Abstract
We propose the use of entropy, H, as an indicator of the equilibrium state of a seismically active region (seismic system). The relationship between an increase in H and the occurrence of a great earthquake in a study area can be predicted by acknowledging the irreversible transition of a system. From this point of view, the seismic system evolves from an unstable initial state (due to external stresses) to another, where the stresses have dropped after the earthquake occurred. It is an irreversible transition that entails an increase in entropy. Five seismic episodes were analyzed in the south of the Iberian Peninsula, the Alboran Sea (Mediterranean Sea), and the North of Morocco: two of them of moderate-high magnitude (Al Hoceima, 2004 and 2016) and three of them of moderate-low magnitude (Adra, 1993-1994; Moron, 2007; and Torreperogil, 2012-2013). The results are remarkably in line with the theoretical forecasts; in other words: an earthquake, understood as an irreversible transition, must suppose an increase in entropy.
Highlights
The second law of thermodynamics postulates that only those phenomena for which the entropy of the universe increases are allowed
We propose the use of entropy, H, as an indicator of the equilibrium state of a seismically active region
Scientific literature on entropy is huge, and it is frequently used in scientific disciplines such as equilibrium and non-equilibrium thermodynamics or statistical mechanics
Summary
The second law of thermodynamics postulates that only those phenomena for which the entropy of the universe increases are allowed. Most works that use entropy values to characterize seismicity changes over an area apply their hypotheses to large earthquakes. The formalism of De Santis et al (2011) was applied to a seismic system that, from a spatial point of view, is a volume of 40 × 50 × 20 km (approximately) of the Abruzzo region in central Italy; it was seismically activated by well-located and large MW = 6.1 earthquake. Several seismic systems will be analyzed in the southern region of the Iberian Peninsula and the Alboran Sea. On the one hand, we will choose a broader seismic system from both the spatial and the temporal point of view; it includes two seismic events of moderate-high magnitude, and we will prove that the entropy increases with the first event, it returns to similar values to those before the earthquake, and it grows again with the second earthquake. The results offer a good correspondence between a sudden change in entropy and the occurrence of a main earthquake in the sequence
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