Activity Tendency and Dynamic Characteristics of Shanxi Fault Zone

The tendency and dynamic characteristics of horizontal movement along the Shanxi fault zone have been analyzed using the data obtained from 6 repeated measurements (1996～2001) in the GPS monitoring network arranged along the Shanxi fault zone. The results indicate: (1) the tendentious activity of the present stage is characterized by a W trending movement along the northern segment of the zone, an E trending movement along the southern segment and counter clockwise differential activity on the whole, but the intensity of the tendentious activity is not high. The tendentious differential movement is only about 3 mm/a in the direction perpendicular to the fault zone from the south to the north, and its stretch in the SN direction is only 1 mm/a and mainly occurs along the north segment of the fault; (2) The azimuth of the principal compressive stress field reflected by the tendentious movement is 72°; (3) The property of annual activity is not the same, even contrary to one another or deviates from the tendentious activity. Therefore, the parameters of the strain field derived from them dont reflect the physical characteristics of the basic stress field. (4) The high frequency movement (yearly) does not only exist but is also complicated by an intensity several times higher than that of the tendentious movement; (5) Obvious differential movements, including strike slip, can not be seen in either in secular activity or annual activity on both sides of any fault. The tendentious movement not only verifies the conjecture of “strong in the south and weak in north”, which is the basic feature forcing the western boundary of the North China area, but it also extends to the hinterland of North China. The fact that there is no obvious differential activity on both sides of the fault might indicate that the differential activity among the intraplate blocks is completed by gradual variation in a certain space, rather than the abrupt change bordered by a fault or narrow stripe zone. The obvious dynamic activity might indicate: (1) there is stress disturbance in the basic stress field; (2) the inhomogeneous or non synchronous variation that appeared in the regional stress and strain fields was due to the different physical property of the medium; (3)the response occurred because of a variety of external variations. The movement in 2001 shows that the Daixian county and its adjacent area might be the boundary segment for the relative differential activity. More attention should be paid here.