CRUSTAL TILTING DERIVED FROM HOLOCENE SEA-LEVEL OBSERVATIONS ALONG THE EAST-COAST OF HOKKAIDO IN JAPAN AND UPPER MANTLE RHEOLOGY

Late Holocene sea-level observations at sites along the east coast of Hokkaido in Japan indicate a gradual decrease of the altitude of relative sea-level eastward toward the tip of Nemuro Peninsula. These observations in seismically active areas can be explained by glacio-hydroisostatic adjustment due to the last deglaciation for an Earth model with a thin lithosphere of 30-40 km thickness and with no low viscosity layer, or with a 25 km lithosphere overlying a low viscosity layer less than 50 km, although more data as a function of time are needed to distinguish these models. Thus the vertical crustal displacement associated with the subduction of the Pacific plate seems to has not been cumulated on a time scale of 10(3)-10(4) years.