Isostasy of the Eastern Anatolia (Turkey) and Discontinuities of its Crust

摘要

This paper presents a probable isostatic model of the East Anatolian Region, which lies in a belt of significant plate movements. Probable locations of the horizontal and vertical discontinuities in the crust structure were determined using the normalized full gradient (NFG) method. For the purpose of explaining the mechanism that supports topography corresponding to the crust thickness in the region, calculations of effective elastic thickness (T e) were carried out initially by utilizing admittance and misfit functions. According to these results, the effective elastic thickness value obtained was less than the crust thickness, even though the isostatic model does not conform with the Airy model. Consequently, it was assumed that there could be problems beneath the crust. Hence, the NFG method was applied on the Bouguer gravity data of the region in order to investigate probable discontinuities in the crust structure. According to the NFG results, vertical structural transitions were observed at a depth ranging between 10 and 30 km, which begin immediately north of the Bitlis Zagros Suture Zone (BZSZ) and continue in a northerly direction. The relationship between the effective elastic thickness (T e; 13 km in average as determined in the last stage), and the seismogenic zone in the region was investigated. If the T e value happens to be less then the crustal thickness, then one can say that there are problems in the crustal structure of the region similar to Eastern Anatolia. Indeed, when NFG results of the study area are examined, numerous vertical and horizontal discontinuities in the crust can be observed. These discontinuities, which correspond to low Bouguer gravity anomalies and shallow focal depth-earthquakes, are probably the source of the factors which rule the tectonic mechanism of the region.