Exploring the structural components of the Bejaia-Babors shear zone (BBSZ) in NE Algeria: Evidence from local earthquake tomography using recent seismic events (2012−2022)

Abstract

In recent years, the Algerian region of Bejaia-Babors (BB) has experienced significant seismic activity, including the Bejaia-Babors seismic sequence in 2012–2013, the Jijel earthquake in 2019, the El Aouana earthquake in 2020, and Bejaia subsequent earthquakes in 2021 and 2022. These seismic events have not only brought to light the existence of the Bejaia-Babors Shear Zone (BBSZ) but have also emphasized the importance of discerning its structural components, depth, and extent. Our study focuses on the analysis of seismological data from 2012 to 2022, with a particular emphasis on elucidating the intricacies of this geological structure. Using the LOTOS (local tomography software) algorithm, we conducted three iterations of tomographic inversion, successfully obtaining horizontal and vertical sections that facilitated the identification and characterization of subsurface anomalies. The resulting 3D velocity models unveiled key tectonic structures within the BBSZ, including the Offshore Faults System of Jijel (OFSJ), South Greater Kabylia Fault (SGKF), Transversal Fault 1 (TF1), and the collision between the Lesser Kabylia Block (LKB) and the Babors (THF-1). Futhermore, brittle-ductile shears were identified along the Aftis Fault (AF) in the east and brittle shears along the Babors Transverse Fault (BTF) in the west. P-wave velocity analysis indicated the presence of rigid blocks. The observed high Vp/Vs ratio near segment 3 of the BTF fault suggests the presence of a fluid reservoir, likely involved in the Bejaia-Babors seismic sequence (2012−2013), as previously documented. These findings provide valuable insights into the tectonic framework of the BBSZ, highlighting major fault systems and the interaction between different tectonic blocks. The presence of brittle-ductile shears along the AF suggests complex deformation processes in this region. Overall, by identifying key fault systems, characterizing subsurface anomalies, and unveiling the presence of fluid reservoirs, our research not only contributes significantly to geodynamic knowledge but also holds immense significance for seismic hazard assessment, resource exploration, and future research in this field.