[SCG58-P08] Slip rate dependence of dynamic water permeability for low permeable fault and the role of fluid
Keywords:permeability, friction coefficient, roughness, slow earthquake, thermal pressurization, slip rate dependence
Evolution of fluid transport and mechanical properties of faults by frictional sliding is key to control slow earthquake and dynamic fault rupture. In this study, change of water permeability of simulated faults (granite and dolerite) by frictional sliding at slow (0.1 mm/s) to fast (1 m/s) slip rate with long slip displacements (~1 m) were investigated in laboratory experiments. Rotary shear apparatus was used in the laboratory tests at 2 MPa of normal stress. Elix pure water was used as pore fluid to measure permeability.
Water permeability suddenly increased by sliding to achieve to steady state values. After slip stopped, permeability decreased gradually to initial permeability or below initial values in several ten minutes. Both dynamic permeability and friction coefficient show slip rate dependence that both permeability enhancement and reduction of friction is significant at high velocity sliding. Velocity step change tests confirmed the positive slip rate dependence of permeability. The slip rate dependence is explained by dilation of hydraulic aperture due to frictional heating because pore pressurization and thermal expansion of pore spaces on slip plane are effectively induced by thermal pressurization at high slip rate. The change of water viscosity by frictional heat in part explains the apparent permeability recovery after sliding. The lower dynamic permeability and lower friction of granite than those of dolerite is explained by rich in quartz minerals that polish slip surface strongly to reduce hydraulic apertures.
The laboratory results suggest the importance of permeability evolution on slow to fast earthquake processes; coseismic fault slip induces significant permeability enhancement that fail to occurrence of pore pressurization, whereas temporal small permeability change during slow slip suggests the difficulty in large pore pressure drop.
Water permeability suddenly increased by sliding to achieve to steady state values. After slip stopped, permeability decreased gradually to initial permeability or below initial values in several ten minutes. Both dynamic permeability and friction coefficient show slip rate dependence that both permeability enhancement and reduction of friction is significant at high velocity sliding. Velocity step change tests confirmed the positive slip rate dependence of permeability. The slip rate dependence is explained by dilation of hydraulic aperture due to frictional heating because pore pressurization and thermal expansion of pore spaces on slip plane are effectively induced by thermal pressurization at high slip rate. The change of water viscosity by frictional heat in part explains the apparent permeability recovery after sliding. The lower dynamic permeability and lower friction of granite than those of dolerite is explained by rich in quartz minerals that polish slip surface strongly to reduce hydraulic apertures.
The laboratory results suggest the importance of permeability evolution on slow to fast earthquake processes; coseismic fault slip induces significant permeability enhancement that fail to occurrence of pore pressurization, whereas temporal small permeability change during slow slip suggests the difficulty in large pore pressure drop.