Controls on the occurrence of submarine landslides around carbonate platforms and atolls in the northwest South China Sea

Submarine landslides are important hazards around carbonate platforms, posing a significant threat to coastal communities by generating tsunamis, while potentially damaging vital submarine infrastructure. Yet, the factors controlling slope instability near carbonate platforms remain poorly understood. In this study, we use high-resolution multibeam bathymetric and seismic reflection data to investigate submarine landslides on the flanks of carbonate platforms in the northwest South China Sea. We identify plastered and mounded contourite drifts that host submarine landslides of multiple sizes, with an area of 2.1−306 km2 and failed volumes of 0.03−11.8 km3. A global comparison of failed contourite drifts reveals that slope angle around carbonate platforms is lower (∼3.75°) than that on siliciclastic continental slopes (∼8.93°). We attribute this difference to the lower shear strength of the predominantly calcareous contourite drifts around carbonate platforms and atolls compared with siliciclastic continental slopes. Our findings show that intrinsic sediment weakness is a critical control on slope instability around carbonate platforms, highlighting it as an underestimated geohazard in carbonate depositional environments. Our results provide crucial information to develop robust risk assessment strategies and safer engineering practices around carbonate platforms and atolls.