Late Holocene uplift of the Izu Islands on the northern Zenisu Ridge off Central Japan

摘要

To clarify the Holocene uplift history of the Izu Islands, Japan, we analyze the elevations and_(14)C ages of emerged sessile assemblages measured by accelerator mass spectrometry (AMS) on the islands of Niijima, Jinaijima, Shikinejima, and Kouzushima, on the northern Zenisu Ridge. The results suggest that uplift events took place after AD 1950 (uplift event 1), during AD 786–1891 (uplift event 2), during AD 600–1165 (uplift event 3), and during AD 161–686 (uplift event 4), although uplift events 3 and 4 are identified only at Kouzushima. The minimum amount of uplift was estimated to be 0.4–0.9?m in uplift event 1, 2.4–2.7?m in uplift event 2, 3.6?m in uplift event 3, and 3.3–8.1?m in uplift event 4. These events could have been caused by volcanic activity or strong earthquakes. There also remains the possibility that uplift event 2 was caused by the AD 1498 Meio earthquake; in contrast to the previous interpretation, the ages of uplift events are significantly older than the earthquake, based on conventional (non-AMS) methods.