Hydroacoustic observations of a submarine landslide along Trou Sans Fond Canyon offshore Ivory Coast in March 2024 on CTBTO network

Underwater communication cables are critical components of global infrastructure, carrying over 99% of international data traffic. On 14 March 2024, a significant disruption to this network occurred due to 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 March and 22 March on the two hydrophone triads (H10N and H10S) installed near Ascension Island by the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). 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 seconds on the north triad compared to 45 seconds 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 38.8 ± 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. Additionally, template matching shows that the same signal was not recorded in the preceding and following 8 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 investigating the causative submarine landslide events is also needed to realize the potential of these hydroacoustic methods for hazard risk assessment.