含水团山砂岩破裂孕育过程中的Q值变化及声发射

本文采用滇西地震预报实验场基地团山砂岩浸泡一个月后进行真三轴压缩试验。结果发现:最小主应力轴方向和中间主应力轴方向Q值都有异常峰值,且变化不同。它们分别在破裂应力的40％—70％和50％—70％之间。而异常峰值后,又都在一段正常值,破后又都上升。从谱振幅随压力的变化看出,异常峰值的出现是由于高频成份的增加大于低频成份。峰值后的正常值出现是由于低频成份的增加及高频成份减小所致。而破后Q的上升则是由于低频振幅减小更多所致。声发射率也有峰值—相对平静——第二峰值—缓裂特征。

THE VARIATION OF Q-VALUE AND ACOUSTICEMISSION DURING THE RUPTURE-FORMATIONING PROCESSUSING WATER-SATURATED TUANSHAN SANDSTONE SAMPLES

This paper introduces the laboratory experiments using Tuanshan sandstone samples collected from the compound of the Western Yunnan Earthquake: Prediction Study Area headquarters. The rock samples were coaked in water for one month before being placed under true triaxial compression. Result from the laboratory study shows that abnormal peaks of the Q-values are observed respectively along the intermediate and minimun principal stress axes and that those abnormal peaks present dissimilar changes which respectively occur at 40%-70% and 50%-70% of the rupturing stress. Such abnormal peaks are followed by segments of normal values which again show rises after the rupturing. Viewing from the pressure-dependent spectral amplitude variations, it can be observed that the emergence of abnormal peak values is due to that the increments of high frequency components are much greater than that of the low frequency components. The emergence of normal values after the peak values is resulted from the fact that the low frequency component increases whereas the high frequency component decreases. The Q-value rises after the rupturing are caused by further decrease of the low frequency amplitude. The acoustic emissions also show features of peak value-relative quiescence-second peak value-retarded rupturing.