Fault zone hydrogeology

Fault zone hydrogeology is the study of how brittlely deformed rocks alter fluid flows in different lithological settings, such as clastic, igneous and carbonate rocks. Fluid movements, that can be quantified as permeability, can be facilitated or impeded due to the existence of a fault zone. This is because different mechanisms that deform rocks can alter porosity and permeability within a fault zone. Fluids involved in a fault system generally are groundwater (fresh and marine waters) and hydrocarbons (Oil and Gas). Please note that Permeability (k) and Hydraulic Conductivity (K) are used interchangeably in this article for simplified understanding__TOC__ A fault zone can be generally subdivided into two major sections, including a Fault Core (FC) and a Damage Zone (DZ) (Figure 1). The fault core is surrounded by the damage zone. It has a measurable thickness which increases with fault throw and displacement, i.e. increasing deformations. The damage zone envelopes the fault core irregularly in a 3D manner which can be meters to few hundred meters wide (perpendicular to the fault zone). Within a large fault system, multiple fault cores and damage zones can be found. Younger fault cores and damage zones can overlap the older ones. Different processes can alter the permeability of the fault zone in the fault core and the damage zone will be discussed respectively in the next section. In general, the permeability of a damage zone is several orders of magnitude higher than that of a fault core as damage zones typically act as conduits (will be discussed in section 3). Within a damage zone, permeability decreases further away from a fault core. There are many classifications to group fault zones based on their permeability patterns. Some terms are interchangeable; while some have different subgroups. Most of expressions are listed in the following table for comparison. Dickerson's categorisation is commonly used and easier to understand in a broad range of studies. The classification of a fault zone can change spatially and temporally.