Holocene Crustal Movements around Sagami Bay as Inferred from Holocene Marine Deposits

摘要

This paper describes Holocene marine depos- its around Sagami Bay and discusses Holocene crustal movement in relation to crustal defor- mation associated with great earthquakes in the Sagami Trough. Flights of Holocene marine terraces are distributed on the coasts along the Oiso Hills and Miura Peninsula, which are uplifted regions located on the northeastern side of the Sagami Trough. Marine terraces located in the southern part of Miura Peninsula indicate that the emergences occurred around 6,000 yrs BP, 4,000 yrs BP, and 3,000yrs BP on the basis of the ages of sea caves and archaeological data. Remarkable uplifted features in the Holo- cene are observed along the northeastern part of Sagami Bay; to the north of this uplifted zone a belt of subsidence in the Holocene is located on the line connecting Hadano to Kanazawa-Hakkei through Ofuna. The emergence of the southwestern part of the Oiso Hills around 6,500yrs BP is inferred from the fossil molluscan assemblage, the K- Ah (Kikai--Akahoya) volcanic ash, and related carbon-14 dates. The Kozu--Matsuda active fault which delineates the western margin of the Oiso Hills did not move at the time of the emergence around 6, 500 yrs BP. The Oiso Hills to the east of the Kozu--Matsuda fault have uplifted and the Morito River Lowland to the west of the fault has subsided along with the slip of the Kozu--Matsuda fault since 6, 500 yrs BP. Marine sediments that emerged around 4, 500 yrs BP are present over 5 m above the present sea level in Odawara city, which is located in the southwestern margin of the Ashigara Low- land. The upper