3.7 Highlights on Tectonic Regimes and Groundwater Flow with Opportunities to Exercise Knowledge Gained by Reading Sections 1, 2 and 3

The most important implications of the tectonic regimes and fracture patterns (i.e., parallel and conjugate) for groundwater flow in a fracture network are:

• Connectivity and, possibly, the aperture of some fractures, can be enhanced by the generation of faults and joints not simultaneously but in the same tectonic event.
• Flow channels can potentially be formed along fault intersections, being horizontal for thrust and normal conjugate faults, and vertical for strike-slip conjugate faults.
• Hydraulic conductivity (K) of low dip or horizontal fractures, generated in the compressive tectonic regime, is more likely to show a decrease with depth due to the increasing overburden stress of the rock column weight. Thus, the closer to the surface, the more transmissive horizontal or low-dip fractures tend to be. On the other hand, K of vertical fractures, either joints or faults, is likely less affected by depth.
• The structures formed where strike-slip faults overlap (i.e., transpression and transtension zones) provide connection between otherwise non-intersecting faults. At these overlaps groundwater flow may be enhanced by either horizontal or vertical joints in the transpression and transtension zones, respectively.

Thus, understanding how tectonic regimes are related to stress orientation and fracture types is important for a better assessment of groundwater flow paths and the connectivity in fractured media. In order to learn these implications in practical terms, Exercises 8 through 14 provide ways of identifying fracture type based on field data. Additionally, they investigate the relationships between fracture type, tectonic regimes, and fracture orientation.

The information collected in the field and provided by exercises 8 through 14 are: fracture orientation (strike and dip), features observed on fracture faces, fracture patterns (parallel or conjugate), groundwater flow evidence along fracture traces, as well as sketches and photographs of outcrops. These exercises explore a number of topics, such as what evidence of groundwater flow along fractures can be observed in the field; the role of sheeting joints in groundwater flow; the implications of fracture patterns and persistence for the connectivity of the fracture network.

Links to the exercises are provided here: Exercise 8; Exercise 9; Exercise 10; Exercise 11; Exercise 12; Exercise 13; and Exercise 14.