The upper mantle structure beneath the Alpine-Himalayan orogenic belt (AHB) at depths from 100 to 500 kin has been studied by ITS tomographic inversion of P-wave travel times from earthquakes that occurred in the region and were recorded by the worldwide seismological network at teleseismic distances (from the ISC catalogues). The resulting maps were obtained as a sum of independent inversions in about 60 overlapping blocks 600-800 km in diameter. This approach is similar to high-frequency spatial filtration, and allows investigation of much subtler structures than in global inversion. High-velocity linear pattems along the AHB have been interpreted as traces of continental or oceanic lithosphere sinking to the upper mantle under the effect of active regional compression. The tomographic maps show well-pronounced traces of subduction. in the region of Cretan arc, Hindukush, and Burma, also confirmed by independent data, as well as other less certain evidence of subduction. Positive anomalies in the western part of the AHB are attributed to subduction in the area of Cyprus and along the Caucasus-Kopet-Dagh-Lut plate. In the tomographic maps one can see traces of the subducted Indian slab under western part of Himalayas. Beneath eastern Himalayas, the upper mantle is rather hot. Zones of sinking lithosphere are traceable around the Tarim block. A strong low-velocity anomaly in Mongolia is apparently related to the Hangai plume whose existence was inferred from geological and geophysical evidence. (C) 2002 Published by Elsevier Science B.V.
