【作者】 黄耘；

【导师】 李清河；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理， 2009， 博士

【摘要】 江苏及邻区在大地构造位置上跨越中朝断块区、扬子断块区和昆祁秦断褶系三大一级构造单元。研究区内有切割岩石圈级的深大断裂郯庐断裂,有大别-苏鲁超高压变质带,地质构造非常复杂。本文首先回顾了研究区的地质构造背景,分析了研究区已有的深部结构研究成果,然后采用多种方法系统研究了江苏及邻区的深部结构。本文具有以下几个创新点:1、有效地将双差法和遗传法两种定位方法相结合,第一次对研究区丰富的地震进行重新精确定位,克服了一种方法在精确定位研究上的局限性。通过对大量的精确定位地震的结果分析,获得了研究区地震发生的主要层位、不同大地构造震源深度差异和断裂位置的新认识。2、利用重新精确定位后的地震资料,用走时反演方法获得了研究区较细的地壳速度结构三维成像结果,填补了江苏以东南黄海海域缺乏深部结构研究的空白。3、采用远震体波接收函数方法,研究了江苏及邻区不同构造部位台站下方的深部结构,第一次获得了研究区不同构造块体的岩石圈厚度,为该区地球动力学模型的研究提供了一定的证据。4、通过对三个二级构造单元的各层速度分布、加权RMS速度、莫霍面深度、震源深度以及岩石圈埋深等深部结构进行分析,研究了江苏及邻区大地构造区域的深部结构特征差异。本文研究表明:1.地震定位的精度得到了很大改善,地震在空间上更加集中分布在某些区域,地震震源深度分布结果更加合理。2.下扬子块体江苏段和研究区中的华北块体两个构造单元地震震源深度特点相似,在10～11km、15～17km深处存在二个明显的地震优势分布,推测分别在上地壳底面和中地壳;大别山地区地震的震源深度与下扬子块体和华北块体的地震震源深度存在明显的差异,主要差异为大别山地区lOkm以上的浅源地震十分发育,在6～7km的深处有一地震优势分布,该深度附近可能地震波速度较高。而在10km以下差异不大。3.获得了研究区间距为40×40公里较精细的地壳速度结构三维成像结果,反演结果与精度较高的HQ-13剖面和高淳—南京人工地震剖面做对比分析,结果基本一致,表明我们给出地壳速度结构成像结果精确度较高。4.研究区莫霍面埋深东西差别较大,总体呈现东浅西深,北浅南深。不同的构造单元莫霍面深度有明显的不同。大别山地区莫霍面明显深于周围地区,而华北块体的莫霍面深度总体来看比扬子块体的莫霍面深度浅些。苏鲁断块莫霍面深度和周边地区有所不同,有明显的上隆,深度在32公里左右。5.大地震的发生地点与P波速度异常区有明显的关系,大地震往往不是发生在速度高值区,也不是发生速度低值区,而是发生在速度高值区和低值区的交界部位。地震发生的强度与高速区和低速区的速度梯度大小没有明显的关系。6.远震体波接收函数反演研究结果显示,华北块体和扬子块体的台站下方岩石圈厚度差别不大,约在90多公里,扬子块体岩石圈厚度略大于华北块体;位于郯庐断裂带内部的宿迁台下方岩石圈厚度最薄,为76公罩左右,表明该地岩石圈存在较为明显的上隆现象;大别山地区的合肥下方岩石圈厚度最深,为128公里左右。7、本研究区各构造块体的深部结构差异较明显,大别造山带地壳最厚,震源深度较浅,各层速度和RMS速度最高,岩石圈厚度埋深较深:中朝断块区地壳厚度相对较浅,震源深度较深,各层速度和RMS速度相对居中,岩石圈埋深略浅于扬子块体;下扬子地块地壳厚度比中朝断块区厚,但比大别造山带浅,震源深度与中朝断块区相近,各层速度和RMS速度最低,岩石圈厚度与中朝断块区内的厚度差异不明显,略深于中朝断块。更多还原

【Abstract】 Jiangsu and its adjacent area is located in the intersection of three main blocks: Sino-Korea Block, Yangtze Block, and Qin-Qi-Kun Fold Zone. There are Tanlu Fault extending to Lithosphere, Ultra High-Pressure Metamorphic (UHPM) Belt in Dabie-Su-Lu Orogenic Zone in the reseach area that shows complicated tectonic features.In the paper, the geological background and existing deep structure results are introduced, and the new results about deep structure in the research area are systematically obtained by multi-methods. The innovations in the paper are:1. The earthquakes in research area with both the Hypo-DD and GA methods were relocated. Thus, the limit of using one method can be refrained. By analyzing relocated seismic events, some new results are available, such as focal depths ,the depth differences in different tectonic elements, and the position of interested faults.2. The 3D image results of crustal velocity structure is obtained by traveltime inversion using relocated seismic events, which improves the deep structure research in Jiangsu and southern Yellow Sea.3. On the basis of teleseismic Body-wave Receiver-Function method, deep structures below stations in different tectonic parts are studied. The depth of lithosphere in the research area is available for the first time, which is useful for geo-dynamic research.4. The differences in deep structure of three sub-blocks in research area are analyzed with several parameters, such as respectively interval velocity, weighted RMS velocity, Moho depths, focal depths, and the depths of lithosphere.The main results in the paper are:1. The accuracy of seismic locations is greatly improved by relocating calculation, the seismic events are more focused on some certain areas, and the focal depths are more reasonable.2. The focal depths are similar in Lower Yangtze Block (Jiangsu part) and North China Basin. The events are mainly located in the depths of 10～11km, 15～17km, corresponding to the bottom of upper crust and middle crust respectively. The focal depths in Dabie Orogenic Belt are quite different from another two blocks. The shallow earthquakes (less than 10km) are quite predominate in Dabie Orogenic Belt, especially in the depths of 6～7km, possibly relating to high-velocity area, but the difference is not obvious deeper than 10km.3. The 3D crustal velocity image is obtained in 40×40km. The inversion results are consistent with HQ-13 and Gaochun—Nanjing DSS profiles, which means that the accuracy in the paper is quite good.4. The Moho depths are different from the east to the west, and the Moho depths are shallower in eastern and northern research area, deeper in western and southern research area. The Moho depths are quite different in different tectonic element. The Moho depths in Dabie Orogenic Belt are deeper in surrounding area, while the Moho depths in North China Basin are shallower in Lower Yangtze Block. Sulu sub-block shows obvious differences in Moho depths (about 32km), which is uplifted.5. The position of great earthquake is related to the P velocity abnormality. Great earthquake usually occurred in the transition area of higher and lower velocity, but not in higher or lower velocity. The magnitude of seismic event is not quite related to velocity gradient slope.6. On the basis of teleseismic Body-wave Receiver Function, it is shown that the thickness of lithosphere (about 90 km) in North China Basin is a little less than it is in Lower Yangtze Block. The thinnest lithosphere (about 76km) in the research area is below Suqian station, in Tanlu Fault, which hints that uplift phenomenon is observed. The thickest lithosphere (about 128km) is below Hefei station in Dabie-Su-Lu Orogenic Zone.7. The deep structure is quite different for different tectonic unit in the research area. Dabie Orogenic Belt shows deepest crust, shallow focal depths, highest interval velocity & RMS velocity, and thick lithosphere. Sino-Korea Block shows comparatively shallower crust, deeper focal depths, moderate interval velocity & RMS velocity, shallower lithosphere than Lower Yangtze Block. Lower Yangtze Block shows deeper crust than Sino-Korea Block, shallower crust than Dabie Orogenic Belt, similar focal depths with Sino-Korea Block, lowest interval velocity & RMS velocity, similar lithosphere thickness with Sino-Korea Block, a litter deeper than Sino-Korea Block.更多还原