Development of subcracks betweenen echelon fractures in rock plates

Uniaxial compression tests on marble plates containing two prefabricateden echelon fractures were performed in this study. Photographs showing the typical characteristics of subcrack development were taken under direct scanning electron microscope (SEM) observation during the test. From these photographs, the effects of the lengthL of a single fracture, the separation distanced and overlapping proportiona/L between two prefabricateden echelon fractures on the development of subcracks were analyzed. The results show that the interaction betweenen echelon fractures strengthened with decreasingd. FordL, there was little interaction and the development of subcracks near one of theen echelon fractures was unaffected by the existence of the other. Whereas ford, the number of subcracks in the area intermediate betweenen echelon fractures tended to increase with increasinga and decreasingd. In order to ascertain whether the experiment can furnish some implications for research on earthquake prediction and neotectonic activity, the test results were compared with the spatial-temporal development of foreshocks and ground-water anomalies before the 1975 Haicheng earthquake and the structural framework of the Ganzi pull-apart basin. The results of the comparison are encouraging. According to the similarity between the test results in the laboratory and the natural phenomena in the field, the fault on which the Haicheng earthquake would occur, could be inferred immediately from the relative geometry of the two sub-parallel active faults in the area. Thus, it is considered that the test results would advance our understanding of the process of neotectonic activities and give us inspiration for earthquake prediction.