Cross-well seismic tomographic delineation of mineralization in a hard-rock environment

Seismic first-arrival times from a cross-well experiment are inverted by an iteratively reweighted least squares method for the velocity distribution between boreholes. The inversion is carried out in a multiresolution manner in which long wavelength features are reconstructed first and short wavelength features are gradually introduced into the solution model. As such, the inverse problem is overdetermined at the beginning and becomes mixed-determined as the constraint on the solution is relaxed. The reconstruction procedure is independent of the initial model and very robust. An accurate and efficient first-break traveltime calculation scheme is employed to eliminate the possibility of phase mismatches, which can arise with traditional ray shooting or bending methods. Shot static delays are included with the model parameters as unknowns and are recovered simultaneously with the velocity distribution.