滇西北地磁短周期变化特征研究

发布时间：2018-05-09 01:12

本文选题：地磁测深 + 地磁短周期变化异常　；参考：《中国地震局地球物理研究所》2015年硕士论文

【摘要】：滇西北地区位于欧亚板块和印度板块相互作用的边缘地带,构造环境复杂、地震活动频繁,一直以来都被作为研究大陆动力学、大陆强震孕育环境和预测未来强震危险区的理想场所。由于学科背景的差异和研究思路的不同,科学家们对滇西北中下地壳和上地幔普遍存在的低速高导层的成因、地震的形成机制以及地球动力学机制等问题还存在着争议和分歧。岩石电导率作为揭示地球内部状态的重要物理参数之一,对地球内部温度、流体、熔融和挥发分的存在以及它们的体积、含量等比较灵敏。因此,研究滇西北深部电性结构将有助于探查川滇活动块体的深部构造,剖析不同圈层的耦合关系,解释板块运动、软流圈对流、地震成因和深部动力学等问题。本论文基于滇西北地磁台阵8个测点的资料,采用地磁测深的方法对地下深部电性结构进行研究。文中挑选视周期3-60min范围内共183个地磁短周期事件,并对事件的地磁三分量变化幅度进行统计,分析发现滇西北地区存在一条北北西向的分界线,在分界线两侧垂直分量的变化幅度AZ反向,表明地下存在着明显的电阻率异常。不同周期垂直分量变化幅度和水平分量变化幅度的比ΔZ/AH的等值线图反映了高导带的走向和位置随深度的变化情况。通过对8个测点转换函数的计算,获取了2-256min周期范围内的威斯矢量,结果显示在分界线两侧威斯矢量的指向相互背离,且威斯矢量的大小和指向随周期的增大不断变化。根据研究区内大地电磁测深结果,计算出周期—视等效深度曲线,可知高导带从中下地壳一直延伸至上地幔,且位置和走向随深度不断变化。利用三维交错采样有限差分法对研究区内高导带的简化模型进行数值模拟,结果表明不同周期的磁场分布与观测到的地磁短周期变化特点相符,证实了该区高导带的存在。根据以上地磁短周期变化异常以及高导带的分布特点,结合前人的研究成果,文中尝试对高导带的成因做一定的分析论证,并认为高导带可能是由于部分熔融和流体的综合作用造成的。根据地质与地球物理资料推测印度板块与欧亚板块的碰撞、上地幔上隆及热物质入侵可能成为滇西北地区现代地壳构造运动及地震活动的主要动力源。
[Abstract]:Northwest Yunnan is located on the edge of the interaction between the Eurasian plate and the Indian plate. The tectonic environment is complex and the seismicity is frequent, so it has been used as a study of continental dynamics. The preparation environment of strong earthquakes on the continent and the ideal place to predict the danger areas of strong earthquakes in the future. Due to the difference of subject background and research ideas, there are still controversies among scientists on the origin of low-velocity and high-conductivity layers, the formation mechanism of earthquakes and geodynamic mechanisms, which are common in the middle and lower crust and upper mantle of northwestern Yunnan. As one of the important physical parameters to reveal the state of the earth, the conductivity of rock is sensitive to the temperature, fluid, melting and volatile matter, and their volume and content. Therefore, the study of the deep electrical structure in Northwest Yunnan will be helpful to the exploration of the deep structure of the Sichuan-Yunnan active block, the analysis of the coupling relationship between different circles, the interpretation of plate movement, the convection of the soft circulation, the seismicity and the deep dynamics, and so on. Based on the data of 8 points of geomagnetic array in Northwest Yunnan, this paper studies the electrical structure of underground depth by using the method of geomagnetic sounding. In this paper, 183 geomagnetic short-period events are selected within the range of apparent period 3-60min, and the variation amplitude of geomagnetic three components of the events is statistically analyzed. It is found that there is a north-northwest dividing line in Northwest Yunnan. The amplitude of variation of vertical component AZ on both sides of the boundary line is reversed, which indicates that there are obvious resistivity anomalies underground. The isoline map of the ratio 螖 Z/AH of the variation amplitude of the vertical component and the horizontal component of different periods reflects the variation of the strike and position of the high conductance band with the depth. The Weiss vector in the range of 2-256min period is obtained by calculating the transformation functions of eight measuring points. The results show that the direction of the Weiss vector deviates from each other on both sides of the boundary line, and the size and direction of the Weiss vector vary with the increase of the period. According to the results of magnetotelluric sounding in the study area, the periodicity-apparent equivalent depth curve is calculated. It can be seen that the upper mantle extends from the middle to the lower crust of the high conductivity zone, and the position and strike change with the depth. The simplified model of high conductance band in the study area is simulated by using three dimensional staggered sampling finite difference method. The results show that the magnetic field distribution in different periods is consistent with the observed geomagnetic short period variation, and the existence of high conductance band in this area is confirmed. According to the anomaly of geomagnetic short period variation and the distribution characteristics of high conductance zone, combined with the previous research results, this paper attempts to make a certain analysis and demonstration of the origin of the high conductivity zone. It is suggested that the high conductivity band may be due to the combination of partial melting and fluid. Based on geological and geophysical data, it is inferred that the collision between the Indian plate and the Eurasian plate, the upwelling of the upper mantle and the invasion of thermal matter may be the main power sources of the modern crustal tectonic movement and seismic activity in the northwest Yunnan.
【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】：P315.721

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