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 x 10(16) Nm, while spectral analysis yielded a value of 3.9 x 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.