Left-lateral shear inside the North Gulf of Evia Rift, Central Greece, evidenced by relocated earthquake sequences and moment tensor inversion

• First time that left-lateral shear is clearly documented inside the Gulf of Evia rift.
• Aftershock depths indicate a seismogenic (brittle) zone of about 15 km in depth for the Gulf of Evia rift.
• The left-lateral kinematics indicates crustal strain partitioning because of E-W horizontal compression.

The use of local velocity model in the analysis of seismicity recorded by the Hellenic Unified Seismological Network (HUSN), provides the opportunity to determine accurate hypocentral solutions using the weighted P- and S-wave arrival times for the November 2013, November 2014 and June 2015 North Gulf of Evia (Euboea) sequences. The hypocentral locations, including the determination of the location uncertainties, are obtained applying the non-linear probabilistic analysis. We also calculated the moment tensor solutions for the main events as well as for the strongest aftershocks. The accurate determination of seismicity showed the activation of two left-lateral, NW-SE striking, near-vertical faults, one onshore near village Taxiarchis (2013 sequence) and one offshore (offshore Malessina Peninsula, 2015 sequence). The 2014 sequence, also offshore Malessina Peninsula ruptured an oblique-slip, north-dipping normal fault with a strike of N280–290°E. All three faults occur at depths 10–16 km, with rupture zone dimensions 5–6 km along strike and 3–4 km along dip. These aftershock depths indicate a seismogenic (brittle) zone of about 15 km in depth for this rift. The left-lateral kinematics indicates strain partitioning inside the rift because of E-W horizontal compression, also evidenced by GPS data. The moderate magnitude of earthquakes (M5.2 ± 0.1) indicates that strike-slip events have a minor contribution to the crustal deformation and to active tectonics of the Gulf.