Earthquake-Induced Landslide in the Foreland of the Algerian Alpine Chain: The Case of El Kherba Landslide Triggered by the 07 August 2020 Mila Earthquake Mw = 5

In Algeria, the north part is known by complex geological structures with a very important topography. This area is characterized by medium to high seismic activity, with a relatively high magnitude Mw of 5–7 and a maximum intensity of XIII. In the North-East, the Mila region, which is part of the North-East Algeria Alpine Chain, is exposed to this seismic hazard. The earthquakes that affected this region over four months have triggered landslides and rock falls. The 07 August 2020 main shock Mw = 5, which shook the region, triggered three large landslides, El Kherba, Grarem Gouga, and Azzeba, located respectively to the south, southwest, and southeast within a radius of 15 km from the epicentre. The most spectacular landslide triggered by this earthquake is the one affecting El Kherba city, which forms the western extension of the Mila city. This large-scale landslide has caused significant damage to the built environment, roads, and various installations. Field observation, geological, geotechnical, and geophysical survey campaign is carried out to characterize the affected formations and the triggering factors. They are composed mainly of 32 boreholes from 50 to 80 m in deep and 29 electrical profiles. In this study, we present an overview of the geological context and the seismicity of the Mila region, a geotechnical characteristic, and modelling of the triggered landslide with a determination of the passive and active factors that contributed to the different instabilities triggering. Particular emphasis is accorded to the direct or indirect effect of the main choc on triggering this landslide. The result shows that the landslide surface is deep, between 70 and 80 m, in a very weathered clay level. Its triggering is the result of the interaction of several factors, mostly passive like the lithological nature, the slope, the presence of water in deep and active as the main shock Mw = 5.