Radiocarbon analysis of tree ring for a catastrophic collapse in the northern Yatsugatake volcanoes: Its implication for seismotectonics in southwest Japan

Abstract In the late ninth century, the northern Yatsugatake volcanoes in central Japan experienced a catastrophic collapse, simultaneously causing a debris-avalanche. Such failures have been related to the AD 887 Nin'na earthquake, which occurred along the Nankai Trough. However, supportive evidence of the hypothesis remains unavailable. The present study reports wiggle match radiocarbon (14C) dating of a buried tree excavated from a deep part of the debris deposit. The death year of the buried tree was dated as AD 838 ± 17. The date exactly matches an inference of the AD 887 earthquake obtained from historical documents and field records of archaeological ruins, considering that 14C ages of Japanese trees have a regional offset of ≈30 years greater than the IntCal dataset. Our result suggests that the AD 887 earthquake occurred along about 700 km extending from the western margin of the Nankai Trough to the central segment of the Itoigawa-Shizuoka Tectonic Line.