AFFECT OF THE SEVIER-TOROWEAP FAULT ON GROUND-WATER MODELING OF THE KAIBAB PAIUTE RESERVATION, NORTHERN ARIZONA

The ability of ground-water models to simulate a flow system varies greatly with the accuracy of the conceptual model. The conceptual model is a graphical representation of the entire flow system. There are many parameters of the flow system that can be described at best within an order of magnitude or two. The geologic framework is one aspect of the model where that variability that can be greatly reduced through accurate analysis of the area.

I am currently working on a project to delineate source water protection areas on the Kaibab Paiute Reservation in northern Arizona. The delineation of these capture zones will be done with a numerical ground-water flow model. In order to accurately create the geologic framework model, detailed geologic mapping of six previously unmapped USGS 7.5' quadrangles was performed: Kaibab, Fredonia, Moccasin, Pipe Spring, Pipe Valley and Clear Water Spring. The structure of the area, as well as the hydrogeology, is dominated by subhorizontal lower Mesozoic strata and the north-south striking Sevier-Toroweap fault. The fault is a steeply west dipping normal fault with a sinuous trace that appears to be due to the overlap and linkage of multiple fault segments. About 1km north of Pipe Spring National Monument, one splay of the fault branches off to the west for 8km. 10km north of the National Monument, the Sevier fault has two overlapping segments with a possible relay ramp between. The only major sources of water in the area are found in the brittle fracture zone associated with the west branch of the Sevier-Toroweap fault. There are several exposures north of the springs along the west branch of the fault that allow the accurate description of the fracture zone associated with the fault. By using such data in the geologic framework of the ground-water model, we can greatly inhance the accuracy and confidence of the model.