Crustal density structures and isostasy beneath the Western North China
craton, Trans-North China Orogen, and surrounding regions
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Abstract
To determine the lateral and vertical variations in crustal structure and their influence on the seismicity of the
Western North China Craton, the Trans-North China Orogen, and the surrounding regions, the wavelet multi-scale
structures, Moho depth, crustal density structures, and isostatic state are modelled using Bouguer gravity anomaly
data, topography, and earthquake focal mechanisms. We obtained homogeneous crustal densities and deviations
of <1 km between the crustal thicknesses estimated from the isostatic model and those inverted from the Bouguer
gravity anomalies in the Ordos Block, the Inner Mongolia Suture Zone, the Sichuan Basin, and the Jizhong
Depression. These results provide new evidence for relatively simple and stable continental crustal structures, and
indicate that these regions will remain stable in both the vertical and lateral directions. The Hetao Graben,
Yinchuan Graben, Weihe Basin, and Shanxi graben system have heterogeneous crustal densities and are
isostatically over-compensated. In contrast, the crust beneath the Yinshan Uplift, Lvliang Uplift, and northern and
central Taihang Uplift is thin and under-compensated. The heterogeneous crustal densities and non-isostatic state
beneath the Tibetan Plateau and Qinling Central China Orogen indicate that these two blocks are unstable in the
vertical and lateral directions. Although Cenozoic deformation of the North China Craton is thought to be driven
by lithospheric stresses related to the India-Eurasia collision and Pacific slab retreat in South East Asia, we suggest
that gravitational potential energy created by the heterogeneous crustal structure modulates these first-order
forces. The results of this study could constrain the causes of seismicity in systems surrounding the Ordos Block.
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