S wave components with polarization direction in the horizontal and vertical planes with respect to the propagation direction of the S-wave ray.The amplitude ratio between the SH and SV component of the S-wave particle motion recorded at a seismic station depends on the slip direction in the double couple source with respect to the take-off angle from the source of the seismic ray arring at the station. For a vertically heterogeneous medium, the SV part of an S wave can be converted into a P wave and vice versa, The SH part of an S wave cannot interact with Pwaves and is usually simpler than the SV part. In an anisotropic medium in which shear-wave splitting occurs SH and SV are coupled, making this classification less meaningful or even useless. shadow zone Distance range along the Earth's surface in which a direct phase is not observed as a result of downward deflection of the ray path by a low velocity zone at depth. See section 2.5.3.3 ??? and Figure 2.30 ??? in Chapter 2 of this Manual, and Lay (2002)