Microseism Generation by Two Consecutive Super Typhoons Crossing the Ryukyu Arc Observed with Ocean-Bottom Seismometers

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Abstract
Typhoons generate powerful ocean gravity waves that interact with the seafloor, producing microseisms detectable by remote seismometers. This study analyzed microseism generation associated with two consecutive super typhoons, Trami and Kong-Rey, which traversed the Ryukyu arc in 2018. Using continuous seismic and pressure records from ocean-bottom seismometers (OBSs) and nearby land stations combined with ERA5 reanalysis and WAVEWATCH III wave model outputs, we investigated the spatiotemporal evolution of typhoon-driven microseism sources across the subduction margin. We identified distinct short-period (2–6 s) and long-period (6–10 s) double-frequency microseisms. As the typhoons approached the OBS array, microseism power surged, the spectral bandwidth broadened, and the dominant period shifted to longer periods, exhibiting strong correlations with decreasing sea surface pressure and increasing significant wave height. Source tracking reveals two dominant excitation mechanisms. The first involves coastal reflections of storm-induced waves along the Ryukyu island arc (class II), generating opposing swells that interact with incident waves. The second corresponds to single-storm opposing-swell interactions (class IIIa), in which a rapidly moving storm overtakes its previously generated swell, creating new opposing waves that interact with the pre-existing swell. Our results confirm the role of the Ryukyu subduction system in modulating the transfer of ocean wave energy into seismic ground motion and demonstrate the effectiveness of OBSs in tracking typhoon-induced microseism sources.

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