Softening rocks with stress-activated electric current

When rocks are subjected to mechanical stress, dormant electronic defects become activated. This activation produces electron-hole pairs, which increase the electrical conductivity of rocks by releasing highly mobile defects electrons, equivalent to O^- in a matrix of O^2-, called positive holes and symbolized by h*. The h* charge carriers can spread from the stressed rock into surrounding unstressed rocks. Preventing the outflowof h* alters the mechanical properties of the rocks: they become softer andweaker. Ongoing studies point to a delocalization of the wave function associated with the h* charge carriers, which is far-reaching and affects many neighboring O^2-. Although the number density of positive holes may be as low as 1 in 1000, essentially all O^2- in the rock subvolume lose some of their electron density. This loss weakens the interatomic bonds between anions and cations, thus affecting the mechanical properties of rocks.