3:30 PM - 5:00 PM
[SCG56-P02] Estimating mechanical properties of the island-arc crust based on time-dependent geodetic deformation data
Keywords:inelastic deformation, constitutive relation of the crust, GNSS
Crustal deformation in the Japan islands mostly accumulates elastic strain energy in the crust and causes devastating earthquakes, while a part of the strain accumulates over time and forms topographic and geologic structures. The former has been contributed to understanding the earthquake cycle in conventional seismological and geodetic studies, but the heterogeneity of the actual crust appearing as an inelastic strain has not been considered. On the other hand, in the recent crustal deformation studies, we use high-precision geodetic observation data, which is obtained as daily coordinates at ~1300 Global Navigation Satellite System (GNSS) stations throughout Japan; Meneses-Gutierrez and Sagiya (2016) revealed persistent inelastic deformation in the short-wavelength deformation field before and after the 2011 Tohoku-oki earthquake (Mw 9.0).
In this study, we try to separate crustal macroscopic mechanical properties into elastic and inelastic one based on the following idea: the observed deformation is the sum of the elastic and inelastic deformation. In general, the deformation of an object is described by the “constitutive relation”, which is an equation relating stress and strain (strain rate). Considering deformation in one dimension, the strain change (Δε) and stress change (Δσ) in elastic deformation can assume linear constitutive relation (Δσ =kΔε) using an elastic constant k. Assuming that stress changes in neighboring areas are approximately equal, the temporal change of strain rates in both areas follows a linear relation; the slope of it equals the ratio of elastic constants. Then, the systematic offset (intercept) of the line is the relative inelastic component when comparing the two areas. By repeating such estimation, the distribution of elastic constants and inelastic deformation can be quantitatively estimated. In the estimation, the most important point is that the 2011 Tohoku-oki earthquake gives us a chance to examine the crustal mechanical response to a large temporal change of the deformation field.
In this study, we try to separate crustal macroscopic mechanical properties into elastic and inelastic one based on the following idea: the observed deformation is the sum of the elastic and inelastic deformation. In general, the deformation of an object is described by the “constitutive relation”, which is an equation relating stress and strain (strain rate). Considering deformation in one dimension, the strain change (Δε) and stress change (Δσ) in elastic deformation can assume linear constitutive relation (Δσ =kΔε) using an elastic constant k. Assuming that stress changes in neighboring areas are approximately equal, the temporal change of strain rates in both areas follows a linear relation; the slope of it equals the ratio of elastic constants. Then, the systematic offset (intercept) of the line is the relative inelastic component when comparing the two areas. By repeating such estimation, the distribution of elastic constants and inelastic deformation can be quantitatively estimated. In the estimation, the most important point is that the 2011 Tohoku-oki earthquake gives us a chance to examine the crustal mechanical response to a large temporal change of the deformation field.