Relationship between crustal magnetic anomalies and strong earthquake activity in the south segment of the China North-South Seismic Belt

The south segment of the China North-South Seismic Belt is located in the southeast margin of the Qinghai Tibet Plateau. This region is characterized by the frequent seismic activity in Chinese mainland. In this paper, the geomagnetic field model NGDC-720 and the data of terrestrial heat flow are used to investigate the distribution of crustal magnetic anomalies, the depth of Curie surface, and the characteristics of the crustal thermal structure in the south segment of the North-South Seismic Belt. The distribution characteristics of the vertical component Δ Z and the magnetic declination Δ D in the area with earthquakes over a magnitude of 6 and their aftershocks since 1970 are focused on. The results show that the earthquakes are mainly observed in the area of negative magnetic anomaly or the strong and weak transition zone. It especially shows in the Δ D. The Curie surface in the study area varies significantly, ranging from 20.8 to 31 km. The uplift area of the Curie surface is consistent with the high-value area of terrestrial heat flow. The high geothermal area corresponds to the strong earthquake activity area. The focal depth of most strong earthquakes is shallower than the depth of the Curie surface. The strong earthquakes mainly occur in the deep-shallow transition zones of the Curie surface. The results can be used as a reference for strong earthquake prediction in this area.