Superficial structures cartography of the Essaouira basin under ground (Morocco), by small refraction seismic: contribution of the static corrections in the reinterpretation of the speeds variations.

^1,3 Université Mohammed V, Faculté des Sciences, laboratoire Géophysique et Risques naturels, structure Géorisk, Avenue Ibn Battouta, BP 1014, Rabat, Maroc
^2,6 Université Mohammed V, Faculté des Sciences, laboratoire GEOS, structure GEORISK, Avenue Ibn Battouta, BP 1014, Rabat, Maroc
^4,5 Office National d’Hydrocarbures et des Mines, (ONHYM), Rabat, Maroc

Abstract

The static corrections are a necessary step in the sequence of the seismic processing. This paper presents a study of these corrections in the Essaouira basin. The main objective of this study is to calculate the static corrections by exploiting the seismic data acquired in the field to improve the deep structures imaging. It is to determine the roof and the basis of the superficial layers which constitute the weathered zone while calculating the delays of seismic wave’s arrivals in these layers. The purpose is to cancel the effect of the topography and the weathered zone, in order to avoid any confusion when the seismic and geological interpretation. The results obtained show the average values of the static corrections varying between - 127 and 282 ms (double time), with existence of high values by location, particularly in the Eastern and North-Eastern of the basin, which meant the presence of altered zone with irregular topography and whose thickness and speeds vary laterally. In effect the variations of velocities in the fifty meters from the surface may introduce significant anomalies in seismic refraction, with heavy consequences when the interpretation or the drilling establishment. These variations are mainly due to lateral changes in facies and variations in the formations thickness. The calculation of the static corrections, revealed high values at certain areas (East and North-East), which will enable us to better orient the future campaigns in these zones. It is therefore necessary to concentrate the seismic cores drillings and the small refraction seismic profiles by tightening the seismic lines meshes in order to have the maximum values of static corrections and thereafter a better imaging of the reflectors.