Long-period seismograms of nuclear explosions and natural earthquakes in central Asia, recorded at three digital stations of the Laboratoire de Détection Géophysique (LDG) network in France, attest to a significant propagation effect in the Tien Shan area. This allows for an investigation of the deep structures under the range, which has been the site of particularly intense intracontinental deformation since about the middle Miocene. Group velocity curves have been obtained by regionalization for pure paths across either the central or eastern Tien Shan. They indicate a crust of approximately 50-55 km in thickness, and particularly low shear-wave velocities under the central Tien Shan. Our study suggests lateral variation of the deep structures under the range, which could be related to a westward increase along the range of cumulative amount and rate of shortening.