On the generation of stress-induced charges for electromagnetic precursors in the fault zone

Abstract

Pre-seismic stress-induced electric charges might be generated in the fault zone for producing the electromagnetic (EM) precursors. The peroxy defect (PD) theory has been considered to interpret the generation of stress-induced charges. The critical-earthquake (CE) model has been applied to explain the underground electric currents. It is necessary to explore both the presence of PD in the seismogenic zone of earthquakes and the production of EM precursors based on the CE model. First, we study the relationship between the PD theory and the seismogenic zone. Secondly, we examine the CE model based on the estimates of the depth ranges for generating stress-induced charges/currents for yielding an average normal stress that is strong enough to generate the electric charges and depth-dependent electric properties of fault zones. Results show that the dip angle and faulting type are significant factors in influencing the depth ranges that are similar for thrust and strike-slip faults and wider for normal faults. For a same depth range, the ability of producing electric currents is almost the same for thrust and strike-slip faults, but lower for normal faults. The underground spatial distribution of resistivity may control the stress-induced currents. The permeability barrier or transition layer also influences the stress-induced charges. The low-resistivity lower crust would reduce the up-going p-holes and thus is not beneficial for generating ground currents as expected by the CE model.