单斜地形情况下的磁共振测深方法反演研究  

Inversion of magnetic resonance sounding under the condition of surface slope

作　　者：李凡[1] 周明 李开天 鲁恺 李振宇[1] LI Fan;ZHOU Ming;LI Kai-Tian;LU Kai;LI Zhen-Yu(Institute of Geophysics&Geomatics,China University of Geosciences(Wuhan),Wuhan 430074,China;Guangxi Communications Design Group Co.,Ltd.,Nanning 530012,China)

机构地区：[1]中国地质大学(武汉)地球物理与空间信息学院,湖北武汉430074 [2]广西交通工程检测有限公司,广西南宁530012

出　　处：《物探与化探》2021年第3期712-725,共14页Geophysical and Geochemical Exploration

基　　金：国家重点基础研究发展计划项目“973计划”(2011CB710600)。

摘　　要：磁共振测深方法是一种基于地磁场中地下水氢核的弛豫特性差异进行探测的地球物理勘查方法,它可以无损探测地下水含量及分布。近年来,随着磁共振测深方法的应用范围不断扩大,该方法常面临地表有较大坡度情况下的探测,使用传统手段反演时,容易导致反演结果不准确。本文对地磁场矢量与线圈所在平面之间的夹角——等效地磁倾角进行介绍,并据此给出了单斜地形情况下的磁共振测深方法的反演方法。依据地质资料或其他物探方法提供的先验信息,可以计算得出磁共振测深方法平行分层核函数或水平分层核函数的分布,从而对倾斜地表情况下的核磁共振信号进行反演。本文构建了倾斜地表情况下的地下一维含水层及二维含水体模型,通过正演计算求得相应的核磁共振信号,并分别采用等效地磁倾角计算得到的核函数及直接计算的核函数进行反演。反演结果显示,在地表倾斜的情况下,传统的磁共振测深反演方法会产生误差,而采用等效地磁倾角构建的核函数进行反演能够压制单斜地形的影响。对白水河滑坡区磁共振测深数据的反演工作验证了该方法的有效性及可行性。因此,本文所提出的基于等效地磁倾角的单斜地形反演能够极大提升磁共振测深方法的适用范围。Magnetic resonance sounding is a geophysical exploration method based on the difference of relaxation characteristics of hydrogen proton in geomagnetic field. It can detect the content and distribution of groundwater without damage. In recent years, with the expansion of the application of magnetic resonance sounding, this method is often faced with the detection when the surface has a large slope. When traditional inversion methods are used, inaccurate inversion results often occur. In this paper, the angle between the geomagnetic field vector and the coil is introduced, which is called the effective geomagnetic inclination, and the inversion method of the magnetic resonance sounding under surface slope is given. According to the prior information provided by geological data or other geophysical methods, the distribution of parallel or horizontal layered kernel functions of the magnetic resonance sounding is obtained, so as to carry out the inversion of the NMR signal under the condition of surface slope. In this paper, 1 D and 2 D aquifer models are constructed with the sloping surface, the corresponding NMR signals are obtained by forward calculation, and the kernel functions calculated by effective geomagnetic inclination and traditional method are used for inversion. The results show that, in the case of surface slope, the traditional inversion method of magnetic resonance sounding will inevitably produce errors, while the kernel function calculated by effective geomagnetic inclination can suppress the influence of surface slope. The validity and feasibility of the method were verified by the inversion of the filed NMR data in Baishuihe landslide area. Therefore, the inversion method based on the effective geomagnetic inclination proposed in this paper can greatly improve the application scope of magnetic resonance sounding.

关 键 词：磁共振测深方法 单斜地形 反演 等效地磁倾角 

分 类 号：P631[天文地球—地质矿产勘探]