STUDY ON THE STRUCTURE OF DEEP S WAVE VELOCITY INSIDE AND OUTSIDE MACROSEISMIC REGION OF HEBEI PROVINCE

The shear velocity structure under 3 stations in-the old earthquake region of Shacheng and its neighboring areas is inversed with short-period S wave records.All the results are analyzed by comparison.Combined with the velocity structures under other 5 stations in Xingtai and Tangshan earthquake region,the commoncharacters of the velocity structures under macroseismic region are found,i.e.(1)the thickness of the crust is thinner than that of the stations around;(2)the velocity in low velocity layer of S wave is much lower than that of its vicinity,and the difference between high and low velocity layer is much bigger;(3)the S wave velocity in upper-mantle layer is lower under the region;(4)strong earthquakes usually took place in the high veliocity layer above a low velocity layer or on the interface of high and low velocity layer;(5)usually,the earthquake prone layer is the high velocity interlayer of two low velocity layers.(The earthquake prone mechanism of such structure is analyzed).In short,the occurrence of strong earthquake is closely related with the low velocity layer,which shear wave is sensitive to its structure.So the study on S wave velocity structure is significant to revealing the background of deep structures and focal mechanism under strong motion region.Simultaneously,these common characters under strong motion region provide a scientific basis for the division of macroseismic risk region and the place prediction of potential strong earthquake.