Finite-Frequency Traveltime Tomography for Active-Source Seismic Data

Infinite-frequency traveltime tomography/inversion is the most common approach for modeling active-source wide-angle data. This study-in-progress considers the advantages of using finite-frequency traveltime tomography for active-source data. In theory, finite-frequency methods should provide higher spatial resolution and more accurate recovery of anomaly magnitudes. For active-source data a nonlinear iterative gradient approach is necessary since there is no reference model capable of providing accurate ray or wave paths for a typical dataset. The forward step solves the acoustic wave equation using a finite-difference scheme, and the first-arrival times are determined using a limited amount of manual picking to train an automatic picking algorithm. The inverse step uses Fresnel-zone sensitivity kernels and conventional smoothing regularization. Applications to both synthetic and real high-resolution near-surface data are presented. Preliminary results suggest that regularization and appropriate data fitting act to defeat the potential advantages of the finite- frequency approach. As a result, this study suggests that the precise form of inversion methodology is the critical factor in determining the need for a finite-frequency approach.