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MAIN CAUSE OF THE PLANETARY SEISMICITY - THE RADIAL (PULSATORY) MOVEMENTS OF THE EARTH

Mircea Ticleanu, Radu Nicolescu

Abstract

The quasi-permanent seismic activity that characterizes our planet can be very well explained through the geodynamic pulsatory model for Earth. The cosmic cycles governing effectively TerraпїЅs evolution can provide a current and pretty realistic image compatible with sustained seismic activity of the Earth. More exactly, the phases of these dynamic cycles are crucial because they correspond to a trend of planetary expansion or contraction for Terra. From this point of view there are especially important two cycles, respectively the Vail-Payton (V-P) mega-cycle (?icleanu et al., 2002), with a period of about 362 ma, and the Raup-Sepkoski cycle, with a period of about 26 ma which was considered by us a result of a pulsatory пїЅ type movement of our galaxy (the Milky Way). The Vail-Payton mega-cycles can explain the ample stages in EarthпїЅs volume variations in which dry land prevailed and those with oceans waters domination (with withdrawls and advances of the shorelines), stages known especially during the Phanerozoic. In relation with this first dynamic cycle now our planet suffers an expansion phase that began at the end of the Cretaceous (about 66-67 ma ago), a phase which will continue for about 115 ma from now on. The V-P cycles could be due to the possible variations in the total intensity of the metagalactic gravitational field, specific to the cloud of galaxies including the Milky Way. The radial expansion phase of the Earth related to this dynamic cycle explains, for example, the regional separation of the Paratethys from the Tethys Sea and then, the gradual surface restriction for different basines in the Paratethys until the present (with the isolation of the Caspian Basin and the disappearance of the Dacian and Pannonian basins). The second dynamic cycle which counts in this context, respectively the R-S cycle (possible pulsations of our galaxy) has a much smaller period (about 26 ma). In accordance with its phases we are currently also in expansion phase. It started about 2.58 ma ago, in the moment of the Wallachian tectonic phase which marked the sudden inversion of our galaxy to a new expansion phase (?icleanu et al., 2013). If we admit the dynamic cumulative effect of these two cycles mentioned above it follows that the Earth is envolved, starting from the moment of the Wallachian tectonic phase, in a process of relatively accelerated expansion which will manifest in this way untill the end of the current expansive phase of the R-S cycle, so for about 10 ma in the future. But the radial expansion of the Earth cannot be under any circumstances uniform at a planetary scale, due to the evident inhomogeneity of the terrestrial crust. So it will result tangential forces on the surface which will cause some structural re-balancing in the most tectonically sensitive areas. These areas include a great number of seismic sensibility lines (as defined by Atanasiu I. At his time, 1949). But also they contain a great number of very sensitive points. They correspond basically to the known seismic outbreaks, most often located at the intersection of these seismic lines. According to such a dynamic perspective we believe that the current seismicity of our planet could be a direct reflection of the radial movements of the Earth, induced by variations of the total intensity of the major gravitational fields (galactic, meta-galactic) which determine the evolution of the solar system and of the Earth. Also a such point of view imposes at least a reconsideration of the global tectonics theory based on the axiom of a ultramobilist planet at its crust level, with constant planet volume, considered completely isolated of its cosmic context.

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DOI resolver: doi.org/10.5593/sgem2017/14/s05.029

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