STUDY ON THE STRUCTURE OF THE CRUST AND UPPER MANTLE IN LINFEN EARTHQUAKE REGION IN SHANXI

On the basis of the results obtained previously, we further interpret the observed D. S. S. data of Taihang As-Jingbian section of Zhengzhou Linfen-Jingbian profile. Our results show that the structures of the crustal and upper mantal in Linfen are very different from that of its east and west sides. The main characteristics of these structures are as follows:1. The strong seismic phases P₂ appeared at the west of Linfen were interpreted. P₅ reflection wave from the lower crust was recognized before Pm wave; 2. Based on the P_g and P₂ waves to the west of Linfen, we think that there is a low velocity body being about 50 km long in the depth of 8-12 km of upper part of middle crust under Lin fen basin and its west side; 3. Because the average velocity obtained from P₄ wave in the east section of Lin fen basin is lower than that from P₃ wave, we infer that there is a low velocity layer whose depth ranges from 15 -22 km. The low velovity layer was replaced by a very weak low velocity layer beneath Linfen basin and its west side; 4. The difference of the velocities of the lower crust at both sides of Linfen basin is small; 5. The Moho depth in Fushan and Qinshui to the east of Lin fen is 41.5 km and changes to 38 km at the place of 20km from Fushan. Linfen basin corresponds to the uplift of upper mantal which decline down gradually towards the west; 6. There is a deep fracture under the fractured basin in Linfen region. The upwelling of the mantal substance along fractured zones may be the reason causing the abnormal crust and mantal structure.