TRANSIENT ELECTRICAL-ACTIVITY ACCOMPANYING ROCK UNDER INDENTATION LOADING

Laboratory experiments have been conducted to investigate the geoelectrodynamics associated with rock fractures in the earth's crust. That is, when rocks were subjected to indentation fracturing in two ways, the electric charges generated were detected; namely, (1) a direct charge collection method using an electroconductive indenter serving as the collecting electrode (referred to as near-field test), and (2) an indirect collection method in which an electrode was placed on rocks at a specific distance from the indentation fracture zone (referred to as far-field test). As near-field test results, higher electric charge signals were detected during the loading cycle when cracking occurred around the indent on granite and on moist andesite. Also in the far-field test, the charge signal propagating through the rock during fracturing could be detected; the signal intensity decreased as the distance between the indent and electrode increased. Possible mechanisms for fracture-induced charge generation and their propagation through rock media are discussed.