Characteristics of T-wave generation around submarine volcanoes

Unexpected major tsunamis have often occurred at Sumisu Caldera and Sofu Seamount, submarine volcanoes far south of Japan. Large T waves from the accompanying seismic events were observed during these tsunamigenic events. Characteristics of T waves could be useful as monitoring metrics for seismicity and tsunami excitation at submarine volcanoes. To understand T-wave generation around submarine volcanoes, I conducted numerical simulations of seismic-acoustic wave propagation from regions around Sumisu Caldera and Sofu Seamount and evaluated T-wave characteristics at various source locations. For sources just below the seafloor, efficient T waves are generated in wider areas of the simulation regions. As depth below the seafloor increases, epicenters with efficient T waves are concentrated within the submarine volcanoes of Sumisu Caldera, Sofu Seamount, and Sofugan Volcano. Efficient T waves at a certain seismic station are generated in regions around the steep (> 10º) downslopes against the seismic station. Even in regions with steep downslopes, efficient T waves from regions without downslopes against the seismic station could not be observed. The heterogeneous variation of downslopes at submarine volcanoes also causes anisotropic azimuthal patterns of T waves at far stations. The heterogeneities of bathymetric features around source regions cause variability of T-wave characteristics, and consequently, horizontal and vertical locations of seismic events could be constrained by comparing the characteristics of both observed and synthetic T waves.