Pseudo-isotropy about the X axis

Completely equivalent results are obtained by switching W₁₁ and W₃₃ wherever they occur. Thus for P waves

(<I>W₁₃I> + <I>W₄₄I>)² = (<I>W₁₁I> - <I>W₄₄I>)² (28)

and for SV waves

(<I>W₁₃I> + <I>W₄₄I>)² = (<I>W₁₁I> - <I>W₄₄I>)(<I>W₃₃I> - <I>W₄₄I>) (29)

and for SH waves

<I>W₄₄I> = <I>W₆₆I> (30)

Note that shear waves, SV or SH, the same condition holds in both the X and Z paraxial approximations.