Although passive continental margins have long been regarded as low seismicity and with limited tsunamigenic potential, historical records reveal that active faults within these tectonic settings can, in fact, generate tsunamis. Firstly, this study evaluates the tsunamigenic potential of the Qiongdongnan segment of the Continental Slope Fault Zone (QDN-CSFZ), a newly identified intraplate fault in the northern South China Sea (SCS). We constructed 280 earthquake scenarios (Mw 6.6–8.0) with different source mechanisms and incorporated a stochastic source model to capture heterogeneous rupture patterns. Our simulations reveal that tsunami wave propagation is governed by regional bathymetry, causing waves to travel mainly perpendicular to the fault strike and rapidly across deep basins toward the Xisha Islands. Earthquakes above Mw 7.4 on the QDN-CSFZ generate regionally significant tsunamis. Under the extreme Mw 8.0 scenario, maximum tsunami wave amplitudes could be >7 m at the Qiongdongnan, >6 m at the Xisha Islands, and >5 m at the Vietnam Coast. The QDN-CSFZ constitutes a “multi-mechanism, short-lead-time” near-field tsunami threat, which is fundamentally distinct from the “high-potential, long-lead-time” far-field threat associated with the Manila Subduction Zone. This study underscores the need for a paradigm shift in tsunami assessment and for developing tailored near-field warning systems in the northern SCS.
Du et al. (Tue,) studied this question.