# Correlation of Gravity and Magnetic Field Changes Preceding Strong Earthquakes in Yunnan Province

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## Abstract

**:**

## Featured Application

**The analysis of the fusion characteristics of gravity and magnetic fields has a certain significance for the prediction of strong earthquakes.**

## Abstract

## 1. Introduction

## 2. Data Processing and Accuracy

#### 2.1. Gravity and Geomagnetic Field Data Acquisition Instrument and Research Area

^{−8}m·s

^{−2}. The relative observation instrument is CG-5. The relative gravimeter has an observation accuracy of 10 × 10

^{−8}m·s

^{−2}; there are 130 geomagnetic vector measurement points, of which the GSM-19T proton precession magnetometer (PPM) is used to observe the total geomagnetic intensity, the instrument resolution is 0.1 nT, and the observation accuracy is 0.5 nT.

#### 2.2. Data of Gravity and Geomagnetic Total Intensity

#### 2.2.1. Gravity Data Processing and Accuracy

^{−8}m·s

^{−2}, the average point value accuracy is 8.5 × 10

^{−8}m·s

^{−2}, and the difference between the posterior median error and the prior median error is small, reflecting the reliable quality of gravity observation data, which can be used to reflect the space–time dynamic evolution process of the regional gravity field.

#### 2.2.2. Geomagnetic Data Processing and Accuracy

#### 2.3. Calculation Method

#### 2.3.1. Grid Interpolation

#### 2.3.2. Normalization Processing and Correlation Coefficient Calculation

## 3. Results

#### 3.1. Histogram and Nuclear Density Plot of Consistent Data Quantity in the Change Interval

#### 3.2. Calculation of the Correlation Coefficient of Gravity and Magnetic Field Data

## 4. Discussion

## 5. Conclusions

- (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.
- (2)
- 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.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**The spatial distribution of the annual difference in gravity and magnetic anomaly fields for each of the two years that precede strong earthquakes in the Yunnan area. (

**a**) Annual changes in gravity from 2013 to 2014; (

**b**) Annual changes in total geomagnetism from 2013 to 2014; (

**c**) Annual changes in gravity from 2019 to 2020; (

**d**) Annual changes in geomagnetism from 2019 to 2020. Epicenter and focal mechanism are shown for earthquakes that occurred within a year of the respective time period end.

**Figure 2.**Distribution map of gravity survey points, geomagnetic survey points, and faults in Yunnan Province.

**Figure 3.**The histogram and nuclear density map of the uniform number of grid point changes in the gravity and magnetic field after normalization from 2011 to 2021. (

**a**) Histogram of uniform number of grid points of gravity and magnetic field after normalization (the ordinate represents the quantity and the abscissa represents the normalized interval value); (

**b**) The normalized gravity and magnetic field grid points change uniform number nuclear density map (the ordinate represents the kernel density value, and the abscissa represents the normalized interval range value).

**Figure 4.**The strong earthquakes in Yunnan Province from 2011 to 2021 and the changes in the correlation coefficient of gravity and magnetic field within the three-year earthquake area before the earthquakes. (

**a**) Yingjiang ${M}_{s}$6.1 earthquake in 2014; (

**b**) Ludian ${M}_{s}$ 6.5 earthquake in 2014; (

**c**) Jinggu ${M}_{s}$ 6.6 earthquake in 2014; (

**d**) Yangbi ${M}_{s}$ 6.4 earthquake in 2021.

Data Group | Mean of Value Precision /10 ^{−8} m·s^{−2} | Posterior Error /10 ^{−8} m·s^{−2} | Posterior In-Error Minus Prior-In-Error /10 ^{−8} m·s^{−2} |
---|---|---|---|

March 2011 | 8.6 | 8.3 | 0 |

September 2011 | 7.5 | 9.7 | 0 |

March 2012 | 6.6 | 6.8 | 0 |

September 2012 | 10.5 | 6.4 | 0 |

March 2013 | 8.9 | 4.7 | 0 |

September 2013 | 10.4 | 8.2 | 0 |

March 2014 | 9.1 | 5.9 | 0.6 |

September 2014 | 7.3 | 6.5 | 0 |

March 2015 | 7.4 | 6.3 | 0.6 |

September 2015 | 8.4 | 7.0 | 0 |

March 2016 | 8.3 | 8.6 | 0.4 |

September 2016 | 8.3 | 8.5 | 0.5 |

March 2017 | 8.8 | 8.6 | 0.4 |

September 2017 | 9.1 | 8.8 | 0.2 |

March 2018 | 8.1 | 9.6 | 0.4 |

September 2018 | 10 | 11.1 | −1.1 |

March 2019 | 8.5 | 9.9 | 0.1 |

September 2019 | 7.9 | 11.5 | −1.5 |

March 2020 | 6.9 | 9.9 | 0.1 |

September 2020 | 9.3 | 10 | 0 |

March 2021 | 10.5 | 11.5 | −1.5 |

September 2021 | 7.6 | 8.0 | −0.4 |

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**MDPI and ACS Style**

Liu, D.; Li, J.; Ni, Z.; Zhao, Y.; Zheng, Q.; Du, B.
Correlation of Gravity and Magnetic Field Changes Preceding Strong Earthquakes in Yunnan Province. *Appl. Sci.* **2022**, *12*, 2658.
https://doi.org/10.3390/app12052658

**AMA Style**

Liu D, Li J, Ni Z, Zhao Y, Zheng Q, Du B.
Correlation of Gravity and Magnetic Field Changes Preceding Strong Earthquakes in Yunnan Province. *Applied Sciences*. 2022; 12(5):2658.
https://doi.org/10.3390/app12052658

**Chicago/Turabian Style**

Liu, Dong, Jiancheng Li, Zhe Ni, Yufei Zhao, Qiuyue Zheng, and Bin Du.
2022. "Correlation of Gravity and Magnetic Field Changes Preceding Strong Earthquakes in Yunnan Province" *Applied Sciences* 12, no. 5: 2658.
https://doi.org/10.3390/app12052658