The theory of poroelasticity-one of the theories addressing deformation-fluid flow coupling processes-which can be used to explain processes occurring in the geosphere, is described. Both undrained and drained conditions are explained in some detail to make it easier to understand both coupled and uncoupled processes under this theory. Then, the following three examples of applications of this theory to earth sciences are presented ; 1. redistribution of strains due to an earthquake and temporal changes of displacement and pore fluid pressure ; 2. pore pressure fluctuations due to cyclic loads such as atmospheric pressure and earth tides ; and, 3. the effects of pore pressure change on in-situ stress in a sedimentary basin. Finally, extending this theory to anisotropic materials is discussed, and the importance of anisotropy under low-effective stress conditions is emphasized.
