[S-CG62] Rheology, fracture and friction in Earth and planetary sciences

[SCG62-P13] Surface topography of microcracks in granitic rocks and its implication for pressure dependence of elastic wave velocity

*Tohru Watanabe¹ (1.Faculty of Sustainable Design, University of Toyama)

Keywords:microcrack, surface topography, asperity, elasticity

Physical properties of rocks are strongly affected by microcracks. Microcracks have rough surfaces and asperities on them come into contact under pressure. Contacting asperities control mechanical properties, and the resulting space between surfaces controls transport properties. The increase in elastic wave velocity under pressure is caused by the increase in crack stiffness due to the increasing contacting asperities. Our aim is to relate the pressure dependence of velocity to the surface topography of microcracks. We conduct velocity measurements on thermally cracked granitic rock samples (Aji granite, Kagawa Pref.). Based on elastic wave velocities measured under confining pressures, bulk and shear compliances (1/K, 1/G) are expressed as A+B/(p+C), where p is the confining pressure. A is the intrinsic compliance of the solid phase. C is the initial pressure, which describes the pressure state when the confining pressure is zero. B reflects the crack density and surface topography of microcracks. We study the surface topography of microcracks in Aji granite by analyzing SEM images to understand the physical meaning of B.