5:15 PM - 6:45 PM
[SCG55-P10] The investigation of macroscopic mechanical properties in the Niigata-Kobe Tectonic zone using GNSS data
Keywords:Niigata-Kobe Tectonic Zone (NKTZ), GNSS, Inelastic deformation, constitutive relations of the crust, crustal deformation, 2011 Tohoku-oki earthquake
The Niigata-Kobe Tectonic Zone (NKTZ) is a strain concentration zone based on GPS observation and a tectonically active region in central Japan. Recently, persistent inelastic deformation in the NKTZ was detected under variable stress conditions before and after the 2011 Tohoku-oki earthquake. However, the details about the constitutive relations of the medium in the NKTZ are poorly understood. Investigating constitutive relations is essential in understanding the tectonics of the NKTZ that are related to seismic activities or the formation of geomorphologic structures. In this study, we mainly focus on the crustal response to stress perturbations due to the Tohoku-oki earthquake based on the dense GNSS observation over the last two decades. Then, we consider the constitutive relations of the NKTZ from the relationship between localized inelastic deformation and stress change.
In this study, we analyzed the daily coordinates of GNSS sites from 1999 to 2021 provided by the Geospatial Information Authority of Japan (GSI). From the temporal change of the localized shortening in the NKTZ based on the GNSS velocity field every 2 years, we cannot see a clear recovery of the localized shortening in the northern parts of the Niigata area in the postseismic period. That implies the possible stress dependency of localized deformation because the northern parts are closer to the source region of the Tohoku-oki earthquake and have experienced a large coseismic stress drop. Thus, to investigate the macroscopic crustal response to stress change, we separated the observed strain into elastic and inelastic components based on the deformation in the E-W direction. Assuming that the eastern edge of the study area (outside of the NKTZ) is an elastic body, we evaluated the stress change in that area from the elastic deformation at the eastern edge. As a result, the persistent localized contraction in the NKTZ before and after the Tohoku-oki earthquake can be separated as an inelastic component. In addition, from the relationship between strain rate and stress change before and after the Tohoku-oki earthquake, the inelastic strain rate in the NKTZ seems to be variable depending on the stress change due to the large earthquakes. Therefore, assuming the simple linear viscosity as an inelastic element, the viscosity of the NKTZ can be estimated to be about 1019~1020 Pa·s from the slope of the strain rate-stress change diagram.
In conclusion, we demonstrate the potential to investigate the crustal mechanical properties based on spatiotemporal variations of crustal deformation observed by the dense GNSS network. The continuous GNSS observation can contribute to further understanding of constitutive relations from the temporal change of strain rate-stress relations.
In this study, we analyzed the daily coordinates of GNSS sites from 1999 to 2021 provided by the Geospatial Information Authority of Japan (GSI). From the temporal change of the localized shortening in the NKTZ based on the GNSS velocity field every 2 years, we cannot see a clear recovery of the localized shortening in the northern parts of the Niigata area in the postseismic period. That implies the possible stress dependency of localized deformation because the northern parts are closer to the source region of the Tohoku-oki earthquake and have experienced a large coseismic stress drop. Thus, to investigate the macroscopic crustal response to stress change, we separated the observed strain into elastic and inelastic components based on the deformation in the E-W direction. Assuming that the eastern edge of the study area (outside of the NKTZ) is an elastic body, we evaluated the stress change in that area from the elastic deformation at the eastern edge. As a result, the persistent localized contraction in the NKTZ before and after the Tohoku-oki earthquake can be separated as an inelastic component. In addition, from the relationship between strain rate and stress change before and after the Tohoku-oki earthquake, the inelastic strain rate in the NKTZ seems to be variable depending on the stress change due to the large earthquakes. Therefore, assuming the simple linear viscosity as an inelastic element, the viscosity of the NKTZ can be estimated to be about 1019~1020 Pa·s from the slope of the strain rate-stress change diagram.
In conclusion, we demonstrate the potential to investigate the crustal mechanical properties based on spatiotemporal variations of crustal deformation observed by the dense GNSS network. The continuous GNSS observation can contribute to further understanding of constitutive relations from the temporal change of strain rate-stress relations.