Evaluation of the horizontal-to-vertical spectral ratio method for marine subsurface assessment under ocean-bottom currents

Abstract

Understanding the characteristics and long-term stability of shallow submarine geological structures is a key challenge in marine engineering geology. The horizontal-to-vertical spectral ratio (HVSR) method offers a promising approach to addressing this challenge. However, unlike terrestrial environments, marine settings are influenced by dynamic factors such as ocean currents, whose potential impacts remain unclear. In this study, we conducted laboratory flume experiments to analyse the noise characteristics generated by currents at different velocities and their effects on HVSR spectral curves and directional features. Combined with in-situ seafloor observations, we assessed the applicability of the HVSR method in marine engineering geology. Results showed that currents amplified HVSR spectral amplitudes in the low-frequency range (<1 Hz) and that the direction of maximum HVSR amplitude was approximately orthogonal to the direction of flow. This phenomenon reduced the maximum resolvable thickness for HVSR-based stratigraphic interpretation and affected the determination of subsurface interface geometry. Additionally, temporal variability in currents interfered with the detection of long-term changes in sediment stability. To mitigate these effects, we recommend optimising sensor deployment through shielding or buried ocean bottom seismometer configurations and integrating time–frequency analysis with concurrent flow-field monitoring to identify stable observation windows. This study systematically demonstrates how seafloor currents influence HVSR calculations, providing a theoretical basis and technical support for geological hazard mitigation in marine engineering applications, including methane hydrate extraction and ocean drilling.