11:15 AM - 11:30 AM
[SCG54-09] Frictional properties of incoming sediments and rocks at shallow conditions of the Japan Trench subduction zone
Keywords:incoming sediments and rocks, frictional properties, shallow conditions of the Japan Trench subduction zone
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 (a − b) value (rate dependence of μss) decreases with increasing temperature. (a − b) 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 (a − b) 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 a − b >0 to potentially seismic faulting with a − b <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.
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 (a − b) value (rate dependence of μss) decreases with increasing temperature. (a − b) 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 (a − b) 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 a − b >0 to potentially seismic faulting with a − b <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.