DEEP TECTONIC BACKGROUND OF THREE Ms ＞ 7.0 STRONG EARTHQUAKES IN BOHAI AND ITS ADJACENT REGION
渤海及邻区3次7级以上地震的深部构造背景

Through synthetic analysis and interpolation to the results of deep seismic sounding profiles,the crustal thickness graph of Bohai sea and its adjacent region is obtained. Combining with other geophysics results, some opinions about deep structure background of three Ms>7.0 strong earthquake in Bohai sea and its adjacent region during 1969 to 1976 are proposed that the Bohai region is the center of upper mantle upheaval, where the thinnest crustal thickness is only 28 km;furthermore, this region is also the center of high thermal flow, vertical deformation of crust and the Curie surface upheaval and the raised region is a NNE-striking belt and is corresponding to the strike of Tancheng-Lujiang fault belt.The Bohai earthquake, the Haicheng earthquake and the Tangshan earthquake all occured in the edge of the raised region and it maybe related to the stress field caused by the upper mantle upheaval and the thermal stress field caused by the abnormal thermal activities.