High resolution Rayleigh wave group velocity tomography in North China from ambient seismic noise

P>This study presents the results of the Rayleigh wave group velocity tomography in North China performed using ambient seismic noise observed at 190 broadband and 10 very broad-band stations of the North China Seismic Array. All available vertical component time-series for the 14 months between 2007 January and 2008 February are cross-correlated to obtain empirical Rayleigh wave Green's functions that are subsequently processed, with the multiple filter method, to isolate the group velocity dispersion curves of the fundamental mode of the Rayleigh wave. Tomographic maps, with a grid spacing of 0.25 degrees x 0.25 degrees, are computed at periods of 4.5, 12, 20 and 28 s. The maps at short periods reveal lateral heterogeneity in the crust of North China, in good agreement with known geological and tectonic features. The North China Basin is imaged as a broad low velocity area, while the Taihangshan and Yanshan uplifts and Ordos block are imaged as high velocity zones, and the Quaternary intermountain basins show up as small low-velocity anomalies. A well-defined low velocity zone in the Beijing-Tianjin-Tangshan region is observed at 28 s period. The low velocity zone may be associated with the upwelling of hot mantle material. The group velocity maps at 4.5, 12 and 20 s are consistent with Bouguer gravity anomalies measured in the area of the Taihangshan fault, that cuts through the lower crust at least.