High-resolution S-wave velocity structure of Lithosphere beneath North China Craton based on Eikonal surface wave tomography

We have obtained high-resolution Rayleigh surface wave phase velocity at 10-120s and three-dimensional S-wave velocity structure from Eikonal surface wave tomography in North China Craton and its surrounding region. Additionally, lithosphere thickness is estimated based on this 3D S-wave velocity model. The surface wave data comes from the portable stations of ChinArray Phase II and III, and some permanent stations of China National Seismic Network (CSN). The lithosphere is thick in the west and thin in the east in North China Craton, in addition to this foremost characteristic there are also some smaller scale variations of lithospheric thickness. For examples, (1) within the Ordos block, the lithosphere is thinner in the north than that in the south, (2) within the peripheral rift zone around Ordos block is characterized by significantly heterogeneous thinned lithosphere, and (3) there is obvious difference between Yinshan-Yanshan Belt and North China plain to the south. In Shanxi rift zone, both the northern and southern regions exhibit varying degrees of low velocity anomalies in the upper mantle (<100km), which are separated by a high velocity anomaly zone in the central area. At depth of more than 150km, a remarkable low-velocity anomaly belt oriented NNE is observed from the southern edge of Taihang Mountain to the northern edge of Shanxi rift zone, indicating that the shallow upper mantle low-velocity anomalies are connected in the deep. Combined with some other research findings, we speculate that these low-velocity anomalies may stem from a greater depth (>200km), potentially linked with the stagnant dehydration of the subducted Pacific plate and consequent upwelling of thermal material in the upper mantle, as well as small-scale mantle convection. The lithospheric structures of the Yanshan belt is obviously different from North China Plain, with former experienced much less destruction and reconstruction. The Zhangjiakou-Bohai seismic zone is located at the transitional region between these two distinct crust-mantle structures, characterized by intense seismic activity. We conclude that the combination of significant differences in deep structure and thermal action, as well as the far-field extrusion effect of the Qinghai-Tibet Plateau, mainly contributes to the intense seismic activity in this zone.