Quaternary sediment thicknesses, paleochannels and hazard assessment revealed by a dense array in the Guangdong-Hong Kong-Macao Greater Bay Area

The Guangdong-Hong Kong-Macao Greater Bay Area (GBA), a densely populated region, plays a vital role in the economic development of East Asia. The accurate thickness of near-surface loose sediment layers plays an important role in the construction and development of the GBA. However, traditional drilling and active source methods that can obtain this property are often not suitable for large-scale applications in densely populated areas due to their high cost and destructive nature. The ambient noise tomography method based on dense array is an economical and environmentally friendly approach with the advantages of a broad detection range, high resolution and high detection accuracy. Using this approach, a dense array comprising 6214 stations spanning over 60*60 km² was deployed, and the noise horizontal-to-vertical spectral ratio method was employed to determine fundamental frequency (f₀) and peak amplitude. The Quaternary sediment thickness was further estimated based on their empirical relationships with f₀. The comparison with the drilling results shows that our estimation is accurate. More importantly, several buried paleochannels were identified, manifesting deep valleys on the vertical section and curved stripes on the horizontal section. Combining regional drilling data and sites of geological disasters in the past, we conclude that the paleochannels pose the highest risk of seismic and geologic hazards. This study provides scientific basis for urban construction and disaster prevention.