UTILIZING SURFACE CHARACTERISTICS TO INFER HYDRAULIC CONDUCTIVITY IN THE FAULT ZONE

There have been continuing efforts in recent years to increase the knowledge base of fault permeability, both in the laboratory and in the field. However, in many cases, the analysis cannot be directly utilized in numerical modeling applications due to scaling issues, and similarly, many studies performed at one scale of interest cannot be easily compared to studies conducted at another scale. One possibility to infer hydraulic conductivity in fault zones at a scale applicable to numerical models is through the surface expression of thermal springs. Borax Lake Hot Springs, near the Nevada border in south eastern Oregon, is one location where this procedure can be utilized. Temperature data were taken from thermal springs overlying a left-stepping echelon fault and examined using geostatistical analysis. Sequential Gaussian simulation generated a thermal field representing expected ground water temperature, conditioned on the characteristics of nearby springs. The results indicate that the Borax Lake fault zone consists of a highly heterogeneous, anisotropic permeability structure with a few, discrete areas of high flux, and broad areas of low or no flow capabilities. These findings are in line with those of other investigators, but provide a description of fault hydraulic structure directly applicable to field scale numerical simulation.