Contribution of the Combined Analysis of Gravity and Seismic Data in the Study of the Main Hydrogeological Prospects of the Essaouira Basin (Morocco)

This study aims to analyze the deep structure and depression of the thick sedimentary layers to better understand the
geometry and hydrogeology of the aquifers in the Essaouira basin which have been processed through various filters and
transformations. The residual map provides valuable information on density variation, the observed anomalies in the study
area interpreted in term of the topography of the basement, the present of salt deposit and the thickness variation of the
sedimentary series. The seismic reflection profiles covering a limited area in the central-western part of the basin confirm the
gravimetry results and shows that the basin's structure is characterized by a series of anticlines and synclines., resulting from
the combined influences of Atlas tectonics and diapirism. As a result, the shallow aquifer system is broken up into blocks
lifted and collapsed by faults. The result is discontinuous groundwater flow and variable hydrodynamic distribution.
Based on the gravity data processing the principal deep parts of the basin were delineated, including their probable
interconnections-oriented N-S and NNE-SSW. As well, major density contacts (faults) were derived from the enhanced total
horizontal gravity gradient. Their prevailing direction in the central and northern parts of the basin is also N-S and NNE-
SSW; however, it is rather E-W in the southern side. Not all these gravity-based structural-tectonic features match with
geologically mapped faults of NE-SW and NNW-SSE orientation.
The compiled data allowed us to create a structural map that reveals a compartmentalized aquifer system with clearly defined
sub-basins. Additionally, the faults within the Essaouira basin have been precisely mapped. Their predominantly NNE-SSW
orientation suggests a connection to the Triassic rifting of the Atlantic Ocean. It also reveals that the Essaouira basin was
structured in the Triassic and Jurassic periods by a series of deep faults trending in three main directions: NNE-SSW, N-S and
E-W. These results will be invaluable for future oil exploration and hydrogeological research.