Abstract
Geophysical studies have revealed Earth’s structure as profiles of physical properties such as seismic velocity and electrical conductivity. Deciphering these profiles to infer constituent materials and their physical states requires a good understanding of physical properties of rocks. In this paper, I review the state of our understanding of seismic velocity and electrical conductivity of rocks in the crust and mantle. It should be noted that materials in the crust and mantle are generally a composite of solid and fluid phases. I summarize the dependence of seismic velocity and electrical conductivity on the properties of solid and fluid phases, the geometry and topology of fluid phases, and the volume of fluid phase. We can use at most three observations: compressional and shear wave velocities and electrical conductivity. It is impossible to decipher observations without a priori information. I summarize a priori information about lithology; physical properties, geometry and topology of fluid phases, and show proposed ways of deciphering. I review geophysical observations around the Japanese islands and their interpretations, focusing on the transport of water in subduction zones. I also summarize properties of serpentinized peridotites. In the last section, I point out problems to be solved: (1) elastic constants of important rock-forming minerals like serpentines, (2) electrical conductivity of crustal materials, (3) nature of crustal fluids, (4) statistical nature of cracks, and (5) elastic anisotropy in a rock where the principal axes of elastic anisotropy due to fluid distribution are oblique to those due to lattice preferred orientation.
