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Abstract. In the Yucatán Peninsula (YP), southern Mexico, cities and towns are settled on a platform of calcareous sedimentary sequence, where karst processes have formed numerous sinkholes, underground water conduits, and caverns. Anthropogenic activities there threaten the only source of freshwater supply, which is in a regional unconfined aquifer; there are no lakes or rivers on the surface. For the sustainable management of this resource in the YP, mathematical tools are needed in order to model groundwater. To determine the geometry of the aquifer, for example the positions of caves, sinkholes, and underground principal conduits, we modified a software to invert three-dimensional electromagnetic low-induction number (3-D EM-LIN) data for a set of profiles at arbitrary angles. In this study we used the EM-LIN geophysical method to explore the Chac-Mool sinkhole system in the state of Quintana Roo, Mexico. We performed inverse modeling in 3-D using the EM-34 instrument for vertical and horizontal magnetic dipoles. The 3-D inversion process yields models that enable us to correlate the path of the underground principal conduits with the subsurface electrical resistivity. In this work we show that inverse modeling of EM-LIN data can give us information about how close to surface the underground water conduits and the location of the boundary between fresh and salty water are.

Abstract.In southern Mexico at the Yucatan Peninsula (YP), cities and towns are settled on a platform of calcareous sedimentary sequence which has originated a wide formation of sinkholes, underground rivers and caverns due of karst 10 process. The anthropogenic activities threat the only source of fresh water supply which is located in a regional unconfined aquifer; there are not lakes and rivers. For sustainable use of these resources at the YP, it is required to develop mathematical tools to help the groundwater modeling. In order to determine the geometry of the aquifer as the positions of caves, sinkholes and underground rivers we have developed software to invert three-dimensional electromagnetic low-induction numbers (3D EM-LIN) data for a set of profiles at arbitrary angle. In this work we have explored with the aid of EM-LIN 15 geophysical method, the Chac-Mool sinkhole system at the state of Quintana Roo, Mexico. We have performed inverse modeling in 3D using the EM-34 instrument for vertical and horizontal magnetic dipoles. The 3D inversion process gives us models that allow us to correlate the path of the underground rivers with the subsurface electrical resistivity. In this work we have shown that inverse modeling of EM-LIN data is necessary to explore and understand coastal karst systems.