Holocene Terraces and Seismotectonics around Sagami Bay

摘要

Coseismic uplift probably contributed to the emergence of Holocene marine terraces around Sagami Bay. The highest of these terraces emerged about 6,000 years ago. Its height dis- tribution reflects subduction of the Philippine Sea Plate, collision of part of this plate (Izu Peninsula), and crustal shortening in the conti- nental plate. Two kinds of coseismic uplift probably occur at eastern Sagami Bay, on the southern part of the Boso Peninsula. One type, represented by the Kanto earthquake of 1923 (in the Taisho era), was due to interplate slip along the Sagami Trough. The other type is represent -ed by the Kanto earthquake of 1703 (in the Genroku era), the hypocentral area of which consists of the area along Sagami Trough and its southeastern extension. Various combina- tions of Taisho and Genroku earthquakes can account for the height of the highest Holocene marine terrace on the Boso Peninsula. The best such combination gives a mean recurrence in- terval of 500--600 years for Taisho-type earth- quakes. Since the accuracy and resolution of the height and formative age have not been so high, a consistent explanation of the formative history of Holocene marine terraces through- out Sagami Bay area remains to be given.