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Reverse propagation of T waves from the Emperor seamount chain

Analysis of seismo‐acoustic T waves associated with an intermediate‐depth earthquake beneath northern Japan reveals that the detected T waves are secondary waves scattered by distant seamounts. The timing of T‐wave onset, 3000 s after occurrence of the earthquake, indicates that the detected T waves did not follow a direct path from the solid‐liquid conversion point near the Japan Trench to the observation stations in northeast Japan. It is hypothesized that the original T waves were reverse‐scattered back toward Japan by peaks of the Emperor seamount chain after propagation in the northern Pacific Ocean. The synthesized envelope patterns for acoustics scattered at the seamounts considering this multi‐path effect reproduce the travel time and amplitude pattern of the observed T waves well, with each seamount group producing a discrete amplitude peak of the scattered wave. These observations suggest that topographical obstructions act as a secondary source for T‐wave propagation in the ocean.