Asthenospheric upwelling-induced seismic activity in the eastern North China Craton: Evidence from viscosity obtained from an MT study

The eastern North China Craton (NCC) suffers from severe seismic hazards. This study investigates the crustal and mantle resistivity structure to constrain the deep tectonic evolution and seismic mechanisms of the eastern NCC. In this paper, the magnetotelluric sounding array deployed in the eastern NCC by the SINOPROBE project was used for data analysis and 3D inversion, and a 3D electrical structure model of the eastern NCC was obtained. The effective viscosity of the lithospheric mantle of the eastern NCC was calculated by combining the Arrhenius equation and the flow law of dislocation creep of wet olivine. The resistivity model shows that the low-resistivity anomalies in the middle and upper crust are mainly distributed in the Bohai Bay Basin. The lithospheres of the Yinshan-Yanshan Block, the Sulu Orogenic Belt, and the Taihang Uplift show high-resistivity anomalies. However, the lithospheric mantles of the Shanxi Graben, the Luxi Uplift, and the southern Taihang Uplift show pronounced low-resistivity anomalies. The low-resistivity anomalies are separated by the high-resistivity lithospheric anomalies in the Yinshan-Yanshan Block and the middle of the Taihang Uplift. The mantle viscosity model calculated using the relationship between conductivity, temperature, and viscosity indicates that the effective viscosity of the lithospheric mantle in the low-resistivity and high-temperature Bohai Bay Basin is lower than that in the high-resistivity and low-temperature Yanshan Block and Taihang Uplift. According to the upwelling shape of the low-resistivity anomalies, the thermal materials beneath Tangshan and Xingtai have the characteristic of upwelling along the tectonic boundaries. It is concluded that after the low-viscosity asthenospheric upwelling to the cold and rigid Yanshan Block and Taihang Uplift, stress accumulates on the side of the high-resistivity anomalies, eventually leading to crustal and mantle seismic activity.