North China sub-craton lithospheric structure elucidated through coal mine blasting

Abstract

We present a super-range seismic observation along the >1300-km-long profile passing through the Yinchuan basin and the Ordos block from the blasting point towards the southeast triggered by a large-(dynamite) scale coal blast in the Ningxia Hui Autonomous Region’s Helan Mountain (yielded a profile). The seismic wave information from the uppermost mantle reflecting different depths was obtained by the China continental seismic survey. Pn refracted waves from the uppermost mantle were effectively traced up to 500 km and beyond. The stable dynamic and kinematic characteristics of the Pn wavegroup indicate that the uppermost mantle below the Ordos block is a gently changing structure with a weak positive gradient. If Pm1, Pm2 waves are considered as the wave groups from the upper mantle, there may be distinct structural strata in the upper-mantle structures with average velocities of 7.70–7.80 km/s and 8.10–8.20 km/s, respectively. Based on the travel-time curve feature of Pm1, Pm2 waves, there may be a certain layer with a reverse velocity between the M1 and M2 interfaces. The depth range indicated by them is about 110–120 km and 200–220 km. These phenomena basically reflect the structural features of the upper-mantle lithosphere in this region. The information obtained may provide meaningful references for surveying North China craton lithospheric structures, as well as understanding the shapes and structures of different spherical layers within the upper-mantle.