The 18th March, 2021 Bejaia (North-East Algeria) Earthquake Mw: 5.9

On March 18th, 2021, at 00h04mn (UTC), a moderate earthquake (Mw: 5.9) hit Bejaia city, located 200 km east of Algiers, the capital of Algeria. This event happened more precisely 17 km northwest of Cap Carbon inside the large bay of the city. This earthquake, the largest recorded offshore event since the May 21st, 2003 Boumerdes earthquake, triggered several aftershocks and caused damage to 2000 houses and social infrastructures, but no fatalities were reported. Onshore, the earthquake induced many rock falls along the rocky coastline. Offshore, this event also produced a small tsunami (a few cm) recorded by Spanish tide gages. In addition to the permanent Algerian seismic network, several portable stations were installed in the epicentral region to constrain the aftershock locations better. The waveform inversion of the main shock and the first day’s aftershock analysis allowed us to give the main preliminary characteristics of the event. This analysis revealed that the event occurred along an EW reverse southward dipping offshore fault in the western part of Bejaia Bay with a seismic moment of 8.70e + 17 Nm corresponding to Mw 5.9. The earthquake does not seem to be associated with the main NW–SE striking strike-slip fault, the so-called Babors transverse fault (BTF) recently identified (Boulahia et al., Pure and Applied Geophysics 178:1253–1279, 2021). This event belongs to the series of numerous earthquakes which affected the Lesser Kabylia block region from 2017 to 2021. It is typical of the African-Eurasian incipient subduction process along the northern Algerian margin. The study of this event is in progress and will allow us to better define the geometry of the fault and the rupture process. The occurrence of such offshore events, together with historical seismic events, highlights the necessity to re-evaluate the seismic risk for the City of Bejaia, where major seismic events could occur like the previous Boumerdes event of May 21st, 2003 (Mw: 6.8).