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The reflected P-wave is propagating only while its normal wavenumber is real, equivalently while $|\sin \varphi |\le 1$. Sinceit is evanescent whenPutThen its spatial factor iswhich decays as $z\to -\infty$. The reflected SV amplitude becomesThe numerator and denominator have equal complex modulus, soThus evanescent mode conversion changes the reflected SV phase but not its amplitude, as described by Unit-modulus SV reflection with evanescent P conversion.