Joint refraction traveltime migration and tomography

Migration and tomography represent two major techniques in state-of-the-art seismic imaging technology. Migration maps interfaces in the subsurface by reconstructing physical raypaths from a downward continuation process, while tomography reconstructs a physical model by inverting recorded data. For interpreting refraction traveltimes, we present two approaches that combine migration and tomography in one joint imaging process in an iterative manner. The slowness parameters on a regular grid can be updated on the basis of fitting traveltimes as well as defining interfaces associated with the migrated traveltime image. The first method, model-interface method, assumes that the migration image corresponds to a slowness discontinuity in the model. Therefore, an a priori curvature constraint is emplaced at the image location by way of Tikhonov regularization. The second approach places a discontinuity in the regularization (Laplacian) operator according to the location of the migration image, thus it is called derivative-interface method. The first method gives a stronger model constraint, while the second one relies more on the data. We demonstrate that both methods are capable of reconstructing a reliable velocity model with sharp features.