The tilt derivatives (or angles) are determined using the gravity gradient tensors (GGT) from two horizontal components (Gx, Gy) and vertical component (Gz), and the magnitude of the horizontal components (MHC). We show that the tilt derivatives from GGT and MHC are highly suitable for mapping linear geological structures or edges of target geology. The results obtained from theoretical data, with and without random noise, have been analyzed in this study. The tilt derivatives from GGT and MHC allow imaging the horizontal boundaries of gravity sources with a high resolution and show an improvement performance as edge detectors since they are ultra sensitive for detecting source boundaries.The tilt derivatives from GGT and MHC over the northeast of the Biga Peninsula in northwestern, Turkey are interpreted to image the edges of geological structures. Tilt derivatives provide a quick method which works well to obtain a detailed structural image of the complex area, with the most precision. The results indicate that the most predominant structural trends are in a NE-SW direction. Therefore, a good correspondence is recognized between structures well known by surface geology and many other lineaments which are unknown or only partially known.

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Over the course of history Marmara region in Northwestern Turkey has been the site of numerous destructive earthquakes. Based on historical and instrumental earthquake records, the Marmara sea region is one of the most seismically active regions of the Eastern Mediterranean. The Marmara region is under the influence of the western part of the North Anatolian Fault Zone (NAFZ) and the N-S extensional regime of Western Turkey. Therefore, the earthquake risk analysis is very important for the MARMARAY Project. 76 km-long MARMARAY Project is an important project not only for Turkey but also for the world because it joins the two continents through railway. It will also serve for a comfortable and healthy way of environment, providing a contemporary solution for urban transportation. Geotechnical and geological parameters of the region were obtained from analyses of seven boreholes. In this paper, using average wave velocities in layers, thickness, density and formation data based on the PS logs, 43 m and 65.5 m depths ranging from 7 different boring logs in a ground-wise different geological regions in İstanbul, ground response functions were obtained. Based on the soil profiles transferred to EERA (Equivalent-Linear Earthquake Site Response Analyses of Layered Soil Deposits) and NERA (Nonlinear Earthquake Site Response Analyses of Layered Soil Deposits) softwares, the rock soil record of August 17, 1999 Kocaeli earthquake in İstanbul-Beşiktaş Ministry of Public Works and Settlement (IBMPWS), response and design spectrums that may be considered crucial in case of an earthquake were obtained. The acceleration record was used as an input motion having PGA value of 0,04287 g (east-west component) which was applied on sublayers (i.e. sand, gravel, clay) using EERA and NERA programs. The analysis is done by keeping constant damping ratio of 5%. Also nonlinear analysis was compared with the linear method of analysis. Stages involved in ground response analyses to develop site-specific response spectra at a soil site are summarized. Some of the known site response analysis methods are summarized and similarities and diff erences between linear and nonlinear methods.