Evaluating Stability in Vado Ligure offshore (Liguria, NW Italy) Through the MLD Method

Submarine landslides are  significant marine geological hazards, potentially affecting offshore infrastructure anchored to the seafloor, including oil and gas facilities, submarine pipelines and cables, and coastal engineering projects. Given the critical role of offshore areas in current and future energy production, anticipating potential landslide events is essential for effective planning and risk mitigation.
In this context, the present study investigates the landslide potential of the offshore area of Vado Ligure (Northern Italy), a strategically important site for the deployment of a gas pipeline that connects a ship mooring to the coast (https://fsruitalia.it/vado-ligure/). The area is located near the head of a submarine canyon carving the shallow water platform, approximately 2 km east of the harbour of Vado Ligure.

In the absence of detailed studies describing potentially unstable masses along this submarine structure, we evaluated seabed stability along the proposed pipeline route by applying the Minimum Lithostatic Deviation (MLD) method, developed by Tinti and Manucci (2006, 2008) as a reformulation of the classic Limit Equilibrium Method. We took into consideration various potential sliding surfaces along a series of transects intersecting the pipeline route and partially covering the steep slope characterizing the canyon.

An analysis of the Parametric Catalog of Italian Earthquakes (CPTI15 v4.0.0) (Rovida et al., 2020) reveals the occurrence of historical earthquakes with moderate magnitudes (4–5) in the Vado Ligure area. At the same time, the Database of Individual Seismogenic Sources -- DISS database (DISS Working Group 2021) identifies seismogenic structures in the region capable of generating earthquakes with magnitudes up to 7.4. These findings emphasize the importance of including seismic loading in seabed stability assessments. Accordingly, a sensitivity analysis was conducted, varying the Peak Ground Acceleration (PGA) between 0.2 g and 0.7 g to account for uncertainties and assess its influence on slope stability.

Furthermore, a second sensitivity analysis focused on key geotechnical parameters, such as cohesion and friction angle, which play a crucial role in slope stability evaluation and which are poorly known for the studied area. The combined results of these analyses indicate that the offshore area under investigation is stable, even under the worst-case assumptions.

 

References:

DISS Working Group, “DISS, Version 3.3.0: A compilation of potential sources for earthquakes larger than M 5.5 in Italy and surrounding areas. Istituto Nazionale di Geofisica e Vulcanologia (INGV).” https://diss.ingv.it/index.php, 2021.

Rovida A., Locati M., Camassi R., Lolli B., Gasperini P., “The Italian earthquake catalogue CPTI15.” Bulletin of Earthquake Engineering, vol. 18, no. 7, pp. 2953–2984, 2020.

Tinti, S. and Manucci, A., “Gravitational stability computed through the limit equilibrium method revisited”, Geophysical Journal International, vol. 164, no. 1, pp. 1–14, 2006.

Tinti, S. and Manucci, A., “A new computational method based on the minimum lithostatic deviation (MLD) principle to analyse slope stability in the frame of the 2-D limit-equilibrium theory”, Natural Hazards and Earth System Sciences, vol. 8, no. 4, pp. 671–683, 2008.