Exploration of Coastal Zone Noise Characteristics and Shallow Stratigraphic Exploration Methods: A Case Study of Dong'ao Island in Zhuhai

The coastal zone, a critical interface between land and sea, is characterized by intense human activity and development, making it a key area for multidisciplinary research. However, achieving accurate shallow subsurface detection in these areas, including nearshore waters, remains challenging due to limitations in current exploration technologies and the distinct challenges of marine and land-based survey methods. This study tackles this issue by investigating the western coastline of Dong'ao Island, Zhuhai. A network of 22 node seismograph stations were deployed across varied coastal environments—hillside, beach, and seafloor—to systematically analyze seismic ambient noise characteristics in each setting. The research aims to enhance understanding of seismic noise in different coastal contexts, contributing to improved techniques for shallow subsurface detection in coastal zones. Key findings from the analysis can be summarized as follows:

• Submarine stations exhibit higher seismic ambient noise energy levels compared to their hillside and beach counterparts. Dominant frequency bands concentrate within the ranges of 2~10 s and 0.5~0.01 s. Sources of this noise are primarily attributed to mechanical disturbances originating from coastal and offshore maritime activities, alongside anthropogenic influences such as nearby human activities and road traffic. High-frequency seismic background noise greater than 1 Hz in the three environments is rich in information and balanced in signal, which meets the needs of shallow strata imaging in coastal zones.
• Employing F-K inversion techniques, a two-dimensional shear wave velocity profile was successfully generated for the study area, delineating the depth of the basement interface beneath the sedimentary layer. The viability of utilizing ambient noise for probing coastal zones was substantiated via comparison with results obtained from the horizontal-to-vertical spectral ratio (HVSR) method and corroborated by adjacent drilling data. This outcome underscores the potential of passive seismic methodologies for investigating complex coastal geophysical structures.
• To derive high-order mode dispersion curves characterized by energy concentration, comparative experiments were conducted with varying operational parameters for data acquisition. Subsequently, a joint inversion of both high-order and low-order modes was performed, yielding higher-resolution and more accurate velocity structure imaging results beneath the coastal zone.
• The successful acquisition of two-dimensional shallow shear wave velocity profiles in the western coastal zone of Dong'ao Island unequivocally validates the feasibility of employing passive source node seismograph exploration technology to eliminate blind spots in shallow strata exploration within coastal zones. This approach transcends the limitations imposed by traditional exploration techniques, achieving seamless integration of land-to-sea seismic exploration. It is anticipated that this research will furnish robust technical support for engineering projects and resource development initiatives in coastal regions.

This research was granted by the National Natural Science Foundation of China (No. 42106078) and the Guangzhou Science and Technology Plan Project (No. 2023A04J0243).