Seismo-acoustic anomalous interference pattern in shallow water

Abstract

In shallow water layered leaky waveguide, the sound energy below the cut-off frequency is coupled to the seismic sound field. Very low frequency (VLF) sound is propagated in both water-borne and bottom-trapped modes. Under these circumstances, the interference characteristics of sound field and its application are different from those of medium and high frequency, which is the subject of this study. In a multi-channel seismic exploration experiment in the South Yellow Sea, an anomalous interference pattern for the VLF band, e.g., the waveguide invariant of interference striations changes from positive to negative with increase of frequency, was observed in the range-frequency domain. Numerical simulations and modal analyses show that the anomalous interference pattern corresponds to the interference between waterborne modes and bottom-trapped modes, because the group velocity for these two types normal modes change differently in the VLF band.