deviation from the conventional strength profile of continental crust.
4. Conclusion
This study elucidates the spatial distribution of inelastic deformation in southwest Japan. The characteristic strain fields observed in the Niigata-Kobe deformation zone and along the Median Tectonic Line suggest a strong link between inelastic deformation and seismic activity. Applying this methodology to other regions will contribute to the understanding of the general mechanisms of inelastic deformation.
References
• Sylvain Barbot, James D. P. Moore, Valère Lambert; Displacement and Stress Associated with Distributed Anelastic Deformation in a Half-Space. Bulletin of the Seismological Society of America 2017, 107 (2): 821–855, doi:10.1785/0120160237
Japan is located at the convergence of multiple tectonic plates, leading to highly active seismic and volcanic activity. Crustal deformation is caused by the interactions between subducting oceanic plates and the overriding continental plates, with high strain rates observed particularly along coastal regions. Traditionally, these strain distributions have been explained by interplate coupling; however, the influence of inelastic deformation related to brittle failure and plastic deformation within the crust has also been recognized as an important factor. In general, crustal strength increases with depth, reaching a maximum before decreasing due to temperature-induced plastic deformation. The distribution of crustal strength is crucial for understanding the boundary between brittle and plastic regions and serves as a fundamental framework for considering the depth of seismogenic layers and faulting mechanisms. This study aims to estimate the three-dimensional tomography-like spatial distribution of inelastic deformation, which is strongly related to crustal strength, and to examine its relationship with the crustal strength structure.
2. Methodology
In this study, we adopt the generalized strain representation of inelastic deformation proposed by Barbot et al. (2017) and develop an inversion method to estimate the three-dimensional distribution of inelastic strain rate using GNSS data. The estimated inelastic strain is represented as a six-component strain tensor in three-dimensional space. The observed displacement data are converted into strain data using Delaunay triangulation, and the inelastic block strain components are determined using a minimum-norm solution approach. To apply this method to actual GNSS data, we use velocity data obtained from GNSS observations in southwest Japan, after removing the influence of the subduction of the Philippine Sea Plate. Inelastic blocks are arranged at 10 km intervals horizontally, and a three-dimensional tomography-like analysis is performed with a 10 km vertical resolution, excluding the shallowest layers.
3. Results and Discussion
The analysis reveals a strong correlation between the spatial distribution of inelastic deformation and the distributions of active faults and earthquakes. The estimated inelastic strain values decrease with depth, and spatial heterogeneity also diminishes. In particular, inelastic deformation is concentrated at depths shallower than 30–40 km in the Niigata-Kobe deformation zone, where compressional and shear strain fields dominate. Additionally, significant inelastic deformation is observed along the Median Tectonic Line, with deformation concentrated at depths shallower than 20 km, where shear strain fields are predominant. These results suggest that the depth of inelastic deformation varies by region, indicating a significant deviation from the conventional strength profile of continental crust.
4. Conclusion
This study elucidates the spatial distribution of inelastic deformation in southwest Japan. The characteristic strain fields observed in the Niigata-Kobe deformation zone and along the Median Tectonic Line suggest a strong link between inelastic deformation and seismic activity. Applying this methodology to other regions will contribute to the understanding of the general mechanisms of inelastic deformation.
References
• Sylvain Barbot, James D. P. Moore, Valère Lambert; Displacement and Stress Associated with Distributed Anelastic Deformation in a Half-Space. Bulletin of the Seismological Society of America 2017, 107 (2): 821–855, doi:10.1785/0120160237