= SH ray-tube amplitude transport
{c}
{title2=$\rho\beta a^2J=\mathrm{constant}$}
For a leading <wavefront> singularity or discontinuity in a smooth isotropic <shear-horizontal wave> field, the ray transport equation conserves the displayed quantity along a tube of <elastic rays>. Here $J$ is transverse tube width in two dimensions and area in three. Cylindrical spreading has $J\propto r$, so the leading <wave amplitude> is proportional to $r^{-1/2}$. This rule excludes the immediate source neighborhood and <caustics>.
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