Observed relative sea-level (RSL) changes during the past ~130kyr make it possible to evaluate the vertical crustal movement due to several tectonic processes such as the subduction of oceanic plates. Here we infer average rates of tectonic crustal movement along the Japanese coastlines on three typical timescales of ~50yr, ~6kyr and ~125kyr based on tide gauge and Holocene RSL observations and the altitudes of marine terraces formed at the Last Interglacial (LIG) phase at ~125ka. The rates on a timescale of ~50yr are derived from tide gauge data, thermosteric sea-level changes due to thermal expansion of the oceans and predictions due to the glacio-hydro isostatic adjustment (GIA) for the last deglaciation and also recent melting of the mountain glaciers and Greenland and Antarctic ice sheets. Those for ~6kyr and ~125kyr are based on the RSL observations and the predictions by GIA modelling, considering uncertainties for temporal changes in eustatic sea-level for the mid- to late-Holocene and LIG phase. The inferred rates for ~50yr are significantly different from those for ~125kyr in most sites, particularly for sites along the coastline from eastern Hokkaido to northeastern Japan, Shikoku and south Kyushu facing the Pacific Ocean. In these regions, the rates for ~125kyr and ~50yr are positive (uplift) and negative (subsidence), respectively. Also, the observed RSL changes at ~6ka are consistent with the inferred RSL changes using the rates for ~125kyr and GIA-predictions in many sites, but inconsistent with those for ~50yr in most sites except for a few sites. These results suggest that the rates on a timescale of ~50yr are not representative of the tectonic crustal movements for timescales longer than ~6kyr in most sites along the Japanese coastlines. However, the inferred rates on these timescales may be useful in discussing the recurrence of megathrust earthquake with its interval of ~1kyr such as the 2011 earthquake off the Pacific coast of Tohoku.
All Science Journal Classification (ASJC) codes
- Global and Planetary Change
- Ecology, Evolution, Behavior and Systematics