GROUND SURFACE DEFORMATION OF THE HAICHENG (海城)EARTHQUAKE OF MAGNITUDE 7.3
THE GEODETIC SURVEY BRIGADE FOR EARTHQUAKE RESEARCH, NATIONAL SEISMOLOGICAL BUREAU
Ground deformation took place before and after the Haicheng Earthquake of magnitude 7.3. During the few decades before the, earthquake vertical crnstal movement was observed over a very broad area around the earthquake region and the epicenter of the earthquake happened to be situated at a place where two belts of steep gradients of vertical movement intersect. During the 18 months before the earthquake the short levelling base line at the Jin Xian (金县) station, about 200 kms from the epicenter, recorded a set of data involving several stages of crustal deformation : the initial stable state of the ground surface, then beginning of tilting in one direction, followed by tilting in the opposite direction and stages of rapid tilting and finally slow variation of the tilt direction. Such a sequence of observations provided one of the bases for intermediate and short term prediction of the Haicheng Earthquake. Surveys made after the earthquake give the magnitude and the area of the deformation associate with the earthquake. The stress condition inferred from crustal deformation observation seems to be in good agreement with that inferred from other observations.In The Haicheng Earthquake prediction, a rather successful attempt was carried out in a way by combining observations of crustal deformation at fixed stations, along lines arid over a broad area and also combining closely with other kinds of observations.