Geological model for the fault electric field and its significance for earthquake prediction

Seismic electric precursors (SEPs) and their related earthquakes are two different geophysical phenomena observed on the ground surface. The temporal relationship between SEPs and earthquakes observed from several historical cases in China and Japan suggests that both were resulted from the same geological process, and as evidenced experimentally, in association with stress accumulation and release in a deeper crust. Here a model named the fault electric field (FEF) is proposed to account for this geological process and its relationship with SEPs and earthquakes. The FEF model indicates that slip along an undulated fault plane causes the asperities on both hanging wall and footwall of fault to close together, thus results in stress concentration around the asperities, forming a seismogenic region (SR); simultaneously, a pair of rock batteries develop on the either side of fault plane, producing a fault electric field (FEF) centered around the SR, which is related to the SEP observed on the ground. When the deflection angle of the normal stress axis exceeds a threshold, rapid slip of the fault with sudden release of elastic energy during earthquake happens. The FEF model effectively explains the geophysical observations on the SEP-earthquake relationship and the experimental investigations on the mechanic-electric effect of rocks. For testing the model, five FEF surveillance stations have been employed on different faults in the Pearl River Delta, South China, and the monitor results from those stations demonstrate the existence of the FEF in each surveyed fault. This research provides a feasible way to detect the process of stress concentration in the deeper segment of a seismogenic fault, which is significant for the earthquake prediction.