Relative sea levels of Japan from tide-gauge records
We attempted to separate tectonic, ocean-ographic, and eustatic components of change in relative sea levels derived from the many tide-gauge records of Japan acquired during the past 50 yr. A modified eigenanalysis permitted use of station data of unequal lengths. Regression analysis and eigenanalysis revealed systematic spatial differences in relative sea-level rise of ∼25 mm/yr. Although the difference is too great to be solely eustatic in origin, data are insufficient to permit accurate separation of tectonic and eustatic effects on relative sea levels. The low-frequency patterns (periods longer than 50 yr) may have been derived from subduction of the Pacific and Philippine plates beneath Japan. Higher frequencies (12-, 6-, and 2-yr periods) are correlated with oceanographic factors such as shifts in the position of the Kuroshio and the El Nino/Southern Oscillation. The contours of relative change in sea levels provide convincing evidence that neither a single nor several Japanese tide gauges can be selected to authentically demote present or past eustatic sea-level rise.