Study of fast joint physical inversion methods of gravity and magnetic data with undulating observation surface constraints
Received date: 2023-09-01
Online published: 2024-09-29
Copyright
Joint inversion of gravity and magnetic can directly obtain the underground density and magnetic distribution by synthesizing the characteristics of gravity and magnetic data,and effectively reveal different lithology distribution and underground structure,which is an important means of mineral resources exploration. The actual surface of the earth and the observed surface of the airborne gravity and magnetic survey that fluctuates along the terrain are both undulating. In order to realize the highly efficient joint inversion of the undulating observation surfaces,we have established a fast joint physical inversion method for gravity and magnetic data under the constraints of undulating observation surfaces. Firstly,the data is flattened according to the maximum observed height. Then,Block-Toeplitz-Toeplitz-Block(BTTB)-FFT is used to achieve fast inversion,and the space between the converted observation plane and the actual observation plane is used as a constraint to eliminate the multiple solutions caused by the calculation of invalid grid cells. Therefore,this method can achieve high efficiency inversion without increasing the multiplicity of solutions due to additional partition elements. Model tests show that this method can effectively improve the computational efficiency by more than 32 times without losing the accuracy of inversion calculation,and has good stability for noisy data inversion. Finally,we applied this method to Sankeshu Depression,Tonghua Basin,eastern Jilin Province,China,and obtained the distribution of basement and igneous rocks in this area. The average depth of basin basement in this area is about 2.5 km,and the development of igneous rocks is mainly concentrated in the area with large basement depth,which provides important basic geological information for the next oil and gas exploration.It also provides important guiding significance for oil and gas exploration and deployment in the eastern peripheral new area of Songliao Basin.
LiLi LI , JianYe ZHOU , GuoQing MA , ZongRui LI . Study of fast joint physical inversion methods of gravity and magnetic data with undulating observation surface constraints[J]. Progress in Geophysics, 2024 , 39(4) : 1447 -1456 . DOI: 10.6038/pg2024HH0390

图3 起伏地形重磁联合反演对比图(a)起伏地形常规重磁联合反演密度结果切片图(y=10000 m);(b)起伏地形常规重磁联合反演磁化强度结果切片图(y=10000 m);(c) 起伏地形常规重磁联合反演三维密度分布(大于0.195 g/cm3);(d) 起伏地形常规重磁联合反演三维磁化强度分布(大于0.115 A/m;(e)曲化平重磁快速联合反演密度结果切片图(y=10000 m);(f)曲化平重磁快速联合反演磁化强度结果切片图(y=10000 m);(g)曲化平重磁快速联合反演三维密度分布(大于0.195 g/cm3);(h)曲化平重磁快速联合反演三维磁化强度分布(大于0.115 A/m). Fig 3 Contrast of results of joint inversion of gravity and magnetic with undulating terrain (a) Slice of density result of gravity and magnetic joint inversion of undulating terrain (y=10000 m); (b) Slice of magnetic result of gravity and magnetic joint inversion of undulating terrain (y=10000 m); (c) Three-dimensional density distribution of undulating terrain retrieved by joint inversion of gravity and magnetic (>0.195 g/cm3); (d) Three-dimensional magnetization distribution of undulating terrain retrieved by joint inversion of gravity and magnetic (>0.115 g/cm3); (e)Slice of density results of fast joint inversion of gravity and magnetic (y=10000 m); (f) Slice of magnetization results of fast joint inversion of gravity and magnetic (y=10000 m); (g) Three-dimensional density distribution of fast joint inversion of gravity and magnetic (>0.195 g/cm3); (h) Three-dimensional magnetization distribution of fast joint inversion of gravity and magnetic (>0.115 g/cm3). |
表1 起伏观测面规则网格剖分与曲化平后规则网格剖分时间对比(单位:秒)Table 1 Comparison of regular grid generation time between undulating observation surface and curved flat (unit: s) |
| 网格剖分数量 | 30×20×10 | 40×20×10 | 40×40×10 |
| 起伏地形直接联合反演 | 116.04 | 194.27 | 805.51 |
| 曲化平后快速联合反演 | 3.68 | 4.28 | 5.40 |
图4 起伏地形重磁模型位置与含5%噪声正演结果图(a)密度模型与含5%噪声重力正演结果;(b)含5%噪声磁化强度模型与磁法正演结果. Fig 4 Model position and contains a 5% random noise forward results under undulating terrain (a) Forward model and contains a 5% random noise gravity anomaly; (b) Forward model and contains a 5% random noise magnetic anomaly. |
图5 起伏地形重磁联合反演方法加噪对比图(a)含5%噪声起伏地形常规重磁联合反演密度结果切片图(y=10000 m);(b)含5%噪声起伏地形常规重磁联合反演磁化强度结果切片图(y=10000 m);(c) 含5%噪声起伏地形常规重磁联合反演三维密度分布(大于0.195 g/cm3);(d) 含5%噪声起伏地形常规重磁联合反演三维磁化强度分布(大于0.145 A/m);(e) 含5%噪声曲化平重磁快速联合反演密度结果切片图(y=10000 m);(f) 含5%噪声曲化平重磁快速联合反演磁化强度结果切片图(y=10000 m);(g)含5%噪声曲化平重磁快速联合反演三维密度分布(大于0.195 g/cm3);(h)含5%噪声曲化平重磁快速联合反演三维磁化强度分布(大于0.145 A/m). Fig 5 Under 5% random noise, contrast of results of joint inversion of gravity and magnetic with undulating terrain (a) Slice of density result of gravity and magnetic joint inversion of undulating terrain (y=10000 m); (b) Slice of magnetic result of gravity and magnetic joint inversion of undulating terrain (y=10000 m); (c) Three-dimensional density distribution of undulating terrain retrieved by joint inversion of gravity and magnetic (>0.195 g/cm3); (d) Three-dimensional magnetization distribution of undulating terrain retrieved by joint inversion of gravity and magnetic (>0.145 g/cm3); (e)Slice of density results of fast joint inversion of gravity and magnetic (y=10000 m); (f) Slice of magnetization results of fast joint inversion of gravity and magnetic (y=10000 m); (g) Three-dimensional density distribution of fast joint inversion of gravity and magnetic (>0.195 g/cm3); (h) Three-dimensional magnetization distribution of fast joint inversion of gravity and magnetic (>0.145 g/cm3). |
感谢审稿专家提出的修改意见和编辑部的大力支持!
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