THE FEN WEI GROUND-FISSURE AND MODERN SEISMIC ACTIVITY

In recent years,ground fissures occur at 101 sites in the FEN WEI region. Among all the ground fissures,62 per cent are controled by active faults,20 per cent resulted from extention of the fracture networks which consist of regional tectonic joints of loess,and 18 per cent are nontectonic ground fissures,due to gravity,wet--subsidence etc. By investigation,we found that the anomalous behavior of ground water,water temperature,mordern minor and major seismicity all go through a cycle of rise and full every four years with ground fissuring in the FEN WEI region. They are the precursor information that the regional tectonic stress is strengthening contineously. Since the response of the behavior of ground water to regional stress is most sensitive,its high tide of anomaly appears most early. Because the occurrence of earthquakes due to tectonic fractures which need the accumulation of stress and is a slow process,and the transmission of the fracturing to the surface of the earth also requires some time,the high tide of activity of earthquakes and ground-fissures is respectively later than that of ground water by about 1-2 years.