Waveform tomography of a 2D land data set acquired along a crooked line with rough topography

We apply Laplace-Fourier 2D and 2.5D waveform tomography to a challenging wide-angle land data set from a geologically complex region in Japan. The survey line is crooked (up to 500 m deviation from the 2D line over the 16 km line length), and the area contains significant topographic relief (up to 400 m) and near-surface weathering layers. The lack of reflections previously prevented conventional reflection processing. We demonstrate that 2D acoustic waveform tomography is capable of extracting a reliable velocity model from refractions and wide-angle reflections with carefully designed data-preconditioning and inversion strategies. Sources and receivers are projected onto a 2D plane without preserving offsets: we eliminate traces where errors in offsets are large. We restrict the inversion to phase information at lowest frequencies, and discretize the model with a fine grid, in order to minimize the effects of the crooked line and the topography. We use balanced data amplitudes (using surface-consistent static deconvolution) to conduct the source estimation. We extensively validate the obtained velocity model by comparisons with a well log and observed waveforms, through scrutiny of the resulting reverse-timemigration image. An additional test with 2.5D waveform tomography demonstrates that 2D waveform inversion is adequate for these data.