Appraisal of Joint Refraction and Reflection Travel-time Tomography in the Context of Weathering Correction

We propose an application of joint refraction and reflection travel-time tomography to determine both velocity and thickness of the weathering layer to be used in statics correction. This low velocity layer affects the quality of seismic images. The innovative aspect of our approach is the use of refracted and reflected phases. This remarkably reduces the trade-off between depth and velocity. First arrivals can be automatically picked and the reflection at the layer bottom can be easily identified because of the high impedance contrast with the basement. Synthetic data are generated for a reference model with an acquisition geometry simulating production experiments. The reference model is modified by adding a velocity perturbation and displacing the reflector to create the initial model for the inversion. Travel-time residuals decrease from ~1 s to ~0.1 s and the reflector is recovered to within ±2 m. A Monte Carlo analysis is performed to calculate the mean deviation and its reduction as a measure of the model parameters uncertainty. The improvement (10-50%) is more significant in areas covered by reflections and refractions, while the reflector is again limited to a ~2 m range. We are testing this application with real data.