5:15 PM - 7:15 PM
[HQR05-P05] Three-dimensional Urban Geological Map: tectonic movements and buried valley topography of the Pleistocene Shimosa Group in the southeastern part of Saitama Prefecture
Keywords:Three-dimensional Urban Geological Map, Saitama Prefecture, Pleistocene, Shimosa Group
Understanding the subsurface geology in urban areas is crucial from the perspectives of geotechnical engineering and disaster prevention. In this study, we analyzed the stratigraphy and geological structure of the Pleistocene Shimosa Group in the southeastern part of Saitama Prefecture as part of the "Three-dimensional Urban Geological Map"[1] project undertaken by the Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST).
The Three-dimensional Urban Geological Map integrates and analyzes a large volume of borehole data, including those from AIST's own drilling surveys as well as publicly available data from local governments and public works projects. This enables the broad correlation of stratigraphy and the visualization of its three-dimensional distribution. By making the subsurface geology intuitively accessible via a web-based platform, the map enhances the understanding of the underground environment. Previously, Three-dimensional Urban Geological Maps were published for the "Northern Area of Chiba Prefecture" (2018) and "Central Tokyo" (2021). In 2025, the map for the "Southeastern Area of Saitama Prefecture" is scheduled for release. This presentation reports on the stratigraphy and geological structures identified in the process of creating this map.
The Shimosa Group in the study area (MIS 12–5c) is subdivided into the Jizodo, Yabu, Kamiizumi, Kiyokawa, Kioroshi, and Omiya formations in ascending order. The elevation of the base of each formation in the Shimosa Group tends to be higher in the west (around Kitamoto City) and lower in the east (around Shiraoka to Kuki cities). Notably, the lower formations show greater differences in elevation, suggesting the cumulative effects of tectonic movement. A particularly significant relative uplift is observed around Kitamoto city, where the Kioroshi Formation (MIS 5e) is completely lacking due to erosion at the base of the overlying Omiya Formation (MIS 5c).
Furthermore, the lower part of the Kioroshi Formation exhibits a valley-fill distribution, predominantly consisting of soft mud strata (N-value≦5). These valley-fill deposits extend southeastward along the western margin of the Omiya Upland from Okegawa City and also appear as small-scale valley-fill sediments southeastward from Niizutsumi in Minuma ward, Saitama City. The valley-fill deposits in the subsurface of the Omiya Upland were previously noted by Nakazawa and Endo (2002)[2] and Nakazawa et al. (2006)[3]. However, in this study, we analyzed a large volume of borehole data, revealing the detailed three-dimensional distribution of these deposits.
The use of the Three-dimensional Urban Geological Map has enabled high-precision visualization of the geological structures and buried valleys in the southeastern part of Saitama Prefecture. This advancement is expected to contribute to the assessment of groundwater resources, geological contamination surveys, and disaster risk analysis in urban areas.
Reference
[1] Urban Geological Map, URL: https://gbank.gsj.jp/urbangeol/
[2] Nakazawa and Endo (2002) Quadrangle Series, 1: 50,000, Omiya district.
[3] Nakazawa et al. (20006) J. Geol. Soc. Japan, 112, 349–368.
The Three-dimensional Urban Geological Map integrates and analyzes a large volume of borehole data, including those from AIST's own drilling surveys as well as publicly available data from local governments and public works projects. This enables the broad correlation of stratigraphy and the visualization of its three-dimensional distribution. By making the subsurface geology intuitively accessible via a web-based platform, the map enhances the understanding of the underground environment. Previously, Three-dimensional Urban Geological Maps were published for the "Northern Area of Chiba Prefecture" (2018) and "Central Tokyo" (2021). In 2025, the map for the "Southeastern Area of Saitama Prefecture" is scheduled for release. This presentation reports on the stratigraphy and geological structures identified in the process of creating this map.
The Shimosa Group in the study area (MIS 12–5c) is subdivided into the Jizodo, Yabu, Kamiizumi, Kiyokawa, Kioroshi, and Omiya formations in ascending order. The elevation of the base of each formation in the Shimosa Group tends to be higher in the west (around Kitamoto City) and lower in the east (around Shiraoka to Kuki cities). Notably, the lower formations show greater differences in elevation, suggesting the cumulative effects of tectonic movement. A particularly significant relative uplift is observed around Kitamoto city, where the Kioroshi Formation (MIS 5e) is completely lacking due to erosion at the base of the overlying Omiya Formation (MIS 5c).
Furthermore, the lower part of the Kioroshi Formation exhibits a valley-fill distribution, predominantly consisting of soft mud strata (N-value≦5). These valley-fill deposits extend southeastward along the western margin of the Omiya Upland from Okegawa City and also appear as small-scale valley-fill sediments southeastward from Niizutsumi in Minuma ward, Saitama City. The valley-fill deposits in the subsurface of the Omiya Upland were previously noted by Nakazawa and Endo (2002)[2] and Nakazawa et al. (2006)[3]. However, in this study, we analyzed a large volume of borehole data, revealing the detailed three-dimensional distribution of these deposits.
The use of the Three-dimensional Urban Geological Map has enabled high-precision visualization of the geological structures and buried valleys in the southeastern part of Saitama Prefecture. This advancement is expected to contribute to the assessment of groundwater resources, geological contamination surveys, and disaster risk analysis in urban areas.
Reference
[1] Urban Geological Map, URL: https://gbank.gsj.jp/urbangeol/
[2] Nakazawa and Endo (2002) Quadrangle Series, 1: 50,000, Omiya district.
[3] Nakazawa et al. (20006) J. Geol. Soc. Japan, 112, 349–368.