The Problems of Contemporary Concept of Isostasy and Scale Effects for Fractured Earth’s Crust of Continents and Oceans

Bogdanov V. I., Malova T. I.

Isostatic ideas appeared within the framework of E. de Beaumont’s contractional hypothesis, which based on views of Kant–Laplace as well as on ideas of primarily smelted Earth and processes of its gradual cooling and compression. Formed as a shell Earth’s crust gradually increased the thickness with clenching into the folds and stay in hydrostatical balance with the underlying substratum. During triangulations of XVIII—XIX centuries differences between the measured deflection of the vertical near mountain ranges and estimates were fixated, so J. Pratt and G. B. Airy had an opportunity to suggest the existence of deep compensating masses. C. E. Dutton, the author of the term «isostasy», considered the wide range of geological problems. Distinction of measured deflection of the vertical is explained by known in gravimetry effect of «neighbor» masses, which formed the North-Atlantic and Indian planetary anomalies of geoid, as well as by real «macrodesdensity» of rock massifs, which is not detected by surveying of density and porosity of small samples of rocks. Modern difficulties with the concept are connected with the explanation of global displacements of asthenosphere masses in planetary eustasy, hydro- and glaciostasy on the rotating Earth as well as the explanation of negative result of gravimetrical experiment for the verification of Fennoscandian «floating»’ isostatic mechanism. The reaction of Earth surface and oceans’ bed to the changes of external loads is usually considered according the unified process of maintaining the isostatic equilibrium. These hypotheses are contradicted with the facts of «high crustal sensitivity» even to small oscillations of external loads as well as total fracturing of the Earth’s crust and scale addictions of its physical and deformation properties from the size of the application area loads. Two mechanisms of the crust’s reaction are suggested: «compression–dilatation» of macropored areas in the layer of 0—10 km and, according to the results of ultradeep boring on the Kola Peninsula, — the phase mechanism at great depths. The ways of experimental research of such effects in the areas of abnormal natural and anthropogenic stresses are discussed.

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