Analysis of the radar images obtained by Veneras 15 and 16 leads to the conclusion that the ridge-and-groove structures on the surface of Venus are the result of tectonic deformation. Although the mechanism of such deformation cannot yet be unequivocally deduced, several styles of deformation can be described. Areal deformation occurs where horizontal stresses have operated over large areas. Shear deformation appears in bands showing differential longitudinal deformation. Transversal stresses operating over long and relatively narrow areas have produced belt deformation. Circular deformation is related to a specific locus of the stresses. The absence of densely cratered areas indicates that the terrains were deformed after the period of heavy bombardment. The origin of the stresses could be drag of the lithosphere by asthenospheric currents or gravity-induced spreading of surface material over upwellings. A general conclusion is that in the surveyed area of Venus neither terrestrial plate tectonics nor lunar-highland-type terrain exists.
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