Velocity structure of the crust and upper mantle in Xingtai earthquake region and its adjacent area

Abstract: Two seismic refraction profiles which are perpendicular to each other, running through Xingtai earthquake region, reveal the anomalous variations of crust-mantle velocity structure and deep tectonics. Pg wave attenuates rapidly with distance in the earthquake region. A group of strong reflections from a depth of 21.0 km can be identified along the section from Longyao to the piedmont of Taihang Mountain, but P_m waves characterized generally by strong amplitude are not obvious. Under the earthquake region and its western neighboring region, the crustal velocity structure features high and low velocities changed alternatively. From North China plain to Shanxi plateau, the velocity at the top of the upper mantle decreases progressively, while crustal thickness increases by 11 km. Moho uplifts locally in the earthquake region. The crustal fault stretching deeply to Moho and the discontinuous sections of Moho in the earthquake region are supposed to be the channels and zones for magmatic intrusion. The uplifting of upper mantle and magmatic intrusion are responsible for the formation of anomalous crust-mantle structures and extending basins, and for the occurrence of Xingtai earthquake as well.