Abstract
High spatial resolution and deep detection depths of seismic reflection surveying are conducive to studying the fine structure of the internal solitary wave. However, seismic images are instantaneous, which are not conducive to observing kinematic processes of the internal solitary waves. We improved the scheme of seismic data processing and used common-offset gathers to continuously image the same location. In this way, we can observe internal fine structure changes during the movement of the internal solitary waves, especially the part in contact with the seafloor. We observed a first-mode depression internal solitary wave on the continental slope near the Dongsha Atoll of the South China Sea and short-term shoaling processes of the internal solitary wave by using our improved method. We found that the change in shape of waveform varies at different depths. We separately analyzed the evolution of the six waveforms at different depths. The results showed that the waveform in deep water deforms before that in shallow water and the waveform in shallow water deforms to a greater degree. We measured four parameters of the six waveforms during the shoaling including phase velocity, amplitude, wavelength, and slopes of leading and trailing edge. The phase velocity and amplitudes of waveforms in shallow water increase, the wavelengths decrease, and the slopes of trailing edge gradually become larger than that of the leading edge, while the amplitudes of the deep water waveforms do not change significantly and the phase velocities decrease. Our results are consistent with previous studies made by numerical simulations, which suggest the effectiveness of the new processing scheme. This improved scheme cannot only study the internal solitary waves shoaling, but also has great potential in the study of other ocean dynamics.
Highlights
Internal solitary waves are an important oceanographic phenomenon, which affect the marine environment, and affect human activities in the ocean
The observation direction is from southeast to northwest, which is almost the same as the propagation direction of most internal solitary waves near the Dongsha Atoll
We found a first-mode depression internal solitary wave in seismic line Ls
Summary
Internal solitary waves are an important oceanographic phenomenon, which affect the marine environment, and affect human activities in the ocean. The South China Sea is a region where the internal solitary waves are well developed (Zhao et al, 2004; Zheng et al, 2007; Cai et al, 2012; Guo and Chen, 2014) and the shoaling internal solitary waves are often observed on the continental shelf-slope. For this reason, the region is an excellent site to study the interaction between the internal solitary waves and submarine topography. We decided to use this region to develop a seismic data processing scheme that can study the evolution of the internal solitary waves
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