Permeability Structure of a Strike-Slip Fault

A study was conducted on the Wildcat Fault in Berkeley, CA to develop a methodology for characterizing the hydrologic properties of a fault. The rocks are extensively sheared and fractured. The Wildcat, a strike-slip fault, appears to consist of multiple fault planes. That the exact location of the main fault is still at dispute among participating researchers highlights the fact that it is very difficult to uniquely characterize such a complex fault zone. The hydrologic characteristics of the Wildcat Fault zone suggest a dual nature – with high permeability along the direction of the fault zone and low permeability across it. Data from pumping tests conducted in the high permeability zone along the fault plane exhibit 10:1 near-horizontal anisotropy. The main philosophy behind our overall approach to the hydrologic characterization of such a complex fractured system is to let the system take its own average by conducting large scale tests and conducting long term monitoring instead of collecting a multitude of data at small length and time scales, or at a discrete fracture scale and to "up-scale," which is extremely tenuous at best.