The Initial Energy of the Landslide-Induced Tsunami in Tracy Arm Fjord, Alaska, on 10 August 2025, Estimated from Long-Period Seismic Records

Global climate change is gradually reducing slope stability in high-latitude permafrost regions, and the resulting tsunamis are posing increasing threats to local life and property. In landslide-induced tsunamis, energy transfer from the sliding material to the water controls the tsunami evolution process; however, insufficient direct observations hinder understanding of the process. We take the landslide-induced tsunami that occurred in the Tracy Arm Fjord on 10 August 2025 as an example to show that the incomplete landslide force recorded by the solid Earth can be recovered from broadband seismic data. By best-fitting the reconstructed horizontal trajectory to post-event satellite imagery, we estimate that the sliding mass was about 120 ± 6 Mt. The residual speed at the end of the landslide was about 54.1 ± 2.7 m/s, predominantly in the westward direction. We further estimate that the energy transferred from the sliding material to the water to generate the tsunami is approximately 1.46 ± 0.07 kJ per kilogram, for a total of 1.76±0.09×1011 kJ. Based on a dynamic sliding model, the incomplete landslide force history can serve as a dynamic constraint for numerical simulation of the landslide-induced tsunami.