Using high-resolution acoustic images to reconstruct the evolution of an underwater cable breakage accident initiated by unsecure ship anchorage

Accidents of undersea cable breakage caused by unsecure anchorage occur from time to time, and reconstructing the time course elucidates the causes and provides valuable information for avoiding similar accidents in the future by developing response strategies when accidents occur. High-resolution acoustic images of the seafloor in the accident area provided detailed geomorphic and man-made resurfacing features of the seafloor, thus providing evidence and clues for accurately reconstructing the accident process. On October 4, 2022, a submerged cable severed when an anchor line to a cargo ship that had been sheltered from the wind dragged across the submerged cable in the central Bohai Sea in China. Twenty-five days after the accident, we used remote ultrasound sensing equipment for acoustic underwater scanning of the incident area. Based on the processed high-resolution acoustic images, we reconstructed the time evolution of the accident by analyzing the detailed features of the ship's anchor traces. We took into account visualized evidence from undersea mounds and depressions from cables in the seabed and conducted physical analyses of anchor and chain tracks, as well as the abandoned anchor. The results indicate that continuing to cut the anchor chain after the cable breaks is not effective. Instead, an attempt should be made to retract the anchor. If successful, some of the economic loss will be averted. • High-resolution acoustic images of the seabed of an undersea cable breakage accident initiated by unsecure ship anchorage. • Identifications and interpretations of anchor traces, cables, and abandoned anchor chains based on acoustic images. • Deduction of the accident process based on detailed characteristics of anchor traces, cables, and abandoned anchor chains. • Evaluation on the rationality of response strategies of the involved ship during the accident.