中国东部及其邻区上地幔顶部Pn波速度结构及各向异性

发布时间：2018-09-03 10:35

【摘要】：中国东部由中国东北地区(中亚造山带东段)、华北克拉通、苏鲁造山带及华南地块构成,地处欧亚板块东南部,紧邻西太平洋俯冲带。受太平洋板块西向俯冲的影响,该区有着复杂的地质构造背景和深部结构特征,研究该区上地幔顶部的结构有助于我们更好地理解在大陆动力演化过程中深部对浅层结构的影响。早期的结果主要应用了来自地震观测报告(中国地震年报及各省区域台网观测报告)的Pn到时资料,最近的研究除了利用地震观测报告的资料外,主要补充了中国西部特别是青藏高原流动地震台阵记录的Pn到时数据,重点研究了中国西部地区上地幔顶部的速度结构和各向异性。本文收集了 ISC (国际地震中心)报告、中国地震年报和中国区域地震台网观测报告的Pn到时资料,并截取了中国东北、华北流动台阵和区域台网记录的地震事件,同时专门挑选了华南地区固定台站记录的该区中小地震事件,由专业人员对这些事件手动拾取了大量高精度的Pn波到时数据,最终挑选出24072次地震的240814条Pn波到时数据,这些数据是由区域内2049个台站记录的。本研究大量数据的应用使Pn射线密集覆盖了整个中国东部地区。我们采用Pn波层析成像方法反演获得了中国东部及其邻区上地幔顶部Pn波速度结构及各向异性,并对反演结果的分辨率进行了详细的测试。结果表明,中国东部地区上地幔顶部平均速度为8.06 km/s,速度变化范围为7.81-8.32 km/s。东北地区东部表现为显著的低速异常,可能是受太平洋板块俯冲的影响并代表长白山火山区上涌的热物质;华北克拉通中、东部Pn呈现低速,而西部地区则表现为高速异常,这或许说明西部的鄂尔多斯为稳定的块体,而中东部区域则经历了破坏或改造;稳定的华南地块主体表现为高速。反演结果还揭示小型的江汉盆地、下辽河盆地、二连及海拉尔盆地都显示出高速,而大型的四川盆地和松辽盆地内部则呈现出不均匀的结构特征。四川盆地的高速异常显示出明显的分块现象,这可能是该盆地在沉积前具有不同的基底物质;松辽盆地的北部呈现为高速,而南部却表现为低速异常,这可能意味着该盆地南部的岩石圈已经遭受了改造。上述盆地的细结构特征与重力异常和大地热流研究相吻合,由此说明本研究获得了较高分辨率的结果。本研究进一步揭示Pn各向异性与速度结构的分布存在一定的关联,Pn波低速区和高低速过渡带的各向异性也较为强烈,而大部分强震都发生在这些区域之上的地壳内,可能说明这些部位容易发生变形而应力集中或产生应力差。一些盆地附近的Pn各向异性较为强列,这可能反映了盆地演化过程中的伸展构造背景。
[Abstract]:The eastern part of China is composed of northeast China (eastern section of Central Asian orogenic belt), North China Craton, Sulu orogenic belt and South China block. It is located in the southeast of Eurasian plate and adjacent to the western Pacific subduction zone. Influenced by the westward subduction of the Pacific plate, the area has complicated geological tectonic setting and deep structural characteristics. The study of the structure of the top of the upper mantle in this area is helpful for us to better understand the influence of the deep layer on the shallow structure in the process of continental dynamic evolution. The early results mainly used the Pn time data from the seismological report (China earthquake Annual report and the observation report of the regional network of various provinces). In addition to using the data from the seismic observation report, recent studies have been carried out. This paper mainly supplements the Pn time data recorded by the mobile seismic array in western China, especially the Qinghai-Tibet Plateau, and focuses on the velocity structure and anisotropy of the upper mantle in the western part of China. In this paper, the Pn time data of ISC (International Seismic Center) report, China earthquake Annual report and China Regional Seismic Network observation report are collected, and the earthquake events recorded by Northeast China, North China Mobile Array and Regional Seismic Network are intercepted. At the same time, the small and medium earthquake events recorded by the fixed stations in South China were specially selected. A large number of high-precision Pn wave arrival data were manually picked up by professionals for these events, and finally 240814 Pn wave arrival data of 24072 earthquakes were selected. These data are recorded by 2049 stations in the region. The application of a large amount of data in this study results in the intensive coverage of Pn rays throughout eastern China. The velocity structure and anisotropy of Pn wave at the top of the upper mantle in eastern China and its adjacent regions are obtained by using Pn wave tomography method. The resolution of the inversion results is measured in detail. The results show that the average velocity of the upper mantle in eastern China is 8.06 km/s, ranging from 7.81-8.32 km/s.. In the eastern part of Northeast China, there is a significant low velocity anomaly, which may be influenced by the subduction of the Pacific plate and represent the upwelling heat material in the Changbai Mountains. In the North China Craton, the Pn in the east shows a low velocity, while in the western region, it shows a high velocity anomaly. This may indicate that Ordos in the west is a stable block, while the central and eastern regions have undergone destruction or transformation, while the main body of the stable South China block is characterized by high speed. The inversion results also reveal that the small Jianghan basin, the lower Liaohe basin, the Erlian basin and the Hailar basin all show high speed, while the large Sichuan basin and the Songliao basin show uneven structural characteristics. The high speed anomaly of Sichuan basin shows obvious fragmentation phenomenon, which may be that the basin has different basement materials before sedimentation, while the north of Songliao basin presents high speed, while the south shows low velocity anomaly. This may mean that the lithosphere in the southern part of the basin has been transformed. The fine structure of the basin is consistent with the gravity anomaly and the study of the geothermal flow, which shows that the results obtained in this study are of high resolution. The present study further reveals that there is a certain correlation between the Pn anisotropy and the distribution of velocity structure. The anisotropy of the low velocity region of PN wave and the transition zone of high and low velocity is also strong, and most of the strong earthquakes occur in the crust above these regions. It may indicate that these parts are prone to deformation and stress concentration or stress difference. The Pn anisotropy near some basins is relatively strong, which may reflect the extensional tectonic background during the evolution of the basin.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P315.2

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