The crustal structure beneath the Shidao Station on Xisha Islands of South China Sea
南海西沙石岛地震台下的地壳结构研究

We installed a temporary earthquake station at Shidao on Xisha Islands of South China Sea to study the seismicity and lithospheric structure of the region,and carried out the observation experiment for more than one year.Although the seismic data in reef and island areas have relatively large background noise,especially during the passage of a tropical cyclone,earthquakes above M-W 6 can still be recorded.In this paper,those teleseismic records with clear P waveforms are chosen to carry out receiver function analysis and modeling.A simple crustal structure model beneath the station is obtained,in which the Moho depth is 28 km.On the top of the upper crust is a 2 km-thick low velocity layer with a shear wave velocity of only 2.3 km/s.The shear wave velocity increases gradually with depth to 3.8 km/s in the lower crust.We compared this model with previous results and discovered that the models of Shidao Station and Qiongzhong Station(QIZ) are the natural extensions of the Xisha Trough section.The crustal structure of Xisha Block consists of thinned continental crust,with a velocity structure that is similar to the normal continental crust of South China Block.