Marine seismic observation of internal solitary wave packets in the northeast South China Sea

Abstract

Recently the novel seismic oceanography method has been reported to be an effective way to study the energetic internal solitary waves (ISWs) in the northern South China Sea. An optimized seismic‐oceanographic cruise was carried out to observe such near‐surface ISWs on Dongsha Plateau in July 2014. Several soliton trains rather than single solitons were captured using the seismic technique. After seismic data processing, one prototypical rank‐ordered ISW packet on northeast side of Dongsha Island was clearly identified for further analysis. This included waveforms, propagation velocities, and vertical velocities for individual solitons. In this study, an improved scheme was applied to derive the transient phase velocities from the seismic data which is verified from independent satellite and hydrographic data. Analytical predictions from Korteweg‐de Vries equation fit better than the extended Korteweg‐de Vries equation ignoring background currents. Our results show that the seismic method can be successfully used to image targets in shallow water below 40 m and that seismic oceanography is a promising technique for studying near‐surface phenomena with high spatial resolution.

A Locally Generated High‐Mode Nonlinear Internal Wave Detected on the Shelf of the Northern South China Sea From Marine Seismic Observations

“…There should be a fourth NIW event after the third packet (NIW_R) during the spring tide period (Tang et al, ). This subsequent NIW, however, is not evident neither on the seismic image nor the satellite image.…”

“… Note . NIW_14 and NIW_15 are the waves present in Tang et al (), respectively. NIW_R is the leading soliton of the remotely generated packet (Figure c).…”

“…The missing low-frequency component hampers the accurate derivation of absolute values of the water parameters. Zhao et al, 2004;Tang et al 2015). The black box outlines the study region enlarged in Figure 8.…”

“… Bathymetry map of the northeastern South China Sea. Orange curves are the surface spread of satellite‐imaged NIWs (extracted from Zhao et al, ; Tang et al ). The black box outlines the study region enlarged in Figure 8.…”

“…The conventional marine multichannel seismic (MCS) imaging technique used for studying the Earth's lithospheric structures is a preferential approach that has been proven to be suitable for detecting NIWs (Tang et al, 2014(Tang et al, , 2015(Tang et al, , 2016. Seismic oceanography (SO) was first proposed by Holbrook et al (2003) and has been widely employed to investigate a variety of oceanic phenomena including eddies (Biescas et al, 2008;Pinheiro et al, 2010), currents (Tsuji et al, 2005), internal waves (Holbrook & Fer, 2005), staircases (Biescas et al, 2010;Fer et al, 2010), Kelvin-Helmholtz (KH) instability , and turbulence (Holbrook et al, 2013;Sheen et al, 2009).…”