Seismic impedance
= Seismic impedance
{title2=$Z=\rho\beta=\sqrt{\rho\mu}$}
For a one-dimensional shear <elastic wave>, the <seismic impedance> is the magnitude of the ratio of <stress> to particle <velocity> in a progressive wave. With the positive coordinate aligned with <elastic wave> propagation and tension-positive <stress>, $\sigma=-Zv$ for the forward wave and $\sigma=Zv$ for the backward wave. Its instantaneous <elastic-wave energy flux> is $-v\sigma$.