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PRELIMINARY STUDY ON MOTION CHARACTERISTICS OF LONGMENSHAN FAULT BEFORE AND AFTER Ms8.0 WENCHUAN EARTHQUAKE

In this paper by utilizing the mobile short-line leveling data across the Longmenshan fault the variation characteristics at each observation site before and after the Wenchuan earthquake are analyzed.By analyzing the motion type and stress pattern of the Longmenshan fault we investigated the seismogenic process and mechanism of the earthquake.The preliminary results are as follows.a)Before the Wenchuan earthquake the cross-fault short-line leveling in 2006 showed the activity at all of the stations of Longmenshan fault with a characteristic of accelerative movement to different degrees.b)Before the earthquake the short-line leveling indicated that the middle-south segment of Longmenshan fault showed reverse faulting movement,and the fault deformation was of inversive "S" type.c)Before and after the Wenchuan earthquake the cross-fault displacement measurements reflected the spatial-temporal evolution of the accumulation and release of regional surface stress,the interpretation of their mechanism is basically consistent with the focal mechanism solution.