| 摘 要： | By analyzing the gravity,magnetic,seismic and drilling data,the authors in this paper calculate and construct the density structure of the crust and upper mantle along the Haoding-Chengde and Zhangjiakou-Tanggu profiles and residual gravity anomalies in the region.The compiled residual gravity anomalies g2 and g4 maps reflect qualitatively the spatial distribution of the density structure of the crustal "seismogenic layer" and the uppermost mantle layer at depth of 50-75 km in the region.In order to reveal the relationship between density structure and seismicity,a great number of statistic calculations and comparisons of the available data and the results indicate that the seismicity in the crustal "seismogenic layer" is characterized by block movement:moderate-small earthquakes occurred generally within the blocks,moderate-strong earthquakes mostly along the borders of the blocks,strong earthquakes mostly at the edges and corners of the blocks.And aftershocks of strong earthquakes tended to occur at o
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