ANALYSIS ON DEEP CRUSTAL STRUCTURE ALONG THE ONSHORE-OFFSHORE SEISMIC PROFILE ACROSS THE BINHAI (LITTORAL) FAULT ZONE IN NORTHEASTERN SOUTH CHINA SEA
ZHAO Ming-Hui 1,2 QIU Xue-Lin2 YE Chun-Ming3 XIA Kan-Yuan2 HUANG Ci-Liu2 XIE Jian-Bo3 WANG Ping2 1 Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China 2 Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology & Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510301, China 3 Earthquake Administration of Guangdong Province, Guangzhou 510070, China
The onshore-offshore deep seismic experiment was carried out for the first time and filled the blankness of the seismic surveys in the transition area between South China and northeastern South China Sea. The seismic data were analyzed and processed. The different seismic phases were identified and their travel time arrivals were modeled by ray-tracing to study the P-wave velocity crustal structure of this area. The crustal structure of this area is the continental crust. The crust thickness is gradually decreasing southward along the on-shore-offshore seismic line. The low-velocity layer(5.5～5.9 km·s -1)exists generally in the middle crust (about 10.0～18.0km)with about 2.5～4.0 km thickness, which is also thinning seaward. No obvious high-velocity layer appears in the lower crust. The Binhai (littoral) fault zone is a low velocity zone, which is located about 35km southeast to the Nan’ao station and corresponding to the gradient belt of gravity magnetism anomalies. The depth of the fault zone is close to the Moho discontinuity. The littoral fault zone is a boundary between the normal continental crust of South China and the thinned continental crust of the sea area.