We present geologic evidence for middle-late Holocene paleo-tsunamis and coseismic uplift based on analyses of coastal sediments from the Shizuoka Plain at the west coast of Suruga Bay and Minami Izu at the southern Izu Peninsula, Japan. We also discuss tsunami deposits from a coastal lowland area at Shimoda city, southern Izu Peninsula, Japan, as identified in sediment cores (8–10 m long) from eight sites. The results are summarized as follows.
1. Three possible tsunami deposits detected from the Shizuoka Plain are dated at ca. AD 1000, 3565–3486 cal BP, and 4080–3900 cal BP (Kitamura et al., 2013a). These deposits are not found at the southern Izu Peninsula.
2. In the coastal lowland area of downtown Shimoda, at least four washover sand beds occur in back-marsh deposits that are younger than 3500 cal BP.
3. Emerged marine sessile assemblages indicate that three episodes of coastal uplift have occurred at the southern Izu Peninsula, at AD 570–820 (uplift of 0.9–2.0 m), AD 1000–1270 (0.3–0.8 m), and AD 1430–1660 (1.9–2.2 m)(Kitamura et al., 2014). These paleo-earthquakes may have occurred on an unknown, reverse fault located offshore from Shimoda.
2014 公益社団法人 東京地学協会