[S-CG52] 変動帯ダイナミクス

[SCG52-07] 電気伝導度プロファイルは変形強度を反映しているのだろうか？

*渡辺 了¹、一松 駿斗² (1.富山大学学術研究部都市デザイン学系、2.富山大学大学院理工学教育部)

キーワード：地殻、電気伝導度、クラック、流体

Aqueous fluids must play important roles in geodynamic processes including seismic activity. Geophysical mapping of fluids will give us insights into geodynamics. Electrical conductivity profiles have suggested fluids exist pervasively within the crust. Interpretation of geophysical observations requires a thorough understanding of the pore structure that governs physical properties of rocks under high pressure. In the crust, there should be cracks with various sizes: from grain boundary to large faults. Cracks should be a key component of pores to govern seismic velocity and electrical conductivity. Because of their rough surfaces, cracks split into smaller segments under pressure. Crack segments with small aspect ratios are easily closed at low pressure, while segments with large aspect ratios remain open at high pressure. Stiff segments form an interconnected network to govern transport properties of rocks under high pressure. They can explain the observed moderate variation in seismic velocity and large variation in electrical conductivity. Our experiments on cracked rock samples suggest that shear displacement along a crack increases the number of stiff crack segments that remain open at high pressure. Compared with an intact sample, brine-saturated thermally cracked samples show distinctly lower velocity and higher conductivity at high pressure. High pressure electrical conductivity of a brine-saturated rock sample with a through-going fracture increases with increasing shear displacement along the fracture. The variation in conductivity reflects that in the intensity of deformation. Crustal deformation is localized to the observed high conductive regions.