[H-CG28] Nuclear Energy and Geoscience

[HCG28-P03] Advanced examination technique for crustal deformation in stable area: a case study of the Kanto Plain, Japan

*Nakanishi Toshimichi¹, Tetsuya Komatsu¹, Misao Hongo², Marie Noguchi³, Tatsuki Miyamoto⁴, Taiga Kimori⁴, Toshihiko Sugai⁴ (1.Japan Atomic Energy Agency, 2.Alps Technical Research Lab. Co. Ltd., 3.Paleo Labo Co. Ltd., 4.Univ. Tokyo)

Keywords:Sea-level change, crustal deformation, chronology, late Quaternary, Kanto Plain

Evidence of uplift and subsidence are scarce in a tectonic stable area, because the topography and strata due to glacial sea-level changes had been difficult to accumulate. To recognize them in such area, comprehensive consideration would be needed based on the uplifted terraces and drilling logs. In order to quantitatively verify the uncertainty of the above issues, the following research was conducted on the northern part of the Kanto Plain where there is few existing information (Tajikara, 2000; Sugai et al., 2013). To identify the distribution of the Marine Isotope Stage (MIS), three drilling cores were drilled at the Takagi Plateau (emerged at MIS 4; Kaizuka et al., 2000) along the Kinugawa River. These drilling sites are located from upstream to downstream in the order of GC-OY-2, GC-OY-1, and GC-NG-1, with hole elevations of 34.0 m, 29.5 m, 20.6 m and excavation length of 86.0 m, 90.0 m and 74.6 m, respectively. Using these cores, lithology, assemblages of diatom and pollen, and tephra analysis were performed. Drilling cores are mainly composed of Pleistocene sediments formed in various sedimentary environments from land to sea. The upper part has transitioned to the loam layer, and a mud bed with severely alteration (Kazusa Group) is distributed below the depth of 79.43 m of the GC-OY-2 core at the uppermost stream. In addition, many vitreous ash layers, pumice layers and scoria layers were found in the three cores. The Pleistocene at a depth of less than 90 m was divided into beach, upper outer, lower outer, inner bay, meandering river and reticulated river. As a result of diatom and pollen analysis, high sea level sediments corresponding to MIS5e and a dominant layer of Quercus spp. Corresponding to MIS11 were identified. Many strata corresponding to these are also found in the central part of the Kanto Plain (Nakazawa and Endo, 2000; Nakazawa and Tanabe, 2011; Naya and Yasuhara, 2014). Examining their distribution and sedimentary environments, we want to establish a method for estimating crustal deformation in the uplift / subsidence boundary area. This study is conducted in collaboration with the University of Tokyo. Topographical development since MIS5 and sea level change before MIS6 have been presented by Kimori et al. (2020) and Miyamoto et al. (2020) at this conference, respectively. We hope fruitful discussion with you.



Acknowledgments: This study was carried out under a contract with the Agency of Natural Resources and Energy, part of the Ministry of Economy, Trade and Industry of Japan as part of its R&D program supporting development of technology for geological disposal of high-level radioactive waste.


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