Abstract:
The crustal and mantle shear wave velocity structures 100km beneath Taihang Mountain and its neighboring areas were calculated with pure S wave inversion and T function method.The results show that there is obvious difference in the crust and mantle structures at the southern, middle and northern part of Taihang tectonic zone.In the southern segment, Xingtai and Handan region, there is a 10km low velocity layer in the lower crust.In the middle segment, Shijiazhuang to Baoding region, the crustal structures near the mountain is relatively steady, but it becomes complicated toward to the basin.The northern segment, Beijing area, which is the crossing region of Taihang and Yanshan tectonic belt, shows an unstable state.Some alternated layers with high and low velocity appear in the middle and lower crust of the segment.The eastern boundary of Taihang tectonic belt is the seismically active belt-Hebei plain seismic belt.Compared the velocity structures with the distribution of earthquakes, it is found that the characteristic in the distribution of small earthquakes on different segment is closely related to the low velocity layer or unstable structures.Combined with upper mantle velocity structures beneath this area, it is thought that, the middle segment of Taihang Mountain may be correlated to the large scale lithospheric thinning activity in North China since Mesozoic and Cenozoic, while beneath the southern and northern segments, the mantle media is active at present time, and tectonic activity is stronger.