Broadband ambient noise tomography in Yunnan Province

In this paper, the Rayleigh wave empirical Green’s functions are retrieved from cross-correlation of the ambient noise data recorded by the 46 permanent stations of Yunnan Regional Seismic Network from November 2007 to October 2009. The regional phase velocities with periods from 8 s to 40 s are then inverted using the generalized Backus-Gilbert method. The results show that low-velocity anomalies at shorter periods associate with the faulting area and sedimentary basins. The difference between north and south across Honghe fault due to substantial variations at shorter period phase velocity maps coincides with distribution of earthquakes. As the period becomes longer, low-velocity anomalies around the Honghe fault and Xiaojiang fault are still visible, which suggests that they are probably correlated with the high heat flow from the deeper area and the faults have cut through the crust. The phase velocities at the junction of the Xiaojiang fault and Honghe fault exhibit high-velocity anomalies that maybe, to an extent, hinder the materials of Sichuan--Yunnan block moving towards the south. These phase velocity dispersion maps provide necessary information to construct a 3-D shear velocity model of the crust in Yunnan Province.