断层模型音频大地电磁测深数值模拟及应用

为探究音频大地电磁测深(AMT)对断层模型识别的效果,对不同倾角的断层模型进行数值模拟研究。采用MT2DModeling软件进行正演模拟,得到的初始模型加入10%的噪声后再采用Occam方法进行反演,数值模拟结果表明:1)音频大地电磁测深整体上对断层模型较为敏感,TE模式的纵向分辨率高,对模型的上下边界识别较为清晰,TM模式的横向分辨率高,对模型水平方向边界识别更好;2)对于不同电性组合断层模型,AMT对相对低阻断层的模型识别效果优于相对高阻断层的模型,其中TM模式对于高阻的识别效果要好于TE模式;3)对于不同倾角的低阻断层模型,TM模式对于反演结果上、下盘梯度变化率反应明显,即变化率大的方向为倾斜方向;4)TE模式正演结果对于断层倾角变化的反应明显,可以作为识别断层倾角的参考。通过对AMT法在琼北锦山地区活动断裂(马袅-铺前断裂东段)勘测的实际资料及钻孔结果进行分析,得到了断裂空间展布的定量认识,表明断裂自第三纪以来均有剧烈活动,活动期次已达到全新世。研究结果为海南地区开发建设提供了地质地球物理依据,也为其断层活动性、岩浆活动性等的进一步探究打下了良好的研究基础。

Numerical simulation and application of audio-frequency magnetotelluric method based on fault models

In order to explore the effect of audio-frequency magnetotelluric (AMT) method on fault model recognition, the fault models with different dip angles were simulated. MT2DModeling software was used to carry out forward simulation, from which the initial model was obtained. Then the initial model was added with 10% noise and inverted by Occam method. The numerical simulation results show that: 1) AMT is sensitive to the fault model on the whole. TE mode with high vertical resolution identifies the upper and lower boundaries of the model more clearly; while TM mode with high horizontal resolution identifies the horizontal boundaries of the model better; 2) For different electrical combination fault models, the recognition effect of AMT on relative low resistivity fault model is better than that of relatively high resistivity fault model, among which TM mode is better than TE mode in identifying high resistivity fault; 3) For the low resistivity fault models with different dip angles, TM model has obvious response to the gradient change rate of the upper and lower walls of the inversion results, that is, the direction with large change rate is the trend direction; 4) The forward modeling results of TE model have obvious response to the change of fault dip, which can be used as a reference to identify fault dip. Through the analysis of the actual data and drilling results of the survey of the active faults (the east section of Maxiao-Puqian fault) in Jinshan area of Qiongbei by AMT method, the quantitative understanding of the spatial distribution of the faults is obtained, which indicates that the faults have been active since the Tertiary, and the active period has reached the Holocene. The research result provides a geological and geophysical basis for the development and construction of Hainan area, and lays a good research foundation for further exploration of fault activity and magmatic activity in this area.