**2.1 Infinite horizontal slab equation (IHSE)**

The gravity effect or the Bouguer gravity anomaly can be calculated at any point of Cartesian coordinates (x, z) on the surface of the earth or reference measured datum, due to BHS or IHS is given by the Eq. (1) as follows:

$$\text{gB}(\mathbf{x}, \mathbf{z}) = 2\pi \text{phG} \tag{1}$$

where gB: is the gravity effect or Bouguer gravity anomaly due to slab in m. Gal (10�<sup>5</sup> m/s<sup>2</sup> ).

ρ: is the density of the horizontal slab in gm/cm<sup>3</sup> (10<sup>3</sup> kg/m<sup>3</sup> ).

h: is the thickness of the IHS in km (103 m).

G: is the Universal Gravitational Constant (6.67 � <sup>10</sup>�<sup>11</sup> Nm<sup>2</sup> /kg<sup>2</sup> ), N: is referring to Newton or force unit.

The Eq. (1) can be rewritten in a modified form for the new method purpose as follows:

$$\mathbf{gB(x,z)} = 2\pi \mathbf{G} \sum\_{i=1}^{N} \overline{\Delta \rho}(\mathbf{i}) \Delta \mathbf{z}(\mathbf{i}) \tag{2}$$

where Δρ: is the average vertical density-contrast in gm/cm<sup>3</sup> (10<sup>3</sup> kg/m<sup>3</sup> ). Δz: is the difference between the depth of top and bottom the IHS in km (10<sup>3</sup> m).

i: is the index number (i = 1, 2, 3 … N).

N: is the number of rocks 'formations, and

$$\overline{\Delta\rho} = \frac{\sum\_{i=1}^{N} \rho(\mathbf{i})}{\mathbf{N}} - \rho\_{\text{basement}} \tag{3}$$

where P<sup>N</sup> i¼1 ρð Þi <sup>N</sup> : is the average density, and ρbasement: is the density of basement rock.

In the proposed method, the Infinite Horizontal Slab Equation (IHSE) is used to calculate the gravity effects at the earth's surface (or any reference datum) for each subsurface rock' formation that, covering the basement rocks for any sedimentary basin area, and using the IHSE ability, efficiency in the estimating, tracing the formations' thicknesses (or depth), relative to the underlying basement rocks. By using the prior information of control point (or borehole), through profile (s) line (s) of Bouguer gravity anomaly which represents the vertical cross-section (s) for the area of study.

Simply the idea of the new method is based on the assumption that: the sedimentary rock' formations covering the basement rocks are the formations deposited individually in form of layers, or a group of HIS, of different densities distributions is being stacked in columns over the basement's rocks (**Figure 1**). And hence for any point (1, 2, 3, and 4) at the earth's surface (or datum), the total gravity effect is the summation of all gravity effects (at point 4) contributed by each individual slab (1, 2, and 3) along the vertical axis of that point at the earth's surface, were using the average vertical density-contrast (Δρ), between each formation's slab individually with basement rocks at points 1, 2, 3, and at point 4. Here is the new keen point of view that is: the average vertical densities'-contrasts between the stacked vertically of the IHSs and basement rocks are used in inversion calculations instead of densities'-contrasts between IHSs and their surrounding rock materials, through the

**Figure 1.**

*Bouguer gravity anomalies comparable to all possible rock' formations overlying the basement rocks.*

importance for this concept, it being became possible for some extent to separate of Bouguer gravity anomaly to its components that representing probably of all possible rock' formations overlying the basement rocks, according to the prior known information about those rock' formations (thicknesses, depths, and densities), either from subsurface (borehole, etc.) or the surface geology (field, etc.).
