Clarification of spatial-temporal change of rock permeability and its application to prediction of long-term groundwater flow

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Comprehensive studies including permeability measurement, chemical analysis, microcrack extraction, and characterization of microcrack properties of rocks have been implemented by selecting the Toki granitic body, central Japan as a test site. By integrating the results at site scale with a simulation result of regional 3D fracture distribution, a multi-scale structure of permeability was clarified. The integration suggested that the hydrothermally-altered zones had maintained high permeability for the period of several ten million years, while the gouge-rich fault zone had acted as a water shielding structure. Therefore, the permeability structure of rock body can be considered to be almost the same for the period of several thousand years. Topographic change by weathering and its accompanying change of hydraulic boundary conditions, generation of fractures and cracks by fault movements, and local enhancement of permeability may cause the temporal change in groundwater-flow patterns.