The estimated death toll of the 1792 Unzen earthquake and tsunami was 15,000 people. It was Japan’s deadliest volcanic disaster, caused by a chain of earthquakes, volcanic activity, a massive landslide, and the tsunami that followed.
On May 21, 1792, the southern flank of Mayuyama, a dome near Mount Unzen on Japan’s Shimabara Peninsula, collapsed. The landslide rushed into Ariake Bay and displaced enough water to create a destructive megatsunami. Waves struck both sides of the bay, including Higo Province—now part of Kumamoto Prefecture—and later rebounded toward Shimabara.
The total is an estimate rather than an exact modern census. Historical reconstructions commonly divide the approximately 15,000 deaths into roughly 5,000 people killed by the landslide, 5,000 by the tsunami in Higo, and another 5,000 by the returning waves in Shimabara.
The question’s wording can cause a subtle misunderstanding: the earthquake itself was not the sole cause of the fatalities. The earthquake helped trigger the Mayuyama collapse, while the landslide and tsunami produced the overwhelming majority of deaths. The event is therefore also known as the 1792 Unzen landslide and tsunami.