Late Quaternary uplift rate inferred from marine terraces, Shimokita Peninsula, northeastern Japan: A preliminary investigation of the buried shoreline angle

Abstract

After estimating tectonic uplift rates along the northern part of the northeast Japan forearc (the overriding plate in the northeast Japan subduction zone) by mapping the elevation of the inner edges of marine terrace surfaces, we refined this estimate through elevation measurements of the buried shoreline angle beneath well-dated marine terrace surfaces, from which we could derive more accurate paleo-sea levels. The uplift rate initially inferred from the inner edge of marine terrace T4, correlated with marine isotope stage MIS 5e by tephrochronology, increases eastward from 0.11–0.22mky−1 around the backarc volcanic front to 0.17–0.32mky−1 in the forearc on the peninsula of Shiriyazaki. We refined the uplift rates for T4, on the basis of the shoreline angle elevation, from the reconstructed profile of the paleo-sea cliff and wave-cut platform on a rocky coast and the reconstructed profile of the swash zone sediments and terrace deposits on a sandy coast. The refined uplift rates were 0.14–0.25mky−1 on the rocky coast and 0.14–0.23mky−1 on the sandy coast, slightly slower than the rates we inferred from the height of T4 and about one-half to three-fourths of previously reported rates. By extrapolation from the example of the sandy coast, the refined uplift rate around the volcanic front was 0.09–0.18mky−1. The vertical deformation across the forearc of the Shimokita Peninsula since MIS 5e is possibly associated with regional isostatic uplift of 0.09–0.18mky−1 and anticlinal deformation by an offshore fault, interpreted from acoustic profiles, of 0.05–0.07mky−1.