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[J09-P-08] Estimation of the seismic-motion-generated changes in permeability structure nearby a fault fracture zone by means of a groundwater migration model
We report that permeability structure in a fault fracture zone can be changed every time strong seismic motions occur due to great earthquakes, even though the fault itself is not the seismic one.
Groundwater can easily migrate in a fault fracture zone with higher permeability. The permeability is expected to vary due to crustal stress, alteration of the crust and so on. In fact, permeability in the crust nearby Nojima fault, which was one of the seismic faults for the 1995 Hyogo-ken Nanbu earthquake, was reported to have been reduced gradually after the earthquake (Mukai and Fujimori, 2007). It is considered to reflect the recovery process of the fault.
We have continuously observed groundwater discharge and pore pressure as well as crustal movements at Rokko-Takao station in the western Japan. This station was established in a tunnel across Manpukuji fault. The groundwater discharge and the pore pressure had increased just after some great earthquakes apart from this station. A part of these changes was considered to be caused by permeability changes in the fracture zone, which might result from the outflow of mud due to the strong seismic motions.
We had made a groundwater migration model with homogeneous permeability structure to estimate permeability change (Mukai et al., 2016). We applied the observational data of groundwater discharge and pore pressure to the model and could estimate permeability change just after the 2011 off the Pacific coast of Tohoku Earthquake. In this study, we modified the model as considering the effect of heterogeneous permeability structure, and tried to estimate permeability changes due to some great earthquakes such as the 2016 Kumamoto earthquake. We report the characteristics of the permeability changes and a possible mechanism to cause such changes in consideration of the observed crustal movements which were affected by groundwater migration.
Groundwater can easily migrate in a fault fracture zone with higher permeability. The permeability is expected to vary due to crustal stress, alteration of the crust and so on. In fact, permeability in the crust nearby Nojima fault, which was one of the seismic faults for the 1995 Hyogo-ken Nanbu earthquake, was reported to have been reduced gradually after the earthquake (Mukai and Fujimori, 2007). It is considered to reflect the recovery process of the fault.
We have continuously observed groundwater discharge and pore pressure as well as crustal movements at Rokko-Takao station in the western Japan. This station was established in a tunnel across Manpukuji fault. The groundwater discharge and the pore pressure had increased just after some great earthquakes apart from this station. A part of these changes was considered to be caused by permeability changes in the fracture zone, which might result from the outflow of mud due to the strong seismic motions.
We had made a groundwater migration model with homogeneous permeability structure to estimate permeability change (Mukai et al., 2016). We applied the observational data of groundwater discharge and pore pressure to the model and could estimate permeability change just after the 2011 off the Pacific coast of Tohoku Earthquake. In this study, we modified the model as considering the effect of heterogeneous permeability structure, and tried to estimate permeability changes due to some great earthquakes such as the 2016 Kumamoto earthquake. We report the characteristics of the permeability changes and a possible mechanism to cause such changes in consideration of the observed crustal movements which were affected by groundwater migration.