11:00 〜 13:00
[SCG57-P04] Frictional properties of basalt collected from a seamount and implications for earthquake generation
キーワード：海山、沈み込み、摩擦特性、玄武岩
Subducted seamounts are thought to affect seismic faulting along a subduction zone megathrust by increasing the normal stress on the subduction interface and to act as asperities (e.g., Cloos, 1992). There is also a possibility that they act as barriers for rupture propagation due to the large resistance (e.g., Kodaira et al., 2000). On the other hand, recent studies suggested that they may promote creep or slow slip behavior (e.g., Mochizuki et al., 2008). In spite of many studies on subducting seamounts, frictional properties of seamount materials are still poorly understood. In this study, we have conducted friction experiments to determine the friction parameter (a-b) (rate dependence of steady-state friction) and investigated how this parameter changes with temperature and pore pressure.
We conducted friction experiments on gouge of basalt cored from ~200 mbsf (meters below seafloor) of the Takuyo-Daisan Guyot at Site 879 of ODP Leg 144, at a confining pressure of 150 MPa, pore pressures of 50-125 MPa, temperatures of 25-150℃, and axial displacement rates changed stepwise among 0.1, 1 and 10 μm/s, by using a gas-medium, triaxial apparatus installed at Chiba University. Experiments are still preliminary, but the results at an effective normal stress of 50 MPa show that the (a-b) values of the basalt gouge are positive and do not change noticeably at temperatures of ≦50℃. While at 150℃ they become negative, and stick-slip was observed at 1 μm/s. Thus (a-b) value of the basalt gouge likely changes from positive to negative with increasing temperature. Our results suggest that a seamount may be a site of earthquake nucleation at depths with temperatures of ≧150℃. Experiments on the effect of pore pressure, i.e. effective normal stress are in progress, and their results will also be reported.
We conducted friction experiments on gouge of basalt cored from ~200 mbsf (meters below seafloor) of the Takuyo-Daisan Guyot at Site 879 of ODP Leg 144, at a confining pressure of 150 MPa, pore pressures of 50-125 MPa, temperatures of 25-150℃, and axial displacement rates changed stepwise among 0.1, 1 and 10 μm/s, by using a gas-medium, triaxial apparatus installed at Chiba University. Experiments are still preliminary, but the results at an effective normal stress of 50 MPa show that the (a-b) values of the basalt gouge are positive and do not change noticeably at temperatures of ≦50℃. While at 150℃ they become negative, and stick-slip was observed at 1 μm/s. Thus (a-b) value of the basalt gouge likely changes from positive to negative with increasing temperature. Our results suggest that a seamount may be a site of earthquake nucleation at depths with temperatures of ≧150℃. Experiments on the effect of pore pressure, i.e. effective normal stress are in progress, and their results will also be reported.