CONDITIONS FOR THE ONSET OF THERMAL-CONVECTION OF A HOMOGENEOUS FLUIDIN A VERTICAL FAULT

The problem of the onset of free thermal convection of homogeneous flu id in a vertical fault zone localized within a low-permeable rock bloc k is examined for the case of fixed temperatures at the bottom and top boundaries of the fault. The condition for the onset of convection is characterized by critical values of the Rayleigh number determined fr om linear analysis of the fluid instability problem. The results obtai ned indicate that thermal convection can develop in highly permeable f ault zones under a normal geothermal gradient, which makes it possibil e for aqueous fluids derived from the Earth's surface to penetrate int o midcrustal depths.