基于人工地震与重力约束的川滇地区地壳结构研究
发布时间：2019-03-08 19:17
【摘要】：川滇地区位于青藏高原东南缘,为快速隆升的青藏高原与稳定的扬子地台的过渡带,该区陆内变形强烈,地震活动异常频繁。这种特殊的构造环境,使得该区成为研究大陆动力学、大陆强震孕育环境和监测未来强震危险区的理想场所。本文通过对普洱-泸西人工地震测深剖面资料的模拟解释,获得了沿测线的二维P波速度模型。结果显示：红河断裂带两侧地壳厚度有明显变化,由西南侧约35km增加到东北侧43kmn左右,而且地壳这种厚度变化主要由下地壳的增厚引起；红河断裂两侧上地壳速度变化最为明显,西南侧比东北侧低约0.4km/s,而这种差异随着深度增加明显减小；剖面平均P波速度也低于全球平均水平,红河断裂西南侧为5.90km/s,东北测6.05km/s,向剖面东北端增加到6.13km/s。小江断裂处壳内各界面有明显挠曲现象,但其两侧地壳厚度并未表现出明显差异。通过进一步的重力资料约束,结合接收函数与面波联合反演结果计算了沿剖面不同深度的密度与介质泊松比分布,并根据岩石实验结果对地壳不同深度的物质组成进行了分析。结果表明,红河断裂西南侧的思茅台下方上地壳可能为富含α-相长英质组分的变质杂砂岩,东北侧通海及弥勒台下方上地壳可能为玄武岩；红河断裂两侧中地壳岩石成分基本相同,主要为长英质成分；红河断裂西南侧思茅台下方为成分均一的下地壳,而通海与弥勒台下方下地壳可分为两层,其中顶层成分与思茅台相同,以长英质为主,而底部可能以中性岩石为主。本文结合抛物线密度模型及频率域算法的优点,开展了基于抛物线密度模型的频率域界面正反演研究,并通过理论模型数据与实际数据实验证实了该方法的可行性。基于上述研究,本文还开展了约束变密度界面反演的方法研究。研究中收集了川滇地区22条人工地震测深资料,将其解释结果作为变密度界面反演的约束条件,得到了研究区的莫霍面起伏情况。并通过与接收函数研究结果进行比较,验证了该方法的有效性与准确性。利用川滇地区的约束变密度界面反演结果,结合地形高程数据对该区的地壳均衡情况作了简单分析。从震中分布与均衡异常关系来看,该区内大部分中到强震分布在本文约束变密度界面反演结果与理论均衡地壳深度差值变化较快的地方。
[Abstract]:The Sichuan-Yunnan region is located in the southeastern margin of the Qinghai-Xizang Plateau. It is a transitional zone between the rapid uplift of the Qinghai-Tibet Plateau and the stable Yangtze platform. The intracontinental deformation is strong and the seismicity is abnormally frequent in this area. This special tectonic environment makes this area an ideal place to study continental dynamics, to prepare environment for strong earthquakes on the continent and to monitor the dangerous areas of strong earthquakes in the future. In this paper, a two-dimensional P-wave velocity model along the line is obtained by simulating and interpreting the data of Puer-Luxi artificial seismic sounding section. The results show that the thickness of the crust on both sides of the Honghe fault zone has obvious changes, from about 35km on the southwest side to about 43kmn on the northeast side, and the thickness variation of the crust is mainly caused by the thickening of the lower crust. The velocity variation of the upper crust on both sides of the Red River fault is the most obvious, and the southwest side is about 0.4 km / s lower than that of the northeast side, and the difference decreases obviously with the increase of depth. The average P wave velocity in the profile is also lower than the global average. The average P wave velocity is 5.90 km / s in the southwest side of the Red River fault, 6.05 km / s in the northeast and 6.13 km / s in the northeast end of the section. There are obvious flexure phenomena in the interfaces of the crust at the Xiaojiang fault, but there is no obvious difference in the thickness of the crust on both sides of the crust. In this paper, the distribution of density and Poisson's ratio along different depth along the profile is calculated by using the constraint of gravity data, combined with the joint inversion results of receiving function and surface wave, and the composition of material in different depth of crust is analyzed according to the results of rock experiment. The results show that the upper crust below Simaotai, southwest of the Honghe fault, may be metamorphosed hetero-sandstone rich in 伪-facies felsic components, and basalt may be the upper crust of Tonghai and Mailetai on the northeast side. The rock composition of the middle crust on both sides of the Honghe fault is basically the same, which is mainly felsic. On the southwest side of the Honghe fault, the lower crust is homogeneous in composition, while the lower crust in Tonghai and Mailetai can be divided into two layers, in which the top layer is the same as Simotai, mainly felsic, and the bottom may be dominated by neutral rocks. Combining the advantages of parabolic density model and frequency domain algorithm, the forward inversion of frequency domain interface based on parabolic density model is studied in this paper. The feasibility of this method is verified by theoretical model data and practical data experiments. Based on the above research, the constrained variable density interface inversion method is also studied in this paper. In this study, 22 artificial seismic sounding data in Sichuan-Yunnan area were collected, and the interpretation results were taken as constraints for inversion of the variable density interface, and the Moho surface fluctuation of the study area was obtained. The validity and accuracy of the proposed method are verified by comparing with the results of the receiver function. Based on the inversion results of the constrained variable density interface in Sichuan-Yunnan region, a simple analysis of the crustal equilibrium in this area is made in combination with the topographic elevation data. According to the relationship between epicenter distribution and equilibrium anomaly, most of the moderate to strong earthquakes in this area change rapidly between the inversion results of the constrained variable density interface and the theoretical equilibrium crustal depth.
【学位授予单位】：中国地震局地球物理研究所
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P315
[Abstract]:The Sichuan-Yunnan region is located in the southeastern margin of the Qinghai-Xizang Plateau. It is a transitional zone between the rapid uplift of the Qinghai-Tibet Plateau and the stable Yangtze platform. The intracontinental deformation is strong and the seismicity is abnormally frequent in this area. This special tectonic environment makes this area an ideal place to study continental dynamics, to prepare environment for strong earthquakes on the continent and to monitor the dangerous areas of strong earthquakes in the future. In this paper, a two-dimensional P-wave velocity model along the line is obtained by simulating and interpreting the data of Puer-Luxi artificial seismic sounding section. The results show that the thickness of the crust on both sides of the Honghe fault zone has obvious changes, from about 35km on the southwest side to about 43kmn on the northeast side, and the thickness variation of the crust is mainly caused by the thickening of the lower crust. The velocity variation of the upper crust on both sides of the Red River fault is the most obvious, and the southwest side is about 0.4 km / s lower than that of the northeast side, and the difference decreases obviously with the increase of depth. The average P wave velocity in the profile is also lower than the global average. The average P wave velocity is 5.90 km / s in the southwest side of the Red River fault, 6.05 km / s in the northeast and 6.13 km / s in the northeast end of the section. There are obvious flexure phenomena in the interfaces of the crust at the Xiaojiang fault, but there is no obvious difference in the thickness of the crust on both sides of the crust. In this paper, the distribution of density and Poisson's ratio along different depth along the profile is calculated by using the constraint of gravity data, combined with the joint inversion results of receiving function and surface wave, and the composition of material in different depth of crust is analyzed according to the results of rock experiment. The results show that the upper crust below Simaotai, southwest of the Honghe fault, may be metamorphosed hetero-sandstone rich in 伪-facies felsic components, and basalt may be the upper crust of Tonghai and Mailetai on the northeast side. The rock composition of the middle crust on both sides of the Honghe fault is basically the same, which is mainly felsic. On the southwest side of the Honghe fault, the lower crust is homogeneous in composition, while the lower crust in Tonghai and Mailetai can be divided into two layers, in which the top layer is the same as Simotai, mainly felsic, and the bottom may be dominated by neutral rocks. Combining the advantages of parabolic density model and frequency domain algorithm, the forward inversion of frequency domain interface based on parabolic density model is studied in this paper. The feasibility of this method is verified by theoretical model data and practical data experiments. Based on the above research, the constrained variable density interface inversion method is also studied in this paper. In this study, 22 artificial seismic sounding data in Sichuan-Yunnan area were collected, and the interpretation results were taken as constraints for inversion of the variable density interface, and the Moho surface fluctuation of the study area was obtained. The validity and accuracy of the proposed method are verified by comparing with the results of the receiver function. Based on the inversion results of the constrained variable density interface in Sichuan-Yunnan region, a simple analysis of the crustal equilibrium in this area is made in combination with the topographic elevation data. According to the relationship between epicenter distribution and equilibrium anomaly, most of the moderate to strong earthquakes in this area change rapidly between the inversion results of the constrained variable density interface and the theoretical equilibrium crustal depth.
【学位授予单位】：中国地震局地球物理研究所
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P315
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