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BASIC CHARACTERISTICS OF PRESENT-DAY TECTONIC MOVEMENT IN BOHAI BASIN AND ITS ADJACENT AREAS

On the basis of the data obtained from the GPS networks in the Bohai basin and its adjacent areas in the past decade,the present-day tectonic movement,internal deformation and strain field in this region are analyzed.The Bohai basin and its adjacent areas have a counter clockwise rotation related to the Eurasia plate as while a consistent SE ward movement with a velocity of 2.2-7.2 mm/a.The horizontal deformation field in this region shows an asymmetric four-quadrant distribution.There is relatively consistent NE ward deformation in the western part of Bohai basin and relatively consistent SW ward deformation in the northeastern part,and the two parts are in a NE-SW ward compressive status;there is relatively consistent SE ward deformation in the southern part of Bohai basin and relatively consistent NW ward deformation in the northwestern part,and the two parts are in a NW-SE ward tensile status.In the Bohai basin and its adjacent areas,the principal compressive strain axis is basically in the NEE-SWW direction and the principal tensile strain axis in the NNW-SSE direction,which are totally consistent with the dominant direction of principal compressive strain axis of tectonic stress field in this region obtained with the geophysical method.The principal direction of present-day tectonic stress-strain field in this region has been in stable status since 1969.