A non-extensive view of the Pressure Stimulated Current relaxation during repeated abrupt uniaxial load-unload in rock samples

Abstract

Laboratory experiments have confirmed that the application of uniaxial stress on rock samples is accompanied by the production of weak electric currents, named Pressure Stimulated Currents (PSCs). In the present work the PSC emissions in marble and amphibolite (from the German Continental Deep drilling) samples are studied in the frame of non-extensive statistical mechanics, after having applied sequential loading-unloading cycles. It was ascertained that by increasing the sequential order of the loading-unloading cycle, the emitted PSC exhibits q-exponential behavior with a non-additive entropy parameter q which decreased in each applied uniaxial load-unload cycle. The behavior of the Tsallis q-parameter leads to the conclusion that fracturing is a subadditive process with hierarchically constrained dynamics. Furthermore, assuming an assembly of relaxed subdomains created due to microfracture, a non-extensive behavior of the observed macroscopically PSC relaxation is discussed in the frame of a superstatistical approach.