Fluid-driven processes triggering the 2010 Beni-Ilmane earthquake sequence (Algeria): evidence from local earthquake tomography and 4D Vp/Vs models

Issam Abacha, Bendjama Hichem, BOULAHIA Oualid, Abdelkarim Yelles-Chaouche, Roubeche Khaled, Rahmani sofiane takieddine, Mohamed Anis Melaim, El Mahdi Tikhamarine

Abstract: The 2010 Beni-Ilmane earthquake sequence, with 3 Mw ≥ 5.2 mainshocks, occurred in the southern Tellian Atlas approximately 200 km southeast of the Algiers. We offer updated 3D Vp and Vs models, and we outline the space and time variations in the Vp/Vs ratio of the Beni-Ilmane crust based on 2297 well-located aftershocks representing the complete aftershock sequence. Two main P-wave low-velocity patterns correspond to fault alignments determined from geological studies: the NE–SW thrust fault located at the foot of Djebel Choukchot and the NNW–SSE oriented Samma strike-slip corridor. The former crosscuts the two P-wave high-velocity anomalies of the Kef Ouagnane and Kef Kherrat summits of the Choukchot Mountains. The third high-velocity anomaly represents the Jebel Affroun Mountain in the sub-Bibanic domain. Two high-Vp/Vs ratio patterns were revealed in the central aftershock part and along the NE–SW Ouanougha syncline, which constitutes a fluid reservoir and a fluid-saturated fault zone filled after aftershock activity. The 4D Vp/Vs models monitored fluid migration, and the modeled pore-pressure diffusion revealed that earthquake rupture along an ~ N–S blind strike-slip fault fractured the closed reservoir and released high-pressure fluids, provoking a notable and long-lasting aftershock sequence. Our study underlines that local earthquake tomography (LET) can provide useful insights into the upward migration of fluids from a compartmentalized hydrocarbon reservoir.