Hydroacoustic Signals Recorded by CTBTO Network Suggest a Possible Submarine Landslide in Trou Sans Fond Canyon, Offshore Ivory Coast, March 2024

Abstract Underwater communication cables are essential components of global infrastructure, carrying over 99% of international data traffic. On 14 March 2024, a significant disruption to this network occurred because of a cable break offshore Ivory Coast, leading to widespread internet outages in the West African region. To investigate the cause of this cable break, we analyze hydroacoustic data recorded between 6 and 22 March on the two hydrophone triads installed near Ascension Island by the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization. We detect a low-frequency (<60 Hz) signal on three northern and two southern triad hydrophones on 12 March 2024. The signal had a duration of 85 s on the north triad compared to 45 s on the south triad. We used the generalized cross correlation with phase transform method to show that the detected signal originated at a bearing of 38.9° ± 4.6°, consistent with the location of the cable break off Ivory Coast, and with steep bathymetric slopes mapped in the Trou Sans Fond Canyon. We do not observe associated signals on the nearby land-based seismic stations in Ghana and Ivory Coast, confirming the marine origin of this event. In addition, template matching shows that the same signal was not recorded in the preceding and following eight days, implying that this event was an isolated case. Given the scarcity of natural earthquakes offshore Ivory Coast, this combination of evidence suggests that the hydroacoustic signals are likely caused by a submarine landslide in the Trou Sans Fond Canyon. Our results show that an investigation of the causative submarine landslide events is also needed to realize the potential of these hydroacoustic methods for hazard risk assessment and mitigation.