Presentation Information
[S08-08]Linking Inelastic Deformation to Seismogenic Stress Buildup in Kyushu, Japan
*Angela Meneses-Gutierrez1, Tatsuhiko Saito1 (1. National Research Institute for Earth Science and Disaster Resilience)
Active deformation and seismicity along a right-lateral shear zone in central Kyushu are well documented by geodetic and seismic observations. This zone most recently hosted the 2016 Mw 7.0 Kumamoto earthquake, one of the most devastating events in Japan in recent years, highlighting the need to understand how strain energy is accumulated and released in the area.
Understanding earthquake generation requires quantifying stress accumulation and transfer within seismogenic zones during the interseismic period. The stress build-up process can be quantified in terms of shear strain energy changes in the seismogenic zone, which serves as the energy source driving fault motion (e.g., Kostrov, 1974). Saito et al. (JGR, 2025) developed a 2-D model of the inelastic strain flow beneath the seismogenic zone to evaluate the stress transfer using this framework. In this study, we extend their approach by incorporating a more realistic 3-D distribution of the inelastic strain. We model inelastic strain in the lower crust as a distributed source that induces stress concentration in the overlying seismogenic zone.
Previous studies about the shear zone in Kyushu (e.g., Matsumoto et al., 2016; Yuasa and Matsumoto, 2023) have estimated inelastic strain distribution using focal mechanism datasets and GNSS observations, highlighting its importance in the region's tectonics. Building on these findings, we provide new estimates of inelastic strain and examine how stress concentration varies with depth using the concept of shear strain energy changes, offering additional insight into the role of inelastic sources in transferring stress to seismogenic zones.
We analyzed GNSS data from 149 GEONET stations across Kyushu for the period January 1, 2006–December 31, 2008, a time of relative stability in southwest Japan. Interseismic surface velocities were estimated and corrected for the contributions from the Nankai Trough interplate coupling using the plate coupling model of Saito and Noda (2022). The corrected velocities were converted into reference frame–independent surface-strain distributions to identify zones of strain concentration. We found a maximum shear strain rate of ~1x10-7 yr-1 along the shear zone.
We estimate the distribution of moment density in the lower crust, defined as the product of inelastic strain and the elastic modulus. (e.g., Noda and Matsu'ura, 2010). We constrain the moment density orientation aligned with the regional stress field estimated from the stress tensor analysis and set the average locking depths from the seismicity cutoff depths. Inverting for moment density yields values of ~1x104 Nm/m3/yr, which reproduce the observed strain pattern. Shear strain energy analysis indicates increased energy concentration in the seismogenic zone along the shear zone, supporting the interpretation that lower-crustal inelastic strain plays a key role in stress transfer into the seismogenic zone and earthquake generation.
Understanding earthquake generation requires quantifying stress accumulation and transfer within seismogenic zones during the interseismic period. The stress build-up process can be quantified in terms of shear strain energy changes in the seismogenic zone, which serves as the energy source driving fault motion (e.g., Kostrov, 1974). Saito et al. (JGR, 2025) developed a 2-D model of the inelastic strain flow beneath the seismogenic zone to evaluate the stress transfer using this framework. In this study, we extend their approach by incorporating a more realistic 3-D distribution of the inelastic strain. We model inelastic strain in the lower crust as a distributed source that induces stress concentration in the overlying seismogenic zone.
Previous studies about the shear zone in Kyushu (e.g., Matsumoto et al., 2016; Yuasa and Matsumoto, 2023) have estimated inelastic strain distribution using focal mechanism datasets and GNSS observations, highlighting its importance in the region's tectonics. Building on these findings, we provide new estimates of inelastic strain and examine how stress concentration varies with depth using the concept of shear strain energy changes, offering additional insight into the role of inelastic sources in transferring stress to seismogenic zones.
We analyzed GNSS data from 149 GEONET stations across Kyushu for the period January 1, 2006–December 31, 2008, a time of relative stability in southwest Japan. Interseismic surface velocities were estimated and corrected for the contributions from the Nankai Trough interplate coupling using the plate coupling model of Saito and Noda (2022). The corrected velocities were converted into reference frame–independent surface-strain distributions to identify zones of strain concentration. We found a maximum shear strain rate of ~1x10-7 yr-1 along the shear zone.
We estimate the distribution of moment density in the lower crust, defined as the product of inelastic strain and the elastic modulus. (e.g., Noda and Matsu'ura, 2010). We constrain the moment density orientation aligned with the regional stress field estimated from the stress tensor analysis and set the average locking depths from the seismicity cutoff depths. Inverting for moment density yields values of ~1x104 Nm/m3/yr, which reproduce the observed strain pattern. Shear strain energy analysis indicates increased energy concentration in the seismogenic zone along the shear zone, supporting the interpretation that lower-crustal inelastic strain plays a key role in stress transfer into the seismogenic zone and earthquake generation.