Yoko Tono

Seismic Wave Interactions Between the Atmosphere - Ocean - Cryosphere System and the Geosphere in Polar Regions

At the time of the International Geophysical Year (IGY; 1957-1958), it was generally understood by a majority of seismologists that no extreme earthquakes occurred in polar regions, particularly around Antarctica. Despite the Antarctic being classified as an aseismic region, several significant earthquakes do occur both on the continent and in the surrounding oceans. Since IGY, an increasing number of seismic stations have been installed in the polar regions, and operate as part of the global network. The density of both permanent stations and temporary deployments has improved over time, and has recently permitted detailed studies of local seismicity (Kaminuma, 2000; Reading, 2002; 2006; Kanao et al., 2006).

Source characteristics of ocean infragravity waves in the Philippine Sea: analysis of 3-year continuous network records of seafloor motion and pressure

Continuous 3-year records of broadband ocean-bottom seismometers and pressure gauges of the seafloor network (Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET)) in the Nankai Trough region made it possible to monitor incoming ocean infragravity (IG) waves. Application of a slant-stacking technique revealed that the most energetic IG waves are incoming across the Nankai Trough from the Philippine Sea with limited energy of reflected waves back from the nearest coast. The sources of the most energetic waves are narrowly and stably localized into two closely adjacent azimuthal windows with mutually different wave spectral characteristics. Both sources show a seasonal variation, weak in summer and strong in winter. Although less energetic, IG waves propagating parallel to the trough and coast are observed. Such waves are greatly amplified when IG waves from a distant typhoon are incoming to the trough, suggesting the secondary origin of IG waves that can emit even more energetic waves than the originally incoming waves.