For some reason, a perturbation originates in this central region. From this point the deformation has a wave-like structure which is damped and the wavelength is enlarged. The effect is stronger and sharper in the blue. The wavelength is larger in the red. From the theoretical point of view, several works consider the propagation of corrugation-like waves, differing in the exact nature of the waves and even using different names.
Corrugations are probably a single phenomenon with different assumed simplifying hypotheses.