The crust and upper mantle structure beneath southeastern China

【摘要】：正We analyzed teleseismic waveforms recorded by 44 stations in the Fujian and Taiwan provinces of China and obtained 5344 high quality receiver functions.The crustal thickness(H) and average crustal V_P/V_S ratio(k) beneath every station were estimated using the H-k stacking method.Crustal thicknesses near the Fujian Province range from 28.3 to 32.8 km with an average of 31.1 km,and the corresponding V_P/V_S ratios vary from 1.70 to 1.84 with a mean of 1.76.From inland to offshore of the Fujian Province,the crustal thicknesses decrease and Poisson's ratios increase.These may indicate decreasing SiO_2 and increasing calcalkaline contents in the crust.The discontinuity structures such as the Moho,subducting slab,the 410- and 660-km discontinuities (hereafter we call them the 410 and the 660) are also studied using common converted point(CCP) stacking of receiver functions. Along two NW-SE lines of central and northern Taiwan,the CCP stacking results show a western dipping structure at depths above 50 km,suggesting that the Philippine Sea plate is probably subducting beneath the Eurasian continent plate near the central and northern Taiwan.The CCP stacking results show sharp and flat 410- and 660-km discontinuities,and the transition zone thickness(TZT) is the same as that of ambient mantle beneath Fujian and Taiwan Strait,but thickens in the east of Taiwan.These results suggest that(1) the subducting Eurasian continent plate is confined to the depths above 410 km beneath Fujian and Taiwan Strait;and(2) the South China Sea slab may reach the transition zone beneath the east of Taiwan.