Prominent Holocene marine terraces classified into four levels in southern Boss, have recorded the history of seismic crustal deformation by large earthquakes along the Sagami trough. The mode and amount of the crustal movements are discussed based on the relative sea-level curve reconstructed from topographical and chronological data including 36 ¹⁴ C dates.
1. The relative sea-level curve indicates four times sudden sea-level drops at 6, 150 y. B. P., 4, 350 y. B. P., 2, 850y. B. P. and 250y. B. P., caused by seismic upheavals associated with -earthquakes like that of Genroku Taisho type (Fig. 5).
2. The duration of interseismic period relates to the amount of upheaval associated with the preceding earthquake which measures 5.5m, 5m, 7m and 5.5m respectively.
3. Using the method of least squares, long-term mean uplift rate is calculated 3.0mm/year based on the relative altitude of sea-level (H) and the period (T) just before each earthquake (Fig. 7).
4. Trend of sea-level change deduced from difference between the long-term mean uplift rate and the uplift rate calculated by each earthquake, exhibits general regression toward 2, 700y. B. P. and transgression thereafter.
5. The same kind of seismic crustal movement and trend of sea-level change are also revealed from the data of Holocene emerged coral reefs in Kikaijima, the Ryukyu Islands (Figs. 6 and 7).