High school students from Shizuoka Prefecture’s Iwata-Minami High School found data on an unrecorded tsunami after studying geological formations near their school. The tsunami, which is estimated to have happened 1,300 years ago, was discovered while studying a stratum near a river improvement site, 3.5 kilometers from the sea.
The research began when the geoscience club of the school studied geological formations nearby and unearthed white objects that was found to be fossil shells of a type of shellfish. The shellfish fossils discovered were analyzed by the students and the club’s adviser, Akira Aoshima, and found to be that of Cyclina sinensis and an oyster, none of which could be brought to the area with normal flooding of the river. This led them to conclude that the sand within the area had probably come from waters near the prefecture, as it contains similar components with those found on the offshore seabed.
Seeking a confirmation on their hypothesis, the students sent their research to the National Institute of Advanced Industrial Science and Technology’s Active Fault and Earthquake Research Center. The center established the age of the layer of stratum through carbon-dating of wood chips found in the deposit sample. The findings showed the layer to be as old as the time of the Hakuho Earthquake that happened in 684 CE, according to the Nihon Shoki (“The Chronicles of Japan”), which centers on the Nankai Trough, southwest of Tokyo. The earthquake was believed to have set off a tsunami that hit Shizuoka Prefecture and other nearby places in the region of Tokai some 1,300 years ago. Senior researcher from the center, Osamu Fujiwara, and some of his colleagues worked to help the students with their research and conclusion.
The students from Iwata-Minami High School’s geoscience club were in awe of their discovery of the strata. Club member Keito Mori said that what she enjoyed most with their research is “proving their theory.” They also found two upper layers of strata with garnets. As previous studies by the club already confirmed the existence of garnets that came from waters off the prefecture, they surmised that the material have come from the sea brought by a tsunami after the 1096 Eicho and 1498 Meio earthquake.
[via Asahi Shimbun]