【作者】 潘军；

【导师】 刘保华；

【作者基本信息】 中国海洋大学 ， 海洋地球物理， 2013， 博士

【摘要】 渤海湾盆地富含油气资源,地壳深部结构和构造演化控制着盆地的形成,进而控制着盆地内油气的生成、运移和聚集；环渤海湾地区经济发达,人口稠密同时又是地震的多发区域,探明深部构造对于研究地震发震机制、提高地震预报准确性,以减少地震灾害造成的人员、财产、经济损失具有重要意义；渤海是华北克拉通东部地块破坏的关键地区,而这种重大基础地球科学问题的解决也依赖于深部构造的研究。因此本文以国家高新技术研究发展计划海洋技术领域重点项目“海陆联合深部地球物理探测关键技术研究”及国家自然科学基金重点项目“渤海及邻域深部结构及其对华北克拉通破坏的响应”为依托,对渤海地区的深部构造进行研究。论文以OBS-2011深地震探测为例,系统总结了深地震探测的原理与技术方法,对深部构造成像进行了研究,主要研究成果如下：(1)根据渤海深部构造研究的目的,详细论证了OBS-2011测线观测系统设计的原理和方法。OBS观测系统设计时遵循炮间距与OBS间距为等间隔设计,且OBS间隔与炮间距成倍数关系的基本原则,这种设计使得观测系统设计较为简单,在资料处理时也更加容易和精确。(2)总结了OBS-2011测线野外施工的基本情况,对OBS数据质量进行对比分析,在此基础上对OBS记录的有效震相进行分析和识别：2011年OBS道集中记录的震相比较丰富,有效震相包括Ps, Pg, PMP, Pn和Ph,但是其信噪比较低。(3)对OBS共反射叠加法和广角反射动校正原理进行研究,利用常速叠加的方式实现对莫霍面的速度分析,渤海地区OBS共反射叠加法成像结果表明：共中心点叠加法在大偏移距和探测目的层很深的情况下获得了较连续的叠加剖面,这也是共反射叠加法在渤海OBS深地震探测中的首次成功应用。(4)在震相识别与分析的基础之上,利用层析成像法反演了渤海2011年OBS测线的二维地壳结构模型,并分析了研究区的地壳结构特征。通过震相对比技术解决了在没有多道地震约束的浅水地区震相识别和对比困难的问题,在背景噪音较大的渤海地区获得了较好的浅层构造。利用层析成像反演获得的新生代基底构造较复杂,整体上渤中凹陷从SSW至NNE方向深度逐渐增大,最大深度为5.8km,而石臼陀凸起处埋深变化较大,中间部位还存在明显的凹陷结构。在37-39号OBS位置处存在明显的高速异常体,其层速度明显高于周围速度。结晶基底大致在10km深度,最浅处在石臼陀凸起处,基底埋深大致在9km附近,速度大致为6km/s。莫霍面埋深在渤中凹陷处明显抬升,深度大致在27km附近,而在石臼陀凸起莫霍面埋深变大,最深可达29.5km,在秦南凹陷和秦南凸起处埋深又变浅,最浅处埋深仅有26.3km。而莫霍面速度横向变化较明显,在27号OBS处存在明显的低速异常。(5)共反射叠加法最终获得莫霍面反射特征,而层析成像方法获得了莫霍面的深度-速度参数,两者从不同角度反映了莫霍面的构造特征,从两者的对比结果看,两种方法所做的莫霍面的构造形态基本一致。从处理角度讲,共反射叠加法的核心在于对叠加速度的选择,处理的基本原则是“速度连续,构造连续”；层析成像法最重要的工作在于震相的正确拾取,处理中主要工作在于不断“试错”以确保震相拾取正确。共反射叠加法在剖面上识别出比较明显的断层；而层析成像由于算法本身的原因难以获得准确的断裂构造。此外层析成像法可以获得相对复杂的地壳深度-速度模型,但同时工作量也较大；而共反射叠加法可直接对莫霍面成像,相对比较简单,但是只能获得莫霍面的构造特征。两者在实际资料处理中可以进行相互补充。(6)3D重力层析成像结果与深地震探测结果趋势上基本一致,但重力层析成像反演结果在精度方面误差较大,深地震探测的方法获得了更为精确的莫霍面构造特征。(7)层析成像反演结果表明在39号OBS对应的新生代基底下存在明显的高速异常,此外,33号OBS下方也存在强度稍弱的高速异常。推测岩浆的侵入可能是造成石臼陀凸起处新生代基底隆升的主要原因。此外岩浆活动可能对于此地区的油气生成也具有一定的促进作用。(8)共反射叠加法和层析成像法两种方法在CMP700附近都存在低速异常。从低速异常与居里等温面的对比结果看,两者存在高度的相关性,由此推测速度变小的原因在于深部强烈的岩浆或其他地热活动产生的高温使得莫霍面的塑性增强而降低了地震波传播的速度。而地热活动较为剧烈则与盆地拉张及地幔上涌的动力学背景有关,也说明了这一地区莫霍面附近地热流偏高。莫霍面附近的低速异常造成的区域应力分布不均匀以及上地幔隆起活动可能与渤海频繁发生的大地震密切相关。(9)莫霍面南北隆起区的对比结果表明北侧隆起区为深部构造活动的稳定区而南部仍旧为现代构造运动比较剧烈的区域。更多还原

【Abstract】 Bohai Bay basin is rich in oil and gas. Deep crustal structure and tectonic evolution control the formation of the basin, which influences hydrocarbon generation, migration and accumulation of oil-gas. The Bohai Bay area is a populated region with economy developed, where the earthquake occurred frequently. It is very important to detect the deep structure for seismogenic mechanism of earthquake which may improve the accuracy of earthquake forecast for reducing casualties, property and economic losses caused by earthquake. Bohai is the critical area of North China craton breaking, and the solution also relies on the study of deep crustal structure.The paper is based on the national high-tech research and development plan "The research on key technology of offshore-onshore deep seismic exploration" and the Key project of National Natural Science Fund "Bohai and neighboring deep structure and its influence on the destruction of the North China Craton response".The paper summarizes the principle and technical method of deep seismic exploration and studies the deep structure imaging which is based on the OBS-2011deep seismic exploration survey.The main research work is as follows:(1) The paper demonstrates the principles and methods of the geometry about OBS-2011line, the OBS geometry follows the principle that the shot spacing and OBS spacing are of equal distance and multiples.(2) The paper summarizes the data acquisition of OBS-2011line, does the contrast analysis on the quality of OBS data, then recognizes the seismic phase of the recorded data.The main phases which are relatively rich include Ps, Pg, PMP, Pn and Ph. however, the S/N ratio is low.(3) The paper demonstrates the CMP stack method and the wide-angle reflection NMO principle. The velocity analysis is based on the constant velocity stack method. Real data processing of Bohai Sea in China demonstrates that this method can depict Moho structure clearly in the condition of large offset and deep target and it is also the first successful application in Bohai Sea.(4) After phase recognition, the paper inverses the2D velocity-depth model of the line using travel time tomography. The phase contrast technology is used to control the shallow phase which achieves better shallow structure. The research found that the Cenozoic basement is complex, it deepens from SSW to NNE in Bozhong Depression and the largest depth is5.8km. In Shijiutuo uplift Cenozoic basement rises sharply, however, a depression exists between the uplift areas. The depth of crystalline basement is about10km, where the shallowest depth is about9km located in Shijiutuo uplift and the velocity is about6km/s.The depth of Moho in Bozhong Depression is about27km, it deepens northwards which the largest depth is about29.5km in Shijiutuo uplift. It rises in Qinnan Depression and Qinnan uplift where the shallowest depth is26.3km.(5) CMP stack method finally obtains the reflection characteristics of Moho while tomography method obtains the Moho depth-velocity parameters.Compared with the two results, the Moho structures are almost the same. From processing perspective, the core parameter of the CMP stack method is the stack velocity which the selection principle is "velocity continuous, structure continuous", the correct phase is the basic work of the tomography and we have to use trial and error to find the reasonable result. Fault of Moho can be recognized by CMP stack method and it is also interesting to notice that the Bohai earthquake with magnitude of7.5was just in this place in1888, however, it is hard for tomography to obtain the fault structure because of the algorithm itself. In addition, the tomography method which the workload is bigger can obtain relatively complicated crustal depth-velocity model; while the CMP stack method which is relatively simple can only obtain Moho structure. The two methods are complemented in actual data processing.(6)3D gravity inversion result and deep seismic exploration results agree basically. However, the gravity inversion result has larger error while deep seismic exploration results obtain more precise Moho structure.(7) The result of the tomography shows that the high velocity anomaly exists clearly below the Cenozoic sedimentary formation under OBS39and OBS33within Shijiutuo uplift along the line.It is concluded that the intrusion of magma results in the rise of Cenozoic basement. In addition, the magmatic activities may also have a certain role in promoting the oil and gas generation.(8) The low velocity anomal of Moho was found by the CMP stack method and tomography which was well constrained with curie iso-geothermal surface and it may be related with the imbalance among temperature caused by mantle plume. Acute geothermal activity is related with the dynamics background of basin extension and mantle upwelling, which also indicates the high heat flux of Moho in this area. The heterogeneity of regional stress distribution adjacent to Moho which may be caused by the low velocity anomaly and upper mantle uplift activities may be associated with the frequent occurrence of large earthquakes in Bohai Sea.(9) Compared with the south uplift area of seismic line, it is concluded that the tectonic activity of the north uplift area is weaker than that of the south uplift area.更多还原