Sustaining Post-peak Pressure-Stimulated Rock Current from Bi-axially Loaded Sandstone and Diorite Specimens

Pressure-stimulated rock current (PSRC) is an important rock petrophysical phenomenon. It offers critical insights into anomalous electric fields, magnetic fields, and electromagnetic radiation related to rock fracturing and tectonic earthquake. However, the previous research on PSRC mainly focused on pre-peak loading processes, whereas PSRC remains unexplored under post-peak loading regimes that more closely approximate actual geological conditions. In this paper, we performed biaxial loading experiments on sandstone and diorite specimens with simultaneous current and acoustic emission measurements, and kept post-peak loading after rock failure, aimed to explore the characteristics and mechanisms of post-peak PSRC. The results show that: (1) In the processes of post-peak loading and unloading, subject to friction and relative slip, there were furrow effect, adhesive friction and slip shear between rock fragments, resulting in the further breaking of peroxy defects and dislocation sliding, which contribute jointly to PSRC rise with increasing displacement in both naturally dried and fully dried sandstone and diorite specimens; (2) the extensive expansion of crack area during post-peak significantly enhanced the activation of positive holes (P-holes), resulting in higher PSRC in post-peak than that in pre-peak. However, fracture surfaces in post-peak impeded P-holes transmission, resulting in a less-pronounced PSRC rise than the crack area increase. It was implied that at large scale, such as earthquake, a large number of P-holes are to be activated during pre-seismic and post-seismic slip in addition to the co-seismic fracturing, which will transmit to and accumulate on ground surface and cause seismic anomalies. This study enriched the phenomenon and mechanism of PSRC, which is of reference meaning for seismic anomalies monitoring and earthquake precursors’ identification.