New progress of deep crust sounding in the southern margin of the South China Sea using Ocean Bottom Seismometers
WU Zhen-li1,2,3, RUAN Ai-guo3, LI Jia-biao3, NIU Xiong-wei3, LI Xi-bing3, LIU Hong-yang3(1. Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; 2.Graduate University of Chinese Academy of Sciences, Beijing 100049,China; 3. Second Institute of Oceanography, SOA,Laboratory of Submarine Geosciences, SOA,Hangzhou 310012,China)
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.