Verification of Hole Activation in Gabbro Blocks Subjected to Non- uniform Loading by Means of Hot Point Probe Tests

Olivine and gabbro has been investigated to understand the electrical conductivity structure of the Earth’s lower crust and mantle. To simulate a certain deep environmental circumstance, a rock sample is generally placed under a certain confining hydrostatic pressure at a certain temperature. Nowadays, it is known that the electric conduction property of olivine is p-type, which is driven by the small polaron of FeMg • and the V´´Mg as the main charge carriers at low and high temperatures, respectively [1]. However, when we turn our eyes to rocks on the crustal scale, the pressure-temperature condition is not homogeneous. The stress-strain distribution in the Earth’s crust changes statistically and dynamically accompanied with seismic, volcanic and tidal activities. This may generate new electric phenomena on the crustal scale. In early laboratory experiments, when a part of an air-dried rock volume was uniaxially loaded, an electric current flowed from the unloaded part to the loaded part via the electrometer connecting to both parts, i.e., the generation of the electromotive force (EMF) which the electric potential of the unloaded part became high relative to the loaded part [2-4]. Based on a number of such experiments, it was expected that holes were activated in the loaded volume and diffused into the unloaded volume. However, this activation is not proved yet. Here, we try verification of this activation by means of hot point probe tests; we can judge the increase or decrease of the hole concentration based on the change of thermo-EMF as explained below. Prior to hot point probe test, we first tried reconfirmation of EMF induced by non-uniform loading.