CHARACTERIZING FRACTURE NETWORK PATTERNS IN THE TETON ANTICLINE, SAWTOOTH RANGE, MONTANA

Fracture network patterns have been studied for exposures of dolomitic limestones on Teton anticline, in the Sawtooth Range, Montana. GIS-based techniques were used to study the two-dimensional distribution of fractures on exposed bedding planes. A series of eight 100 square meter patches in different structural positions were selected for the study. Individual fracture characteristics, such as fracture length, orientation, and density were analyzed along with pattern of fracture networks. The latter parameter is important in determining whether the fractures are isolated or form an extensive connected pathway. The fracture network size was calculated by summing the lengths of fracture traces in the largest cluster divided by the sum of all fracture traces within the mapped area. Higher cluster size values correspond to greater connectivity for the fracture network.

Four main sets of fractures were found, with two orthogonal sets, approximately parallel and transverse to the anticlinal axis, being the dominant sets. The densities of these different sets of fractures were found to vary considerably between different outcrops. Results showed that the cluster size varies between 0.06 and 0.76, with structural position being one of the important parameters controlling its magnitude. The cluster size was sensitive to the total fracture intensity as well as the variation in fracture orientation. The fracture orientations, lengths and intensities of the different fracture sets in the network were used to successfully simulate fracture maps that mimic the overall network connectivity of the fracture patterns over larger areas.