Extension to Threedimensional Problems Concerning an Approximate Correction Method for Refraction in Reflection Seismic Prospecting*

The formulas derived by the author in a preliminary paper for taking into consideration refraction when dealing with the problem of a vertical plane are extended to the three‐dimensional case. Vector analysis is extensively applied. Among others it is shown that in the general case the 3 horizontal twodimensional vectors, i.e. the gradient of the time of reflection the direction of true dip the vector from the shot point to the projection of the reflecting point, point into 3 different directions.