Rayleigh wave group velocity tomography beneath Dabie-Sulu and its adjacent areas from ambient seismic noise

The Dabie-Sulu orogenic belt is one of the major structural belts in eastern China. In order to obtain the S-wave velocity structure beneath the study area, we obtain Rayleigh wave empirical Green’s functions after cross-correlation and stacking between all possible station pairs using continuous vertical components seismograms recorded by Shandong, Anhui, Jiangsu, Henan and Hubei seismograph networks and China Broadband Digital Seismograph Network during May 2009 to May 2011. Then we extract nearly 4000 Rayleigh wave group velocity dispersion curves by using the multiple filtering method, and group velocity maps at 10—25 s are reconstructed by inversion. The ambient noise group velocity maps reveal that there are evident Rayleigh wave group velocity differences among different tectonic regions. ① Tanlu fault and its surrounding areas including Luxi block and Jiaobei block exhibit higher velocity anomaly in the crust, which may be caused by the enrichment of the higher velocities and higher density metamorphite rocks in the crust in the extensional environment. ② Rayleigh wave group velocity is apparently higher beneath the Sulu high-pressure metamorphic belt at the period of 10—25 s. Upper, middle and lower crust presents higher group velocity structure, which implies that the metamorphic belt extends probably down to the lower crust. On the other hand, it is difficult to define the range of the Dabie high-pressure metamorphic belt, because high velocity appears only at the period of 10—15 s. ③ Lower velocity characteristic of upper, middle and lower crust beneath North China block indicates that the crust there is thinning.