About the Biot's second wave.

Abstract

　The Biot's second P-wave is well known as a kind of sound wave that propagates through the fluid in a pore network inside the porous rock. In the Japanese science community, however, researchers lack interest in the second P-wave. This article will show background information about Biot's second wave and the relationships between equations and parameters relevant to waves propagating in porous rocks by solving the elasticity equations of motion for a fluid-solid system. The equation is basically an eigenvalue problem of displacement vectors for fluid and solid. Through an example of the solutions for sandstone, we see the physical characteristics of the second P-wave. The diffusion coefficient in porous rock is derived. The coefficient contains the three bulk moduli; those of drained and undrained conditions, and the Biot modulus. A well-considered experiment demonstrated the second wave is the sound wave.