STATE OF MODERN TECTONIC STRESS FIELD IN EAST CHINA MAINLAND

The characteristics of the modern tec-stress field in the eastern part of the China Mainland are comprehensively studied in this paper based on in-situ stress measurements (overcoring and hydrofractering) combined with logging data of oil-wells, focal mechanism solutions and recent activities of faults.Our finding is as follows:1. The stress state seems to be different in different regions: the direction of major horizontal principal stress in North China is about E-W, the direction in the area to the west of Mt. Taihang is N-NE and in South China almost N-W. The direction of the major principal stress in a region remains the same from tens of meters to 4000 meters below surface.2. The major horizontal principal stress at depth of tens of meters in North China ge-nerolly has a magnitude of 2-6 MPa, slightly less than that in South China. The average differences between the major and minor principal stresses in both regions are also different.3. The shear stress on the active Tanlu fault is much less than that in areas surrounding the fault and tends to the regional magnitude at some distance removed from the fault.4. The occurrence of a major earthquake noticeably affects the stress field in the area surrounding the epicenter but after a certain period of time the stress field will recover its normal state.