Subsurface Structures of the 2016 Mihoub Earthquake Sequence in North-Central Algeria Using Local Earthquake Tomography

Abstract

This study investigates the Mihoub region within the Blida Mountains of the Tellian Atlas(Abacha et al., 2014), an area prone to earthquakes due to the Africa-Eurasia plate convergence since the Late Cretaceous. We present both the 1910 Aumale earthquake (Ms 6.6 and I0=VIII) and the 2016 seismic sequence (Mw 5.3). Using local seismic tomography (LET) with Local Tomography Software in its twelfth version (LOTOS 12), we analyze velocity anomaly patterns and their correlation with subsurface structures in the Mihoub area. Our dataset includes 503 well-localized aftershocks from the 2016 seismic sequence. Results show consistent patterns, with positive anomalies associated with rigid block structures and negative anomalies associated with basins, recent formations, and tectonic structures. In particular, a NE-SW corridor of low-velocity anomalies aligns with Miocene and Oligocene formations. Mainshock and aftershock epicenters from the 2016 sequence align with the boundary between low and high-velocity anomalies, indicating the Mihoub Fault zone. Fault depth analysis suggests a maximum depth of 8 km, consistent with previous research. Vertical sections confirm similar azimuths and dips of fault segments involved in the 2016 and 2014 mainshocks. This study provides valuable insights into velocity anomaly patterns and their relationship to fault structures, enhancing the understanding of fault systems and seismic hazards in the Mihoub area.