Slow dynamics under high confining pressure in saturated sandstone with pore pressure.

Slow dynamics (SD) is a time-dependent, nonlinear elastic behavior occurring in a variety of consolidated or damaged materials, including rocks. The influence of relative humidity and confining pressure on SD has been studied but not that of full saturation and effective pressure. We show that SD can occur under high confining pressure in fluid-saturated sandstone if the effective pressure is low enough. This suggests that effective pressure determines whether SD can be observed, explaining why field observations of SD are possible not only near the surface but also in environments with high pore pressure such as fault zones or volcanoes.