**2. Forward modeling**

A closed-form solution for the gravity anomaly caused by simple geometric structures at a measured point (*xj*) along a profile (**Figure 1**) is given by [29, 50, 51].

$$\mathbf{g}(\mathbf{x}\_j, \mathbf{x}\_o, \mathbf{z}, \mathbf{z}\_o, \eta, q, A) = A \frac{(\mathbf{z}\_o - \mathbf{z})^\eta}{\left[ \left( \mathbf{x}\_j - \mathbf{x}\_o \right)^2 + \left( \mathbf{z}\_o - \mathbf{z} \right)^2 \right]^q}, \quad j = 1, 2, 3, \dots, n \tag{1}$$

where *xj* and *xo* are the X-coordinates of the measured points and the buried body center, *z* and *zo* are the Z-coordinates of the measured point and the subsurface source (the *z* axis is chosen positive downward) (**Figure 1**), *q* is the shape, and *A* is the amplitude coefficient. The appropriate explanations of *A*, *q*, and *η* for the above-mentioned simple bodies are shown in **Table 1**.
