日本地球惑星科学連合2023年大会

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[J] 口頭発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG56] 変動帯ダイナミクス

2023年5月26日(金) 10:45 〜 12:00 302 (幕張メッセ国際会議場)

コンビーナ:深畑 幸俊(京都大学防災研究所)、岩森 光(東京大学・地震研究所)、大橋 聖和(山口大学大学院創成科学研究科)、座長:大橋 聖和(山口大学大学院創成科学研究科)、田村 友識(山口大学大学院(現所属:国立研究開発法人日本原子力研究開発機構))

11:45 〜 12:00

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

★Invited Papers

*武藤 潤1、Masuti Sagar2,1、Rybacki Erik2 (1.東北大学大学院理学研究科地学専攻、2.GFZ German Research Centre For Geosciences, Potsdam, Germany)

キーワード:遷移クリープ、下部地殻、グラニュライト、バーガースレオロジー、余効変動

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.
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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 Mw 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.