Rayleigh Wave Group Velocity Maps of East Guangdong and Its Surrounding Regions from Ambient Seismic Noise Tomography

We perform Rayleigh wave tomography in east Guangdong and its surrounding regions by applying the ambient noise method to broadband data recorded at 26 stations from Guangdong,Fujian and Jiangxi Digital Seismic Networks.Cross-correlations of verticalcomponent ambient noise data are computed in one-day segments and stacked over seven months from March to September,2011.Then Rayleigh wave group dispersion curves are measured using the frequency-time analysis method.Group velocity maps at periods from5s to 15s are inverted.The resulting group velocity maps generally show good correlation with tectonic features,reflecting the velocity variations in the shallow crust.The basin areas are clearly resolved with lower group velocities at the short periods due to thick sedimentary layers,and the mountain areas with higher group velocities due to thin sedimentary layers.The variations of group velocity on the map can draw out the distribution of basins and mountains in study areas.The geothermal field can change the group velocity obviously,and lower group velocities are always found in high geothermal areas.The velocity maps indicate that a low-velocity layer may be found in the study areas.