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Geological information is essential for a country like Japan, located at a tectonically active area, to ensure a safe and secure society. The Geological Survey of Japan gathers, compiles, and provides geological information and promotes its wider use. We also develop technologies to overcome various difficulties related to global environment protection, exploration of minerals and energy resources, and natural disaster mitigation, and coordinate international cooperation as a national representative.
AIST started to publish a series of the distribution maps of 12 Holocene-Pleistocene large-volume ignimbrites produced by massive eruptions in Japan. The first issue is the distribution map of the Ito ignimbrite ejected by a massive eruption of the Aira caldera in the southern part of Kyushu Island, Japan around 30,000 years ago. This “Distribution maps of large-volume ignimbrites in Japan” series provides the distribution and other geological dataset of the large-volume ignimbrite that occurred within the last 120,000 years in Japan in unified style, based on the compiling the field and borehole data. The first publication of this series is the distribution map of the Ito ignimbrite, that provides the distributions of the reconstructed distributions, surface altitude, thickness of the ignimbrite deposit, with the size and orientation of the clasts in the deposits. The total amount of the volcanic products of the eruption, including the Ito ignimbrite and associating volcanic ash, was re-estimated as 800-900 km3, which is approximately 1.5 times greater than the previous estimate. Catastrophic eruptions are infrequent but have a devastating impact in wide area when they occur. This publication series will contribute to the disaster prevention plans and national land use plans in preparation for catastrophic eruptions.
Distributions of the representative large-volume ignimbrites and associated volcanic ash fall deposits within the last 120,000 years in Japan
AIST has published a next-generation geological map “Urban Geological Map of Central Tokyo (Special Wards Area)”. It visualizes the subsurface geological structures beneath central Tokyo to a depth of tens of meters in three dimensions. It was difficult to accurately express subsurface geological structures beneath urban areas with conventional planar geological maps. Analysis of large amounts of survey data from as many as 50,000 sites with originally developed 3D modeling technology enabled to visualize the detailed subsurface geological structure of central Tokyo in three dimensions. As a result, the distribution of a valley-filling soft stratum called the post-Last Glacial Maximum (LGM) deposits in the lowlands of downtown Tokyo was depicted in great detail. Furthermore, it was clarified that a weak stratum similar to the post-LGM deposits is also distributed in a part of the Musashino Upland in the Yamanote area, which had generally been considered hard ground. This 3D geological map can be easily viewed by anyone free of charge, so widespread use is expected such as for earthquake hazard maps and urban infrastructure development in central Tokyo (special wards area). The map was released on the “Urban Geological Map of Central Tokyo” page of the AIST website on May 21, 2021.
3D image of the subsurface geology of central Tokyo, shown as “Urban Geological Map” on the AIST’s website
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