Group velocities of fundamental mode Rayleigh waves of 109 wave paths within Eurasia have been measured by an improved frequency-time analysis technique. Stochastic inversion theory is applied to the mixed-path measurements to extract pure path group velocities of 10¿¿10¿ grid elements that form the subdivisions of Eurasia. Then a three-dimensional crust and upper mantle structure of the Eurasian continent to a depth of 300 km is constructed. The average crustal thickness of Eurasia is found to be about 40 km. Abnormally thick crust from 50 to 65 km is obtained in areas of Tien Shan, the Altai mountains, Afghanistan, Pamir, Tibet, and Burma. Among them, Tibet has the least dense crust and highest elevation. This implies that at least part of the elevation of Tibet is due to isostatic compensation. The upper mantle seismic velocity of the tectonically active regions of Asia is considerably lower than that of the European and Siberian cratons. If high velocity implies high rigidity, this explains that large-scale tectonic deformations of Eurasia occur in regions with weak upper mantle that deforms more plastically. Regions with stronger upper mantle remain relatively undeformed. This is especially evident for the Tertiary tectonic deformation as a consequence of the collision of India with Eurasia.