Tsunami wave characteristics of the 2024 and 2025 Hyuganada earthquakes

Abstract The Hyuganada Sea in Japan, located at the southwestern edge of the Nankai subduction zone, is a region where Mw 7-class interplate earthquakes have repeatedly occurred. On 8 August 2024, an Mw 7.1 earthquake occurred in the Hyuganada Sea, triggering a moderate tsunami. Five months later, on 13 January 2025, an Mw 6.8 event in the same region also generated a tsunami. We investigated the wave characteristics of these two events through a combination of tsunami waveform analysis, spectral analysis, and numerical simulation. The maximum tsunami heights were recorded at the Aburatsu tide gauge: 0.40 m for the 2024 event and 0.15 m for the 2025 event. Offshore pressure gauges measured maximum heights of 0.01–0.02 m. Both tsunami events exhibited rapid amplitude attenuation. Spectral analysis revealed similar frequency characteristics in both tsunamis, with energetic peaks at 24.4 and 11.6 min for the 2024 event; 9.8, 28.4 and 6.2 min for the 2025 event. Most stations did not exhibit significant resonance, but a mild resonance effect was observed at Murotomisaki during the 2025 event.