Abstract:Drilling into the MohoroviAcˇiAc' discontinuity (Moho) has always been a human dream. The deep seabed is the closest place to the Moho on Earth. At present, some studies speculate that the South China Sea is one of the shallowest part of the Moho in the world, but there is a lack of sufficient direct evidence.Deep reflection seismic detection can directly reveal the structural form of the lithosphere and is an important means of Moho detection.Based on interpretation, processing, mapping and analysis of the 15000 km deepreflection multichannel seismic profiles and existing research, this paper has formed a preliminary understanding of the reflection characteristics and spatial distribution of the Moho in the South China Sea basin (SCSB). (1) The southern part of the eastern subbasin experienced rapid expansion in the early stage, with sufficient magma supply and little influence of magmatic activity after the expansion stopped. The basement is flat, and the geological structure is relatively simple. At the same time, there is no abnormality in the seismic velocity structure of the oceanic crust, and there are strong wideangle Moho reflection waves and identifiable mantle top refracted waves, which meet the basic conditions for Moho drilling. (2) The intensity of Moho reflection in different regions of the SCSB varies greatly. Among them, the Moho surface reflection in the East subbasin is the strongest and clearest, followed by the Northwest subbasin, while the South west subbasin has only sporadic clear Moho reflections, and the reliability is not high. (3) This study identified the Moho seismic reflection over 3500 km in the SCSB, and formed the spatial distribution map of the Moho seismic reflection in the depth region of the basin for the first time. Compared with the Moho depth obtained by gravity inversion, the Moho depth calculated by deep reflection multichannel seismic is richer in details, and the structure of the Moho can be clearly depicted in vertical direction. On the whole, among the areas with strong Moho seismic reflection and high reliability in the SCSB, the southern part of the East subbasin is one of the areas with shallower Moho, with the shallowest area only about 9.5 km (among them, the water depth is 4. 01 km and the thickness of the ocean crust is only 5. 54 km). Based on comprehensive judgment, the southern part of the East subbasin is an important Moho drilling candidate area in the South China Sea, which is of great significance to the selection of the Moho drilling site.