Rock deformation and fracturing processes due to nonlinear shock waves propagating in hyperthermal fluid pressurized domains

Abstract

An analytical model for rock deformation and fracturing processes due to nonlinear waves of temperature and pressure and evolving with particularly large velocities in a fluid‐saturated rock over a hyperthermal aquifer is here discussed. As in classical studies by Rice and Cleary [1976], McTigue [1986], and also Bonafede [1991] and Natale and Salusti [1996], the upper fluid‐saturated matrix is considered homogeneous, thermoelastic, and isotropic in a one‐dimensional formulation. As regards the nonlinear wave generation mechanism, at the boundary between the two horizons the hot fluid from below is forced upward by a pressure gradient, thus giving rise to strong pressure and temperature perturbations. In such a context, in order to schematize wave‐induced rock deformation and fracturing processes we assume a continuous temperature and pressure dependence of model parameters such as fluid diffusivity and thermal expansivity of the rock and fluid. The solution we obtain is a strong shock wave corresponding to nonlinear fluid migration mechanisms, in turn enhanced by the flow through the induced fractures in the overlying rock. It has to be stressed that once such a process starts off, it may be amplified and also may produce rather catastrophic behavior in the natural system. This model essentially provides a theoretical tool for interpreting such geophysical effects, in particular for volcanic complexes such as the Rabaul caldera, Long Valley caldera, Campi Flegrei, the island of Vulcano, or similar kinds of geological system.