[S-CG56] Dynamics in mobile belts

[SCG56-11] Postseismic deformation in the lower crust and high-temperature transient creep of quartz and feldspar

★Invited Papers

*Jun Muto¹, Sagar Masuti^2,1, Erik Rybacki² (1.Department of Earth Sciences, Tohoku University, 2.GFZ German Research Centre For Geosciences, Potsdam, Germany)

Keywords:transient creep, lower crust, granulite, Burgers rheology, postseismic deformation

Transient crustal deformations, such as post-glacial rebound and postseismic deformation, provide an opportunity to understand the rheological properties of deep Earth, such as absolute viscosity values and their heterogeneity. These comparisons suggest that the upper mantle is generally weaker than the crust. However, depending on time scales, and thermal and tectonic settings, the lower crust can be weaker than the upper mantle (e.g., Ohzono et al., 2012; Moore et al., 2017). In light of this situation, Thatcher & Pollitz (2008) describe that the lower crust has a chameleon-like behavior. Several models have been proposed for the transient behavior of olivine, a main constituent of the upper mantle (e.g., Masuti & Barbot, 2021). Transient creep of the crustal rocks is important to explain time-dependent geological processes such as postseismic deformation following a large continental earthquake. However, the transient behavior of crustal materials is still unknown. Here we show the flow law parameters for both quartz and feldspar using previous experiments of those minerals (quartz by Gleason &Tullis, 1995 and granulite/feldspar by Zhou et al., 2017) uniquely determined using a nonlinear Burgers rheology with Markov chain Monte Carlo (MCMC) method. Modeling results yield that transient creep's stress exponents and activation energies are consistently smaller than steady-state creep for both quartz and feldspar. Combined with the previously obtained olivine results (Masuti & Barbot, 2021), we suggest that the activation energy and stress exponent of transient creep are smaller than those of steady-state creep for all volumetrically important silicate minerals of the crust and upper mantle. Using the estimated flow law parameters of granulite/feldspar and extrapolating to natural conditions, we show the effect of transient creep in the postseismic deformation.

Dhar, S. Muto, J., Ohta, Y. Iinuma, T. (2023 in press) Heterogeneous rheology of Japan subduction zone revealed by postseismic deformation of the 2011 Tohoku-oki earthquake. Progress in Earth and Planetary Science.
Gleason, G.C., Tullis, J. (1995) A flow law for dislocation creep of quartz aggregates determined with the molten salt cell. Tectonophysics 247, 1–23.
Masuti, S., Barbot, S. (2021) MCMC inversion of the transient and steady-state creep flow law parameters of dunite under dry and wet conditions. Earth, Planets and Space 73, 1–21.
Moore, J. D. P. et al., (2017) Imaging the distribution of transient viscosity after the 2016 M_w 7.1 Kumamoto earthquake, Science 356, 163–167.
Ohzono, M., Y. Ohta, T. Iinuma, S. Miura, J. Muto (2012), Geodetic evidence of viscoelastic relaxation after the 2008 Iwate-Miyagi Nairiku earthquake. Earth, Planets and Space 64, 759–764.
Thatcher, W., Pollitz, F. F. (2008) Temporal evolution of continental lithospheric strength in actively deforming regions. GSA Today 18, 4/5.
Zhou, Y., Zhang, H., Yao, W., Dang, J., He, C. (2017) An experimental study on creep of partially molten granulite under high temperature and wet conditions. Journal of Asian Earth Sciences 139, 15–29.