边缘特征和深度加权约束的重力三维相关成像反演

doi:10.11720/wtyht.2024.1053

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Abstract

Correlation tomography is a fast tomography method using correlation coefficients to qualitatively interpret the spatial positions of geobodies. This method, featuring simple, stable, and fast calculations, can quickly and efficiently obtain the distribution of subsurface anomalies without solving large equations. However, the results of direct correlation tomography of gravity anomalies display deep divergence, excessive depth weighting function parameters, and low lateral and vertical resolution between anomalies. According to the fundamental principle of 3D correlation tomography inversion of gravity anomalies, this study introduced the balanced vertical derivative and balanced analytic signal amplitude of gravity anomalies as the edge features to horizontally weight the gravity anomaly correlation tomography, and proposed a more concise depth weighting function. As demonstrated by model tests, the lateral resolution of correlation tomography was improved under the constraint of gravity anomaly edge features, and the vertical resolution of correlation tomography was enhanced using the new depth weighting function. Finally, the method in this study was applied to the actual data of the Australian Olympic Dam polymetallic deposit, yielding consistent weighted tomography results with the actual geological data, thus proving the correctness and effectiveness of the method.

Key words： gravity anomaly correlation tomography horizontal weighting depth weighting edge features

Received: 15 February 2023 Published: 26 February 2024

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	Guo-Qiang AN
	Bao-Liang LU
	Xin-Yu GAO
	Wu ZHU
	Bo-Sen LI

Cite this article:

Guo-Qiang AN,Bao-Liang LU,Xin-Yu GAO, et al. 3D correlation tomography inversion of gravity anomalies constrained by edge features and depth weighting[J]. Geophysical and Geochemical Exploration, 2024, 48(1): 113-124.

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https://www.wutanyuhuatan.com/EN/10.11720/wtyht.2024.1053 OR https://www.wutanyuhuatan.com/EN/Y2024/V48/I1/113

The depth weighting function proposed by predecessors
(z₁=100m,z₂=300m,z_max=500m)

The depth weighting function proposed in this article
(z₁=100m,z₂=300m)

Arctangent balance functions with different balance coefficients

编号	模型名称	x方向位置/m	y方向位置/m	z方向位置/m	剩余密度/ (g·c $m - 3$ )
1	直立长方体	[250,450]	[400,600]	[100,300]	1.0
2	直立长方体	[550,750]	[400,600]	[100,300]	1.0

Model parameters (including 5% noise)

Forward results of two anomalous bodies (including 5% noise) with a residual density of 1.0 g/cm³ and a distance of 100 m
a—gravity anomaly;b—normalize the balanced vertical derivative (nBVDR);c—Normalize the balanced analytical signal amplitude (nBASM)

Weighted results of Correlation tomography of two anomalous bodies (including 5% noise) with a residual density of 1.0 g/cm³ and a distance of 100 m
a—imaging results with depth weighted constraints;b—vertical slice at y=500 m(depth weighted constraints);c—horizontal slice at z=200m(depth weighted constraints);d—imaging results of the method in this article (W_z+VDR weighted);e—vertical slice at y=500 m(W_z+VDR weighted);f—Horizontal slice at z=200 m(W_z+VDR weighted);g—imaging results of the method in this article (W_z+ASM weighted);h—vertical slice at y=500 m(W_z+ASM weighted);i—horizontal slice at z=200 m(W_z+ASM weighted)

编号	模型名称	x方向位置/m	y方向位置/m	z方向位置/m	剩余密度/ (g·c $m - 3$ )
1	直立长方体	[400,800]	[800,900]	[50,300]	1.0
2	直立长方体	[150,250]	[250,550]	[50,300]	-1.0
3	直立长方体	[600,800]	[200,400]	[50,300]	1.0

Complex upright model parameters

Forward results of complex upright model
a—gravity anomaly;b—normalize the balanced vertical derivative (nBVDR);c—normalize the balanced analytical signal amplitude (nBASM)

Weighted results of correlation tomography for complex upright model
a—imaging results with depth weighted constraints;b—vertical slice at y=300 m(depth weighted constraints);c—horizontal slice at z=200 m(depth weighted constraints);d—imaging results of the method in this article (W_z+VDR weighted);e—vertical slice at y=300 m(W_z+VDR weighted);f—Horizontal slice at z=200 m(W_z+VDR weighted);g—imaging results of the method in this article (W_z+ASM weighted);h—Vertical slice at y=300 m(W_z+ASM weighted);i—horizontal slice at z=200 m(W_z+ASM weighted)

编号	模型名称	模型最小埋深/m	模型最大埋深/m	剩余密度/ (g·c $m - 3$ )
1	倾斜长方体	99.547	428.725	1.0
2	倾斜长方体	99.791	383.654	-1.0
3	台阶	100.0	350.0	1.0

Complex tilt model parameters

Forward results of complex tilt model
a—gravity anomaly;b—normalize the balanced vertical derivative (nBVDR);c—normalize the balanced analytical signal amplitude (nBASM)

Weighted results of correlation tomography for complex tilt model
a—imaging results with depth weighted constraints;b—vertical slice at y=250 m(depth weighted constraints);c—horizontal slice at z=250 m(depth weighted constraints);d—imaging results of the method in this article (W_z+VDR weighted);e—vertical slice at y=250 m(W_z+VDR weighted);f—horizontal slice at z=250 m(W_z+VDR weighted);g—imaging results of the method in this article (W_z+ASM weighted);h—vertical slice at y=250 m(W_z+ASM weighted);i—horizontal slice at z=250 m(W_z+ASM weighted)

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Basement geological map of the Gawler Craton Province ^[35]

36]
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Simplified geological map and cross-sectional subsurface structure of the supergiant Olympic Dam breccia complex ^[36]

Drill core measured density curve

Separation results of gravity anomaly at Olympic Dam, Australia
a—gravity anomaly observations;b—regional gravity anomaly;c—residual gravity anomaly

Weighted results of residual gravity anomaly correlation tomography at Olympic Dam, Australia
a—imaging results of the method in this article (W_z+VDR weighted);b—vertical slice at y=6 063.5 km(W_z+VDR weighted);c—horizontal slice at z=750 m(W_z+VDR weighted);d—imaging results of the method in this article (W_z+ASM weighted);e—vertical slice at y=6 063.5 km(W_z+ASM weighted);f—horizontal slice at z=750 m(W_z+ASM weighted)

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