Sediment thicknesses of the western Anatolia graben structures determined by 2D and 3D analysis using gravity data

Western Turkey is tectonically one of the most active and rapidly deforming regions of continental crust in the world. The most pronounced structural and morphological features of this region are defined by normal faulting in an E–W direction, which creates the boundaries of the Büyük Menderes, Küçük Menderes and Gediz grabens. The graben systems may have become active between 11–7 Ma and are now deeper than the surrounding topography. The Gediz and Büyük Menderes grabens exhibit negative Bouguer gravity anomalies. The Bouguer gravity anomalies increase towards the center of the Aegean Sea in a regional sense. The grabens are filled with recent sediments giving rise to relative negative gravity anomalies. These anomalies were interpreted using 2D and 3D gravity inversion techniques in order to determine the depth to the metamorphic basement. Inversion of geophysical anomalies implies fitting the observed data to theoretical anomalies possibly produced by subsurface bodies. Inversion of gravity anomalies is a non-linear problem in the sense that body parameters are not linearly related to the anomalies. Gravity anomalies caused by structures are mostly determined by a 2D model, which has an n-sided polygonal cross-section. For non-linear problems, theoretically it is more suitable to determine the parameters of the structure by a series of juxtaposing prisms or vertical dykes extending to infinity, rather than using a single n-side polygonal model. The depths to the top surfaces of a rectangular prisms with infinite depth represent the relief of the basement. The basement relief can be computed on the basis of density contrast if the reference depth is assessed. As a result of 3D analysis of the Bouguer gravity map, the maximum thickness of sedimentary cover appears to be more than 2.0 and 1.5 km for the Gediz and Büyük Menderes grabens, respectively. Towards the Sarayköy-Kızıldere area, the sedimentary thickness cover thickens to more than 2.0 km. 2D analysis of the Bouguer gravity profiles indicate that the maximum thickness of the sedimentary cover is between 2.5 and 3.5 km in the Büyük Menderes graben, and between 0.5 and 2.0 km in the Gediz Graben.