南海东北部海陆深地震联测与滨海断裂带两侧地壳结构分析

ANALYSIS ON DEEP CRUSTAL STRUCTURE ALONG THE ONSHORE-OFFSHORE SEISMIC PROFILE ACROSS THE BINHAI (LITTORAL) FAULT ZONE IN NORTHEASTERN SOUTH CHINA SEA

南海东北部首次成功实施海陆联合深地震探测 ,填补了海陆过渡带深地震探测的空白 .利用该次海陆联测地震数据 ,通过数据处理、震相分析、射线追踪、走时模拟等方法 ,获得了滨海断裂带附近的纵波地壳速度结构 ,探明了海陆联测剖面中滨海断裂带可能位置 .地壳速度结构为陆壳结构 ,地壳厚度由陆地向海区逐步变薄 ;在上地壳下部普遍存在一层速度为 5 .5～ 5 .9km·s-1、厚度为 2 .5～ 4 .0km的低速层 ,并向海区方向减薄 ,该区未发现明显的高速层 .滨海断裂带为一纵向低速带 ,位于南澳台东南 35km处 ,对应于重、磁异常带 ,断裂带断至莫霍面 ,是华南陆区正常型陆壳与海区减薄型陆壳的分界地壳断裂 .

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.