Earthquake Swarm in Santorini - Greece: Recurrence Quantification Analysis and Investigation of Causal Relationship with Tidal Forces

Stavros Maltezos, Angelika Georgakopoulou

In early 2025, an unusual earthquake swarm initiated in the sea area of the small uninhabited islet Anydros between Santorini and Amorgos islands in Greece. The unusual nature of this seismic activity and its subsequent seismic follow-up, motivated us to study its dynamical and statistical features. Namely, we investigated for a potential causal relationship between a simple
model of perpendicular tidal forces caused by Moon and Sun and the dynamical evolution of this earthquake swarm in this area within the same time period. We have faced this problem deeply applying three methods suitable for understanding this overall seismic activity: the Recurrence Quantification Analysis, with the associated metrics, referring to identify similar states of complex dynamic systems, the linear Granger causality Test and the Convergent Cross Mapping used in for the reconstruction of embedded phase space. Beside the individual results, we have combined them in synergy to obtain a robust concluding result. Moreover, in the same context of investigating causality, we have performed a global statistical study regarding the probability of Moon phases for triggering strong earthquakes in the highest magnitude range, from M6.0 and beyond.