10:00 AM - 10:15 AM
[SCG50-05] Experimental investigation on deydration weakening and embrittlement of hydrous minerals and its relationship to the spectrum of slip behavior in subduction zones
Keywords:Hydrous mineral, Serpentine, Frictional property, Earthquake, Subduction zone
The frictional behavior of hydrous minerals dramatically changes during dehydration reaction. For example, within the stability field under hydrothermal conditions, antigorite serpentine, a hydrated mantle mineral, shows velocity-strengthening behavior. In contrast, at conditions above the stability limit, velocity-weakening behavior is observed. Remarkably, slow stick-slip, which has a much longer rise-time and a smaller stress drop than those of regular stick-slip, was observed at temperature close to the stability limit of antigorite.
Recent high-pressure deformation experiments at mantle pressures (>1 GPa) using solid pressure-medium apparatuses show shear localization within antigorite layers within the stability field. Temperature ramping experiments on antigorite show dramatic weakening during dehydration reactions due to the build-up of the pore fluid pressure, while associating with stable weakening (i.e., without rapid stress drop or acoustic emission). The weakening rate during the dehydration reaction is controlled by the temperature ramping rate and the strain rate.
The stability and the slip behavior of faults depend on the effective stiffness of the system and the critical stiffness calculated from the frictional property and the effective normal stress of the fault zone. The effective stiffness of the solid pressure-medium apparatuses (e.g., Griggs-type apparatuses and multi-anvil presses: >104 MPa/mm) is orders of magnitude higher than that of gas pressure-medium apparatuses (~102 MPa/mm) and natural fault systems (<101 MPa/mm). The large difference in the stiffness between the laboratory, especially solid pressure-medium apparatuses, and the natural setting could imply a difficulty to predict the slip behavior of the dehydrating serpentinite.
Shear stress decreases as pore fluid pressure increases during the dehydration reaction, and thus weakening resulted by dehydration also influences the critical stiffness (owing to the change in effective pressure). We calculated the dehydration-controlled critical stiffness Kcdeh, which mainly controlled by the dehydration kinetics and the sliding velocity, at the lab and the natural fault systems. The slip behavior of dehydrating antigorite in the gas apparatus experiments changes from stable sliding to unstable slip (i.e., stick-slip behavior) with increasing Kcdeh from 10-1 to 105 MPa/mm, which range crosses the value of the apparatus stiffness. In contrast, experiments using solid pressure-medium apparatus show only stable fault slip during syndeformational dehydration of antigorite. This difference might arise from the high stiffness of the solid-medium apparatus relative to Kcdeh (101–104 GPa/mm). The complex nature of slip behaviors of antigorite (e.g., seismic slip in the subducting mantle, slow slip at the mantle wedge, and creeping section at San Andreas fault) can be explained by the balance between dehydration kinetics and deformation rate.
Recent high-pressure deformation experiments at mantle pressures (>1 GPa) using solid pressure-medium apparatuses show shear localization within antigorite layers within the stability field. Temperature ramping experiments on antigorite show dramatic weakening during dehydration reactions due to the build-up of the pore fluid pressure, while associating with stable weakening (i.e., without rapid stress drop or acoustic emission). The weakening rate during the dehydration reaction is controlled by the temperature ramping rate and the strain rate.
The stability and the slip behavior of faults depend on the effective stiffness of the system and the critical stiffness calculated from the frictional property and the effective normal stress of the fault zone. The effective stiffness of the solid pressure-medium apparatuses (e.g., Griggs-type apparatuses and multi-anvil presses: >104 MPa/mm) is orders of magnitude higher than that of gas pressure-medium apparatuses (~102 MPa/mm) and natural fault systems (<101 MPa/mm). The large difference in the stiffness between the laboratory, especially solid pressure-medium apparatuses, and the natural setting could imply a difficulty to predict the slip behavior of the dehydrating serpentinite.
Shear stress decreases as pore fluid pressure increases during the dehydration reaction, and thus weakening resulted by dehydration also influences the critical stiffness (owing to the change in effective pressure). We calculated the dehydration-controlled critical stiffness Kcdeh, which mainly controlled by the dehydration kinetics and the sliding velocity, at the lab and the natural fault systems. The slip behavior of dehydrating antigorite in the gas apparatus experiments changes from stable sliding to unstable slip (i.e., stick-slip behavior) with increasing Kcdeh from 10-1 to 105 MPa/mm, which range crosses the value of the apparatus stiffness. In contrast, experiments using solid pressure-medium apparatus show only stable fault slip during syndeformational dehydration of antigorite. This difference might arise from the high stiffness of the solid-medium apparatus relative to Kcdeh (101–104 GPa/mm). The complex nature of slip behaviors of antigorite (e.g., seismic slip in the subducting mantle, slow slip at the mantle wedge, and creeping section at San Andreas fault) can be explained by the balance between dehydration kinetics and deformation rate.