Non-stationary shear wave statics in the radial trace domain

Raul Cova, David Henley and Kris Innanen

ABSTRACT

Shear-wave statics are one of the main problems in converted-wave processing. The lack of a good correlation between P-and S-wave velocities in the near surface introduces a whole new problem to be solved. Due to its very low velocity values the magnitude of the S-wave statics are several times larger than the P-wave statics, producing a very destructive effect when stacking traces. In this paper it is shown how S-wave statics may also show a non-stationary behaviour. This effect was studied in terms of variations in the transmission angle through the low velocity layer (LVL) due to changes in offset and as a result of the structure of the LVL. An analytic expression for computing deviated travel times through the LVL in terms of its dip, thickness and velocity is proposed here. This expression may be used as the engine for an iterative non-linear inversion algorithm that will allow us to compute velocity models for the near surface given a set of delay times and the ray-path angles associated with them.

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