本文選題：地磁測(cè)深 + 地磁短周期變化異常�。� 參考：《中國(guó)地震局地球物理研究所》2015年碩士論文

【摘要】：滇西北地區(qū)位于歐亞板塊和印度板塊相互作用的邊緣地帶,構(gòu)造環(huán)境復(fù)雜、地震活動(dòng)頻繁,一直以來都被作為研究大陸動(dòng)力學(xué)、大陸強(qiáng)震孕育環(huán)境和預(yù)測(cè)未來強(qiáng)震危險(xiǎn)區(qū)的理想場(chǎng)所。由于學(xué)科背景的差異和研究思路的不同,科學(xué)家們對(duì)滇西北中下地殼和上地幔普遍存在的低速高導(dǎo)層的成因、地震的形成機(jī)制以及地球動(dòng)力學(xué)機(jī)制等問題還存在著爭(zhēng)議和分歧。巖石電導(dǎo)率作為揭示地球內(nèi)部狀態(tài)的重要物理參數(shù)之一,對(duì)地球內(nèi)部溫度、流體、熔融和揮發(fā)分的存在以及它們的體積、含量等比較靈敏。因此,研究滇西北深部電性結(jié)構(gòu)將有助于探查川滇活動(dòng)塊體的深部構(gòu)造,剖析不同圈層的耦合關(guān)系,解釋板塊運(yùn)動(dòng)、軟流圈對(duì)流、地震成因和深部動(dòng)力學(xué)等問題。本論文基于滇西北地磁臺(tái)陣8個(gè)測(cè)點(diǎn)的資料,采用地磁測(cè)深的方法對(duì)地下深部電性結(jié)構(gòu)進(jìn)行研究。文中挑選視周期3-60min范圍內(nèi)共183個(gè)地磁短周期事件,并對(duì)事件的地磁三分量變化幅度進(jìn)行統(tǒng)計(jì),分析發(fā)現(xiàn)滇西北地區(qū)存在一條北北西向的分界線,在分界線兩側(cè)垂直分量的變化幅度AZ反向,表明地下存在著明顯的電阻率異常。不同周期垂直分量變化幅度和水平分量變化幅度的比ΔZ/AH的等值線圖反映了高導(dǎo)帶的走向和位置隨深度的變化情況。通過對(duì)8個(gè)測(cè)點(diǎn)轉(zhuǎn)換函數(shù)的計(jì)算,獲取了2-256min周期范圍內(nèi)的威斯矢量,結(jié)果顯示在分界線兩側(cè)威斯矢量的指向相互背離,且威斯矢量的大小和指向隨周期的增大不斷變化。根據(jù)研究區(qū)內(nèi)大地電磁測(cè)深結(jié)果,計(jì)算出周期—視等效深度曲線,可知高導(dǎo)帶從中下地殼一直延伸至上地幔,且位置和走向隨深度不斷變化。利用三維交錯(cuò)采樣有限差分法對(duì)研究區(qū)內(nèi)高導(dǎo)帶的簡(jiǎn)化模型進(jìn)行數(shù)值模擬,結(jié)果表明不同周期的磁場(chǎng)分布與觀測(cè)到的地磁短周期變化特點(diǎn)相符,證實(shí)了該區(qū)高導(dǎo)帶的存在。根據(jù)以上地磁短周期變化異常以及高導(dǎo)帶的分布特點(diǎn),結(jié)合前人的研究成果,文中嘗試對(duì)高導(dǎo)帶的成因做一定的分析論證,并認(rèn)為高導(dǎo)帶可能是由于部分熔融和流體的綜合作用造成的。根據(jù)地質(zhì)與地球物理資料推測(cè)印度板塊與歐亞板塊的碰撞、上地幔上隆及熱物質(zhì)入侵可能成為滇西北地區(qū)現(xiàn)代地殼構(gòu)造運(yùn)動(dòng)及地震活動(dòng)的主要?jiǎng)恿υ础?br/>[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.
【學(xué)位授予單位】：中國(guó)地震局地球物理研究所
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：P315.721

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