Deepwater guided P waves

Abstract

Seismic velocity inversion of shallow structures in the deep sea is challenging because thick water columns often limit the applicability of conventional inversion techniques. For example, dispersion curves of guided P waves are commonly used for estimating subsurface P-wave velocities in shallow-water environments, where distinct guided P waves can be isolated in waveguides using towed-streamer or ocean-bottom seismometer data. However, these waves are difficult to use in deepwater environments due to interference from subseafloor reflections. In this work, we report the first observation of guided P waves in deepwater environments using towed-streamer seismic data and successfully extract multimode dispersion curves. Synthetic modeling demonstrates that the dispersive modes of deepwater guided P waves are controlled by layered medium beneath the seafloor. The method is further applied to estimate the shallow velocity structures using towed-streamer seismic data from the South China Sea. We theoretically analyze the sensitivity kernel of the extracted dispersion curves to evaluate the detection depth of deepwater guided P waves. The analysis demonstrates that guided P waves can provide a deeper subseafloor imaging capability compared with ray-based refraction methods, particularly when the cable length is limited. In addition, we discuss the applicable water depth ranges and outline the limitations of our method. Analyzing the dispersive modes of guided P waves provides a tool for subsurface structural inversion in deepwater environments.