Variations in the structures exposed in structural domains associated with faults can affect the amount of ground-water recharge to fractured rock aquifers supplying intermontane-basin aquifers. In the south-western Franklin Mountains, El Paso, Texas, an outcrop of the Ordovician Scenic Drive Formation exposes a group of structures including faults, joints, and folds associated with a left-lateral fault striking N74??E and dipping 81??NW. Slip along this fault has produced a structural domain with extensional structures (normal faults and joints) and a domain with contractional structures (folds and joints). These extensional and contractional domains occur on opposite sides of the fault. Properties of fractures within the different structural domains can influence ground-water recharge and migration. For example, the domain with extensional structures contains nearly vertical joints that extend from the soil-bedrock interface to normal faults and along which precipitation can infiltrate. Since the left-lateral fault is approximately normal to the trend of the Franklin Mountains, this fault may be a conduit for ground-water flow from the mountains to the basin. The domain with contractional structures is limited in extent, and the fractures in this domain are poorly connected. Therefore, surface infiltration in this domain is reduced, and may not contribute as much to ground-water migration. Structural domains that are analogous to this outcrop and cover larger areas can be found throughout the Franklin Mountains. Understanding the variations between structural domains can aid in siting water-supply wells and determining contaminant transport in fractured rock.
Additional publication details
Structural domains and their potential impact on recharge to intermontane-basin aquifers