Ambient noise tomography in north China craton

Peking University deployed two linear arrays (140 km apart) of 45 portable broadband seismometers across the southern part of Shanxi Rift during August 2006 to March 2008. Using the ambient noise records at these two arrays and some stations from North China Seismic Array (NCSA) of the Institute of Geophysics, China Earthquake Administration (CEA), permanent stations from Hebei Seismological Bureau and Shanxi Seismological Bureau, CEA, China, we obtained empirical Green's function of Rayleigh wave employing the cross-correlation technique. Then we measured group velocity and phase velocity at periods from 6 s to 40 s for all possible station pairs. The results of tomography show that substantial lateral variations exist between Ordos and North China Basin (NCB). Sedimentary basins of NCB and Shanxi Rift are clearly imaged as low velocity anomalies at periods of 8 s. Low group velocities at 12 similar to 20 s and phase velocities at 12 similar to 16 s may indicate a low velocity layer in the upper and middle crust beneath NCB. However, Ordos and Taihang uplift are imaged as high velocities in the same period range. The rapid change from low velocity anomaly to high anomaly between 16 s and 25 s in phase velocity maps and between 20 s and 30 s in group velocity maps suggests that the Moho depth beneath NCB is much shallower than that beneath Ordos. At longer periods (30 similar to 40 s), phase velocity maps show that the velocity beneath NCB is lower than that of Ordos, which could be related to the thinning of lithosphere and the upwelling of asthenosphere beneath NCB. Datong volcanic region is revealed as low velocity anomaly in group and phase velocity maps from 8 to 35 s, which could be caused either by high temperature or partial melt in the crust resulting from active magmatism.