Some Parameters To Improve A Gravity Network Accuracy: Application To The New Reference Base Stations Network Of The North Of Algeria

Once realizing a base stations network, it is necessary to compensate it to make sure that the results are uniform to avoid several gravity values at the same station. A first gravity network has been made in the 50 s in the North of Algeria by Lagrula (1951; 1959). The accuracy of this network is in the range of 0.2-0.3 mgal while that of the Bouzaréa base is in the range of 1 mgal. In the field, the precise location of this base stations network can hardly be recognized now because of the topographic changes. We have therefore realized a new gravity base stations network in that area, which consists of 74 basis and 5 replacement stations. Its compensation has been made using the auxiliary coefficients method. Measurements are given within 0.06 mgal error in the IGSN71 reference frame. The difference between the values calculated in this system and those using LAGRULA system at the same station is +15.2 mgal. The stations network as well as 150 secondary measurements located between them make possible to map the Bouguer and isostatic anomalies. The observation of Bouguer map reveals the expected anomalies: positive near the coast, negative above important elevations as the high plateaus and the Tellian Atlas whose influence seems to be partly masked by the sea effect. Bouguer anomaly map also shows three main fractures from North to South: The North Atlasic accident, the Southern limit of the high plateaus and the South atlasic flexure. By contrast, the isostatic anomaly map, if it shows that the effect of roots of elevations seems to be well corrected, points out to a negative remaining anomaly in the Aurès region whose minimum drifts to the South above the presaharan basin. This anomaly value suggests a great depth of this basin.