Holocene uplift derived from relative sea-level records along the coast of western Kobe, Japan

Abstract

Mid- to late-Holocene sea-level observations have been obtained from Tamatsu and Tarumi in western Kobe, Japan. In this tectonically active area, we evaluate the local tectonic effect during the Holocene by comparison between observations and predictions of sea-level variations. For the purpose of this study, we analysed the diatom assemblages and carried out sulphur analysis of sediments. These were used along with radiocarbon dates to derive relative sea-level variations for the sites. A rate of tectonic uplift of between 0.1 and 0.3 mm per year, corrected for the prediction, fits well with relative sea-level (RSL) index points of Tamatsu at 6415–5320 cal BP. Depending on the altitude of the RSL index point at about 5700 cal BP, the best estimate of the rate of tectonic uplift for Tamatsu is calculated as 0.11–0.25 mm/yr over the period concerned. A rate of tectonic uplift between 0.3 and 0.5 mm per year is derived for Tarumi at about 7300 and 3835–3365 cal BP. These values may explain the height distributions of the Late Pleistocene marine terraces along the coast of the western Kobe, providing a first approximation for rates of local crustal movements during the Late Quarternary.