Abstract: The onshore-offshore seismic exploration in the northern South China Sea has experienced three stages: initial test using old air-gun source, import and improvement of large volume air-gun, and joint receive air-gun signal of land seismic stations and Ocean Bottom Seismometers. These experiments have filled the gaps in deep structure of land-ocean transitional area. The results show that the Binhai Fault Zone is a low velocity zone in the velocity structure, and reveal that the deep seismogenic structure of continental marginal seismic belt along the northern South China Sea is much involved in coupled function of low velocity zone in crustal structure and intersecting faults. The joint onshore-offshore deep seismic prospect links the crusts of land and sea perfectly; it can also construct the ultra long crustal structure profile across from the northern continental margin of the South China Sea and Xisha Block to Nansha Block. These experiments play an important role in revealing the structure of micro-blocks in Nansha Block, deep velocity structure of Nansha Block and its adjacent area, the integrated geophysical structure of Nansha Block and peripheral basin, and the transitional area between landmasses. Meanwhile, these experiments are conducive to know the current structural state and tectonic evolution history of Nansha Block and to interpret split-breakup process of Nansha Block.

Key words: joint onshore-offshore deep seismic prospect, northern South China Sea, crustal structure, Nansha Block