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Abstract First of all，the feasibility of using a universal distinct element code(UDEC) to simulate stress waves propagation in rockmass has been validated. Then，the study about the rules of stress waves crossing fractures which have various attitudes has been conducted. The three main fractures in Longmenshan region affecting the stress waves propagation are used as an example to validate the rules of stress waves crossing fractures and illustrate the shock isolation effects and the hanging wall effects of the large-scale fracture. The main research results can be summarized as follows：(1) The dynamic responses of the earth?s surface beside the fractures are anomalous compared with that on the fractures；and the dynamic responses of the earth?s surface on the side of hypocenter will be more seriously than that on the other side. (2) With the increasing of fractures attitudes from 0° to 90°，the shock isolation effects of fractures on stress waves firstly will increase and then will decrease；and the dynamic responses caused by transmitted waves will be weaker with the increasing of the amount of fractures. (3) Wenchuan—Maoxian fault and Guanxian—Anxian fault are not coseismic fault；so they have shown good shock isolation in the process of Wenchuan earthquake. Compared to the condition without faults，the vertical peak ground accelerations of hanging wall surface of Wenchuan—Maoxian fault and foot wall surface of Guanxian—Anxian fault decrease 38% and 47% respectively. (4) Because of the faults reflecting the earthquake waves，the dynamic responses of earth?s surfaces of the hanging wall and footwall of Yingxiu—Beichuan fault are serious compared to the state without faults. The vertical peak ground accelerations of the hanging wall and footwall surface of Yingxiu-Beichuan fault increase 41% and 32% respectively. The above research results reflect the shock isolation effect and hanging wall effect of fractures.
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Received: 22 October 2010
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2011, Vol. 30 
