STRESS FIELD OF THE TANGSHAN EARTHQUAKE AREA AND ACTIVE CHARACTERS OF THE EARTHQUAKE FAULT

In this paper, the focal mechanism parameters of the earthquakes of M ≥ 4 occurred from July 28, 1976 to 1989 are colected.The dislocated-slip angle of the fault plane, fault features and rotation mode of the focal mechanisms of the earthquakes in 1976-1979 are determined and added.324 earthquakes occurred in 1976-1989 have been confirmed by computer.The space position of the stress axis, the occurrence nature, rotation mode and dislocated-slip movenent of the fault plane have been studied.The results show that the principal pressure stress in Tangshan area is nearly in the direction EW, the fracture surface strike is NE, the deep angle is large.The faults are mainly the right lateral reverse faults, the horizontal dislocation is 1-2 tiroes the vertical one.Under the effect of the regional stress, the earthquake source mechanism in Ninghe and Luanxian areas show different characters.