Joint Inversion of P and S Traveltime Tomography Data Using Poison Ratio and Cross-gradient Constraints

In order to maximize the amount of information taken from a seismic tomography survey, P and S-wave travel times can be used under the same joint inversion scheme. In this work two different approaches have been used. The first inverts the two data sets subject to constant velocities ratio constraint, while the second uses the cross-gradients function constraint. In both inversion schemes, additional regularization is used and spatially variable Lagrangian multipliers are applied to the model parameters. The obtained solutions suggest that joint inversion can lead to improved results, stabilize the inversion process for both inversion strategies and reduce the non-uniqueness of the problem. However the constant velocities ratio method can create artifacts and reduce the resolution when P and S-waves velocities are uncoupled and vary independently. Therefore, it can only be applied when reliable a-priori information about the investigation area ensures that the models parameters are linked with a constant Vp/Vs ratio. On the contrary cross-gradient method is more robust and does not require any a-priori information, yet its effectiveness is increased when structural similarities exist.