LITHOSPHERIC STRUCTURE IN THE TIBET-JAPAN PROFILE

The authors have utilized the data of surface wave recorded by long period digital seismometers to study the lithospheric structure in the Tibet-Japan profile. In data processing certain computational approaches to pure-path effect of surface waves and the continuous velocity model are taken into account for obtaining velocity distributions in the lithosphere of the Asian continental margin, North China and the Tibetan plateau. The velocity structures of the upper mantle in the first two regions are somewhat similar in the characteristics of thin lithosphere and alternating distribution of high-and low-velocity layers, which show some features of active tectonics. The upper mantle structure in the Tibetan plateau is like that in a stable platform and the corresponding crustal stucture shows active tectonic feature. The differences in the stuctures among the above three tectonic units are likely to extend from the crust down to 200 km deep in the upper mantle, this indicates the different movements of the Indian and Pacific ocean plates. It is inferred that the dynamic process of seismicity in North China and Japan is of the crust-mantle type, however in the Tibetan plateau is of intra-crust type.