Pattern formation in a vibrated granular layer

We report experiments on a vibrated bidimensional granular layer showing peak pattern formation. We measure the dispersion relation and observe two regimes of pattern selection: at low frequency, a parametric excitation of vertical shearing waves, and at high frequency, a crossover to a pattern selection with a constant wavelength. The amplitude of the patterns is proportional to the amplitude of vibration. We study the instability onset at high frequency and we find evidence of burst waves taking place in a subcritical region defined by two acceleration values.