Groundwater flow through anisotropic fault zones in multiaquifer systems

Abstract

Vertical faults through the shallow crust are commonly believed to act as either barriers to horizontal groundwater flow normal to the fault, conduits to horizontal flow tangential to the fault, or a combination of both. In addition, enhanced vertical permeability has been identified as a common feature. We investigate the effects of vertical anisotropy of a fault zone on the distribution of hydraulic head within the fault, using an analytic solution. We conclude that anisotropy ratios greater than 100 result in nearly hydrostatic conditions within the fault zone, despite the existence of significant vertical flow rates. Under these conditions, the Dupuit approximation is adequate for predicting the flow from one side of the fault to the other. We then present explicit analytical solutions to problems of steady groundwater flow in a multiaquifer system cut by a single vertical fault. The fault is linear and of negligible width, is infinite in length, and acts as a conduit for vertical fluid flow. The fault may act as a leaky barrier to horizontal flow normal to the fault, as a conduit to horizontal flow tangential to the fault, or a combination of both. Examples are presented that highlight the effects of enhanced vertical permeability of a fault on aquifer interaction in a multiaquifer system. Particle tracking is used to investigate the effects of the fault on pathlines.