The Intense 2020–2021 Earthquake Swarm in Corinth Gulf: Cluster Analysis and Seismotectonic Implications from High Resolution Microseismicity

The intense 2020–2021 seismic crisis in Corinth gulf, Greece, comprising several hundreds of small earthquakes (maximum magnitude M w = 5.4 on 17 February 2021) is investigated. The spatial and temporal evolution of the seismicity implied the activation of multiple secondary fault segments. To decipher the geometry of the activated structures, we engaged relocation techniques and obtained the precise locations for 3398 earthquakes and 26 moment tensor solutions. The highly accurate seismicity locations and focal mechanisms illustrate the fine scale faulting geometry of a ~ 10–km–long activated area, almost east west striking and north dipping, and extensional kinematics. We grouped events into clusters using nearest–neighbor distances between them and a temporal stochastic point process, the Markovian Arrival Process (MAP). We identified clusters that evidence seismicity migration and organization in both space and time, deciphering the interaction of even tiny fault segments in a fault network. The exhaustive analysis of the swarm spatiotemporal evolution revealed several either distinct or contiguous activated minor fault segments that evolved in multiple structures, participating in the local fracture mesh. Faulting geometry and kinematics of these structures agree with the ~ N–S extension of the rift and north dipping fault planes.