ROCK DEFORMATION AND FRACTURING PROCESSES DUE TO NONLINEAR SHOCK-WAVES PROPAGATING IN HYPERTHERMAL FLUID PRESSURIZED DOMAINS

An analytical model for rock deformation and fracturing processes due to nonlinear waves of temperature and pressure and evolving with parti cularly 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 Salus ti [1996], the upper fluid-saturated matrix is considered homogeneous, thermoelastic, and isotropic in a one-dimensional formulation. As reg ards the nonlinear wave generation mechanism; at the boundary between the two horizons the hot fluid from below is forced upward by a pressu re gradient, thus giving rise to strong pressure and temperature pertu rbations. In such a context, in order to schematize wave-induced rock deformation and fracturing processes we assume a continuous temperatur e and pressure dependence of model parameters such as fluid diffusivit y and thermal expansivity of the rock and fluid, The solution we obtai n is a strong shock wave corresponding to nonlinear fluid migration me chanisms, in turn enhanced by the flow through the induced fractures i n the overlying rock. It has to be stressed that once such a process s tarts off, it may be amplified and also may produce rather catastrophi c behavior in the natural system. This model essentially provides a th eoretical tool for interpreting such geophysical effects, in particula r for volcanic complexes such as the Rabaul caldera, Long Valley calde ra, Campi Flegrei, the island of Vulcano, or similar kinds of geologic al system.