关键词: 青藏高原东北缘, 鄂尔多斯, 华北唐山震区, 地壳结构差异

Abstract: Obvious differences of crustal structures exist in different tectonic blocks of China's continent. These differences can be found mainly in crustal stratification, structural features of the upper and lower crust, degree of crustal heterogeneity, properties of crust-mantle boundaries, distributions of crustal low-velocity layers and the interfaces within the crust, especially the tectonic forms of the Moho. These differences of crustal structures reflect the differences of deformation features and geodynamic processes within the crust of these regions, and may provide some constraints for delineating active tectonic blocks. The descriptions of the degrees of heterogeneities of the active tectonic blocks will help to understand the probabilities of decoupling of these tectonic blocks at different depth levels. The mode of motion of these active blocks is controlled by the behavior of their boundaries and the contacting styles of the blocks. Most of the strong earthquakes in China occur near the boundary belts of these active tectonic blocks. A wide-angle reflection and refraction profile about 1 000km long was deployed in 1999, which crosses through Bayan Har fold belt, Qinling-Qilianshan fold belt, Haiyuan strong earthquake region and Ordos block from southwest to northeast. From the analysis of these data, fine structural models of the crust for the eastern edge of Tibet plateau and Ordos block were established, and the results were compared with those of North China. The differences of crustal structures in Bayan Har block of eastern Kunlun at the northeastern edge of Tibet Plateau, Ordos block and Tangshan earthquake region in North China, as well as their relationships to strong earthquakes are discussed in this paper.

Key words: northeastern edge of Tibet Plateau, Ordos Block, Tangshan earthquake region, crustal structures