Submarine Landslides Could Cause Wide‐Spread Tsunami Impact in the East Sea (Sea of Japan)

Abstract

The East Sea (Sea of Japan) is a seismically active back‐arc basin with a history of devastating tsunamis, yet regional hazard assessments and mitigation planning often overlook the tsunamigenic potential of submarine landslides. This study investigates the tsunami impact of large‐scale mass failures along the southwest (SW) margin of the East Sea, where prominent submarine landslide scarps and related mass‐transport deposits are mapped. Using high‐resolution seismic reflection and multibeam echosounder data, we reconstructed the pre‐failure morphology of a major landslide involving approximately 25 km 3 of material. Landslide runout and subsequent tsunami were simulated using a dynamically coupled landslide–tsunami model in COMCOT. Results indicate that such an event triggers extreme hydrodynamic response, with coastal wave amplitudes reaching 9.3 m and current speeds of 13.3 m s −1 along the coast of Korean Peninsula. These waves cause significant onshore inundation, with flow depth reaching 3 m and penetration distances up to 1.5 km inland. In Japan, coastal amplitudes could reach up to 16.8 m. Crucially, tsunami arrival times to densely populated cities like Ulsan and Busan range from only 25 to 50 min, providing a narrow window for emergency response. Compared to earthquake‐generated tsunamis in the region, landslide‐induced tsunamis exhibit higher amplitudes, stronger currents, and shorter travel times, producing widespread regional impacts. These findings highlight the critical need to integrate submarine landslides into regional tsunami hazard assessments and early warning systems.