Seismic hazards analysis for the Qiongdongnan segment of the Continental Slope Fault Zone in northern South China Sea from dynamic rupture models: Implications for earthquake-induced landslides and tsunamis

Marine earthquakes are extremely dangerous. The Qiongdongnan (QDN) segment of the Continental Slope Fault Zone (CSFZ) in the northern South China Sea poses seismic risks that may trigger submarine landslides and tsunamis. Here, using the curved-grid finite-difference method (CGFDM), we established a dynamic spontaneous rupture model for this region southeast of Hainan Island, China. We simulated the wave propagation and strong ground motion resulting from these earthquakes and produced seismic intensity distribution maps. The maximum magnitude achieved across all models was M W 7.7. A left-lateral strike-slip fault with a dip angle of 59.5° was used in the simulations, and 26 hypocenters at various positions and depths were selected. We further investigated the seismic waves and strong ground motions generated by these events. The results indicated that the velocity structure had a significant influence on the maximum slip concentration on the fault. Additionally, under the considered initial stress conditions, the earthquake magnitudes varied with depth for certain hypocenters. We analyzed the potential risk of earthquake-induced landslides using the pseudostatic method and introduced the factor of safety (FOS). The results showed that the northern landslide area contained a large section where the FOS was less than one, indicating the increased likelihood of landslides. In addition, for hypocenters at a depth of 8 km, earthquake with the smallest magnitude can generate a significantly stronger event than one with hypocenters at depths of 10 and 12 km. Overall, this fault poses significant risk for a chain of earthquake-landslide-tsunami disasters. Our study can provide a reliable reference for the development of disaster warning systems in the region and further our understanding of seismicity along the QDN segment.