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Summary Aegean Graben System is a significant member of the complex geology of western Turkey. The depths to the metamorphic basement reliefs in two major grabens of this system have been reported by many geophysical studies so far. However, the continental sediment thicknesses of these graben basins still remain controversial due to the findings differing from each other. Thus, an attempt has been made here to invert the gravity data of the sedimentary cover–metamorphic basement using a stochastic derivative-free vector-based metaheuristic named differential evolution algorithm (DEA). This is the first application of DEA adapted to the basement relief depth problem. Model parameterizations have been achieved by discretizing the basins using a group of juxtaposed vertical blocks. Before the inversion studies, mathematical nature of the inverse problem has been investigated by producing prediction cost function/error energy maps for some block pairs using a hypothetical symmetric basin model. These maps have shown the resolvability characteristic of the block thicknesses on such inversion problem. Parameter tuning studies for the optimum mutation constant/weighting factor have been also performed to increase the efficiency of the algorithm. The synthetic data have been successfully inverted via the tuned control parameter and some smoothing operators. Probability density function (PDF) analyses have shown that the best solutions of independent runs are within the confidence interval limits without model uncertainties. In the field data case, long-wavelength anomalies originated from both crustal and deeper effects have been removed from the complete Bouguer anomalies through a 2D finite element method (FEM) using the element shape functions (ESFs). Some profiles extracted from the residual gravity anomaly map have been used for the inversion and obtained results have shown that the maximum depths to the metamorphic basement reliefs in the grabens are shallower than the findings of the previous studies. Information obtained from the lithological logs drilled in the grabens has supported our results. Moreover, probability density function analyses have also indicated the reliability of the obtained sedimentary package thicknesses without uncertainties.

On the basis of gravity data, derived anomaly traces were presented for the interpretation of some shallow structural features of Biga and Gelibolu peninsulas. Since building general understanding of subtle details about subsurface geology is of great importance considering that the study area is tectonically important, some advanced data processing techniques were implemented to gravity anomalies in a detailed manner. The procedures were performed using a MATLABbased software package (Gravity and Magnetic Interpretation -GMINTERP). First, a finite element method was utilised to produce the residual data-set which is expected to reflect short wavelength anomalies arising from shallower geological structures, and thereafter some derivative-based algorithms were executed to analyse the residual data. The general anomaly patterns obtained from the applications clearly corresponded to the well-known surface geology map of the study area. Derivative-based anomaly maps put forward some findings about the existence of an old caldera structure in the western part of the Biga Peninsula. Additionally, abrupt lateral changes in anomaly amplitudes indicated the presence of some major structural discontinuities. Thus, findings yielded to make significant geological interpretations that might be important for further investigations. This study also showed that GMINTERP software package proved useful in assisting geological interpretation using geophysical potential field data-sets.