DETERMINATION OF CRUST STRUCTURE OF WESTERN ANATOLIA BY USING THE GRAVITY INVERSION TECHNIQUES

Western Turkey is tectonically one of the most active and rapidly deforming regions of continental crust in the world. The most pronounced structural features of this region are defined by normal faulting in an E–W direction, which creates the boundaries of the Büyük Menderes and Gediz grabens. The Gediz and Büyük Menderes grabens exhibit negative Bouguer gravity anomalies. These anomalies were interpreted using 2D and 3D gravity inversion techniques in order to determine the depth of the crust. 3DINVER.M software program is used to compute 3D geometry of Moho topography. The program based on obtaining the geometry of the density interface related to the gravitational anomaly for three-dimensional extension of the Parker–Oldenburg’s method. The study area is locating between 27.00 – 29.50E longitudes and 37.50- 38.50N latitudes. The parameters used for the inversion are: density contrast of 0.3 g/ cm³ (mantle density minus crust density) and a mean depth for the crust–mantle boundary of 15km. The filter cut-off parameters have been chosen as WH=0.01 and SH=0.012. Finally, the truncation window data length established for the cosine taper window is selected as 10% of the extended data length. Convergence of the iterative procedure has been achieved at the third iteration, with a RMS error of 0.0101 km (the convergence criterion had been established in 0.02 km).

The geometry of the inverted interface shows a maximum depth of about 36 km, located at the east part of study field 1 and 35 km located at the center of study case 2, related to Gediz and Büyük Menderes grabens.

The gravity anomaly map obtained from 3DINVER.M due to the interface topography obtained and it’s a good correlation with the original gravity input map. The difference between the original and computed anomaly maps is also obtained and are in the range between -0.06 and 0.03 mGal.

In order to compare 3D modelled results with the ones obtained by using a 2+1/2D gravity modeling software GIRIS.FOR and CIKIS.FOR, four gravity profiles, which cross the areas vertically and horizontally, have been selected. It can be observed that the Moho relief obtained from the software produces a gravity anomaly similar in shape to the observed anomaly.