AnisDep: A FORTRAN program for the estimation of the depth of anisotropy using spatial coherency of shear-wave splitting parameters

We present a FORTRAN-77 program to estimate the optimal depth of the source of anisotropy using spatial coherency of teleseismic shear-wave splitting (SWS) parameters. For a given assumed depth of anisotropy, the program computes a variation factor which is a weighted sum of the arithmetic standard deviation (SD) of the splitting times and the circular SD of the fast directions over overlapping blocks. The optimal depth of anisotropy corresponds to the minimum variation factor. The program executes computations over different block sizes for testing the stability of the resulting optimal depth. A synthetic shear-wave splitting data set is provided for testing the program. In addition to anisotropy depth estimation, some of the subroutines in AnisDep can be used for other applications such as computing circular mean and SD of the observed fast directions, and for computing the coordinates of ray-piercing points. The program is designed for Linux and Sun Solaris platforms, but can be easily adapted for other platforms.