Tracking seismic regime changes in Central Italy (2005-2024) through variations in the parameters of the q-exponential magnitude distribution

In previous studies (Rotondi et al., Geophys J Int 2022) we examined the seismic sequences related to the strong earthquakes that occurred in central Italy at L'Aquila in 2009 and at Amatrice-Norcia in 2016, estimating the q-exponential probability distribution of the magnitude. Specifically, we considered events with Mw 2+ recorded in the intervals (2005-2009) for the L’Aquila case and (2014-2018) for the Amatrice-Norcia case in order to explore the link between changes in magnitude distribution and various  seismic phases.
The temporal variations were noted in the values of the Tsallis entropy and of the corresponding q entropic index estimate when we evaluated them on time windows with a fixed number of data, that shift at each new event, making inference according to Bayesian MCMC methods (Rotondi et al., Seismol Res Lett 2025). These analyses revealed a link between changes in q and different phases of seismic activity, with low q values potentially marking the preparatory phase preceding strong events.
In the present work, this approach is extended by analyzing all seismic events recorded in Central Italy between 2005 and 2024 as a single unified sequence, and drawing data both from the Italian Seismological Instrumental and Parametric Database (ISIDe) and from the HOmogenized instRUmental Seismic catalog (HORUS), which provides more accurate and homogeneous moment magnitude estimates.
Our goal is to determine whether the temporal variations in Tsallis entropy and its parameter q identified in our previous work truly act as both sufficient and necessary precursory signals of strong earthquakes. It turns out that variations in the q-index alone are not a sufficiently reliable seismic precursor, as low q values may not be followed by strong events.
However, a more reliable identification of periods of heightened seismic activity is achieved by jointly analyzing q and the parameter β, which is physically related to the expected released energy. In particular, the correlation between q and β evaluated through a moving correlation analysis allows the identification of periods of intense seismic activity. A persistent and significant decrease in q, combined with a positive correlation between q and β, suggests the onset of a preparatory phase for an impending seismic event. The use of the HORUS catalog has further strengthened the significance of these conclusions.
This research is supported by ICSC National Research Centre for High Performance Computing, Big Data and Quantum Computing (CN00000013, CUP B93C22000620006) within the European Union-NextGenerationEU program.