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High-resolution seismic reflection profiles and continuously sampled boreholes have been used to investigate the Quaternary offshore sequence that overlies weathered bedrock in Hong Kong. Four formations have been recognized: the lowermost Chek Lap Kok Formation comprises dominantly fluvial sand and mud, much of which probably accumulated prior to 130 000 years BP, during sea-level lowstands of Middle Pleistocene (Oxygen Isotope Stage 6) age and earlier. The upper surface of the Chek Lap Kok Formation is defined by a fluvial/tidal entrenchment surface that is overlain by transgressive, fine-grained, marine sediments of the Sham Wat Formation. These were deposited during the Eemian interglacial (Stage 5c) at a time when sea level was similar to that of today. In southeastern Hong Kong waters, a late Weichselian (Stage 5c) ravinement surface is overlain by submerged shoreface sands, succeeded by a back-stepping wedge of marine sediments that comprise the Waglan Formation. Fluvial/tidal entrenchment of the top of this formation occurred prior to the deposition of the uppermost dominantly marine Hang Hau Formation, deposited during the Late Weichselian to Holocene transgression, the main phase of which is represented by a ravinement surface.

The new Hong Kong Airport at Chek Lap Kok is to be constructed on a 1248 hectare offshore reclamation platform. The design and construction of the airport platform are strongly influenced by the marine geology. A model of the marine geology, as well as a comprehensive understanding of the geotechnical properties of the materials, were essential to the design and construction of the platform and airport structures. 1100 km of seismic reflection survey were carried out to investigate the superficial deposits over the airport site. This was complemented by over 230 boreholes and 400 piezocone tests. This information, along with knowledge of the regional geology, formed the basis for the production of an interpreted 3D digital model of the marine geology.The paper describes the interpretation in developing a consistent model of the marine geology and a framework upon which the engineering decisions can be made. It explains how the seismic interpretation was calibrated using other geotechnical data such as boreholes and penetration tests. The paper makes reference to the engineering decisions that were based partly on the interpretation of the seismics, such as the estimation of settlement and the identification of areas requiring further site investigation. The seismic surveys were also valuable in identifying the more critical areas and horizons in which to install comprehensive suites of instrumentation. It proved a useful and reliable technique in establishing the presence of unconformities linked with palaeosol crusts within the superficial deposits, which had a large effect on the stability of the advancing reclamation tip face.

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