The quantitative interpretation of gravity anomalies due to shallow structures needs separation between long wavelength anomalies (regional anomalies) and short wavelength anomalies (residual anomalies). The regional-residual field separation can be carried out using the polynomial method. In this case, the so-called regional field of order n is treated as a polynomial of degree n. The present study shows that the degree n must vary between a smallest value nmin and a maximum value nmax. This article presents a method to process gravity data that allows determination of nmin and nmax for a given study area. We apply the method to gravity data of the South-West Cameroon zone. In this chosen study area, we find that regional anomaly maps of orders ranging from 1 to 9 and residual anomaly maps of orders ranging from 1 to 8 can be used for suitable interpretation. The analyses show that one may need residual anomaly maps of several orders to perform satisfactory quantitative interpretation of the different intrusive bodies found in a given area.
The Garoua Zone in North Cameroon, the subject of this study, is known to have undergone tectonic movements during the Cretaceous, but the zone’s structural data remain poorly known. This study exploits the Bouguer anomaly to improve knowledge of Garoua tectonics structures. In order to characterize these structures, two methods are used: Euler’s deconvolution method and the method of the horizontal gradient of the vertical derivative. Superposition of the Euler’s solutions map for index N=1 with the map from the horizontal gradient of the vertical derivative method allows determination of gravimetric lineaments, interpreted as faults or as linear contacts, from which we deduce a structural map of the study area. Based on this map, we identify sixteen lineaments, of which we count eight as linear contacts and eight as faults. Among the faults, we denote one of depth between 4 and 8 km, five faults of depth ranging between 8 and 13 km, and two faults of depths between 13 and 36 km. Analysis of these faults shows that the seven deepest faults might present a natural risk in our study area. For purposes of civil protection, such deep faults should be monitored and taken into consideration in the implementation of large public works. The structural map, established herein from data on the in-depth extension of each fault, thus increases scientific knowledge in the area that can be used to site public works in ways that reduce risk.