隐伏断层破碎带的大地电磁二维正演模拟

发布时间：2018-10-20 18:37

【摘要】：隐伏断层的探测对地热资源调查，深部矿床的分布，地下水的赋存，大型工程的选址等都有意义。大地电磁法（MT）因其自身特点在对地下深部断层构造及破碎带的勘探中发挥着重要的作用。通过建立不同的断层破碎带的模型，分析大地电磁法两种极化模式对模型的响应特征，可以为实际资料的解释提供一定帮助。本文基于有限单元法，对所建立的正断层、逆断层、低阻覆盖层模型，进行大地电磁二维正演模拟，得到大地电磁法对不同断层模型的响应特征：（1）阻抗相位相对于视电阻率受低阻覆盖层的影响较小，对地下岩层的电性结构整体形态反映较好。（2）当断层断距较大时，可以根据两种极化模式在高频部分是否出现明显的“逆推”现象来区分正断层与逆断层；当断层的断距较小或低阻覆盖层较厚时，从两种极化模式的断面图中较难区分正断层与逆断层。通过对破碎带模型正演模拟，得到大地电磁的响应特征是：（1）当破碎带的电阻率低于第一层介质的电阻率时，视电阻率和阻抗相位断面图在破碎带处曲线较陡，出现凹陷形态；当破碎带的电阻率大于第一层介质的电阻率时，视电阻率和阻抗相位断面图中凹陷形态消失，在断层破碎带处的曲线变缓。（2）模型中，，断层倾角为30°，45°，60°时，视电阻率断面图中在断层低阻破碎带处都有明显凹陷形态，对破碎带倾角反映不明确，阻抗相位对破碎带倾角反映相对较好。（3）对断层低阻破碎带宽度的正演模拟可知，随着破碎带逐渐变宽，视电阻率曲线与阻抗相位曲线在破碎带位置逐渐变陡。最后，通过对某工作区进行大地电磁测深工作，在分析总结大地电磁对断层模型响应特征的基础上，推断出工作区测深断面图中三处断层的位置，并且与实际地质资料相符，说明本文模型具有一定实用意义。
[Abstract]:The detection of hidden faults is of great significance to the investigation of geothermal resources, the distribution of deep deposits, the occurrence of groundwater, the location of large projects, and so on. Magnetotelluric method (MT) plays an important role in the exploration of deep fault structures and fracture zones because of its own characteristics. The response characteristics of two polarization modes of magnetotelluric method to the model are analyzed by establishing different models of fault fracture zone, which can provide some help for the interpretation of actual data. Based on the finite element method, the magnetotelluric two dimensional forward modeling of normal fault, reverse fault and low resistance overburden layer is carried out in this paper. The response characteristics of magnetotelluric method to different fault models are obtained as follows: (1) the impedance phase is less affected by the low resistivity overburden than the apparent resistivity, and the electrical structure of underground rock is well reflected. (2) when the fault break is large, The normal fault and the reverse fault can be distinguished according to whether there are obvious "backward" phenomena in the high frequency part of the two polarization modes, when the fault spacing is smaller or the low resistivity overburden is thicker, It is difficult to distinguish the normal fault from the reverse fault from the two polarization patterns. Through forward modeling of the fracture zone model, the characteristics of magnetotelluric response are as follows: (1) when the resistivity of the broken zone is lower than that of the first layer medium, the curve of apparent resistivity and impedance phase profile is steep and the shape of depression appears in the broken zone; When the resistivity of the fractured zone is greater than that of the first layer of medium, the shape of the sag in the apparent resistivity and impedance phase profile disappears, and the curve at the fracture zone slows down. (2) in the model, the dip angle of the fault is 30 掳, 45 掳and 60 掳. In the apparent resistivity fracture diagram, there are obvious concave forms at the low resistivity fracture zone of the fault, the dip angle of the fracture zone is not clear, and the impedance phase reflects the dip angle of the fracture zone relatively well. (3) the forward modeling of the width of the low resistivity fracture zone of the fault can be seen. The apparent resistivity curve and impedance phase curve become steeper in the broken zone as the breakage zone becomes wider and wider. Finally, by doing magnetotelluric sounding in a working area, on the basis of analyzing and summarizing the characteristics of magnetotelluric response to the fault model, the location of three faults in the bathymetric section map of the working area is inferred, which is consistent with the actual geological data. It shows that this model has certain practical significance.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.325

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