地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
124 巻 , 4 号
選択された号の論文の11件中1~11を表示しています
表紙
  • 2015 年 124 巻 4 号 p. Cover04_01-Cover04_02
    発行日: 2015/08/25
    公開日: 2015/09/17
    ジャーナル フリー
     三陸は,太平洋プレートの沈み込み帯である日本海溝に面し,日本列島の起源ともいうべき5億年におよぶ大地の歴史を連続的に記録している貴重な地域である.また,2011年3月の東北地方太平洋沖地震だけでなく,歴史的に何度も巨大地震があり,巨大地震の津波を受けた地域でもある.したがって,三陸ジオパークは地球活動の歴史と震災の記憶を後世に伝える学習のフィールドである.このような三陸海岸の中央部に浄土ヶ浜は位置し,地球の活動を体感できる場所になっている.浄土ヶ浜は,岬の形状や岩肌の白い色などが非常に特徴的で,「浄土のような」と例えられる景観美から,三陸海岸を代表する景勝地となっている.また浄土ヶ浜では,「奥浄土ヶ浜」や「臼木山」などの名勝地を遊歩道で散策することができるほか,マグマが冷えて固結する前に流動した跡(流理構造)を露頭で観察することができる.さらに,遊覧船やサッパ船で海から大地の成り立ちと景観美を間近で観察することもできる.
    (写真と説明文:杉本伸一)
論説
  • 太田 慧
    2015 年 124 巻 4 号 p. 525-544
    発行日: 2015/08/25
    公開日: 2015/09/17
    ジャーナル フリー
     Changing land use patterns are clarified from time and space points of view. Relationships are revealed between changing land-use patterns and port functions in the Kaigan area of the Tokyo waterfront, Minato Ward, Tokyo Metropolis. After Tokyo port opened in 1941, the Tokyo waterfront area was used mainly for logistics facilities, such as warehouses and port facilities. However, since the 1960s, the logistics system in the port has been changed by containerization. Port facilities in the Tokyo waterfront area became outdated. In response, the Tokyo waterfront area was redeveloped in the mid-1980s. As a result, significant changes to land use occurred in the Tokyo waterfront area. This study selects three target years, 1985, 1996, and 2012. A mesh analysis is conducted of land use in the Kaigan area, Minato Ward, Tokyo district. From 1985 to 1996, the port policy changed land use in the port district away from logistics facilities, including warehouses and port facilities. From 1985 to 1996, vacant land for redevelopment increased during the period of the asset inflation-led bubble economy. In comparison with the period from 1985 to 1996, during the period of from 1996 to 2012, land use changes in the port district ceased and changes outside the port district continued. These are connected to changing port functions. Since the 2000s, the number of passenger ships using Takeshiba pier has increased, promoting changes to urban land use in the surrounding area. On the other hand, at Shibaura pier, the number of the cargo ships entering remains unchanged, and land in the vicinity has continued to be used for logistics facilities such as warehouses and port facilities. Consequently, relationships are suggested between changing land-use patterns and port functions.
  • 丹羽 雄一, 須貝 俊彦, 松島 義章
    2015 年 124 巻 4 号 p. 545-560
    発行日: 2015/08/25
    公開日: 2015/09/17
    ジャーナル フリー
     The Sanriku coast was believed to have followed an uplifting trend in the geological time-scale on the basis of it being a flat surface interpreted as a Pleistocene marine terrace. On the contrary, geodetic and tide-gauge data show a rapid trend of this area subsiding during the last several decades. This area also experienced extensive subsidence during the 2011 Tohoku-oki earthquake (Mw 9.0). The discrepancy between long-term uplift and short-term subsidence has been pointed out by several researchers, but remains unresolved. Knowledge of sedimentary facies and deposition ages of the Holocene sequence is required to consider this problem. The depositional process of the Holocene sequence and crustal movement is discussed on the basis of coastal geology. A sediment core, KO1, was acquired from the lower reach of the Kesennuma Okawa Plain, southern Sanriku coast. Core sediments show typical deltaic succession influenced by Holocene sea-level change. Relative sea-level (RSL) at 9.6 to 10.1 cal BP is estimated to be −37 to −34 m based on the depositional surface of tidal flat deposits including molluscan shells living in the intertidal zone. Estimated RSL is lower than the theoretical RSL without tectonic effects. A probable cause of this discrepancy is Holocene tectonic subsidence in the area studied. Unlike previous arguments for a long-term uplift, particularly in northern Sanriku, the results of this study reinforce the theory that the south Sanriku coast subsided in the geologic time-scale.
  • 伊藤 英之, 鈴木 正貴, 佐藤 凌太, 杉本 伸一, 関 博充
    2015 年 124 巻 4 号 p. 561-574
    発行日: 2015/08/25
    公開日: 2015/09/17
    ジャーナル フリー
     This study is based on an Internet survey of prospective tourists visiting the Sanriku Geopark, which was conducted to understand their travel habits, impressions of the Sanriku coastal area, general awareness of the Geopark, and motivations for travelling. A principal component analysis (PCA) is also performed using a multivariate analysis technique to examine the characteristics of tourists and images of travel destinations they would want to visit in the future. The results demonstrate low awareness of the Sanriku Geopark, especially in metropolitan areas. The majority of respondents do not have a definitive image of the Geopark. The results also indicate that tourists visiting the Sanriku coast are primarily from neighboring prefectures, such as Miyagi and Aomori, as well as from the Tokyo metropolitan area. This suggests that increasing informational awareness of the Sanriku Geopark in these areas would be effective way for attracting more visitors. Regarding their travel habits, the respondents' answers indicate that they mostly go on two-day family trips in a private vehicle. In the majority of cases, their purpose for travelling is “to feel refreshed” or “to eat delicious food.” Based on these data, a PCA employing variance-covariance matrices reveals that tourists are basically seeking “extraordinary” and “healing” experiences from their travels. The principal component scores from the PCA are used and the average scores of each gender are calculated. A t-test reports no significant difference between genders with regard to seeking an “extraordinary” experience, but it identifies a trend among women of seeking “healing” experiences more actively than men (p < 0.10) at a level of 0.1%. On the other hand, regarding the tourists' impressions of the Sanriku coastal area, the results of the multivariate analysis suggest that prospective visitors tend to perceive the coastal area comprehensively in terms of both “nature and scenery” and “local area and culture” to the same degree as those who have previously visited the place. For the area to be resuscitated as a tourist destination, it is important to construct a regional brand and devise strategies that will lead to the region's rebirth as a top travel destination. This can be achieved by offering higher quality experiences and services without destroying the traditional image of the Sanriku coast.
  • 吉田 英嗣
    2015 年 124 巻 4 号 p. 575-586
    発行日: 2015/08/25
    公開日: 2015/09/17
    ジャーナル フリー
     Hummocks are conically shaped mounds, which occur following catastrophic sector collapses, and are mainly observed around volcanoes. Empirical relationships of hummocks proposed by Yoshida et al. (2012) are basically applicable if hummocks now distributed on a debris avalanche depositional area do not have remarkable disturbances due to topographical barriers or modifications after deposition. Using these empirical relationships, the Old Yotei volcano, whose mega-collapse in the Late Pleistocene has not been clarified yet, is examined. The results show that the size-distance relationship of hummocks (N=297), distributed west of the volcano can be expressed by an exponential function as,
       A=α exp (−β D),
    where A is the average area of a hummock within a certain span and D is the average distance from the source. For the Old Yotei volcano, the values of coefficients α and β of the fitted curve are 170286.4 and 0.000429, respectively. Based on a geomorphological interpretation of both α and β values, it can be concluded that the collapse volume of the Old Yotei volcano is ca.1.3 km3, and the equivalent coefficient of friction of the debris avalanche is 0.129. The latter also reveals a high probability that the pre-collapse summit of the Old Yotei volcano reached 1700 m a.s.l. Thus, the image of the flank collapse of the Old Yotei volcano has been restored more decisively by the distribution of hummocks.
  • 鈴木 ドロータ, 高木 秀雄, 河本 和朗, 中村 祐治, 中村 れいら
    2015 年 124 巻 4 号 p. 587-605
    発行日: 2015/08/25
    公開日: 2015/09/17
    ジャーナル フリー
     本州弧に対する伊豆–ボニン弧への中新世の衝突の影響を受けて,中央構造線の東西走向が,紀伊半島東部伊勢地域で東方に向かって東北東–西南西へと曲がりはじめるものとされている。しかしながら,伊勢地域では第四系堆積物が広く覆っており,都市化も進んでいることから,中央構造線の地表トレースの正確な位置は不明瞭である。中央構造線の位置の正確な把握は,たとえば地盤の違いを反映した地震動予測に資することや,中部日本における中央構造線の折れ曲がりのより正確な説明を与える上でも重要である。本論は伊勢地域(玉城町・伊勢市)に存在する(1)美和ロック玉城工場,(2)伊勢市役所,(3)伊勢観光文化会館のボーリングコアの岩石学的検討を行うとともに,伊勢市内のその他の建設基盤調査資料や,玉城町大池の断層岩類,領家帯に分布すると考えられる宮川沿いの中新統礫岩,伊勢市内に存在する三波川結晶片岩の露頭など,限られた露頭の地質調査結果から,中央構造線の位置をより正確に求めることができた。今回の調査で,三波川変成岩が一部に露出している伊勢神宮外宮に存在する中央構造線が正宮付近に想定され,ジオツーリズムとリンクしたその教育的活用が望まれる。
  • 杉戸 信彦, 近藤 久雄
    2015 年 124 巻 4 号 p. 607-631
    発行日: 2015/08/25
    公開日: 2015/09/17
    ジャーナル フリー
     The Uemachi fault zone extends north to northeast for about 51 km across metropolitan Osaka, southwest Japan. We conducted paleseismological surveys along the fault zone to estimate the timing of recent faulting events. We identified two reverse faulting events in the northern section of the fault zone, including the latest event, which occurred after ca. 2400 yr BP. In the southern section, the timing of the most recent event is estimated to be ca. 2200–2300 yr BP or later. The timing of the latest events in the northern and southern sections is coincident, implying that the most recent event was a multi-segment rupture through the whole Uemachi fault zone. We also examined geomorphic changes around the fault zone resulting from the most recent faulting event, based on previously reported archaeological and geological studies. As a result, we found: 1) coastal uplift occurred in the Osaka Castle Town archaeological site on the hanging wall side of the fault zone at the end of the middle Yayoi period; and, 2) numerous archaeological sites around the old Lake Kawachi were abruptly submerged at the end of the middle Yayoi period, and the submerged area had not been in residence again until around the final stage of the Yayoi period. These major, simultaneous geomorphic changes can be explained only by crustal movements resulting from a faulting event in the Uemachi fault zone. Thus, the timing of the most recent faulting event is estimated to be at the end of the middle Yayoi period. To evaluate the total risk due to active faulting, we have to understand not only tectonic landforms and coseismic surface ruptures, but also related regional abrupt geomorphic changes such as coseismic broader submergence in the Kawachi Plain from the perspectives of tectonic geomorphology and paleoseismology.
  • 中畑 浩基, 磯﨑 行雄, 小坂 和夫, 坂田 周平, 平田 岳史
    2015 年 124 巻 4 号 p. 633-656
    発行日: 2015/08/25
    公開日: 2015/09/17
    ジャーナル フリー
     The overall configuration of the Cretaceous subduction-related arc-trench system in Japan is preserved in the current distribution of the relevant orogenic components; i.e., the coeval set of accretionary complexes formed at the trench (Sanbosan and North Shimanto belts) , high-P/T meta-ACs along the Wadati–Benioff zone (Sanbagawa and Shimanto metamorphic belts) , arc batholiths (Ryoke–Sanyo and San-in belts) , and fore-arc basin strata (Ryoseki–Monobegawa and Izumi groups) . To document the sediment distributary pattern within the Cretaceous arc-trench system and the composition of relevant provenance, detrital zircon dating was conducted for the Upper Cretaceous sandstones (Atogura and Tochiya formations) from the northern Kanto Mountains. These strata occur immediately to the south of Median Tectonic Line of SW Japan, and as klippe with unknown origin. The results of U-Pb dating by LA-ICPMS show that three sandstones have common age spectra with four major age groups; i.e., 120–150 Ma (Early Cretaceous) , 170–200 Ma (Jurassic) , 250–300 Ma (Permian) , and 1600–2200 Ma (Paleoproterozoic) , with minor amounts of much older grains up to 2900 Ma (Archean) . These age spectra are unique, when compared to other coeval Cretaceous fore-arc and/or intra-arc sandstones in Japan. The Early Cretaceous grains were obviously derived from a proximal source to the depositional site, probably the Cretaceous volcanic arc of the Ryoke–Sanyo belt in SW Japan. The dominant grains of the Jurassic and Permian ages were probably derived from coeval plutonic belts in the provenance, whereas the Paleoproterozoic grains were probably derived from continental blocks in East Asia with crusts of corresponding ages, such as the North and South China blocks. Except for the Cretaceous arc source, Jurassic and Permian granitoids are extremely rare in major parts of Japan, and the Paleoproterozoic crust is totally absent. The only exception to the occurrence of Jurassic and Permian granitoids exists in the Hida belt of SW Japan. The age spectra of the analyzed Upper Cretaceous sandstones differ remarkably from those of other coeval fore-arc sandstones, whereas they clearly show similarities to Cretaceous sandstones in the Hida belt. This suggests that the analyzed Upper Cretaceous sandstones were primarily deposited in a domain far from the present position but with a close link to the Hida belt, which is located more than 100 km away to the northwest. Tectonic emplacement onto the present position immediately above the Cretaceous high-P/T meta-ACs probably took place during the Paleogene and Neogene, likely in relation to Miocene rifting of the Japan Sea. This study provides the first evidence of the across-arc geotectonic link between back-arc and fore-arc domains of Cretaceous Japan.
短報
  • 松田 時彦, 松浦 律子, 水本 匡起, 田力 正好
    2015 年 124 巻 4 号 p. 657-664
    発行日: 2015/08/25
    公開日: 2015/09/17
    ジャーナル フリー
     There are two emerged abrasion platforms on Enoshima Island, Kanagawa Prefecture, Southern Kanto district: the 4.0-meter-high Ryoshimachi surface, and the 1.0–1.3-meter-high Iwaya surface. Both emerged prior to the 1703 Genroku Earthquake. Considering uplift due to the 1923 Taisho Kanto Earthquake and non-seismic subsidence since the Genroku Era, uplift due to the 1703 Genroku Earthquake was 0.7 m or less, assuming that the height of Ryoshimachi surface before the Genroku Earthquake was 3 m or higher. This indicates that uplift of the Genroku Earthquake at Enoshima was smaller than that of the Taisho Earthquake, and the focal regions of the two earthquakes were different in the Sagami Bay. These two earthquakes are not repeating earthquakes at the Sagami Bay area.
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