Shear wave velocity structure in the earth from differential shear wave measurements

Three methods for reducing the effects of systematic errors in the S travel times were used: (1) adjusting observed differential S-P times to account for the effects of ellipticity and hypocentral depth; (2) weighting the equations of condition to reduce the effects of nonrandom distributions of seismographic stations and epicenters on the earth's surface and effects of nonrandom azimuthal distribution of stations and epicenters; and (3) simultaneously estimating azimuthally dependent source and station adjustments along with the cubic spline coefficients which were used to represent the differential S-P travel times. Statistical tests were constructed to determine if the selected stations and epicenters were randomly distributed on the earth's surface. Statistical tests were also constructed to test if the azimuthal distributions of the stations about the epicenters and vice versa are random.