<p>Unexpected major tsunamis have occurred at Sumisu Caldera with an interval of about 10 years. Recently, a similar unexpected major tsunami from Sofu Seamount was reported. Sumisu Caldera and Sofu Seamount are submarine volcanoes far south of Japan. Large <i>T</i> waves from the accompanying seismic events were observed during these tsunamigenic events. Characteristics of <i>T</i> waves could be useful as monitoring metrics for seismicity and tsunami excitation at submarine volcanoes. To understand <i>T</i>-wave generation around submarine volcanoes, I conducted numerical simulations of seismic-acoustic wave propagation from regions around Sumisu Caldera and Sofu Seamount and evaluated <i>T</i>-wave characteristics at various source locations. For sources just below the seafloor, efficient <i>T</i> waves are generated in wider areas of the simulation regions. As depth below the seafloor increases, epicenters with large-amplitude and short-duration <i>T</i> waves are concentrated within the submarine volcanoes of Sumisu Caldera, Sofu Seamount, and Sofugan Volcano. Large-amplitude and short-duration <i>T</i> waves at a certain seismic station are generated from the seismic source located near the steep (&gt; 10º) downslopes oriented toward the seismic station. Large-amplitude and short-duration <i>T</i> waves from regions far from steep downslopes oriented toward the seismic station could not be observed at the station. Both slope angle and downslope direction are important for <i>T</i>-wave generation. The heterogeneous variation of downslopes at submarine volcanoes also causes anisotropic azimuthal patterns of <i>T</i> waves at far stations. The heterogeneities of bathymetric features around source regions cause variability of <i>T</i>-wave characteristics, and consequently, horizontal and vertical locations of seismic events could be constrained by not only body and <i>T</i>-wave travel times, but also <i>T</i>-wave characteristics.</p> Graphical Abstract <p></p>