Long‐Period Seismic Waves From Seawater Disturbances During the 2018 Anak Krakatau Volcanic Island Collapse

Abstract Landslides often generate long‐period seismic waves that propagate over large distances. During volcanic island collapses and their intrusion into seawater, seismic signals of >1 min periods are widely observed. The physical sources of these signals remain poorly understood due to complex landslide‐water interactions. In this paper, we perform coupled landslide‐tsunami‐seismic simulations for the 2018 Anak Krakatau flank collapse, and compare the results with seismic records at regional and teleseismic distances. We find that the landslide alone cannot explain the observed signals. The reaction force from the disturbed seawater also generates long‐period seismic waves, with a contribution comparable to that of the landslide. A combined landslide‐seawater source model better reproduces the recorded waveforms overall. These findings advance our understanding of seismic excitation by tsunamigenic landslides and underscore the importance of water‐induced forces in seismic source studies.