ANALYSIS OF FAULT NETWORKS USING AIRBORNE ELECTROMAGNETIC DATA IN NORTHERN SHELBY COUNTY, TENNESSEE

The Memphis aquifer, located in the south-central portion of the United States, is a critical groundwater source, providing drinking water to much of western Tennessee. The aquifer primarily comprised of Eocene-age sand, with lesser silt, clay, and lignite. The study area lies within the New Madrid Seismic Zone (NMSZ), a historically active fault zone associated with intraplate seismic activity. This tectonic setting plays a significant role in the structural deformation of the Memphis aquifer and overlying strata, with numerous faults that offset the Eocene strata, potentially affecting permeability and aquifer connectivity. High-spatial-density airborne electromagnetic (AEM) surveys were carried out in northern Shelby County, Tennessee, to delineate subsurface features and characterize the aquifer and aquitard geometry. The AEM data reveal variations in the resistivity that assist in identifying stratigraphic formations that vary in regard to low-resistivity clay and high-resistivity sand content. In addition to resolving resistivity contrasts, AEM profiles reveal offsets and curved geometry in otherwise homogeneous layers, indicating the presence of faults and folds. The offsets, characterized by abrupt changes in resistivity, provide direct evidence of structural displacement in the subsurface. Fault characterization identifies vertical zones of higher resistivity, where sand-rich fault gouge may focus groundwater flow, as well as vertical low-resistivity zones, where clay-rich fault gouge may act as a barrier to flow, potentially compartmentalizing the aquifer. Unlike traditional methods, AEM covers extensive regions, providing a consistent dataset to capture fault continuity and aquifer geometry. This broad-scale analysis helps reduce uncertainties in subsurface models, offering a clearer picture of how faulting influences groundwater movement, aquifer compartmentalization, and recharge areas. These advancements are critical for managing water resources and assessing vulnerability to contamination in faulted and deformed aquifer systems.