Submarine landslides in the southern margin of the Alboran Sea

In the southern margin of the Alboran Sea, several submarine landslides (ranging from 0.01 to 15 km³ in volume) are preserved within the sedimentary (contouritic) cover of the past million years. Historical earthquake records indicate that regional seismicity is predominantly associated with strike-slip faults, which exhibit minimal or no vertical displacement, thereby limiting the potential for significant tsunami generation. Consequently, submarine landslides emerge as the primary candidates for tsunami triggering in the area. To better understand the occurrence of submarine landslides and their associated risks in the Alboran Sea, three French research projects were conducted: (i) the ANR Albamar project (2018-2023), (ii) the CNRS-IRD Alarm project (2018-2021) and the (iii) French fleet cruise Albacore (2021, https://doi.org/10.17600/18001351). The purpose of this communication is twofold: (i) to present the major findings of these projects and (ii) to analyze the causal factors of a selected landslide event.

The spatial distribution of submarine landslides does not appear to be directly linked to the active Al Idrissi Fault System (AIFS), which has been responsible for three moderate earthquakes (6.0 < Mw < 6.4) over the past 30 years. Instead, the head scarps of landslides exhibiting seafloor expressions, located west of the AIFS, coincide with the edges of the thickest contourite drifts in this margin. This observation suggests that landslide initiation may be related to localized high sedimentation rates, which potentially induce elevated pore water pressures at the drift edges, driving upward fluid flow. Furthermore, the edges of these contourite drifts are intersected by blind thrust faults, which were initiated during the Tortonian due to Eurasian-African plate convergence. Evidence of recent activity along these faults implies that tectonic processes could also facilitate fluid migration. These combined mechanisms—sedimentation-driven fluid overpressure and tectonically induced fluid flow—likely act to reduce effective stresses along the contourite edges, thereby preconditioning the slopes to a metastable state. Although the spatial separation between the investigated landslides and the AIFS does not provide direct evidence for earthquake-triggered failures, the possibility of long-distance earthquake effects on fluid-influenced metastable slopes remains an open question. This is further supported by the presence of pockmarks, which indicate fluid expulsion in the region. The integration of sediment core data, including age dating of recent landslides, with in situ geotechnical measurements collected during the Albacore cruise, has significantly improved our understanding of the timing and mechanisms of landslide events. For the most recent landslides, which are dispersed across tens of kilometers, sediment drape analyses suggest ages ranging from 5 to 6 kyr. This likely points to a period of increased landslide activity during that time.