The Lithosphere-Atmosphere-Ionosphere Coupling of Multiple Geophysical Parameters Approximately 3 Hours Prior to the 2022 M6.8 Luding Earthquake

Abstract

Investigating various geophysical parameters from the Earth’s crust to the upper atmosphere is considered a promising approach for predicting earthquakes. Scientists have observed that changes in these parameters can occur days to months before earthquakes. Understanding and studying the impending abnormal phenomena that precede earthquakes is both urgent and challenging. On 5 September 2022, a magnitude 6.8 earthquake occurred in Sichuan, China, at 4:52:18 (Universal Time). The earthquake happened approximately 175 km away from an instrumental array established in 2021 for monitoring vibrations and perturbations in the lithosphere, atmosphere, and ionosphere (MVP-LAI). This array consisted of over 15 instruments that regularly monitor changes in various geophysical parameters from the subsurface up to an altitude of approximately 350 km in the ionosphere. Its purpose was to gain insights into the mechanisms behind the coupling of these different geospheres during natural hazards. The seven geophysical parameters from the MVP-LAI system simultaneously exhibited abnormal behaviors approximately 3 h before the Luding earthquake. These parameters include ground tilts, air pressure, radon concentration, atmospheric vertical electric field, geomagnetic field, wind field, and total electron content. The abnormal increase in radon concentration suggests that the chemical channel could be a promising mechanism for the coupling of geospheres. Furthermore, air pressure, the geomagnetic field, and total electron content exhibited abnormal characteristics with similar frequencies. Horizontal wind experienced temporary cessation or weakening, while vertical wind displayed frequent reversals. These anomalies may be attributed to atmospheric resonance before the earthquake. The results demonstrate that the coupling of geospheres, as indicated by the anomalous phenomena preceding an earthquake, could be influenced by multiple potential mechanisms. The multiple anomalies observed in this study provided approximately 3 h of warning for people to prepare for the seismic event and mitigate hazards.

The Study on Anomalies of the Geomagnetic Topology Network Associated with the 2022 Ms6.8 Luding Earthquake

“…In addition to geomagnetic data, significant progress has been made in investigating the precursors associated with the Luding earthquake over the past two years [11]. Wu et al [56] analyzed the variations of the atmospheric electric field (AEF) in the 15 days leading up to the Luding earthquake.…”

“…In particular, the development of the lithosphere-atmosphere-ionosphere coupling (LAIC) mechanism has brought us new findings and understandings of the process of earthquake preparation [5][6][7]. Currently, the most reliable methods of recognizing earthquake precursors are considered to be the multicomponent and multi-method analysis [8][9][10][11]. For example, Pulinets et al [12] adopted a multi-method way to validate the precursory phenomena in the ionospheric of the 1999 Hector Mine and 2019 Ridgecrest earthquakes: firstly, they computed the time-series of ∆TEC% around the earthquakes and found there are likely positive night-time deviations before the earthquakes; secondly, they started cognitive recognition through the precursor mask approach [13], which is a special visualization pattern analysis to check the possible precursors; thirdly, they revealed the increased spatial variability by calculating the root mean square deviation (RMSD) to further validate the precursor mask; next, to further prove that suspicious variations, they used a cross-correlation technique to reveal the reliability of the precursor mask [14]; and lastly, they demonstrated the precursors based on the physical mechanisms of their generation and the morphology of their behavior during the precursory period.…”