HOW FLAT IS TIBET

High resolution digital topography (three are-second grid) for most of Tibet provides new information to characterize the relief of the high est and largest plateau on Earth. The arid to semiarid central and nor thern part of the plateau interior has low relief (average slopes of s imilar to 5 degrees over 250 m windows) and a mean elevation of 5023 m above sea level. At moderate wavelengths of similar to 100 km, relief is similar to 1 km or less for most of Tibet, as opposed to the much higher relief of up to 6 km on the plateau edges, where glacial and fl uvial dissection is greater because of higher levels of precipitation. The only faults manifesting significant topographic relief are the re latively small scale, generally north-trending graben systems, primari ly in southern Tibet, and several large-scale fault systems near the e dges of Tibet. The flatness of Tibet implies that (1) there has been l ittle deformation (especially shortening) of the uppermost crust north of the graben systems during the late Cenozoic, and (2) shallow crust al isostatic compensation has been acting to level the surface of the plateau.