Fine Crustal Structure Beneath the Capital Area of China Derived from Gravity Data

Abstract

AbstractIn this paper the multi‐scale wavelet method is used to separate gravity field. Moho topography of Capital area is determined using 3D Parker density interface inversion method and variable density model, constrained by deep seismic data. And at last, two typical gravity profiles are modeled. The results indicate that the crustal structure of Capital area rebuilded by multiple tectonic movements is very complicated, with adjoining depressions and uplifts, alternating basins and hills, and inhomogeneous density. Influenced by strong extension, thinning and erosion of North China Craton lithosphere, Moho topography around Capital area fluctuates greatly. The dominating tectonic direction of the Moho topography strikes from NE to NNE. Two steep slopes exist between North China Basin and Western Taihang uplift and Northern Yanshan uplift, respectively. Moho depth in North China Basin varies greatly, with the largest difference of 5 km, but the average thickness of crust in the basin is small. The thinnest is about 29 km, beneath Beijing and Tangshan area. The thickest crust is about 34 km in Wuqing depression. Adjusted by gravity equilibrium, crust thickness of western Taihang uplift area increases greatly. However, the density of western area is lower than the eastern basin. Gravity anomalies in upper and middle crusts are related to surface relief and topographic features. Affected by Cenozoic rifting, crustal structure of Capital area is very complicated in upper and middle crusts. Many geological tectonic units striking NNE are formed in different tectonic movements. Most faults cut through to the middle crust. Fold structures are formed in lower crust. High and low density anomalies are distributed alternatively. Crustal density in Capital area is remarkably inhomogeneous. Research concludes that occurrences of strong earthquakes in Capital area are probably related to upwelling of asthenosphere and uppermost mantle high density materials.