Characterization of El Kherba landslide triggered by the August 07, 2020, Mw = 4.9 Mila earthquake (Algeria) based on post-event field observations and ambient noise analysis

On 7th of August 2020, a M w = 4.9 earthquake occurred in Mila province (Northeast Algeria). Consequently, more than 2000 houses were indirectly affected (partially damaged or collapsed) within 10 km from the earthquake’s epicenter, in the locality of El Kherba. According to field surveys conducted 3 days after the earthquake, damages and casualties were directly linked to an earthquake-induced landslide that occurred after the main shock. This was evidenced by numerous cracks in the site’s soil mainly perpendicular to the landslide direction. Local characteristics (i.e., geology, geomorphology) and anthropogenic activities expose this area to landslide hazard. This study shows the reliability of the ambient noise horizontal to vertical spectral ratio (HVSR) method in the characterization of an active landslide. Ambient noise records were processed through spectral ratio techniques to identify the landslide’s geometry based on spectral responses analysis. The obtained results allowed the landslide’s slip surface mapping and boundary delineation, which correlates well with the field observations. After the rotation of the signal’s horizontal components, large variations in the experimental spectral ratios, in both amplitude and direction, revealed site effects (soil remoulding, crack network) on the soil dynamic behavior.