EVALUATION OF HOLOCENE CRUSTAL MOVEMENT IN THE AKO PLAIN, WESTERN JAPAN

Abstract

Holocene sea-level observations have been obtained from the Ako Plain in western Japan. In this coastal area, the Holocene crustal movements have been evaluated, except the crustal response due to the last deglaciation, by comparing observations and theoretical predictions of relative sea-level (RSL) variations. Analyses of diatom assemblages and sedimentary sulphur in core sediments were used along with radiocarbon dates to derive the RSL variations. A crustal movement rate between +0.2 mm and-0.2 mm per year, corrected for the prediction, fits well with the observed RSL index points. Owing to the constraint of the reconstructed palaeo-mean sea level (PMSL) at 7300 cal. BP, the coast of the Ako Plain may have the best estimate of a tectonic subsidence rate of 0-0.2 mm/yr. The tectonic uplift rates along the tectonically active coast of western Kobe were derived to be 0.3-0.7 mm/yr and 0.11-0.45 mm/yr for Tarumi and Tamatsu, respectively, relative to Ako over the period concerned. The relative uplift along the traverse from Ako to western Kobe is primarily the result of the crustal movement resulting from the active faulting of the Rokko-Awaji fault system (RFS).