静岡大学地球科学研究報告
Online ISSN : 2436-7184
Print ISSN : 0388-6298
最新号
選択された号の論文の11件中1~11を表示しています
  • 2022 年 49 巻 p. cover-1-
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
  • 宮坂 晃, 狩野 謙一
    2022 年 49 巻 p. 1-31
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
    The Central Uplift Belt of the North Fossa Magna region, central Japan, has long been believed to be a non-folded or weakly-deformed area except for its western area. The Uchimura Formation in the southern part of this belt is mainly composed of basaltic-andesitic lavas and volcaniclastic rocks of the syn-rifting stage of Sea of Japan interfingered with clastic sedimentary rocks of the late Early to Middle Miocene in age. In addition with the precise geological surveys of this formation, We statistically evaluated the distribution patterns and dispersion-concentration ratios of the attitudes of bedding planes applying the orientation tensor method. As the results, we recognized complicated folded structures of the Uchimura Formation in contrast with previous research reports. The folded structures were produced by multi-phase deformations since the late Middle Miocene. The first phase deformation was the formation of gentle-open folds of more than several tens of meters in wavelength with non- to gently-plunging axes under a horizontal compressive regime. Then, vertical-axis rotations of gently-moderately dipping strata and overprinting of multiphase foldings in different directions resulted in the formation of complicated structures until the Late Miocene in association with a regional tectonic block rotation to form the Akaishi-Kanto Syntaxis and the Fossa Magna due to the lateral collision with the northern tip of the Izu-Bonin Arc. These folds were then re-folded during the Pliocene, probably due to the E-W horizontal compression that affected widely the back-arc side of the Northeast Japan Arc. The latest phase deformation occurred during the Middle Pleistocene, including local foldings, faultings and formations of flexures, further superimposed on the pre-existing structures. The rapid uplifting of the Central Uplift Belt to form the present-day Chikuma Mountains and the surrounding subsidences of the Suwa, Matsumoto and Ueda Basins have occurred during this latest phase deformation in association with a left-lateral motion of the Itoigawa-Shizuoka Tectonic Line on the southwest.
  • 石橋 秀巳, 鬼塚 寛士, 岩城 吉春, 森 英樹
    2022 年 49 巻 p. 33-43
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
    One-atmosphere heating experiments were carried out for the 2 cm sized cubic samples of the phenocryst-rich basaltic lava (Suijin lava from Fuji volcano, Japan) to examine how the rheological behavior of the phenocryst-rich lava depends on temperature and time. The fO2 condition was not controlled during the experiments, but oxidation was not significant except for only near the surface of the run sample. At 1150°C, the lava was not deformed by its weight at least within 90 min. At 1155°C, the lava partly deformed at 45 min. At 1160°C, the lava was not deformed at < 20 min, but the deformation onset at 25 ± 5 min and perfectly flowed at > 37 ± 7 min. The onset time of deformation decreased as temperature increased. The rheological behavior of the lava changes drastically from solid to liquid within narrow ranges of temperature and time. Textural analyses of the run samples heated at 1150°C, 1155°C and 1160°C for 45 min suggest that the phenocryst content was almost constant at ~37 vol% regardless of heating temperature. In contrast, crystal content in the groundmass decreases from ~9.5 vol% to ~2.5 vol% as the temperature increases from 1150°C to 1160°C. This behavior can be explained by a crystal content-dependent change of relative viscosity with Φm ~ 0.437‒0.476, where Φm is the critical crystal content at which rheological transition occurs. Present results suggest that in phenocryst-rich lava, a slight increase/decrease in groundmass crystals causes the total crystal content to exceed/fall below the critical crystal content at which the solid-liquid transition occurs. Therefore, cooling has to be suppressed during flow for phenocryst-rich lava in order to flow over long distances.
  • 千木良 雅弘, 北村 晃寿, 木村 克己, 市村 康治
    2022 年 49 巻 p. 45-59
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
    On 3 July 2021, a heavy rainstorm induced landslide of an embankment in Atami, Shizuoka Prefecture; it transformed into debris flow along the Aizome River hit a town of Izusan causing heavy damage including 26 fatalities and 1 missing. The cause of the landslide of the embankment was first attributed to probable inappropriate workmanship and poor drainage control of the embankment. We performed careful field survey after the landslide, and found that the area used to be covered by fluvial deposits (chaotic debris flow deposits). These fluvial deposits overlie hydrothermally altered andesite rich in smectite, which likely caused their landslide with the sliding surface in between since geological past. The fluvial deposits covered not only the Narusawa River but also the upstream of the Aizome River, where the shape of fluvial cone has been erased because of recent artificial modification. The embankment was made above the fluvial deposits. The landslide scar after the event suggested that water had gushed out from the basal parts of the old landslides. The water is assumed to be not only from the catchment of the Aizome River but also from that of the Narusawa River through the fluvial deposits, particularly along the basal part of the old landslides on the impervious clayey materials.
  • 北村 晃寿, 山下 裕輝, 矢永 誠人, 本山 功, 中西 利典, 森 英樹
    2022 年 49 巻 p. 61-72
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
  • 北村 晃寿, 岡嵜 颯太, 近藤 満, 渡邊 隆広, 中西 利典, 堀 利栄, 池田 昌之, 市村 康治, 中川 友紀, 森 英樹
    2022 年 49 巻 p. 73-86
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
    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 destroyed numerous houses and flowed into Sagami Bay. In this study, two samples of embankment, three debris flow deposits and two soil samples from around the Aizome River valley were analyzed for grain size, and geochemistry and grain compositions for each mud and sand particles. The most important result was the discovery of radiolarian chert fragments in black embankment sediments and debris flow deposits. These chert fragments are useful as tracer material for black embankment sediments. Furthermore, the radiolarian chert was found to have been deposited near the Permian/Triassic boundary and later into the Jurassic and Early Cretaceous. This is an important finding for identifying the source of black embankment sediments.
  • 北村 晃寿, 矢永 誠人, 岡嵜 颯太, 片桐 悟, 中西 利典, 森 英樹
    2022 年 49 巻 p. 87-95
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
    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.
  • 北村 晃寿, 山下 裕輝, 矢永 誠人, 中西 利典, 森 英樹
    2022 年 49 巻 p. 97-103
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
  • 北村 晃寿
    2022 年 49 巻 p. 105-137
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
  • 北村 晃寿, 戸田 健太郎
    2022 年 49 巻 p. 139-142
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
  • 2022 年 49 巻 p. cover-2-
    発行日: 2022/07/31
    公開日: 2022/07/31
    研究報告書・技術報告書 フリー
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