渤海东南部深地震探测与地壳结构研究新进展——OBS2013剖面数据处理分析

The new progress of deep seismic survey and crustal structure in southeast of Bohai sea-based on the data processing and analysis of OBS2013 line

OBS2013测线沿NNW-SSE方向跨越渤中坳陷和胶东隆起次级构造以及张家口-蓬莱和郯庐两每深大断裂带。对测线上13个站位折合剖面进行震相分析，识别出丰富的Ps、Pg、PcP、Pn和PmP震柏。通过射线追踪和走时拟合，建立了二维P波速度结构模型。模型将渤海深部速度结构分为6层，最上部两层为新生界，速度由1.8～2.0km／s变化为4.4～4.7km／s，埋深为0.5～7.2km，并向胶东隆起方向逐渐尖灭。向下依次分为上地壳下部、中地壳和下部地壳，地壳速度由5.6～5.9km／s变化为7.0km／s，其中上地壳底芥面埋深11.1～12.9km，中地壳底界面埋深18.0～18.9km，莫霍面在渤中凹陷处埋深最浅为25.5km，向胶东隆起方向逐渐增大叫30km。莫霍面之下上地幔顶部速度为8.0～8.1km／s。渤海下部地壳厚度变化接近5km，从下地壳到上地幔顶部均无明显的大尺度横向速度变化，岩装底侵不发育。结合已有研究成果，推测渤海东南部与华北克拉通中部相比，下地壳厚度减薄9～13.4km，地壳减薄非常有限，具有典型陆壳特征。

The deep seismic survey line using Ocean Bottom Seismometers （OBS） which deployed along NNW-SSE dirction with stretching across Jiaodong uplift, Bozhong depression, Zhangiiakou-Penglai fault zone and Tanlu fault zone, is the third active source deep seismic survey line executed in Bohai Sea. Abundant of seismic phases are identified by analyzing the obtained 13 reducing sections based on wide angle reflection and refraction theory, such as Ps,Pg,PcP,Pn and ProP. A 2D P- wave velocity model along the line is constructed by ray tracing and travel time fitting. The Bohai crustal structure are divided into 6 layers in the model, the upper two layers are Cenozoic sediments whose velocity range from 1.8～2. 0 km/s to 4. 4～ 4.7 kin/s, with a burial depth of 0. 5～7. 2 kin, while the second sendimentary layer comes up with a pinch out in Jiaodong uplift. The deep crustal is divided into 3 layers with a velocity ranging from 5.6～5.9 km/s to 7. 0 km/s by upper and middle crust bottom boundary whose burial depth are respectively 11.1～12. 9 km and 18. 0～18. 9 krn. The Moho has a shallowest burial depth of 25. 5 km in Bozhong depression and gradually deepens to 30 km towards Jiaodong uplift. While beneath Moho, the top of upper mantle has a velocity of 8.0～ 8. 1 km/s. The crustal thickness of Bohai area varies less than 5 km, and large scale velocity anomaly is not detected. Thinking about the former two OBS surveys and previous research results,the thickness of lower crust in southeast of Bohai Sea has a reduction of 9 to 13. 4 km comparing with the middle of North China Craton. Speculating that the lithospheric thinning of Bohai Sea in east of North China Craton mostly happens in lithospheric mantle.