瞬变电磁法三维模型数据的一维反演效果研究

发布时间：2018-07-16 14:59

【摘要】：目前国内瞬变电磁数据处理与解释主要停留在一维阶段,但实际数据均来自地下三维结构.针对这一现状,本文采用三维有限差分正演程序生成三维模型的瞬变电磁数据,然后利用Levenberg-Marquardt(LM)方法对数据进行一维反演,以探讨三维模型数据的一维反演效果.大定源回线数据的一维反演结果表明,当水平尺度足够大时,在测点范围内能获取异常体的准确信息,而随着异常体水平尺度的减小,所获取的异常响应会逐渐减小,测点范围内的异常体结构恢复程度也会逐渐降低,尤其当异常体水平尺度明显小于大定源尺度时,所获得的异常响应比较微弱,且单纯增加异常体的垂直尺度并不能增强异常响应.而由异常体三维效应引起的反向异常则会随着异常体水平尺度的减小而先增大,而后随着总体异常响应的减小而减小.中心回线与大定源回线一维反演结果对比表明,中心回线反演可能得到更强烈的异常响应,但对于削弱三维异常体所引起的反向异常可能没有效果,反而可能在获取更强异常响应的同时进一步放大这种反向异常.要使一维LM方法获取与真实异常体比较接近而反向异常比较弱的一维反演结果,可能需要异常体水平尺度相对异常体垂直尺度、异常体的埋深、发射线框的尺寸均比较大.
[Abstract]:At present, transient electromagnetic data processing and interpretation mainly stay in one dimensional stage, but the actual data come from underground three-dimensional structure. In this paper, the transient electromagnetic data of the 3D model are generated by using the 3-D finite difference forward program, and then the one-dimensional inversion of the data is carried out by Levenberg-Marquardt (LM) method, and the one-dimensional inversion effect of the 3D model data is discussed. The results of one dimensional inversion of the large fixed source loop data show that, when the horizontal scale is large enough, the accurate information of the abnormal body can be obtained in the range of measurement points, but with the decrease of the horizontal scale of the abnormal body, the obtained abnormal response will gradually decrease. The recovery degree of anomalous body structure in the range of measured points will also decrease gradually, especially when the horizontal scale of anomaly body is obviously smaller than that of large fixed source scale, the abnormal response obtained is relatively weak. And simply increasing the vertical scale of the abnormal body can not enhance the abnormal response. However, the reverse anomaly caused by the 3D effect of the anomalous body will first increase with the decrease of the horizontal scale of the anomaly body, and then decrease with the decrease of the total abnormal response. The comparison of one-dimensional inversion results between the center loop and the large fixed source loop shows that the center loop inversion may get stronger anomalous response, but it may not be effective for the reverse anomaly caused by weakening the three-dimensional anomaly body. Instead, it is possible to further amplify the reverse exception while obtaining a stronger exception response. In order to obtain the one-dimensional inversion results which are close to the real anomaly and weak in the reverse anomaly, the horizontal scale of the anomalous body is relative to the vertical scale of the anomalous body, the buried depth of the anomalous body and the size of the emission line frame are all relatively large.
【作者单位】：北京大学地球与空间科学学院地球物理学系;北京矿冶研究总院;中国国土资源航空物探遥感中心;
【基金】：国家自然科学基金项目(41504060,41574104)联合资助
【分类号】：P631.325

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