On March 20th, 2006, a moderate earthquake (M w = 5.2) struck the Laalam (NE-Algeria). The damage was centred in the Laalam village where four deaths, 68 injured and more than 40 housing units destroyed making dozens of peoples homeless. Damage and casualties are directly related to an earthquake-induced landslide occurred at 10 km far from the epicenter (ISC relocation). The landslide rupture, mapped by using a ground based survey, is striking NE-SW along a 1-km length rupture with a 45 cm of lateral displacement. The rupture plan is dipping 40°at the surface and showing horizontal striations. A 75 cm of pre-2006 lateral displacement is also observed indicating a repetitive behaviour of the landslide. The last time where the landslide was activated extends back to 1974 following another moderate earthquake. This landslide reminds us the high level hazard of induced ground failures due slope instabilities in mountainous zones of seismically active areas.
Coastal Quaternary deposits of western Oranie show typical soft-sediment deformations including sedimentary dykes, sand volcanoes, sismoslumps, thixotropic bowls, thixotropic wedges, diapir-like structures, and faults grading. Field observations indicate that these deformations exist at several levels of the studied deposits along the west Oranian coast. This study demonstrated that these structures are earthquakes-related, by analysis of potential trigger sources. Several arguments demonstrate the seismic origin: the depositional environment rich in water that located in an active tectonic region, the thixotropic nature of deformations and their large vertical and horizontal diffusion in the Quaternary series consistent with a seismic recurrence. This allows characterizing these Quaternary soft-sediment deformations as seismites that were triggered by earthquakes
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