著者

小山 真人

出版者

国立大学法人 静岡大学理学部地球科学教室

雑誌

静岡大学地球科学研究報告 (ISSN:03886298)

巻号頁・発行日

vol.50, pp.115-142, 2023-08-02 (Released:2023-08-08)

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Based on field surveys and terrain analysis using open data of aerial LiDAR point cloud (VIRTUAL SHIZUOKA), we analyzed the characteristics and causes of flooding in the lower basin of the Tomoe River caused by the heavy rains associated with Typhoon 15 in 2022. The water level of the main river was diverted into the Oya drainage channel and dropped once, but the level rose again and overflowed where the tributaries merged. The levee itself was not damaged or breached. Tributaries that had not undergone sufficient river improvement, and thus still had many meanders and shallow channels, flooded significantly, while tributaries that had undergone advanced river improvement also flooded due to increased water levels before joining the main river. Tributaries often overflowed in front of the insufficient cross-sectional area of the river channel where they passed under roads and railroads. Comparison of the flood depth distribution with existing hazard maps showed that the main channel flooding was generally on the planned scale. Some of the tributary flooding corresponded to the assumed maximum magnitude, while others fell far short of it. The high resolution of the topographical map based on point cloud data is considered effective for understanding flood risk and raising public awareness because it realistically reconstructs the flooded urban landscape.

著者

北村 晃寿 矢永 誠人 岡嵜 颯太 片桐 悟 中西 利典 森 英樹

出版者

国立大学法人 静岡大学理学部地球科学教室

雑誌

静岡大学地球科学研究報告 (ISSN:03886298)

巻号頁・発行日

vol.49, pp.87-95, 2022-07-31 (Released:2022-07-31)

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On July 3, 2021, a debris flow caused by a landslide from an embankment occurred along the Aizome River in the Izusan area of Atami City, Shizuoka Prefecture, central Japan, and buried sabo dam which was located approximately 450 m downstream of the embankment. Shizuoka Prefectural Government sampled one 13.1-m long core of deposits buried in the sabo dam in late August 2021. In this paper, radiocesium concentration was measured and grain compositions was investigated for this core sample. As a result, 134Cs and 137Cs released from the Fukushima Daiichi Nuclear Power Plant in mid-March 2011 were detected, and these markers specified the depositional surface at mid-March 2011 at 3.95-3.85 m core depth. In addition, the occurrence of fragments of both mudstone and chert in the overlying sediments indicates that the 3.74 m-thick portion was definitely the debris flow deposit.

著者

木村 浩之

出版者

国立大学法人 静岡大学理学部地球科学教室

雑誌

静岡大学地球科学研究報告 (ISSN:03886298)

巻号頁・発行日

vol.47, pp.Intro-1-Intro-9, 2020-07-31 (Released:2021-11-18)

著者

狩野 謙一 小田原 啓 山本 玄珠 伊藤 谷生

出版者

国立大学法人 静岡大学理学部地球科学教室

雑誌

静岡大学地球科学研究報告 (ISSN:03886298)

巻号頁・発行日

vol.46, pp.19-49, 2019-07-31 (Released:2021-11-18)

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We have examined the surface geology and tectonic landforms of the Hoshiyama Hills and its surrounding areas in the Fujikawa-kako Fault Zone (FKFZ), central Japan. The FKFZ is generally regarded as a collision zone between the Honshu Arc, mainly composed of the pre-Neogene accretionary and the Neogene collisional complexes of South Fossa Magna region, and the Neogene Izu-Bonin Volcanic Arc on the Philippine Sea Plate. This zone is believed to be the most active and dangerous area of Japan in association with violent earthquakes. One of the keys to understand the activities of this zone since the Pleistocene is to reveal the geologic structures of the Hills, as well as the characteristics of the Omiya and Iriyamase Faults along the northeastern and southeastern margin of this Hills, respectively. Our surface geological survey reveals that the upper Lower-lower Middle Pleistocene Ihara Group, main constituent of the basement of the Hoshiyama Hills, has complicated structures including several-hundreds meters scale steeply-dipping beds without distinctive preferred orientations. The structures also include chevron-shaped anticlines and flat synclines, suggesting that the E-W horizontal shortening due to fault-related foldings was the main cause of their formations. The flexure-landform associated with the Omiya Fault clearly suggests that the Fault, previously believed to be a high-angled normal fault dipping toward NE, is a reverse fault dipping toward SW. However, the landform around the Iriyamase Fault, also believed to be a NW dipping reverse fault, show no evidence of its existence. Finally, we have summarized the tectonic and volcanic events in and around the FKFZ since about 1 Ma. These results suggest that the Quaternary tectonics and seismic activities of the FKFZ should be necessary to re-evaluate based not only on the surface geological and landform data but also on the subsurface geological structures now being poorly known.

著者

北村 晃寿 平田 将也

出版者

国立大学法人 静岡大学理学部地球科学教室

雑誌

静岡大学地球科学研究報告 (ISSN:03886298)

巻号頁・発行日

vol.48, pp.23-26, 2021-07-31 (Released:2021-11-18)

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The present study detected pumice grains of Kawagodaira Pumice, which was erupted at 3160‒3137 cal BP, from the >0.063 mm size fraction of cored deposits of the Upper Holocene at site 3 of Nakazato, Yaizu City. We inferred the initial stratigraphic position of the pumice at a core depth of 6.51 m (elevation −3.70 m).