Fig. 6From: Anatomy of phreatic eruptionsHarmonic Tremor at White Island. Harmonic tremor recorded at White Island after a seismic quiescence of 20Â min, and lasting for 8Â h. The fundamental frequency evolves from \(\sim\)Â 0.8 at the onset of the tremor to \(\sim\)Â 1Â Hz when it ends. The frequency of \(\sim\)Â 0.8Â Hz implies a source excitation of \(\sim\)Â 1.3Â s. We used a window of 512 samples with a 25-sample overlap to create the spectrogramBack to article page