Love wave group velocity tomography in Dabie-Sulu and its adjacent areas from seismic ambient noise

The Dabie-Sulu orogenic belt is one of the major tectonic zones in eastern China Continent. In order to obtain the velocity structure of the crust and upper mantle, we collected the continuous horizontal components seismograms recorded by Shandong, Henan, Anhui, Jiangsu, Hubei seismography networks and China Broadband Digital Seismography Network during May 2009 through May 2011.Firstly, component cross-correlations (E-E, E-N, N-N, N-E) for every station pairs were performed; secondly the four component cross-correlation functions were stacked by using the phase-weight stacking method; thirdly the components (E-E, E-N, N-N, N-E) were rotated into the radial (R) and transverse (T) components to obtain empirical Green’s functions of Love waves; finally more than 4000 Love wave group velocity dispersion curves are got by frequency-time analysis (FTAN), and the Love wave group velocity maps in the period of 6—40 s were reconstructed. The group velocity maps from 6 s to 10 s are well consistent with surface geological features. The results reveal high velocity anomalies in Dabie orogenic belt, Sulu orogenic belt and western Hubei uplift. North China exhibits low velocity due to its basin structure; Jianghan, Nanxiang and Hefei basins also show low velocity structures. The Love wave group velocity maps at the period of 6—30 s indicate that there are high velocity anomalies in Dabie and Sulu orogenic belts, while the low velocity anomalies in the middle crust in the previous studies cannot be found in this study. On one hand, it may be due to poor depth resolution of Love waves group velocity; on the other hand, this is probably because the metamorphic rock zone extends deeper than that in the previous studies. High velocity anomalies appear in Tanlu fault zone and its adjacent regions at the group velocity maps in the periods of 6—30 s, which may be caused by the upwelling of the mantle material and the mass exchange between the lower crust and upper mantle in the state of extension since the Cretaceous.