Geological structure of South Caspian depression and onshore of Azerbaijan based on temperature data and gravimetric modelling

The paper aims to justify the thickness of sedimentary cover along the aquatory of South Caspian basin and Azerbaijan onshore (including South and Middle Kur basin and Yevlakh-Aghjabedy downfall), the cover thickness of crystalline basement, specifying its structural position and key tectonic borders, as well as the confirmation of some issues on geodynamic evolution. Such comparison was carried out via published seismic temperature, gravimetric and magnitometric data. Definite dependences of geothermal gradients, the thickness of sedimentary cover and crystalline basement depth have been specified.

Estimation of Bouguer correction density based on underground and surface gravity measurements and precise modelling of topographic effects – two case studies from Slovakia

We present a simple and straightforward method for estimating the mean density of topographic masses based on underground gravity measurements along with topography modelling. Two examples under different conditions are given, the first coming from a railway tunnel passing through a Mesozoic karst area and the second from an active coal mine situated in a Neogene sedimentary basin. Relative gravity measurements were processed and corrected by topographic effect modelling based on high-precision airborne LiDAR-derived elevation models. In addition, detailed mining tunnel gravimetric modelling based on terrestrial laser scanning data is presented. Resulted mean (bulk) densities are compared with those obtained from detailed surface gravity measurements as well as with available rock-samples density analysis.

Microgravimetric and GPR surveys for detection of unconsolidated zones in a levee

Selected results of complex geophysical surveys carried out on the Vistula river flood levee in Cracow are herein presented. Two complementary geophysical methods were applied for detection of potential unconsolidated zones in the body of the levee, i.e. microgravimetry and ground-penetrating radar (GPR). The surveys were carried out in 2D mode, along a profile at the crown of the flood levee. Microgravimetric data reveal anomalies showing zones of decreased bulk density. These zones provide information about poor quality of the levee. The main anomaly was interpreted in a quantitative manner using gravity modelling. Non-standard GPR processing and visualization of radargrams were employed to better extract information concerning the distribution of unconsolidated zones. High resolution GPR surveys allow to outline such zones which was the basis for construction of the 2D model used in the gravimetric modelling. Integration of these two geophysical methods provided important information about the spatial variations of mass density in several unconsolidated zones within the body of the flood levee.

On Vening Meinesz-Moritz and flexural theories of isostasy and their comparison over Tibet Plateau

Gravity and topographic/bathymetric data are used for gravimetric modelling of Moho discontinuity by hydrostatic or flexural theories of the isostasy. Here, two hydrostatic models, based on the Vening Meinesz-Moritz (VMM) principle, and two based on the loading theories and flexural isostasy are compared over Tibet Plateau. It is shown that theMoho models generated based on theVMM theory and flexural isostasy have very good agreements if the mean compensation depth and the mean elastic thickness are selected properly. However, the model computed based on the flexural isostasy is smoother. A more rigorous flexural model, which considers the membrane stress and curvature of the lithosphere, is used to model the Moho surface over the study area. It is shown that the difference between the Moho models, derived by considering and ignoring these parameters, is not significant. By combination of the flexural and VMM hydrostatic models new mathematical formulae for crustal gravity anomalies are provided and it is shown that the crustal gravity anomalies produced by them are also equivalent.

Subsurface structure and tectonic style of the NE Outer Carpathians (Poland) on the basis of integrated 2D interpretation of geological and geophysical images

Subsurface structure and tectonic style of the NE Outer Carpathians (Poland) on the basis of integrated 2D interpretation of geological and geophysical imagesIntegration of the information from surface and subsurface geological exploration (maps and well sections) and results of geological reinterpretation of more than ten archival seismic sections and several dozen magnetotelluric soundings (MT; published and archival) implies a new structural picture of the Carpathian tectogene, interpreted to depths exceeding 10 km. The tectonics of nappes and their basement is illustrated by four regional cross-sections (derived from geological and petroleum-exploration traverses) and examples of detailed interpretation of zones with complicated structure, as well as results of testing the initial structural models with application of the balanced cross-section method and gravimetric modelling. In the tectonics, a complicated system of overthrusts and detachments of sedimentary covers (from their heterogeneous basement) represents a predominant feature. It induced, within particular nappes and tectonically altered structural-facies units, specific systems of narrow folds with diversified geometries. Broad folds of the intermediate structural stage, which are gently sloping in the hinterland of the nappes, were interpreted on the basis of geophysics as paraautochthonous elements. They cover deep-seated faults with large throws, which obliquely or subvertically dip to the SW and were distinguished in the basement on the grounds of extreme contrasts at the resistivity boundaries. Zones of dramatically low resistivities, which separate blocks of the uplifted basement, were interpreted as tectonic sutures with geometry rebuilt in the stage of the Neogene lithosphere subduction. Therefore, the structural layout of the sedimentary cover is characterized by more gently dipping nappe overthrusts of the sequential type and secondary, out-of-sequence thrust slices, most frequently imbricate ones. The flysch covers resting over the tectonic sutures, particularly in margins of inherited structural depressions, are characterized by more diversified tectonic style in comparison with peripheral, gently-sloping covers thrust over the flexural platform slope, and with steep slices and imbricate thrusts having consequent NE vergence. A specific type of dislocation is represented by flat inversional detachments (seismically documented) which are accompanied by disharmonic folding of "thin-skinned" structural elements. In the eastern part of the foreland of the Dukla overthrust, they form a developed system of backthrusts on the slope of a triangular structure superposed on a "shallower" tectonic suture of the basement; the system replaces sets of fault-propagation folds developed in the eastern part of this zone.