地理情報学と地球統計学: 概要

Polynomial Separation and Gravity Data Modeling with Hyperbolic Density Contrast: Case of Two Profiles along the Mamfe Sedimentary Basin (Cameroon)

Nguimbous-Kouoh JJ, Takam-Takougang EM, Ndougsa-Mbarga T and Manguelle-Dicoum E

The primary objective of a gravity survey over a sedimentary basin is to delineate the shape of the basin. To fulfill this objective, information is needed about the densities within the sedimentary section. Densities of sedimentary rocks increase with depth (mainly due to compaction), approaching that of the basement in deep
basins. Sedimentary basins are generally associated with low gravity values due to lower density of the sedimentary infill. Further, gravity modeling of a basin requires the use of expressions with hyperbolic density contrast concerning the anomaly produced by the model. The variation of the density of sediments with depth
can be represented by a hyperbolic function. In this study, a thirdorder polynomial filtering of Bouguer gravity data from the Mamfe sedimentary basin was performed. The regional and residual third order anomaly maps were fitted for interpretation. Two profiles were plotted above two negative anomalies observed on the basin.
Using the gravity data of both profiles, a workflow was developed to determine the shape and depth of an interface underlying sediments whose density contrast decreases hyperbolically with depth. The approximate depth of the interface at each gravity station was calculated using the gravity formula of an infinite slab with a hyperbolic density contrast. Based on the depth values, the sediment/basement interface were replaced by a sided polygon. The estimated depths of the  sediment/basement interfaces along the two profiles above the Mamfe sedimentary basin gave 1900 and 5073 m, respectively