Elastic-wave-equation traveltime tomography in anisotropic media using differential measurements of long-offset data

Inaccurate source signatures may lead to significant errors in the estimated velocity models obtained using the conventional wave-equation traveltime tomography. We develop a new elastic-wave-equation traveltime tomography method using a double-difference traveltime misfit function to alleviate the impact of unknown source signatures on tomography results. This misfit function is associated with velocity variations around long-offset receiver pairs, reducing the effect of long propagation paths from sources to receivers and thus improving the inversion robustness. In addition, the derivatives of the double-difference misfit function with respect to elastic properties are less sensitive to the errors in the source signature. We verify the effectiveness of our new method using long-offset seismic data to invert for near-surface velocity models in anisotropic media. Numerical results demonstrate that our new method can reconstruct both the P- and S-wave velocity models reliably using incorrect source wavelet for the forward problem.