Structure of the crust and uppermost mantle beneath the North China Craton from long-range seismic wide angle reflection/refraction profile

The North China Craton (NCC) is the oldest craton in China, which formed around 2.5Ga and had a 200 km thick lithosphere during the Paleozoic. The cratonic lithosphere of NCC has experienced strong thinning since the Mesozoic. In the past 30 years, a lot of excellent research about NCC have provided some different tectonic models, however, carton destruction is a sophisticated process. Recent long range seismic wide angle reflection/refraction experiment have been providing new opportunities to obtain better knowledge of seismic structure and properties of lithosphere. A 1500 km long wide angle reflection/refraction profile was completed in 2009. Our long range profile extends from west end of Ordos Plateau, across Shanxi Plateau, Taihang Mountains, to Luxi Uplift. The recording of seismic waves from 11 chemical explorations was conducted in 600 three-component geophones with station spacing of 1~3km. The shooting procedure was employ 2000 ~ 5000kg explosives in 4-5 or 15-23 boreholes at 70-80m depth. The refractions in the upper crust (the Pg phase), the reflections from the Moho (the PmP phase) , the refractions in the uppermost mantle (the Pn phase) and the refractions in the upper mantle (the PL phase) can be easily correlated in all the seismic sections. we focus our attention mainly on the Pg, Pn, PL and PmP arrivals. We follow the standard modelling strategies described by Colin Zelt (Zelt, 1999). The 2D ray-tracing program RAYINVR was used for forward modeling and inversion of travel times (Zelt & Smith, 1992). The travel time modeling was done using'across-and-down' modelling approach layer by layer. Subsequently, the forward model was updated by damped least-squares inversion for the velocity and interface nodes until χ² less than 1. The final velocity model reveals large variations both in structure and velocity, and is demonstrated that a particular model has minimum structure. Supported by NSFC (grant No. 90814012 and No. 41104038)