## 5 Conclusions  
The total geomagnetic intensity was measured in the SD profile of Mongolia. The absolute accuracy of the instrument used for the measurements is better than 0.5 nT. The mean standard deviation \(\sigma\) value of 160 geomagnetic measurement points after diurnal variation reduction is 0.12 nT. The spatial distribution and magnetic anomaly characteristics of the lithospheric magnetic field in the SD profile are calculated and analyzed. The lithospheric magnetic field is decomposed into three components, namely, the basement, middle layer, and shallow surface, by the upward continuation method. This information is combined with the regional geological structure, seismicity, and collected rock sample lithologies. It is found that the lithospheric magnetic field distribution of the SD profile has a certain relationship to the geological structure, rock lithology, seismic activity, natural remanent magnetization, and magnetic susceptibility. The results show that there are obvious zoning characteristics. The shallow rock lithology is mainly magmatic in the area where the lithospheric magnetic field anomalies change dramatically. The magnetic susceptibility and remanent magnetization of the collected rock samples in this area are high, the earthquake magnitude and number are high, and the geological structure is complex. This region corresponds to the Vitrim orogenic belt and Erguna orogenic belt. However, in the area with gentle variation in lithospheric magnetic field anomalies, the shallow rock lithology is mainly sedimentary rock, and the collected rock magnetic susceptibility and remanent magnetization values are low. This region corresponds to the Erhotsk orogenic belt and Southern Mongolia's orogenic belt.  
The spatial distribution of the lithospheric magnetic field is also related to the depth and position of faults. The lithospheric magnetic anomalies can be used as a reference for the location and depth of faults. The variation in the lithospheric magnetic field in the region of the Southern Mongolia orogenic belt is gentle. Still, the seismic activity is high, which is not consistent with the characteristics of other regions. This region is widely covered by Quaternary sedimentary rocks, which may explain the gentle variation in the lithospheric magnetic field. These issues are important directions for further research.  
Data curation, J.Y., Z.W. and C.W.; Formal analysis, J.Y. and C.S.; Funding acquisition, Z.G.; Investigation, J.Y. and C.X.; Methodology, J.Y., C.S. and B.C.; Project administration, J.Y.; Writing--original draft, J.Y. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Special Fund of the Institute of Geophysics, China Earthquake Administration (grant number DQJB22B20, DQJB21X26) and the National International Science and Technology Cooperation project of China (grant number 2011 DFB20210).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
**Acknowledgments:** We thank the researchers of the China Earthquake Administration and Institute of Astronomy and Geophysics, Mongolian Academy of Sciences, for collecting the geomagnetic observation data in the field.  
**Conflicts of Interest:** The authors declare no conflict of interest.