Prediction of fracture-induced permeability and fluid flow in the crust using experimental stress data

The results of a series of two-dimensional photoelastic experiments on dila tional jogs cut in PERSPEX(TM) sheets have been used to determine the secon d-order fracture patterns and fluid-flow network associated with tectonical ly loaded dilational jogs. The stress data derived from these experiments, orientation of the principa l stresses, and the distributions and magnitudes of the differential stress and the mean stress are used in combination with the theory of brittle fai lure to predict the orientation, approximate distribution, and likelihood o f formation of second-order brittle structures associated with the modeled jog geometries. The orientations of brittle structures predicted compare favorably with tho se found in natural large-scale dilational jogs, such as the Vienna basin, the Dead Sea basin, and the Brawley jog (California), as well as in mesosco pic examples and those formed in analog models. From the experimental results it is possible to determine areas of high and low mean stress, and by assuming that fluid migration occurs in response t o mean stress gradients it is possible to predict the fluid migration assoc iated with the development of a dilational jog. In this way, it is possible to show that the intrajog region of "underlapping" and "neutral" dilationa l jogs will not be favorable sites for fluid ingress. When the jog has an " overlapping" geometry, the intrajog region is a mean stress low and, conseq uently, fluid ingress into the jog is more Likely. In addition, as the faul t overlap increases the distribution of mean stress, and thus the associate d fluid flow, in the intrajog region increases in complexity.