Crustal structure and dynamical analysis of seismogenesis in the lower Yangzi Valley — South Yellow Sea area |
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| Authors: | Shengzao Chen |
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| Institution: | (1) Institute of Geophysics, State Seismological Bureau, 100081 Beijing, China |
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| Abstract: | Seismotectonic characteristics and its relationships with crustal structure have been analyzed in the lower Yangzi—South Yellow
Sea area. The finite element method is employed to evaluate the stress-strain status of the lithosphere, and the dynamic origin
of earthquakes is discussed. The moderate-weak earthquake division is tectonically controlled by three first-degree faults
in the Hangzhou bay—Qinling, Tancheng—Lujiang, and the Yangzi River mouth—Jizhou island. The earthquake frequency is higher
than 70% in the major hypocentral layer of the crust at a depth of 5 to 15 km of which the highest frequency particularly
emerges at a depth of 10 to 15 km, and generally, the depth ranges from 5 to 20 km in the predominant hypocentral layer. The
hypocentral layer is superimposed in the crustal magnetosphere with the mid-crustal low density layer. The results from the
finite element analysis show that the maximum horizontal displacements appear in the hypocentral layer of the crust, and that
the radial hypocentral zones on the flanks of the anomalous mantle, accompanied by the faults or fractured zones, correspond
to the gradient zones of the major principal stresses and strains varying within the lithosphere. Therefore, we could consider
the mechanism of the decoupling-drift of the lithosphere and the crustal sliding or detachment, from the continent to the
sea, as a main dynamogenesis of the earthquakes in the area studied.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 164–171, 1992.
This research was supported by the China National Post-Doctoral Research Foundation in part. Some contents on the aeromagnetic
anomalies and their mathematical processes are deleted in revision. |
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| Keywords: | seismotectonics seismogenesis crustal structure finite element analysis |
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