# Large-Scale 3D Modeling and Inversion of Multiphysics Airborne Geophysical Data: A Case Study from the Arabian Shield, Saudi Arabia

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## Abstract

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## 1. Introduction

## 2. Inversion Methodology

#### 2.1. 3D Potential Field Modeling

#### 2.1.1. Gravity Forward Modeling

#### 2.1.2. Magnetic Forward Modeling

#### 2.1.3. Modeling of AEM Data

#### 2.2. Geophysical Data Inversion

## 3. Description of the Airborne Survey and Data Acquisition Systems

## 4. Geologic Background of the Survey Area

## 5. Constructing 3D Earth Models

#### 5.1. Three-Dimensional Density Model

#### 5.2. Three-Dimensional Magnetic Property Model

#### 5.3. Three-Dimensional Conductivity Model

## 6. Glass Earth Model and Prospective Anomalous Targets for Mineral Resource Exploration

#### 6.1. Regional Structures

#### 6.2. Local Anomalous Structures

## 7. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Layout of the survey design with four blocks outlined in yellow. The actual flight lines for each block plus the gravity flight lines are also shown.

**Figure 4.**Density model recovered from the airborne gravity data. Panel (

**a**) shows a perspective image of the inverse density model as viewed from the southwest. Panel (

**b**) shows a vertical cross section of the density model along line A to B. Note that the apparent vertical elongation of the density anomalies in the vertical cross section is caused by exaggeration of the vertical scale with respect to horizontal scale.

**Figure 5.**Examples of magnetic data fit. Panel (

**a**) shows the observed total magnetic intensity (TMI) anomaly. Panel (

**b**) shows the predicted total magnetic intensity (TMI) anomaly from the recovered model. Panel (

**c**) shows the residual (observed minus predicted).

**Figure 6.**Magnitude of magnetic vector model recovered from the TMI data. Panel (

**a**) shows a perspective image of the magnetic vector magnitude as viewed from the southeast. Panel (

**b**) shows a vertical cross section of the model along line A to B.

**Figure 7.**3D conductivity model. Panel (

**a**) shows a perspective image of the conductivity as viewed from the southwest. Panel (

**b**) shows a vertical cross section of the model along line A to B.

**Figure 8.**Maps of the density (

**top**panel) and conductivity (

**bottom**panel) distribution in the survey area at a depth of 100 m.

**Figure 9.**Local anomalies identified within the “Glass Earth” model. The image shows the conductivity model. Two vertical sections of conductivity are shown. Voxels with conductivities greater than 100 mS/m are shown. Hot colors are conductive, and cool colors are resistive.

**Figure 10.**3D view of a local conductivity anomaly. Voxels with conductivities greater than 100 mS/m are shown, as are cross sections of conductivities.

**Figure 11.**Combined conductivity and magnetic images of the same anomaly shown in Figure 10. Voxels with conductivities greater than 100 mS/m are shown, but the cross sections represent magnitude of the magnetic vector model. The correlation between the magnetics and conductivity are apparent.

**Figure 12.**A perspective view of anomalous structure discovered by Glass Earth survey. Panel (

**a**) shows a conductivity with cut-off of 5 mS/m and a cross section of conductivity. Panel (

**b**) shows the same conductive body from the same perspective, but the cross sections are magnetic vector magnitude.

**Figure 13.**Combined conductivity and magnetic images of the same anomaly shown in Figure 12 along line A to B. Panel (

**a**) shows the conductivity, while panel (

**b**) shows the magnetic vector magnitude.

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**MDPI and ACS Style**

Zhdanov, M.S.; Alfouzan, F.A.; Cox, L.; Alotaibi, A.; Alyousif, M.; Sunwall, D.; Endo, M.
Large-Scale 3D Modeling and Inversion of Multiphysics Airborne Geophysical Data: A Case Study from the Arabian Shield, Saudi Arabia. *Minerals* **2018**, *8*, 271.
https://doi.org/10.3390/min8070271

**AMA Style**

Zhdanov MS, Alfouzan FA, Cox L, Alotaibi A, Alyousif M, Sunwall D, Endo M.
Large-Scale 3D Modeling and Inversion of Multiphysics Airborne Geophysical Data: A Case Study from the Arabian Shield, Saudi Arabia. *Minerals*. 2018; 8(7):271.
https://doi.org/10.3390/min8070271

**Chicago/Turabian Style**

Zhdanov, Michael S., Fouzan A. Alfouzan, Leif Cox, Abdulrahman Alotaibi, Mazen Alyousif, David Sunwall, and Masashi Endo.
2018. "Large-Scale 3D Modeling and Inversion of Multiphysics Airborne Geophysical Data: A Case Study from the Arabian Shield, Saudi Arabia" *Minerals* 8, no. 7: 271.
https://doi.org/10.3390/min8070271