渤海海域郯庐断裂带的地震层析成像特征  

Tomographic evidence of the Tan-Lu fault zone in the Bohai Sea of eastern China

作　　者：胥颐[1] 汪晟[1,2] 孟晓春[3] 

机构地区：[1]中国科学院地质与地球物理研究所,中国科学院油气资源研究重点实验室,北京100029 [2]中国科学院大学地球科学学院,北京100049 [3]防灾科技学院,北京101601

出　　处：《科学通报》2016年第8期891-900,共10页Chinese Science Bulletin

基　　金：中国地质调查局项目(GZH201200504; GZH200900504)资助

摘　　要：渤海是连接郯庐断裂带辽宁段和山东段的重要区域,利用地震层析成像方法重建三维P波速度模型,展示了渤海海域地壳和上地幔结构的变化,揭示出郯庐断裂带的深部构造特征以及与构造活动的关系.分析表明,渤海海域的地壳结构存在明显的横向非均匀性:在辽东湾及渤海中部,郯庐断裂带附近的地壳具有双层结构,浅部为低速沉积层,地壳中、下部速度偏高,未见壳内低速层,显示了相对稳定的地壳结构特征,与现今较弱的地震活动相吻合.在渤海南部及莱州湾,郯庐断裂带受张家口-蓬莱断裂带的影响较大,全新世以来的构造活动使得这一地区的地壳结构极为复杂,成为地震活动频繁发生的重要原因之一.此外,渤海海域地壳中、下部和上地幔平均速度偏低,推测与华北克拉通破坏及地幔上涌存在一定的联系.地幔热流物质有可能沿郯庐断裂带形成的通道向上侵入,在地壳底部冷却后形成高速薄层,对于强化壳幔边界、减缓断裂带的构造活动起到了一定作用.The Tan-Lu fault zone is a huge tectonic belt in eastern China. It extends over 3000 km long and passes through the Bohai Sea from the Shandong peninsula in the south to the Liaodong peninsula in the north. Originating from the collision of the North China block with the South China block in Indosinian period, the fault zone had experienced strike-slipping, extensional, compressional deformation and magma intrusions since Mesozoic Era. It is thought to be a continental-scale fault zone that penetrates the crust into the upper mantle. The Bohai Sea links the northern and southern segments of the Tan-Lu fault zone. Its shallow crust is covered by Cenozoic basins and bounded by a series of basement faults. Some faults may be connected to the Tan-Lu fault zone in the deep crust. Geophysically, the Tan-Lu fault zone is a Bouguer gravity boundary that separates negative anomalies in the east and positive anomalies in the west. On the magnetic map, the northern Bohai Sea is characterized by a NNE-trending positive anomaly zone. This magnetic zone becomes scattered in the southern Bohai Sea, with approximately NWW-trending anomalies parallel to the Zhangjiakou- Penglai fault zone. Seismically, most earthquakes are distributed in the southern Bohai Sea, including the Ms7.4 event in 1969; very few of them took place in the northern Bohai Sea. To determine the relationship between the deep structure of the Tan-Lu fault zone and local tectonic activity, we used seismic tomography to construct a three-dimensional P-wave velocity model for the crust and upper mantle of the Bohai Sea. The data were collected from existing seismic stations around the marine area. Compared to previous tomographic studies, the crust and uppermost mantle of the Bohai Sea are well imaged with good resolution. A strong heterogeneity is observed in the crustal structure of the Bohai Sea, which shows P-wave velocity variations correlated to tectonic activity on the Tan-Lu fault zone and the Zhangjiakou-Penglai fault zone. A low-velocity sediment layer

关 键 词：渤海 郯庐断裂带 地震层析成像 地壳和上地幔 速度结构 

分 类 号：P315.2[天文地球—地震学]