The 24 January 2020 Mw 5.0 El Aouana Earthquake, Northeastern Algeria: Insights into a New NW–SE Right-Lateral Bejaia-Babors Shear Zone

On January 24, 2020, a Mw 5.0 earthquake occurred in the El Aouana region, northeastern Algeria. This region is located at the western end of the Lesser Kabylian Block (LKB), a rigid body that was weakly deformed during the late Cenozoic tectonic phase, and it is characterized by a lower seismic activity than that in its bounding regions. The mainshock focal mechanism was estimated via both the P-wave first motion and waveform modeling methods. The earthquake was associated with the rupture of a NW–SE-oriented right-lateral strike-slip fault, as revealed by a 6 km long and 2 km wide aftershock cluster. The seismic moment estimated through waveform modeling was 3.6 × 10 16 Nm, while spectral analysis yielded a value of 3.9 × 10 16 Nm corresponding to a magnitude of Mw 5.0, a source radius of 1.6 km, and a stress drop of 4 MPa. The spatiotemporal evolution of the aftershock sequence, as modeled using a restricted epidemic-type aftershock sequence (RETAS) stochastic model, yielded a slope p = 1, indicating that the earthquake was generated by tectonic forces and that the aftershock sequence included many subsequences. The calculated stress tensor suggested N–S compression, rotated clockwise relative to NW–SE Eurasia–Africa convergence. Finally, the recent seismic activity (2012–2021) and geological observations in the area led to the suggestion of a new NW–SE right-lateral shear zone, namely, the Bejaia-Babors shear zone, which was incorporated into a seismotectonic growth model involving slip along inherited E–W structures. The pattern of stepover structures throughout this wide shear zone was enhanced during the recent seismic evolution.