GPR imaging of a fracture zone in the Vaucluse Karst Aquifer using 2D eikonal inversion D. Van Vorst, M. Yedlin, Y. Guglielmi, F. Cappa, S. Gaffet, M. Maxwell and D. Oldenburg Published online: 18 March 2011 DOI: 10.1051/idust/201101002