Presentation Information
[T5-O-8]Scaling and Spatiotemporal Evolution of Stress and Strain Governed by Heterogeneous Material Geometry
*Yoshitaka Hashimoto1 (1. Kochi University)
Keywords:
melange,roughness,rheology
The deformation style of fault zones is governed not only by stress conditions and material properties but also by geometric heterogeneity. Fault surface roughness and high-viscosity blocks within low-viscosity matrices are known to promote stress concentration and strain localization, contributing to the spatial variability of shear zone formation and fault slip behavior. These structural heterogeneities can influence both coseismic and aseismic deformation, yet their dynamic roles remain underexplored.Recent observations suggest that slow earthquakes are spatially controlled by structural geometry rather than solely by frictional properties. For example, tectonic tremors are distributed around subducting seamounts in the Hyuga-nada region (Yamashita et al., 2021), and very low-frequency earthquakes correspond to decollement geometry in the Nankai Trough (Hashimoto et al., 2022). Similar effects are observed in tectonic mélanges, where cracks and microfaults within competent blocks reflect spatiotemporal variations in rheological behavior due to embedded heterogeneity (Fagereng and Sibson, 2010; Hashimoto and Yamano, 2014).Numerical modeling using finite element simulations of block-in-matrix rheological systems has provided new insights into such deformation dynamics. These models reveal that intermediate deformation modes—akin to slow earthquakes—emerge between stable viscous flow and localized shear, and are controlled by viscosity contrasts and imposed boundary velocities. Stress and strain rate localize near material boundaries, leading to spatial redistribution of mechanical fields. This reorganization is primarily governed by the geometry of the heterogeneities. Furthermore, deformation mode transitions exhibit scale-free behavior, depending on the ratio of boundary velocity to shear zone thickness.Natural fault zones exhibit heterogeneity across multiple scales, often with fractal or self-affine characteristics. Fault surface roughness follows a power-law spectrum with a constant Hurst exponent (Candela et al., 2011), and particle-size distributions from brittle failure are known to be fractal (Otsuki, 1998). Such multiscale geometries drive stress and strain localization over a range of scales, from millimeters to kilometers, suggesting that a common mechanism underlies deformation concentration across different structural levels. This supports the idea that scaling geometry is key to unifying our understanding of spatiotemporal fault slip behaviors.In conclusion, this study emphasizes that the spatial configuration of material properties—namely, geometric heterogeneity and scaling structure—plays a central role in governing deformation styles within fault zones. Structural features such as rough surfaces and rigid inclusions concentrate stress and strain, influencing slip dynamics over time and space. Their hierarchical nature promotes scale-invariant localization processes, offering a framework for interpreting the diversity of fault slip behavior. A comprehensive understanding of fault mechanics requires integrating observations, numerical modeling, and theory under the premise that “structure governs deformation.”