Mapping complex fracture systems can be as difficult as mapping termite mounds. An entomologist casts a real 3D model of a termite mound by pumping 600°C aluminum melt into the tunnel system. We use a fast-marching algorithm to simulate the casting process to help the interpretation of the complex geologic features such as fractures and collapse features. In our example, we find that the algorithm is fast, amenable to user interaction, can handle complex geometry, and can implicitly handle bad picks. Our current research suggests good potential to build an interactive tool to map complex 3D surfaces by utilizing volumetric seismic attributes and adapting traditional algorithms of traveltime modeling using the fast-marching method.