日本地球惑星科学連合2014年大会

講演情報

ポスター発表

セッション記号 S (固体地球科学) » S-SS 地震学

[S-SS30_29PO1] 海溝型巨大地震の新しい描像

2014年4月29日(火) 18:15 〜 19:30 3階ポスター会場 (3F)

コンビーナ:*金川 久一(千葉大学大学院理学研究科)、古村 孝志(東京大学大学院情報学環総合防災情報研究センター)、小平 秀一(海洋研究開発機構 地球内部ダイナミクス領域)、宍倉 正展(産業技術総合研究所 活断層・地震研究センター)

18:15 〜 19:30

[SSS30-P23] モンモリロナイト―石英ガウジの摩擦挙動に及ぼす剪断変位と断層組織変化の影響

*河合 智章1堤 昭人1 (1.京都大学大学院理学研究科)

キーワード:モンモリロナイト, 摩擦実験, 断層組織

Recent observation of the low frequency earthquakes in the shallow part of the Nankai subduction zone has demonstrated that faulting there is slow yet seismic; suggesting that frictional velocity dependence along the fault would be negative. However, in a widely accepted model, sediments there is expected to exhibit velocity-strengthening frictional behavior. We have reported that the fault material along the megasplay fault in the Nankai Trough exhibited both velocity-strengthening and velocity-weakening frictional behavior [Tsutsumi et al., 2011]. Fault zone structures may be important to understand why the samples exhibited different velocity dependence. In this study, we have conducted frictional experiments on artificial gouges composed of montmorillonite and quartz mixtures, in order to understand the relationship between the fault zone structures and velocity dependent frictional behavior.
We examined frictional behavior and fault zone structure of the artificial gouge samples composed of montmorillonite/quartz mixtures. All of the experiments were conducted under water-saturated conditions at 1 to 5MPa of normal stress, with shear displacement of 30 mm to 14 m, using a rotary-shear friction testing machine. Velocity step tests were conducted in a range of velocities from 0.003mm/s to 30 mm/s, in order to examine velocity dependent frictional behavior.
Results of these experiments reveal influences of normal stress and displacements on frictional behavior. Velocity weakening behavior was observed for the mixtures of montmorillonite/quartz = 20/80 and 40/60 wt%, respectively, at large displacement. In velocity-weakening samples, montmorillonite becomes to be finer-grained and is well mixed with quartz in the gouge layer after long shear displacements and at high normal stresses. These observation demonstrates that frictional behavior of the montmorillonite/quartz gouge changes with the development of the deformation structures. It is suggested that fault zone structure is one of the important factors of describing the frictional behavior along faults at the Nankai Trough.