Tohru Yamanoi

Presence of sonneratiaceous pollen in middle miocene sediments, central Japan

Abstract Numerous sonneratiaceous pollen grains, found in Middle Miocene sediments of central Japan possess both meridional ridges and polar caps with inter-columellate granules Although the exine architecture of these pollen is similar to that of the living Sonneratia alba, a colpal aperture as observable in these fossil pollen grains is only rarely present in Sonneratia or in the fossil Florschuetzia, which is a form-genus showing affinity with the genus Sonneratia. The fossil pollen is described as Florschuetzia claricolpata sp.n. This new species not only has a distributional significance, but also may strengthen the phylogenetic link between the genera Florschuetzia and Sonneratia.

Aftereffects of Subduction-Zone Earthquakes: Potential Tsunami Hazards along the Japan Sea Coast

The 2011 Tohoku-Oki Earthquake is a typical subduction-zone earthquake and is the 4th largest earthquake after the beginning of instrumental observation of earthquakes in the 19th century. In fact, the 2011 Tohoku-Oki Earthquake displaced the northeast Japan island arc horizontally and vertically. The displacement largely changed the tectonic situation of the arc from compressive to tensile. The 9th century in Japan was a period of natural hazards caused by frequent large-scale earthquakes. The aseismic tsunamis that inflicted damage on the Japan Sea coast in the 11th century were related to the occurrence of massive earthquakes that represented the final stage of a period of high seismic activity. Anti-compressive tectonics triggered by the subduction-zone earthquakes induced gravitational instability, which resulted in the generation of tsunamis caused by slope failing at the arc-back-arc boundary. The crustal displacement after the 2011 earthquake infers an increased risk of unexpected local tsunami flooding in the Japan Sea coastal areas.