East China is composed of a mosaic of tectonic blocks and lineated orogenic belts. In most cases, the physical mechanisms that have produced the crustal extension, cratonic rejuvenation, continental collision, and crustal flow that have occurred across parts of east China remain poorly understood. These questions can be illuminated with seismic images of velocity heterogeneities, internal discontinuities, and crustal and mantle anisotropy. The rapid expansion of seismic instrumentation in China over the past few years provides the opportunity to obtain a much more detailed seismological model of the crust and uppermost mantle. Ambient noise tomography is uniquely sensitive to crustal structures, and it is applied here to three classes of data in east China. (1) In north and northeast China, there are more than 300 broad-band seismic stations from Chinese Provincial networks, the Japanese F-Net, and the IRIS Global Seismic Network, providing two years of continuous data from 2007 to 2009. (2) In south China there are two years of continuous recordings of ambient seismic noise observed at 425 stations in the years 2009 and 2010. (3) In central and western China, there are ~600 stations from permanent Chinese Provincial networks, several temporary US PASSCAL installations in and around Tibet, and the Federation of Digital Seismographic Networks (FDSN), providing data between 2003 and 2009. We merge these data sets to produce group and phase velocity maps from 8 sec to 45 sec period for China east of 100oE longitude to obtain Rayleigh wave group and phase speed maps, and eliminate the disturbance of the Kyushu microseism on the dispersion measurements. In most areas, the spatial resolution is about 100km.
Based on these dispersion maps, we further develop a 3-D SV shear wave structure model for the whole area of East China. The 3D structures are in good consistent with the geological structures: In the eastern part of the North China Craton (NNC), high velocity anomalies can be observed at 30-40km, while at 70-80km low velocity can be observed in the same area; on the other hand, low velocity anomalies can be observed in the west part of the NNC, while at the depth deeper than 80km, the shear wave speed keeps high. Considering the differences between th eastern and western part of the NNC strcutures we argue that the lithosphere in the Ordos block and the west part of the NNC are strong and thick, while in the North China Plain the lithosphere is much weaker and thin, which in good consistent with previous studies (e.g, Chen et al., 2009). The high speed in the shallow part of the North China Plain and the low velocity at depth deeper than 70km may argue that there is a strong lid at the top of the lithosphere, and the lower part of the lithosphere has been erosed and thinned by asthenosphere. So our result may support the “bottom-up” model prompted by Menzies et al. (2007) instead of “top-down” rapid delamination.
