Determining Small-Scale Fracture Patterns and their Directionality Using Azimuthal Resistivity and 2D Resistivity Profiles in the Yucatán Peninsula

The Yucatán Peninsula is a complex karstic system with a fast-rising tourism sector and local community that faces many growing pains, especially on the East Coast near Cancun. Due to its highly permeable limestone and lack of sufficient soil for filtration, contamination of groundwater from tourism and expanding local populations put the groundwater at significant risk. Part of knowing how to combat these issues is understanding fracture patterns and their influences on groundwater flow. Previous studies have focused on the larger regional fractures and preferential flow pathways. While this data is vital for understanding the broader long-term effects on water supplies, it often overlooks the impacts of localized fractures. This study proposes to gain better insight into the role of small-scale fractures through the implementation of two resistivity survey methods: an Azimuthal Resistivity survey and a Dipole-Dipole tomography. In both cases, an electrical current is discharged into the subsurface via electrodes arranged in precise formats and measured with a resistivity meter. Depending on the array, data will be used to locate, identify, and even visualize the small-scale fractures with Excel and Res2Dinv Software. The Azimuthal Resistivity array is a Wenner type rotated around a central endpoint at predefined angles. This data can then be interpreted after plotting it on a polar graph. Dipole-Dipole Tomography uses a linear structure to collect raw data and generate cross-sections of the earth. With this data, the direction of the fracture can be determined and compared to groundwater flow data to confirm what impact, if any, these smaller-scale pathways have on the local flow of groundwater. Analysis of data collected is currently underway. Measurements were performed at two sites: a field near the cenote(Sinkhole in Spanish) Yum Kin and a soccer field in the town of Agua Azul. Both sites were chosen for their wide, open spaces with substantial soil coverage which provided ideal conditions for the methods used. Moreover, satellite imagery shows that these two may lie atop a single fracture system stemming from the greater Holbox Fracture Zone. The data will be used to locate and identify the small-scale fractures but also visualize them to better understand groundwater flow and potential contamination flow paths.