Surface wave tomography of Guangdong and its adjacent areas from ambient seismic noise

We obtain the ambient noise cross-correlation curves for most of the station-pairs using 10 months of continuous data from the 104 permanent seismic stations of the Guangdong seismic network and its surrounding regions. Based on these symmetrically superimposed cross-correlation curves, we complete Rayleigh wave group velocity dispersion measurements for the periods from 40 s down to about 5 s using time-frequency analysis method. Ambient noise source analyses show that in Guangdong and its neighbor areas, sources of noise field has a strong directionality. Short-period noise (5—10 s) is mainly from the southeast, and its distribution is consistent with the scope of the coastline, so it may be caused by interaction of coastal land and water. Longer-period noise (15—30 s) mainly comes from the orientation of the Pacific, Atlantic, Indian Oceans. Furthermore， we obtain the Rayleigh wave group velocity distribution maps in the whole studied area for the periods from 5 s to 28 s using the ambient surface wave tomography algorithm. The tomographic results revealed that in Guangdong and its adjacent areas the crustal lateral variation is small, and the surface sediment thickness is thinner, indicating that there may be a widespread low-velocity layer in the crust. According to the characteristics of history earthquakes and surface geological structure, it can be obtained that earthquakes are mainly distributed in the vicinity of high- and low-velocity transitional zone, suggesting there is a strong coupling relationship between surface wave velocity and earthquakes. From low group velocity anomaly, it is inferred that the high geothermal and hot springs widely distributed in Guangdong and its neighbor areas is mainly under the control and influence of the deep structure.