Assessment of Risks Induced by Countermining Unexploded Large-Charge Historical Ordnance in a Shallow Water Environment—Part I: Real Case Study

Nathalie Favretto-Cristini (1) , Thierry Garlan (2) , Olivier Morio (2) , Xavier Demoulin , M. Arrigoni (3) , Anne Deschamps (4) , Mickael Bonnin (5) , Beucler É. (5) , D. Mercerat (6) , David Ambrois (4) , Romain Schwab (7, 8) , Paul Cristini (1) , Fang Wang (1, 9)

1 LMA - Laboratoire de Mécanique et d'Acoustique [Marseille]
2 SHOM - Service Hydrographique et Océanographique de la Marine
3 IRDL - Institut de Recherche Dupuy de Lôme
4 GEOAZUR 7329 - Géoazur
5 LPG - Laboratoire de Planétologie et Géosciences [UMR_C 6112]
6 Equipe-projet Repsody - Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement - Equipe-projet Repsody
7 Lab-STICC_M3 - Equipe Marine Mapping & Metrology
8 ENSTA Bretagne - École Nationale Supérieure de Techniques Avancées Bretagne
9 CGG - Compagnie Générale de Géophysique

The goal of the work presented in a two-companion paper is to pave the way for reliably assessing the risks of damage to buildings on the shore, induced by the detonation of unexploded historical ordnance (UXO) of large weights in variable shallow water environments with a water depth less than 50 m. The risk assessment is quantified through the seismic magnitude on the Richter scale, induced by the detonation of charges of different weights (between 80- and 680-kg TNT-equivalent). This metric is investigated experimentally using a coupled seismo-acoustic approach within the framework of a UXO clearance (countermining) campaign in the Mediterranean Sea. Analysis of real acoustic and seismic data shows that, compared to a charge detonation in water, a similar detonation on the seabed generates seismic signals of lower frequencies and higher amplitudes that propagate in the seabed. The larger the charge weight, the higher the seismic amplitude. Besides the explosion-coast distance, the ground properties also affect the signals. The sediments favor a longer signal duration and the presence of late dispersive and very low-frequency signals with a large amplitude, whereas the rocky grounds better preserve the high-frequency energy propagation. For the local environment considered in this study, a charge detonation on the seafloor generates seismic events of higher magnitudes compared to a detonation in water. However, these magnitudes are likely low enough to prevent any large damage in the nearby inland infrastructures.

Keywords: Damage detection; Detonation; Ordnance; Risk assessment; Seismic waves; Underwater explosions

Domains: Engineering Sciences [physics]; Civil Engineering; Risques; Sciences of the Universe [physics]; Continental interfaces, environment; Engineering Sciences [physics]; Acoustics [physics.class-ph]

Nathalie Favretto-Cristini, Thierry Garlan, Olivier Morio, Xavier Demoulin, M. Arrigoni, et al.. Assessment of Risks Induced by Countermining Unexploded Large-Charge Historical Ordnance in a Shallow Water Environment—Part I: Real Case Study. IEEE Journal of Oceanic Engineering, 2022, 47 (2), pp.350-373. ⟨10.1109/JOE.2021.3111819⟩. ⟨hal-03598273⟩