# Correlation of Gravity and Magnetic Field Changes Preceding Strong Earthquakes in Yunnan Province
## 5 Conclusions  
From the perspective of gravity and magnetic field data fusion, this paper analyzes and studies the characteristics and laws between the occurrence of strong earthquakes and the dynamic changes in gravity and magnetic fields in Yunnan since 2011. The main understandings obtained are as follows:  
1. The fusion of the data for gravitational and the lithospheric magnetic field has a good precursor to the seismogenesis of strong earthquakes. During the seismogenic process, the annual change in gravity and its trend in magnetic field strength have a certain correlation. The positive and negative variation of the gravity field tend to be the same for the total magnetic field intensity, both reaching a maximum one year before the earthquake.  
After the gravity and magnetic field fusion data are normalized, the interannual gravity change and the annual trend change in the total magnetic field strength are converted between \(-1\) and \(1\). The entire survey area can be distinguished in the same way. According to the grid of rate, the coincidence of gravity and magnetic points between \(-1\) and \(1\) with the same trend can be obtained. In the year before the strong earthquake, the coincidence number reaches its maximum, and the peak difference of the nuclear density curve reaches the minimum.
3. The relationship between magnitude and anomalous range, as well as the gravity and magnetic fields, in the area surrounding a strong earthquake were fused. It shows that the correlation coefficients of change all reach their maximum, and the annual change coefficients decrease sharply in the year of the earthquake.
4. Based on the results of this paper, it is feasible to conduct a comprehensive analysis of strong earthquakes by the fusion of multiphysics, but the current problem is that no more intuitive characteristic display is found in the judgement of the location of the earthquake. In the future, ground observation technologies such as GNSS and InSar can be integrated to jointly solve the problem of earthquake elements such as epicenters and accurate determination of earthquake occurrence times.  
Conceptualization, J.L., Z.N. and D.L.; methodology, D.L.; software, D.L. and Y.Z.; validation, Q.Z.; writing: original draft preparation, D.L.; writing: review and editing, D.L. and Z.N.; visualization, B.D. All authors have read and agreed to the published version of the manuscript.  
This project was funded by the Director's Fund of the Institute of Earthquake Research, China Earthquake Administration (No. IS201926302), the 2021 Earthquake Situation Tracking and Orientation Tasks of the Monitoring and Prediction Department of China Earthquake Administration (No. 2021010228), and the Spatial-temporal evolution of the lithospheric magnetic field anomalies and identification of sub-instability in typical earthquake regions study (No. 2018 YFC150330504); Kunming Modern Surveying and Mapping Benchmark Construction (Phase II)--Second-Class Gravity Survey (No. J-CH-2021-020).  
Not applicable.  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
Not applicable.  
We would like to thank the mobile gravity and geomagnetic survey personnel in the Sichuan-Yunnan area for obtaining high-quality data, the expert guidance of the Institute of Earthquake Research of China Earthquake Administration and the Institute of Geophysics of China Earthquake Administration, and the valuable opinions of reviewers.  
No conflicts of interest exist in the submission of this manuscript, and the manuscript has been approved by all authors for publication.