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 MATLAB-based 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.

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 have been reported by many geophysical studies. However, the sediment thicknesses of these graben basins still remain controversial due to the findings differing from each other. Thus, we have inverted 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 parametrizations 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 via prediction cost function/error energy maps for some block pairs using a hypothetical 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 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 are within the confidence interval limits without uncertainties. In the field data case, long-wavelength anomalies caused by both crustal and deeper effects have been removed from the complete Bouguer anomalies through 2-D finite element method using the element shape functions. 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, PDF analyses have indicated the reliability of the obtained solutions without uncertainties.

The Biga Peninsula, the complex geological structure of which has attracted intense attention so far, is located in the north-western part of Anatolia, Turkey. The Peninsula is tectonically very important region where different tectonic zones meet and comprises various kinds of sedimentary, metamorphic and igneous rocks. Among these rocks, igneous rocks occupy a considerably amount of areas in the Biga Peninsula and they are mostly associated with geothermal systems and mineral deposits, and therefore they play an important role in the geology of the Peninsula. In this paper, derived results concerning the geological features and subsurface structures of the igneous rocks in the Peninsula are presented based on analyzing the airborne magnetic anomalies. To this end, a MATLAB-based toolkit named as Gravity and Magnetic Interpretation (GMINTERP) that is composed of a set of linked functions in conjunction with a graphical user interface was developed and used for the interpretation of the airborne magnetic anomalies. Some linear transformations and derivative-based techniques were performed to process the potential field data-set and also to help build a general understanding of the geological details. The close agreement between the derived geophysical anomaly maps and the well-known surface geology map of the Biga Peninsula helped us discuss the geological implications of the geophysical traces. This study also indicated that the developed interactive data processing toolkit may assist geological interpretation even in the areas whose subsurface structure is poorly known.