Electric potential changes associated with slip failure of granite: Preseismic and coseismic signals

摘要: Electric potential changes were measured for stick-slip events in granite samples with a three-block direct shear arrangement at 8 MPa normal stress. Two electrodes mounted on the left- and right-hand blocks, electric difference between each electrode ground was high input impedance recording system of frequency range from DC to 100 Hz. As well as coseismic signals about 1.5 V which appeared moment dynamic slip event, preseismic detected just before event. The signal rises stepwise opposite polarities two exponentially decays time constant e/s, where e is permittivity s conductivity rock sample. We conducted simple test rapid stress drop without slipping observed almost same signal. This suggests that generated by piezoelectric effect. proposed generation model based effect resultant relaxation process obtained theoretical response, agreement experimental data. appears 2–3 event an amplitude 50 mV. local strains along sliding surfaces also monitor growth rupture nucleation zone. When zone occurred left surface, clear block. right shows caused change These antenna, placed away sample surface.