3:30 PM - 3:45 PM
[SCG52-19] Crustal movements since 100 ka along the Sanriku coast from geomorphology/geology studied after the 2011 Tohoku-oki earthquake
★Invited Papers
Keywords:crustal movement, Sanriku coast, Holocene sediment, Pleistocene terrace, 2011 Tohoku-oki earthquake
Along the Sanriku coast, northeast Japan, the discrepancy in crustal movement has been reported between uplift on a scale of 105 years versus subsidence on a scale of 101–102 years. The 105-yr uplift trend along the entire coast has been used to constrain models of megathrust earthquake cycles along the Japan Trench. However, geomorphological/geological studies, which etherealizes the constraint condition, did not progress from 1980’s to 2011 (when the 2011 Tohoku-oki earthquake occurred), indicating need for reconsideration of the constraint condition on the basis of further geomorphological/geological perceptions. In this study, we present interpretation of crustal deformation along the Sanriku coast since 100 ka on the basis of geomorphological/geological study after the 2011 earthquake.
Paleo-sea-level indicators and sediment stacking patterns, which are reconstructed from recent analyses of incised valley fills with extensive radiocarbon dating, indicate relative uplift along the northern Sanriku coast and subsidence along the central to southern coast on a millennial-scale. In addition, detailed analyses conducted recently on topography, tephrochronology, and field observation about marine terrace indicate identifiable uplift along the northern part of the coast only, while no uplift signature with accuracy is observed for the central to southern part. These results obtained after the 2011 earthquake suggest an agreement in the spatial distribution of vertical deformation between the two periods: during the last 100 kyr and during the last several to ten thousand years. The coherence of the spatial distribution of crustal movements over these observational periods implies that an uniform uplifting trend along the whole area of the Sanriku coast on a timescale of 103 – 105 years, which was assumed on the basis of putative marine terrace before the 2011 earthquake and used as constrained condition for modeling megathrust earthquakes, should be modified to acknowledge the variation in vertical deformation along the Sanriku coast; the northern part has been uplifted while southern part has subsided since at least 100 ka.
Paleo-sea-level indicators and sediment stacking patterns, which are reconstructed from recent analyses of incised valley fills with extensive radiocarbon dating, indicate relative uplift along the northern Sanriku coast and subsidence along the central to southern coast on a millennial-scale. In addition, detailed analyses conducted recently on topography, tephrochronology, and field observation about marine terrace indicate identifiable uplift along the northern part of the coast only, while no uplift signature with accuracy is observed for the central to southern part. These results obtained after the 2011 earthquake suggest an agreement in the spatial distribution of vertical deformation between the two periods: during the last 100 kyr and during the last several to ten thousand years. The coherence of the spatial distribution of crustal movements over these observational periods implies that an uniform uplifting trend along the whole area of the Sanriku coast on a timescale of 103 – 105 years, which was assumed on the basis of putative marine terrace before the 2011 earthquake and used as constrained condition for modeling megathrust earthquakes, should be modified to acknowledge the variation in vertical deformation along the Sanriku coast; the northern part has been uplifted while southern part has subsided since at least 100 ka.