 Seismic transmission coefficient

The transmitted-to-incident amplitude ratio at an interface, with physical variable specified. At normal incidence, stress amplitudes give $T_{\sigma }=2Z_b/(Z_a+Z_b)=1+R_{\sigma }$, while particle velocity gives $T_v=2Z_a/(Z_a+Z_b)=1-R_{\sigma }$. The transmitted energy fraction is $4Z_a{Z}_b/(Z_a+Z_b{)}^2$; amplitude greater than one therefore does not by itself violate conservation of energy.