Isostatic status in North China (1) Method and local compensation |
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Authors: | Rui Feng Jun Wang Shuzhen Zheng Guifang Huang Huifen Yan Hainan Zhou and Ruoshui Zhang |
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Institution: | (1) Institute of Geophysics, State Seismological Bureau, Beijing, China;(2) Geophysical Exploration Brigade, State Seismological Bureau, Zhengzhou, China;(3) Institute of Geophysics, State Seismological Bureau, Beijing, China;(4) Peking University, Beijing, China |
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Abstract: | Following Airy and Pratt principles, five kinds of local-compensation models are analysed and a rapid 3-D gravity formula
is utilized to calculate isostatic anomalies for 66 models with different parameters. It is noted that isostatic gravity maps
appear nearly identical in their main patterns and features. The optimum compensation model in North China is one of modified
Airy models in which the different density distribution in the surface, upper crust and lower crust is taken into account
and the standard crustal thickness is about 50km. The position of the complete compensation interface is located in the upper
mantle. The North China platform as a whole is under sub-isostatic equilibrium status with an isostatic anomaly of about 18·10−5 m/s2 on an average. The distribution of isostatic gravity anomaly shows an obvious blockwise pattern. Most positive anomaly areas
occur over the eastern part, the Jiao-Liao Block, Mt. Yan block and northern margin of the Hebei-Shandong block, whereas a
negative area occurs in the Shanxi graben. The comparison of models indicates that the Moho discontinuity is not suitable
to be taken as a compensation interface, and the compensation effects in Airy model are better than that in Pratt model, which
is consistent with the feature of dominant layered structure and less lateral inhomogeneity in crust. Some results about composite
compensation, the basic characteristics of isostatic anomaly and deep stucture will be published later in the second part
of this paper.
Wang Bowen took part in some work in this paper. |
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Keywords: | Isostatic anomaly Compensation Airy Pratt North China |
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