Clues of multiple Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) mechanisms before the medium-large earthquake occurrence

Earthquakes are potentially one of the most catastrophic natural hazards. Predicting earthquakes has always been a dream; presently, this is still impossible. However, there are several pieces of evidence for good candidates of pre-earthquake signals recorded as variations in lithosphere, atmosphere and ionosphere. From a theoretical point of view, several theories of propagation of anomalies generated in the lithosphere upward in the atmosphere and even in the ionosphere have been proposed: a pure electromagnetic Ultra-Low_Frequency wave (e.g., Molchanov and Hayakawa, 1995,  https://doi.org/10.1029/95GL00781), an electrochemical model for producing positive charges from the increase of stress on the faults (Freund, 2011, https://doi.org/10.1016/j.jseaes.2010.03.009), a chemical and physical chain of processes based on air ionization induced by radon (Pulinets and Ouzounov, 2011 https://doi.org/10.1016/j.jseaes.2010.03.005) or a mechanical wave propagating vertical to the ionosphere induced by temperature increase of Earth’s surface, known as Acoustic (or atmospheric) Gravity Wave (https://doi.org/10.1541/jae.31.129). In this presentation, several pieces of evidence of candidates for pre-earthquake signals for the different mechanisms of coupling will be shown. The examples are collected from the analyses of medium-large earthquakes, such as Mw = 6.7 Lushan (China) 2013 (Zhang et al., 2023, https://doi.org/10.3390/rs15061521), Mw = 7.5 Indonesia  2018 (Marchetti et al., 2020, https://doi.org/10.1016/j.jseaes.2019.104097), Mw = 7.7 Jamaica 2020 (Marchetti et al., 2024, https://doi.org/10.1016/j.rse.2024.114146), Mw = 7.2 Haiti 2021 (Marchetti, 2024, https://doi.org/10.3390/geosciences14040096) and other seismic events.

It’s proposed that different models of Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) describe different ways and mechanisms of interactions between the geo-layers of the Earth system. In this frame, one theory does not necessarily exclude another one. Still, the reasons for a specific coupling mechanism require to be further investigated. Among them, focal mechanisms, sea or land location, and geological constraints could play a main role in a coupling or another one.