The upper and middle crustal velocity structure of the northern part of Hebei plain inferred from short period surface wave dispersion

Based on short period Rayleigh wave data recorded by Beliing Seismic Telemetered Network, the dispersion curves of Raleigh wave phase velocity, with period from 2 s to 1 8 s, are calculated by means of two-station method, for 5 paths across the earthquake zone located in the Beijing graben and the Hebei plain. According to the dispersion features, the upper and middle crustal S wave velocity structures are respectively obtained for the northern segment of Beijing graben and the northern part of Hebei plain. The results show that there is an obvious interface at the depth of g kin in the Beijing graben, the velocity varies little with depth in the middle crust, and there is a low-velocity-zone, with a thickness of 5 km and a buried depth of 14.6 km, in the middle crust of the Hebei plain.