Inversion of gravity and topography data for the crust thickness of China and its ad-jacent region

The data of Bouguer gravity and topography are inverted to obtain the crust thickness of China. In order to reduce the effect of regional non-isostasy we corrected the reference Moho depth in the inversion with regional topography relief, and performed multiple iterations to make the result more reliable. The obtained crust thickness of China is plotted on a map in cells of l°×1°. Then we analyzed the correlation between the Bouguer gravity anomaly and fluctuation of the Moho depth. A good linear correlation is found, with a correlation coefficient of -0.993. Different correlation coefficients, 0.96 and 0.91, are found for the data in land and ocean region, respectively. The correlation result also shows that the boundary between land and ocean is generally along the bathymetric line of -800 m. In order to examine the influence of the Earth＇s curvature on the calculated result, we tried two inversion models： the inversion for the whole region and the inversion for 4 sub-regions. The difference in the crust thickness deduced from the two models is less than 5 km. Possible explanation for the difference is discussed. After comparing our result with that of other studies, we suggest that with our method the Bouguer gravity and the topography data can be independently inverted to obtain the crust thickness of China and its adjacency.

Crustal Thickness and Velocity Ratio beneath National Seismic Stations in the Sichuan-Yunnan Area Based on Receiver Function Analysis

By using the teleseismic receiver function method, this paper analyzes the crustal thickness and Vp/Vs ratios beneath the 4 National seismic stations （KMI, TNC, CD2 and PZH） in the Sichuan-Yunnan area. This study gives the variance of Moho depths and velocity ratios of the 4 stations in different directions. The results show that the Moho depth beneath the Kunming station is around 50km, and the vdocity ratio varies between 1.62 and 1.69. The thickness of crust and the velocity ratio do not change much with the direction. The crust beneath Tengchong station shows clear directivity, being 40.7km thick in the northeast and 49.7km thick in the southeast. The difference of the Vp/Vs values is remarkable between the two directions, reaching 0.2. The Chengdu station also has shallow Moho, about 40km, but is 8km deeper in the northeast and southwest and the vdocity ratio has a change of 0.13 between the two directions. The crust beneath the Panzhihua station is stable. In all directions, the Moho depth is around 60km and the Vp/Vs ratio doesn＇t change significantly.