Electric potential changes associated with nucleation of stick-slip of simulated gouges

► Friction experiments with gouges showed electric signals prior to stick-slip events. ► The signals appeared both in piezoelectric and non-piezoelectric gouges. ► The intensities depend on fault slips as the slip-dependent electrification process. ► R1 shears are best developed in the area where strongest electrification occurred. ► Those indicate that seismic nucleation phases can accompany electric precursors.