The eastern North China Craton is one of the most seismically active regions in Chinese mainland. The 1966 Xingtai M_S7.2 earthquake and the 1976 Tangshan M_S7.8 earthquake both occurred within this area, yet its deep seismogenic mechanism remains highly controversial. In this study, broadband and long-period magnetotelluric （MT） data covering the Bohai Bay basin, the southern Yanshan block, the Taihang uplift and their adjacent areas were adopted. Three-dimensional inversion yields a high-precision lithospheric electrical structure model spanning depths of 5–150 km across the study region. On this basis, two models, namely the background conductivity model （BM） and maximum conductivity model （MCM）, were constructed using the Hashin-Shtrikman bounds. Furthermore, quantitative inversion of cumulative plastic strain （ε_p） distribution beneath the Tangshan-Xingtai lithosphere was carried out based on the conductivity-strain exponent model. The results reveal that high-strain zones （ε_p＞50%） are predominantly distributed near the Moho beneath the Taihang uplift and in the middle-upper crust of the Bohai Bay basin, whereas the two zones exhibit distinctly different spatial patterns. The high-strain zone beneath the Taihang uplift presents a continuous horizontal layered distribution, indicating lithospheric flexure or crust-mantle coupling. By contrast, the high-strain zone beneath the Bohai Bay basin shows a fragmented block-like distribution, reflecting strain localization caused by multi-stage faulting under an extensional rift setting. The high-strain zones display good spatial correlation with high-conductivity anomalies （C₁, C_2-1, C_2-2） derived from MT inversion, implying that plastic strain constitutes a dominant control on lithospheric high-conductivity anomalies. Meanwhile, rock weakening and strain localization induced by the accumulation of high-conductive materials may exerts a synergistic effect.

The epicenters of the 1966 Xingtai M_S7.2 earthquake and the 1976 Tangshan M_S7.8 earthquake are both located within zones of steep strain gradients and preferentially lie on the high-resistivity side rather than within the high-strain domains. The cumulative strain gradients at different depths further demonstrate that the superposition of strain gradients induced by upwelling deep hot materials and those associated with upper crustal fault zones jointly governs the seismogenic locations. Geodynamically, high-strain zones act as stress dissipation regions where elastic strain energy is difficult to accumulate. In comparison, regions with steep strain gradients are favorable for stress concentration and pore fluid pressure fluctuation, thereby rendering them more susceptible to earthquake initiation.

This study also discusses the non-uniqueness of the conductivity-strain relationship. We note that high electrical conductivity can also be independently generated by high temperature, elevated water content, highly conductive minerals or fluids. In addition, we explicitly discuss the smoothing effect inherent to MT inversion on strain gradient calculation, along with the implicit assumption underlying our method that high-conductivity zones have undergone sufficient stress loading. The quantitative inversion method linking electrical conductivity and strain proposed in this study provides new insights into characterizing lithospheric deformation intensity from MT observations. Zones with steep strain gradients can serve as an effective indicator for delineating potential seismic hazard zones. Nevertheless, dynamic information constraints including contemporary stress regime, fault locking fraction and fluid activity should be integrated to realize comprehensive regional seismic hazard evaluation.