Report No. : GEO Report No. 355

Report Title : Updating of Hong Kong Geological Survey 1:20,000-scale Maps Major Findings and Revisions Map Sheet 15 - Hong Kong South and Lamma Island (2022), 34 p.

Author : J.C.F. Wong & R. Shaw

Abstract

In view of the vast amount of site-specific information, and geological knowledge, gained since the first edition 1:20,000-scale geological maps were surveyed and published by the Geotechnical Engineering Office (GEO) between 1986 and 1996, the Geological Survey Section of the Planning Division, GEO has implemented a programme to update the existing 1:20,000-scale geological maps and to release them in both printed and digital form. This will make these geological maps more accessible to the public, and more useful to engineers and planners.

The map updating work is being digitized on a GIS platform using a standard GIS template, and the maps are being published and disseminated in ArcReader format.

Geological Map Sheet 15 - Hong Kong South and Lamma Island, surveyed between 1984 and 1985 and published in 1987, is the second of fifteen 1:20,000-scale geological maps to be updated. The map updating programme gives priority to urban areas. Reliability of the geological maps will be improved after incorporation of the vast amount of new site-specific information that has accumulated, and advances in the understanding of the geology of Hong Kong, since the published maps were first surveyed.

The key findings and revisions to Map Sheet 15 are described in this report. They include: revision of the nomenclature, reinterpretation of onshore and offshore superficial deposits, revised intertidal and backshore deposits and boundaries, updated interpretation of magmatic and volcanic events, and improved accuracy of the locations of concealed major faults and rock type boundaries. In addition, a major improvement to the existing map is the introduction of a solid geology only GIS layer, which depicts the first interpretation of the offshore solid geology based on updated onshore geology, and offshore geophysical and borehole data. Furthermore, additional GIS layers of geological and related information have been compiled.

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