Statistical methods for comparing directions to the orientations of focal mechanisms and Wadati-Benioff zones

We propose simple graphical methods for evaluating whether a set of direction vectors are clustered with respect to particular directions, axes, or planes. As examples of these techniques, we present data concerning the relationship between: (1) aftershock/initial event geometry and nodal planes of focal mechanisms; (2) aftershock/initial event geometry and the plane of the Wadati-Benioff zone; and (3) B axes of focal mechanisms and the plane of the Wadati-Benioff zone.