9:15 AM - 9:30 AM
[SSS05-12] Changes in fluid pressure during seismic cycles from geological constraints
★Invited Papers
Keywords:Stress inverse analysis, Fluid pressure, Mineral veins, Subduction zone
Fluids play key roles in deformation and mass transfer along subduction plate interfaces. In particular, fluid pressure along décollement has a significant effect on slip behaviors in subduction zone. Recent studies have quantified of changes in fluid pressure during a part of seismic cycles in seismogenic zones from geological evidences in exhumed accretionary complexes (e.g., Otsubo et al., 2020, Hosokawa and Hashimoto, 2022). However, there did not fully capture the changes in fluid pressure during seismic cycles. Therefore, the purpose of this study is to quantify the changes in fluid pressure during seismic cycles in seismogenic zones. We studied with the extension veins related to a mélanege formation and an underplating thrusting in the Mugi mélange, the Cretaceous Shimanto Belt, SW Japan.
The Mugi mélange is composed mainly of sandstone and black shale. In this study, we used the extension veins related to the mélange formation observed only in the mélange blocks (Type 1 vein) in the Mugi mélange. We also used the other extension veins are related to underplating consisting mainly of basalt rocks. In the mélange just above the fault zone, the extension veins cutting the mélange structures show a network texture. The network veins cut each other, suggesting that the development of the veins was repeated in multiple stages.
We employed the method of Hosokawa and Hashimoto (2022) to constrain the fluid pressure ratio during mélange formation. We used mixed Bingham statistics (Yamaji, 2016) to estimate the paleo-stress state and driving fluid pressure ratio (P *) for Type 1 vein. P * is defined as the maximum fluid overpressure normalized by differential stress (Otsubo et al., 2020). We constrained the rock tensile strength and the formation depth, using the rock failure theory and the fluid pressure variations. Furthermore, we can calculate fluid pressure ratio with the method.
Furthermore, we propose a new method to constrain the differential stress during the network vein formation. We classified based on stress regime from the orientations of network veins, and calculated normalized over fluid pressure ratio. Normalized over fluid pressure ratio is defined as the fluid overpressure normalized by differential stress for each network vein. Fluid temperature and pressure for each network vein were estimated by the fluid inclusion microthermometry. We can constrain the differential stress during the network vein formation, using vertical stress and rock tensile strength (Hosokawa and Hashimoto, 2022), normalized over fluid pressure ratio and fluid pressure from fluid inclusion. Using these results, we constrain fluid pressure ratio and differential stress at the time of a seismic event to be about 0.7-0.9 and about 22.9-77.8 MPa, respectively. We also constrain maximum dynamic fluid pressure rise during seismic events and maximum fluid pressure drop after seismic events to be about 38 MPa to be 1.15 of fluid pressure ratio and about 67 MPa to be 0.7 of fluid pressure ratio, respectively.
We constrained the range of differential stress for a seismic event, then change in fluid pressure during seismic cycles by quantifying the fluid pressure ratio during mélange formation and differential stress during the network vein formation.
References
Otsubo et al., 2020. Sci. Rep.
Hosokawa and Hashimoto, 2022. Sci. Rep.
Yamaji, 2016. Island Arc.
The Mugi mélange is composed mainly of sandstone and black shale. In this study, we used the extension veins related to the mélange formation observed only in the mélange blocks (Type 1 vein) in the Mugi mélange. We also used the other extension veins are related to underplating consisting mainly of basalt rocks. In the mélange just above the fault zone, the extension veins cutting the mélange structures show a network texture. The network veins cut each other, suggesting that the development of the veins was repeated in multiple stages.
We employed the method of Hosokawa and Hashimoto (2022) to constrain the fluid pressure ratio during mélange formation. We used mixed Bingham statistics (Yamaji, 2016) to estimate the paleo-stress state and driving fluid pressure ratio (P *) for Type 1 vein. P * is defined as the maximum fluid overpressure normalized by differential stress (Otsubo et al., 2020). We constrained the rock tensile strength and the formation depth, using the rock failure theory and the fluid pressure variations. Furthermore, we can calculate fluid pressure ratio with the method.
Furthermore, we propose a new method to constrain the differential stress during the network vein formation. We classified based on stress regime from the orientations of network veins, and calculated normalized over fluid pressure ratio. Normalized over fluid pressure ratio is defined as the fluid overpressure normalized by differential stress for each network vein. Fluid temperature and pressure for each network vein were estimated by the fluid inclusion microthermometry. We can constrain the differential stress during the network vein formation, using vertical stress and rock tensile strength (Hosokawa and Hashimoto, 2022), normalized over fluid pressure ratio and fluid pressure from fluid inclusion. Using these results, we constrain fluid pressure ratio and differential stress at the time of a seismic event to be about 0.7-0.9 and about 22.9-77.8 MPa, respectively. We also constrain maximum dynamic fluid pressure rise during seismic events and maximum fluid pressure drop after seismic events to be about 38 MPa to be 1.15 of fluid pressure ratio and about 67 MPa to be 0.7 of fluid pressure ratio, respectively.
We constrained the range of differential stress for a seismic event, then change in fluid pressure during seismic cycles by quantifying the fluid pressure ratio during mélange formation and differential stress during the network vein formation.
References
Otsubo et al., 2020. Sci. Rep.
Hosokawa and Hashimoto, 2022. Sci. Rep.
Yamaji, 2016. Island Arc.