Corrugation model fitted to the Gaia sample. Upper panel: best-fitting double-wave model. The purple points show the mean radial velocity in each radial bin, with error bars indicating the uncertainty of the mean. The red curve represents the best-fitting V_R pattern. The inferred radial displacement ξ_R(R) is shown in blue. Lower panel: same as the upper panel, but using a single-wave model, which fails to reproduce the full structure of the observed V_R pattern.