Seismo-acoustic waves generated by the detonation of UXOs of large charge weights in a shallow water environment
Résumé
Unexploded historical ordnance (UXO) from World War II, that is discovered almost every week close to the French coast, must be destroyed quickly after discovery to ensure the safety of divers and ships. The favored destruction method is countermining, i.e., the use of a high-order detonation conducted by exploding an additional donor charge placed adjacent to the UXO. In the framework of a UXO countermining campaign conducted in the Bay of Hyères (Mediterranean Sea, France) in December 2018, hydro-acoustic and seismic recording systems have been deployed to record the explosion-induced waves in water and the seismic signals on the shore, respectively (POSA project). In this talk, we present the main observations and focus on the impact of the shallow water environment (whose water depth is less than 50 m), and more specifically on the impact of the unconsolidated sedimentary layer, on the recorded signals induced by the detonation of charges with weights ranging from 80 to 680 kg TNT-equivalent. The experimental observations are interpreted in light of physical considerations and numerical modeling of seismo-acoustic wave propagation using a spectral-element method. We also discuss the acoustic-to-seismic wave conversions, including H-phase and I-phase (following the IASPEI nomenclature). This work was part of the POSA project (grant ANR-15-ASTR-0001 POSA).