Surface acoustic wave: retrograde elliptical motion, amplitude decays as e^{-qz}
Rayleigh wave speed: v_R ≈ v_s·(0.862+1.14ν)/(1+ν) where v_s = shear velocity. Depth decay: u_x ∝ e^{-αkz}, u_z ∝ e^{-βkz}. Particle motion is retrograde ellipse near surface, prograde deeper.