CONVECTIVE INSTABILITIES IN VERTICAL FRACTURES AND FAULTS

Natural convection of water contained in a vertical fracture or fault in which the temperature increases with depth is strongly influenced by the heat transport processes not only within the water itself but also by the heat transferred to and from the surrounding rock mass. The results of a linear stability analysis indicate that the critical Rayleigh number R* is time dependent. For spontaneous neutral stability, R* (t = 0 = 10(h/a)2, where h and a are the fault height and aperture, respectively. Since h is equal to or more than a, R*(0) is several orders of magnitude greater than the value 4 eta2 that would pertain to the same situation without the influence of the surrounding rock masses, e.g., a porous bed with large horizontal dimensions. The resultant cell motion consists of rolls about axes parallel to the aperture. -Author