Earthquakes and entropy: Characterization of occurrence of earthquakes in southern Spain and Alboran Sea

The authors wish to acknowledge IAGPDS and IGN for the availability of the seismic dataset. We are especially grateful to Benito Martin (IAGPDS) for his help and advice with the SEISAN and GMT public programs. This work has been partially supported by the RNM104 and RNM194-Research Groups belonging to Junta de Andalucia (Spain). They also received financial support through Spanish National Project No. PID2019-109608GB-I00 and Junta de Andalucia Project No. A-RNM-421-UGR18.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.Research Groups belonging to Junta de Andalucia (Spain) RNM104 RNM194Spanish National Project PID2019-109608GB-I00Junta de Andalucia A-RNM-421-UGR1