Radar images of the surface of Venus show numerous structures that are interpreted as having formed due to horizontal compression and extension of the lithosphere. Many of these features exhibit characteristic scales (widths or spacings) of deformation, one of 10--20 km and another of 100--300 km. For a range of simple models, we test the hypothesis that these length scales are controlled by dominant wavelengths arising from unstable compression or extension of the Venus lithosphere. Results show that the existence of tectonic features consisted of a crust that was relatively strong near the surface and weak at is base and an upper mantle that was stronger than or of nearly comparable strength to the upper crust. The spacings of these features imply crustal thicknesses in the approximate range 5--30 km and a thermal gradient not greater than 25 K km-1.

Features that exhibit only the smaller scale of deformation can be explaind by either a lithosphere with a thick crust that overlies a weak mantle or a lithosphere with a strong mantle but with small internal strength contrasts. For a broad range of parameters, the models require not only that smaller scale compressional and extensional features have similar spacings, but also that the widths and spacings of larger scale compressional features be greater than those formed in extension. This is consistent with observed differences in the characteristic length scales of larger scale surface features, as well as the similarities in spacings of observed smaller scale features. ¿ American Geophysical Union