Abstract
The study of the preparation phase of large earthquakes is essential to understand the physical processes involved, and potentially useful also to develop a future reliable short-term warning system. Here we analyse electron density and magnetic field data measured by Swarm three-satellite constellation for 4.7 years, to look for possible in-situ ionospheric precursors of large earthquakes to study the interactions between the lithosphere and the above atmosphere and ionosphere, in what is called the Lithosphere-Atmosphere-Ionosphere Coupling (LAIC). We define these anomalies statistically in the whole space-time interval of interest and use a Worldwide Statistical Correlation (WSC) analysis through a superposed epoch approach to study the possible relation with the earthquakes. We find some clear concentrations of electron density and magnetic anomalies from more than two months to some days before the earthquake occurrences. Such anomaly clustering is, in general, statistically significant with respect to homogeneous random simulations, supporting a LAIC during the preparation phase of earthquakes. By investigating different earthquake magnitude ranges, not only do we confirm the well-known Rikitake empirical law between ionospheric anomaly precursor time and earthquake magnitude, but we also give more reliability to the seismic source origin for many of the identified anomalies.
Highlights
A large earthquake comes after a long-term preparation phase composed of different stages of seismicity evolution driven by the continuous but variable tectonic stress[1,2]
We analyse the electron density (Ne) and magnetic field data from the three Swarm satellites to detect possible anomalies associated with the earthquakes from 1 January 2014 to 31 August 2018 (30 August for Ne)
The electron density and magnetic field Worldwide Statistical Correlation (WSC) analyses applied to about 4.7 years of Swarm satellite observations highlight that anomalies appear to occur before the earthquake occurrences, between a few days and 80 days before the earthquakes, with larger peaks at around 10, 20 and 80 days
Summary
A large earthquake comes after a long-term preparation phase composed of different stages of seismicity evolution driven by the continuous but variable tectonic stress[1,2]. An alternative mechanism is proposed by Pulinets and Ouzounov[6], based on gas and fluid that could rise up toward the surface in the preparatory phase of the earthquake. Another model was provided by Kuo et al.[12], which relies on a numerical simulation. De Santis et al.[7], Pulinets and Boyarchuk[15] and Hayakawa[16] presented a general review about the processes that can occur in the atmosphere and ionosphere before and during an intense earthquake, and their possible correlations
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