Preliminary study of the gravity field of the southern Urals along the URSEIS '95 seismic profile

Abstract

The gravity field in the southern Urals is investigated using two gridded data sets of the Bouguer gravity that were analyzed and modelled by a two-dimensional method. The first data set covers the entire southern Urals with an underlying grid spacing of 18 km by 18 km. The second data set covers the area of the URSEIS '95 seismic profile and its nearest surroundings with a grid of 9 km by 9 km. For modelling and gravity field data processing, topographical data sets with the same resolution are available for the area. Initial applications of wavelength filtering, depth estimation, and 2D modelling show that most of the Bouguer anomaly variation is caused mainly by two lithospheric density domains. Moho depression causes a large-scale negative gravity effect with wavelengths of about 600 km and a dense, shallow oceanic terrane in the Magnitogorsk Zone causes a positive gravity effect characterized by a wavelength shorter than 180 km. A moderate crustal root is obtained in the area of the southern Urals where the depth of the crust-mantle interface varies from some 40 km up to 50 km. The maximum crustal thickness is located below the Magnitogorsk and East Uralian zones. Preliminary analysis of seismic studies indicates a thickened crust for the lower parts of the model which is not reflective. From the viewpoint of density modelling it is necessary to introduce a transitional zone with a density of 3240 kg/m 3 between the earth's crust (density 2910 kg/m 3) and mantle (3350 kg/m 3).