Shallow crustal permeability enhancement in central Japan due to the 2011 Tohoku earthquake

Pore pressure decreased at the Kamioka mine in central Japan after the Tohoku earthquake (M9.0) on 11 March 2011, which can be attributed to a permeability increase. We focus on the Earth's tidal response before and after the earthquake to evaluate rock permeability change through hydraulic diffusivity change. If we assume a constant elastic modulus, hydraulic diffusivity is found to increase from 3.3 to 6.7m(2)/s after the Tohoku earthquake. We also analyzed data before and after the 2007 Noto Hanto (M6.9) and 2008 Suruga Bay (M6.5) earthquakes, which yield no significant tidal response changes. We examined the amount of dynamic and static stress changes caused by these earthquakes and show that it is difficult to attribute the permeability enhancement solely to dynamic stress, and static stress change may also affect the permeability enhancement.