Spatio-temporal features of seismo-ionospheric influence revealed by the CSES and Swarm-B satellites

Introduction

Short-term earthquake (EQ) prediction is still one of the most challenging targets in Earth science today. The lithosphere–atmosphere–ionosphere coupling mechanism is still unclear. In this paper, the Swarm-B and the CSES satellites, as well as global strong EQs, are employed to investigate the spatio-temporal characters of the seismo-ionospheric influence.

Data and data processing method

Firstly, the electron density data measured by CSES and Swarm-B satellites from August 2018 to December 2021 are collected and 4,846 global strong EQs with M_S ≥ 5.0 are also derived from the GMT catalog (https://www.globalcmt.org/) in this period. These collected earthquakes are de-clustered to 3,577 ones. These events basically form the main seismic belts worldwide (Figure 1), where mid-low latitude (Lat. ≤ 60°) EQs stand for 97.5%.

Figure 1. Spatial distribution of the declustered 3,577 EQs with M_S ≥ 5.0.

Then, ionospheric perturbations (PERs) have been searched within ±65º via software developed by Li and Parrot (2012, 2013) and 39,802 nighttime CSES and 61,556 Swam-B PERs with space size t = 20–120 s and absolute amplitude A less than 100% have been obtained totally. The information for each perturbation includes time, orbit, location (longitude and latitude), space size, amplitude, etc.

Spatio-temporal features of seismo-ionospheric response

Figure 2. Ionospheric PER density as a function of the distance D from epicenter and the time delay from occurrence time of global 3,577 (a) CSES real EQs, (b) Swarm-B real EQs, and (c) randomly generated ones.

The above obtained CSES and Swam-B electron PERs are correlated to 3,577 EQs under conditions of D = 1500 km, T = 15 days and Kp < 3 to avoid the effect from solar activities, respectively. The detected PER densities by subtracting background values of as a function of distance D and delay time T before an earthquake have been demonstrated in Figure 2a and Figure 2b for CSES and Swarm-B, respectively. 

To validate these results, 3,577 points are evenly generated within the latitudes ±65° to replace the locations of the ‘real’ considered events, and the occurrence times are that of ‘real’ ones subtracting one month but without a modification on ‘real’ event magnitudes. Then, this newly generated EQ list is conducted the same statistical process as the ‘real’ ones and the corresponding result is displayed in Figure 2c.

As shown in Figure 2a and Figure 2b, the seismo-ionospheric influence determined by the strong EQs is typically featured by occurring within 5 days before in time and shifts 500–700 km for the first peak from epicenter instead of right above it in space. Then, there are two other plasma density peaks at about 1000 km and 1400 km in Figure 2a and Figure 2b. They are weaker in CSES panel than in Swam-B one as only nighttime CSES PERs have been utilized. These results are validated by random generated EQs as shown in Figure 2c presenting different scene. The seismo-ionospheric influence for mid-low latitude EQs shifts from the epicenter rather than right above it and this conclusion seems to indicate a potential LAI coupling mechanism that seismogenic current propagates along magnetic lines.

To confirm this point, we examine two separated groups of EQs: 742 EQs out of ±40° latitudes and 2307 ones within ±30° latitudes from global 3,577 ones. These two groups of events are under statistical work with the same conditions. The corresponding results are displayed in Figure 3. 

Figure 3. Ionospheric PER density as a function of the distance D from epicenter and the time delay from occurrence time of (a) 742 EQs out of ±40° latitudes and (b) 2,307 EQs within ±30° latitudes.

From Figure 7a, it is obvious that the seismo-ionospheric influence induced by mid-low latitude seismic activities has a significant offset of 900 km and is collectively centering their epicenters within 600 km for mid-high latitude ones. Therefore, the conclusion almost reaches that the location of seismo-ionospheric influence is basically depends on latitude where an EQ occurs.      

Conclusions

In this paper, the electron PERs recorded by the CSES satellite and Swarm-B satellite have been correlated to strong EQs and the statistical results have shown that the seismo-ionospheric influence significantly5 days before in time, and in space shifts 500–700 km for mid-low latitude EQs and at least 900 km for ‘high’ latitude ones from the epicenters instead right above them, and locates within 600 km for ‘low’ ones. These results support the LAI coupling mechanism of seimogenic current propagating along the magnetic lines and will improve our earthquake prediction practice. 

Acknowledgments

This work was supported by the Special Expenses for Basic Scientific Research under grant no. CEAIEF2025030104 and no. CEAIEF20240202, and the National Natural Science Foundation of China (NSFC) under grant no. 42474118.

References

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