Mechanism of transient electric activities associated with rock failure

尽管人们对岩石中的碎片发射现象越来越感兴趣，特别是与观测到的可能与地震有关的电磁异常有关，但迄今为止，关于该主题的实验数据报告有限。本研究对岩石进行了单轴和三轴压缩试验，并以瞬态电荷信号和被测岩石试样所在的薄铜板两个电极之间的电位差的形式测量了断裂诱发电信号。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质岩石在岩石试样主破坏前才检测到电荷信号；(2)在岩石试样主破坏时刻，无论是否存在石英颗粒，都观察到电荷信号和强烈的电场变化。对于含石英的岩石，如花岗岩，石英的压电行为应该在一定程度上有助于在干岩破裂前的前兆期观测到的电信号。然而，我们的研究结果证实，还有其他重要的影响因素。

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.