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Article

Real-Time Foreshock–Aftershock–Swarm Discrimination During the 2025 Seismic Crisis near Santorini Volcano, Greece: Earthquake Statistics and Complex Networks

by
Ioanna Triantafyllou
1,*,
Gerassimos A. Papadopoulos
2,
Constantinos Siettos
3 and
Konstantinos Spiliotis
4
1
Institute of Physics of the Earth’s Interior and Geohazards, Hellenic Mediterranean University Research Center, 73100 Chania, Greece
2
Board of Directors, Hellenic Mediterranean University, Estavromenos Campus, 71410 Heraklion, Greece
3
Dipartimento di Matematica e Applicazioni “Renato Caccioppoli,” Università degli Studi di Napoli “Federico II,” 80121 Naples, Italy
4
School of Civil Engineering, Democritus University of Thrace, 67100 Xanthi, Greece
*
Author to whom correspondence should be addressed.
Geosciences 2025, 15(8), 300; https://doi.org/10.3390/geosciences15080300
Submission received: 12 May 2025 / Revised: 22 July 2025 / Accepted: 23 July 2025 / Published: 4 August 2025
(This article belongs to the Special Issue Editorial Board Members' Collection Series: Natural Hazards)

Abstract

The advanced determination of the type (foreshock–aftershock–swarm) of an ongoing seismic cluster is quite challenging; only retrospective solutions have thus far been proposed. In the period of January–March 2025, a seismic cluster, recorded between Santorini volcano and Amorgos Island, South Aegean Sea, caused considerable social concern. A rapid increase in both the seismicity rate and the earthquake magnitudes was noted until the mainshock of ML = 5.3 on 10 February; afterwards, activity gradually diminished. Fault-plane solutions indicated SW-NE normal faulting. The epicenters moved with a mean velocity of ~0.72 km/day from SW to NE up to the mainshock area at a distance of ~25 km. Crucial questions publicly emerged during the cluster. Was it a foreshock–aftershock activity or a swarm of possibly volcanic origin? We performed real-time discrimination of the cluster type based on a daily re-evaluation of the space–time–magnitude changes and their significance relative to background seismicity using earthquake statistics and the topological metric betweenness centrality. Our findings were periodically documented during the ongoing cluster starting from the fourth cluster day (2 February 2025), at which point we determined that it was a foreshock and not a case of seismic swarm. The third day after the ML = 5.3 mainshock, a typical aftershock decay was detected. The observed foreshock properties favored a cascade mechanism, likely facilitated by non-volcanic material softening and the likely subdiffusion processes in a dense fault network. This mechanism was possibly combined with an aseismic nucleation process if transient geodetic deformation was present. No significant aftershock expansion towards the NE was noted, possibly due to the presence of a geometrical fault barrier east of the Anydros Ridge. The 2025 activity offered an excellent opportunity to investigate deciphering the type of ongoing seismicity cluster for real-time discrimination between foreshocks, aftershocks, and swarms.
Keywords: seismic crisis 2025; Santorini–Amorgos area; Hellenic volcanic arc; foreshocks; aftershocks; swarms; real-time discrimination seismic crisis 2025; Santorini–Amorgos area; Hellenic volcanic arc; foreshocks; aftershocks; swarms; real-time discrimination

Share and Cite

MDPI and ACS Style

Triantafyllou, I.; Papadopoulos, G.A.; Siettos, C.; Spiliotis, K. Real-Time Foreshock–Aftershock–Swarm Discrimination During the 2025 Seismic Crisis near Santorini Volcano, Greece: Earthquake Statistics and Complex Networks. Geosciences 2025, 15, 300. https://doi.org/10.3390/geosciences15080300

AMA Style

Triantafyllou I, Papadopoulos GA, Siettos C, Spiliotis K. Real-Time Foreshock–Aftershock–Swarm Discrimination During the 2025 Seismic Crisis near Santorini Volcano, Greece: Earthquake Statistics and Complex Networks. Geosciences. 2025; 15(8):300. https://doi.org/10.3390/geosciences15080300

Chicago/Turabian Style

Triantafyllou, Ioanna, Gerassimos A. Papadopoulos, Constantinos Siettos, and Konstantinos Spiliotis. 2025. "Real-Time Foreshock–Aftershock–Swarm Discrimination During the 2025 Seismic Crisis near Santorini Volcano, Greece: Earthquake Statistics and Complex Networks" Geosciences 15, no. 8: 300. https://doi.org/10.3390/geosciences15080300

APA Style

Triantafyllou, I., Papadopoulos, G. A., Siettos, C., & Spiliotis, K. (2025). Real-Time Foreshock–Aftershock–Swarm Discrimination During the 2025 Seismic Crisis near Santorini Volcano, Greece: Earthquake Statistics and Complex Networks. Geosciences, 15(8), 300. https://doi.org/10.3390/geosciences15080300

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