The 2020 Perachora peninsula earthquake sequence (Εast Corinth Rift, Greece): spatiotemporal evolution and implications for the triggering mechanism

In this work, we study the January 1, 2020 – June 8, 2021, earthquake activity in the East Corinth Rift (central Greece), one of the most seismically active areas in Europe. During this period an intense earthquake sequence occurred in the Perachora peninsula, presenting the characteristics of swarm activity. We present a relocated earthquake catalogue for the area, derived with the double-difference algorithm, and study the spatiotemporal evolution of the 2020 Perachora peninsula earthquake sequence and the possible triggering mechanisms. The Perachora sequence presents distinct characteristics of earthquake migration along a N 103º E direction, as indicated by the Principal Component Analysis, from the east toward northwest and then west, with successive deepening of the events. This migration pattern is compatible with a pore-fluid pressure triggering front of hydraulic diffusivity of D = 2.8 m2/s and an average velocity of 0.22 km/day. In addition, the sequence presents sub-diffusion, with a diffusion exponent of 0.89 ± 0.06. The analysis, overall, indicates that the Perachora sequence was triggered at shallow depths by fluid overpressures, possibly generated by down-going fluxes of meteoric fluids, and then driven by pore-fluid pressure diffusion along the activated structures.