Coupled Modeling of Gravity and Aeromagnetic Data For Analysis of the Waukesha Fault, Southeastern Wisconsin

Increased concerns recently about the quantity and quality of groundwater resources in Wisconsin have brought about the need for better understanding of the subsurface geologic lithology and structure that controls groundwater flow. Geoscientists, engineers, and community planners often rely on numerical models for groundwater flow to effectively manage this vital resource. These models are typically based on correlating sparse data that are often located large distances apart and are limited in depth. The limited spatial data typically requires simplification of the conceptual model that may add uncertainty to the simulation results and the accuracy of a groundwater model. We propose incorporating potential fields (gravity and aeromagnetic data) modeling into the toolbox of the groundwater modeler to better constrain the conceptual model of a hydrogeologic system. The area near the Waukesha Fault in southeastern Wisconsin provides an excellent research opportunity for our proposed approach because of the strong gravity and aeromagnetic anomalies associated with the fault, the apparent complexity in fault geometry, and uncertainty in Precambrian basement depth and structure. This study will provide a better-constrained subsurface geologic model of the area adjacent to the Waukesha Fault through coupled (simultaneous) modeling of gravity and aeromagnetic data. To our knowledge, coupled modeling of these two potential field data sets simultaneously has not been conducted to date. Strong interest in the Deep Sandstone Aquifer System of southern is prevalent due to extensive drawdown and reduction in groundwater quality. Results from this proposed study may also be useful for evaluating the conceptual model that provided the foundation for the regional groundwater model for southeast. Additionally, with excellent coverage of aeromagnetic and gravity data throughout Wisconsin, successful results from this study would encourage application of potential fields modeling in other groundwater research. Coupled modeling of gravity and aeromagnetic data greatly constrains the possible non-unique solutions that are inherent in any geophysical modeling method. The study will benefit hydrogeologist and groundwater resources managers working in southeastern Wisconsin. In addition, results of this study will illustrate that potential fields modeling is an important tool that can be incorporated into other groundwater studies in Wisconsin.