Static corrections in mountainous areas using Fresnel-wavepath tomography

•A Fresnel-wavepath tomography is developed to build 3-D near-surface velocity models.•Optimal relaxation factors are proposed to enhance the convergence of a revised SIRT.•The traveltime residuals of the tomography are decomposed into short-period statics.•Combining tomographic models with decomposition of the residuals improves statics.

We propose a 3-D Fresnel-wavepath tomography based on simultaneous iterative reconstruction technique (SIRT) with adaptive relaxation factors, in order to obtain effective near-surface velocity models for static corrections. We derived a formula to calculate the optimal relaxation factor for tomographic inversion to increase the convergence rate and thus the efficiency of the Fresnel-wavepath tomography. A forward method based on bilinear traveltime interpolation and the wavefront group marching is applied to achieve fast and accurate computation of the wavefront traveltimes in 3-D heterogeneous models. The new method is able to achieve near-surface velocity models effective in estimating long-period static corrections, and the remaining traveltime residuals after the tomographic inversion are used to estimate the short-period static corrections via a surface-consistent decomposition. The new method is tested using 3-D synthetic data and 3-D field dataset acquired in a complex mountainous area in southwestern China.