Comparison of ray- and adjoint-based sensitivity kernels for body-wave seismic tomography

We compare finite-frequency sensitivity kernels computed from ray-theoretical wavefields ("banana-doughnut" kernels) and from full waveform computations (often called "adjoint" kernels) in order to evaluate resolution, accuracy and computational cost. We focus here on body-wave seismic tomography at regional and local scales. Our results show that: (1) for homogeneous reference media, ray-based and adjoint kernels agree except for the expected differences in the regions close to the source and the receiver, where near-field contributions are neglected in the ray-based kernels; (2) for a smooth 3D background velocity model, the differences in predicted delay times for the two methods are generally well below 10 % of the delay for P waves, though as much as 20 % for S-waves, suggesting that extra care should be taken when performing S-wave tomography with ray-based "banana doughnut" kernels.