Gaussian beam based finite-frequency turning wave tomography

• A Gaussian beam based method is proposed to calculate sensitivity kernels.
• We validate sensitivity kernels by comparing them with analytical and FD solutions.
• An inversion system based on these kernels is proposed for travel-time tomography.
• This is a wave based method but keeps the simplicity of the ray tomography.

We introduce a Gaussian beam based method to calculate finite-frequency sensitivity kernels and use these kernels in seismic turning-wave tomography. The Gaussian beam summation method has the advantage of high computation efficiency and without any angle limitation. Thus, it is suitable in generating sensitivity kernels for high-frequency, long-distance and wide-angle waves, particularly for turning waves in models with vertical velocity gradient. We first validate the Gaussian beam calculated sensitivity kernels by comparing them with those calculated using analytical and finite-difference solutions. Then, we build an inversion system based on these kernels for turning wave travel-time tomography. The proposed method incorporates the wave phenomena into the inversion, avoiding drawbacks usually encountered by the high-frequency asymptotic method. On the other hand, this method still keeps the simplicity of the ray-based travel-time tomography. The numerical results are used to demonstrate the potential applications of this method in building velocity models using turning waves.