SEM study of fracture development in a compressed marble specimen and implications for earthquake precursors : Zhao Yong-Hong, Huang Jie-Fan & Wang Ren, Acta Geophysica Sinica, 36(4), 1993, pp 453–462

Abstract

Uniaxial compression tests of marble plates each containing a slot were conducted under direct SEM observation. The specimen was 20× 10×2.5 mm3 in size. The slat was 7 mm long and 0.44 mm wide and cut through the specimen normally at an inclination of 45° to the loading axis. The initiation, propagation, plan distribution and coalescence of cracks on the specimen surface were monitored throughout the whole test process. From the microphotog-raghs taken at different stages of loading, the opening and closure of microcracks in the frontier area of a propagating fracture were studied, and the variations of fracture width with the loading level and with the position of measuring point were analysed. Based upon the test results, the significant deviation of the fracture energy needed to propagate a macrocrack in brittle rock materials from the value estimated by the theory of linear elastic fracture mechanics was explained, the concept of using a scalar as the damage parameter in rock damage mechanics was put forward and the possible significance of the test results for understanding various earthquake precursors, such as crustal deformation and groundwater anomalies, etc., was investigated. By comparing the test results with the precursory anomalies of groundwater level prior to the 1975 Haicheng earthquake (Ms = 7.3), it was found that the temporal-spatial distribution of groundwater level anomalies had showed many features closely resembling the sequence of crack activities observed in our test.