Mechanism of transient electric activities associated with rock failure

尽管人们对岩石中的破裂发射现象越来越感兴趣，特别是与观察到的可能与地震有关的电磁异常有关，但有关这一主题的实验数据迄今有限。本研究进行了岩石的单轴和三轴压缩试验，并测量了岩石试件所在的两个铜板电极之间的瞬时电荷信号和电势差的断裂诱发电信号。我们的实验结果表明，在两种类型的实验中：(1)只有主要成分矿物为石英的花岗岩才能检测到在岩样主破裂之前出现的电荷信号；(2)在主破裂时刻，无论是否存在石英颗粒，所有被测试件都观察到了电荷信号和强烈的电场变化。对于花岗岩等含石英岩石，石英的压电性对干岩破裂前的前兆电信号有一定的贡献。然而，我们的结果证实了还有其他重要的促成因素。

Despite the increasing interest in fracto-emission phenomena in rocks, particularly in connection with the electromagnetic anomalies observed possibly related to earthquakes, experimental data reported on the topic has so far been limited. In this study, uni-axial and tri-axial compression tests of rocks have been conducted and fracture induced electric signals were measured as a transient electric charge signal and as an electric potential difference between two electrodes of thin copper plates, between which the tested rock specimens sit. Our experimental results showed that in both types of the experiments : (1) Electric charge signals that appeared prior to the main failure of rock specimens were detected only for granitic rocks of which main constituent mineral is quartz, and (2) At the moment of the main failure, however, electric charge signal and intense electric field change were observed for all tested specimens irrespective to the existence of quartz grains. For quartz-bearing rocks such as granite, the piezoelectric behavior of quartz should contribute to some extent to the electric signals observed during the precursory period prior to fracture of dry rocks. Our results, however, confirmed that there are other important contributing factors.