中文摘要：

采用德国SedisIV型海底地震仪（OBS）和中国科学院地质与地球物理研究所自主研发的OBS,以4×24.5L的大容量气枪阵列为震源,于2009年4～6月在南海南部开展了OBS试验,获得了两条勘测线,其中OBS2009-1测线（剖面1）从南海西南次海盆南部陆缘延伸到海盆中央,另一条OBS2009-2测线（剖面2）穿过礼乐滩东部向西北延伸进入海盆。由剖面2的14台OBS采集的广角地震反射、折射勘测地震数据可知,此次试验,OBS地震记录清晰、震相丰富,所使用的气枪有足够的能量输出,显示了其良好的工作能力,是一次比较成功的地震勘测。数据初步处理和初至波层析成像结果表明,礼乐滩地块的基底较高,很有可能与南海北部陆缘存在共轭关系,但与南海北部陆缘不同的是,北部陆缘有较厚的沉积层覆盖,而礼乐滩块体上的沉积层很薄;东部次海盆地壳明显被拉薄,海盆内的地壳也很薄,莫霍面埋深较浅。

英文摘要：

The southern part of the South China Sea（SCS） plays an important role in the evolution of the oceanic basin, but little deep crust structure information has been got in the past because of the limited investigation technology and investigation difficulty in the sea. Many Ocean Bottom Seismometer（OBS） deep sounding experiments for deep crust structure have been carried out in the northern margin of SCS in the recent ten years by Chinese scientists, thus it is good time and chance to do OBS work in the southern part of SCS. During April to June, 2009, under the frame of ＂973＂ project, Ocean Bottom Seismometer（OBS） experiment has been carried out in the southern part of the South China Sea. Scientist and technologist from South Institute of Oceanography of CAS, Second Institute of Oceanography of SOA and Geology and Geophysics Institute of CAS have taken part in the cruise. Sedis IV OBS produced by Germany and 4-channel OBS produced by Geology and Geophysics Institute have been used in the experiment, and the energy source was supplied by 4×24.5 L large volume air-gun. Two high quality profiles have been acquired, profile 1 （OBS2009-1） goes through SW-basin to the southern margin of SCS with 450 km long, while profile 2 （OBS2009-2） goes cross the eastern part of the Liyue Bank with 360 km long. The data of the two profiles can supply evidence for the study of oceanic crust structure of the SW subbasin, boundary of continental crust and oceanic crust and seafloor spreading course, etc.After data processing for the 14 stations of OBS2009-2, we find that the seismic recordings contain various kinds of seismic signals, i.e. P1, P2, PmP and Pn, the longest offset distance is up to 160 km. Seismic phase analysis and first arrival tomography indicate that the basement decreases from the Liyue Bank to SW subbasin. The higher basement of Liyue Bank probable has conjugate relationship with the northern part of SCS, however, the sediment in Liyue Bank is thinner than that in northern part of SCS.