Photolinears, Fractures, and Fallacies: What Can We Assume About the Structures of ASR Host Strata?

There is a general misconception by some in the geologic, and non-geologic communities, that terms “photolineaments” (or “photolinear”) and fractures are synonymous. This fallacy can be very detrimental to scientific/geologic interpretations. For example, a potable well placed at the intersection of two photolineaments may not be productive and would be a costly error if is not ground-truthed, because aerial interpretation of soil tones, for example, can be easily confused with intersecting deer trails. A photolineament assessment is a screening tool which requires verification prior to any further geologic interpretations or opinions. While in other areas of the country there is a higher correlation between photolinears and fractures/fracture systems, due to the cover materials, thicknesses, and karst in Florida, this degree of correlation does not exist. In the State of Florida, there have been four major regional photolinear assessments. To date, the authors are unaware of any literature references documenting the verification of these aerial interpreted features. This has led to the misuse of these assessments in geologic interpretations. The case study discussed herein describes the verification of a photolinear assessment completed in Hillsborough County, Florida and demonstrates how the misuse of photolinear assessments can impact geologic interpretation.

Keywords: “ground-truthed”, “ground-truthing”, photolineament, photolinear, fractures, fissures, joints, faults, fracture trace, geology, stratigraphy, karst, sinkholes, conduits, ground penetrating radar (GPR), seismic refraction, seismic reflection, standard penetration test (SPT) borings, cone penetrometer test (CPT) soundings, and Hillsborough County, Florida