3-D lithospheric structure beneath western North China Craton from Rayleigh-wave tomography

We used 2-year broadband seismographs of China Earthquake Networks Center and 6-month of Peking University to establish the 3-D wave velocity structure beneath the western North China Craton (NCC). We firstly extracted the Rayleigh-wave velocities for period of 20 s to 125 s (frequency of 0.008 Hz to 0.05 Hz) with a newly developed tomography method, two-plane-wave method (Forsyth & Li, 2005). This new method adjusts traditional single plane-wave basis and uses two plane waves to fit teleseismic surface-wave field, getting more realistic results. As Rayleigh wave velocity is most sensitive to shear wave velocity variation, we got the 3-D shear wave velocity structure for the depth of 0~200 km. The results indicate that the Ordos Craton, which has been stable since Archor is obviously high-velocity-anomaly for over 200 km depth. While the Central part of NCC, including the Shanxi Rift, has obviously low-velocity-anomaly from Moho to 200 km. We interpret this enormous velocity changes as an evidence for the apart geologic processes of the eastern and western parts of NCC. The reactivation since Mesozoic of NCC may have caused upwelling of upper mantle right beneath Shanxi Rift.