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《Seismology and Geology》 2003-02
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CHEN Shun yun XU Zhao yong YANG Run hai ZHAO Jin ming (Seismological Bureau of Yunnan Provice, Kunming 650041, China)  
Using the coarse grained granite from Dali, Yunnan, as the test material, a sample of 200mm×200mm×15mm in size was prepared. On the sample, V shaped block boundaries consisting of en echelon faults (slots or prefabricated cracks) were cut, and the slots were filled with gypsum. According to the structural characteristics, the sample was divided into a few zones: zone A where faults converge, zone B where faults form left lateral and left stepping rock bridges, and zone C where faults form right lateral and left stepping rock bridges. Observational study was made by means of biaxial loading. The result of microcrack location shows that acoustic emission (AE) has the features of grouped occurrence in a region and grouped migration. Microcracks migrated from zone A to zone B and finally to zone C. In the initial stage of migration, AE events appeared alternatively in the place of original occurrence and the place where they migrate. In each stage, relatively large AE events occurred in each zone, but they concentrated relatively in zone C where they finally occur, and the sample ruptured finally when rock bridges in zone C broke down. The result of fixed strain showed 3 times sudden change, sudden rise or sudden fall, in accordance with the movement characteristics of AE of the zones A, B, and C. Analysis of the local b value by the "accumulated frequency energy level" relation showed that the b value of the zone C reduced obviously before the main fracture. When examining from the structural characteristics, it can be seen that the three zones are the places where different structures meet each other and therefore are sensitive sections for events to occur. This has led to different orders of fracture or different precursor phenomena.
【Fund】: 国家重点基础研究发展规划项目 (G19980 4 0 70 4 );; 中国地震局双重项目 (96 9130 90 2 0 30 1);; 国 家自然科学基金 (4 6 76 40 10 )共同资助
【CateGory Index】: P315.72
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