日本地球惑星科学連合2021年大会

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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-CG54] 東北地方太平洋沖地震から10年―固体地球科学の到達点

2021年6月6日(日) 10:45 〜 12:15 Ch.17 (Zoom会場17)

コンビーナ:日野 亮太(東北大学大学院理学研究科)、小平 秀一(海洋研究開発機構 海域地震火山部門)、松澤 暢(東北大学大学院理学研究科附属地震・噴火予知研究観測センター)、飯沼 卓史(国立研究開発法人 海洋研究開発機構)、座長:小平 秀一(海洋研究開発機構 海域地震火山部門)、日野 亮太(東北大学大学院理学研究科)

11:15 〜 11:30

[SCG54-09] 日本海溝に沈み込む堆積物・岩石の沈み込み帯浅部条件における摩擦特性

*金川 久一1、嵯峨野 紗弓2、林 拓真3、藤森 純矢2、澤井 みち代1 (1.千葉大学理学研究院、2.千葉大学大学院融合理工学府、3.千葉大学理学部)

キーワード:沈み込む堆積物・岩石、摩擦特性、日本海溝沈み込み帯浅部条件

In order to examine the frictional properties of incoming sediments and rocks at shallow conditions of the Japan Trench subduction zone, we conducted triaxial friction experiments on gouges of the following samples at a confining pressure of 150 MPa, a pore-water pressure of 50 MPa, temperatures of 25−200℃, and axial displacement rates Vaxial changed stepwise among 0.1, 1 and 10 μm/s. We used hemipelagic and pelagic clay samples cored from the cover sediments on the Pacific plate off Sanriku, a chert sample cored from the footwall of the plate boundary thrust near the Japan Trench, and a basalt sample cored from the oceanic basement of the Philippine Sea plate off Kii Peninsula.

The results show that the steady-state friction coefficient μss decreases with increasing content of clay minerals at a given temperature. Although μss of a given sample does not change noticeably with increasing temperature up to 100℃, it increases with increasing temperature from 100℃ to 200℃, which is more pronounced for samples with higher contents of amorphous silica. Fitting the friction data for each step change in Vaxial by the rate-and state-dependent friction constitutive law reveals that (ab) value (rate dependence of μss) decreases with increasing temperature. (ab) values are positive for all samples at temperatures ≦50℃, while they are negative for all samples at 200℃, where all samples showed stick-slip. However, the temperature at which (ab) value becomes negative increases with increasing content of clay minerals; 50−100℃ for the chert sample, ≈100℃ for the basalt sample, 100−150℃ for the hemipelagic clay sample and 150−200℃ for the pelagic clay sample. This implies that the temperature of transition from aseismic faulting with ab >0 to potentially seismic faulting with ab <0 is different among incoming sediments and rocks according to the content of clay minerals, suggesting that a heterogeneous distribution of seismicity at the Japan Trench subduction zone possibly reflects the heterogeneous distribution of fault-zone materials along the plate boundary megathrust.