地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
122 巻 , 5 号
選択された号の論文の9件中1~9を表示しています
表紙
  • 2013 年 122 巻 5 号 p. Cover05_1-Cover05_2
    発行日: 2013/10/25
    公開日: 2013/10/31
    ジャーナル フリー
     ラング氷河に源を発するハビタ川が中央高地から南部低地にでるところに,ハビタ峡谷がある.この峡谷は,長さ 2500 m・深さ 70 mで,北北西―南南西方向に延び,その谷頭にあるのがグトルフォス滝だ.グトルフォス滝は2段の滝から構成され,上部の滝は落差 11 m,下部の滝の落差 21 mで,写真には峡谷と下部の滝と写っている.グトルフォス滝の合計落差は 32 mにすぎないが幅は 110 mもあり,そこから流れ落ちる大量のグレーシャーミルクは圧巻である.右上隅の人物からスケールの大きさがわかるだろう.
     グトルフォス滝は,ゲイシール間欠泉・シングベトリル地溝とともに首都レイキャビクから1日で巡ることができ,ゴールデンサークルと呼ばれるアイスランド観光の人気ルートになっている.
    (写真・文:白尾元理)
総説
  • 山本 純之, 磯﨑 行雄
    2013 年 122 巻 5 号 p. 791-806
    発行日: 2013/10/25
    公開日: 2013/10/31
    ジャーナル フリー
     Ever since the term stromatolith was first coined by Kalkowsky in 1908, research studies on stromatolites have continued for more than a century. This article reviews the study history of living and fossil stromatotelites. The history is divided into two parts by the discovery in 1961 by Logan of living stromatolites in Shark Bay, Western Australia, because this determined the subsequent main trend of studies on both living and fossil stromatolites. Major contributions during the last three decades include documentation of (1) a worldwide bloom of stromatolites in Proterozoic low-middle lateral shallow seas, and (2) oxygen-producing cyanobacterial activity related to stromatolites from the 1990s, resulting in various new aspects being clarified, which include in-vitro cultivation gradually revealing cyanobacterial calcification and dome-formation. Future studies will be directed towards reconciling morphological disparities and formation mechanisms among fossil, living, and cultured stromatolites.
論説
  • 後藤 宏樹, 徳永 朋祥, 山本 肇, 小川 豊和, 青木 智幸
    2013 年 122 巻 5 号 p. 807-821
    発行日: 2013/10/25
    公開日: 2013/10/31
    ジャーナル フリー
     The possibility of dynamic failure and deterioration of the sealing capacity of critically stressed rock due to the infiltration of a compressible non-wetting phase fluid is examined through laboratory experiments. Rock samples were regarded as critically stressed under normal faulting conditions, and was set up to mimic the conditions of the cap rock just above a reservoir layer. Two kinds of external stress conditions were applied to the sample, i.e., close to an isotropic stress condition and close to a critical condition for failure. Air in a gas accumulator was infiltrated into the sample from the bottom end. Axial and circumferential strains of the sample and air pressure at the inlet were monitored during the experiment. Experimental results showed that the sample under stress conditions close to the critical condition became more deformable, resulting in failure, while that under a hydrostatic condition did not deform significantly and behaved elastically. An increase in the permeability of the critically stressed sample was also suggested. Understanding an in-situ stress state and considering a possible progressive failure of the cap rock are considered to be important when evaluating sealing capacity.
  • 宮野 浩, 泉 岳樹, 中山 大地, 松山 洋
    2013 年 122 巻 5 号 p. 822-840
    発行日: 2013/10/25
    公開日: 2013/10/31
    ジャーナル フリー
     This study investigated the relation between long-term changes in springwater temperature and land-use in Tokyo, as well as recent changes in springwater temperature during the period 2006–2011. Field surveys were conducted at 26 springs in Tokyo in both dry and wet seasons.
     Long-term changes in springwater temperature were statistically tested at each spring from the end of the 1980s until 2011 using Mann-Kendall rank statistics. Then, the relation between springwater temperature and land-use change was analyzed as follows. First, the recharge area of each spring was estimated by comparing calculated base runoff and observed discharge in the 1990s, along with the distribution of groundwater level in 1968. Next, changes in land-use between 1994 and 2000–2001 at each recharge area were calculated.
     A comparison with data obtained before 2006 confirmed that many springs showed a significant upward trend in springwater temperature both in dry and wet seasons. The results showed that the ratio of change from rural land-use to urbanized land-use had a positive correlation with the upward trend of springwater temperature. In addition, a negative correlation was found between the ratio of urbanized land-use in 2000–2001 and an upward trend of springwater temperature. Therefore, the authors concluded that the change of water temperature correlated more strongly with the ratio of change to urbanized land-use, rather than the ratio of urbanized land-use itself.
  • 山田 圭太郎, 日野 剛徳, 下山 正一, 竹村 恵二, 檀原 徹, 岩野 英樹
    2013 年 122 巻 5 号 p. 841-853
    発行日: 2013/10/25
    公開日: 2013/10/31
    ジャーナル フリー
     The northern coast of Ariake Bay, which is part of the Tsukushi Plain in Kyushu, Japan, is underlain by thick Quaternary deposits. However, the Late Middle Pleistocene succession had not been found. Recently, the Middle Pleistocene formation (Shagarami Formation) including a tephra bed (Shagarami tephra) was discovered under Aso-3 tephra in a drill core from a site near the mouth of Rokkaku River. This study revealed sedimentary facies of the Shagarami Formation, petrographic characteristics and LA-ICPMS-FT age of the Shagarami tephra. The Shagarami Formation can be divided into two sequence units on the basis of sedimentary facies, and it contains oyster fossils and mud-drape indicative of deposition in marine environments. The Shagarami tephra found in the top of the lower part of the Shagarami Formation mainly comprises pumice, and a zircon LA-ICPMS-FT age of 0.33 ± 0.06 Ma (1σ) was obtained. Therefore, lower and upper parts of the Shagarami Formation were deposited in different marine transgression and regression sequences in the Late Middle Pleistocene, respectively.
  • 神谷 泉, 小荒井 衛, 関口 辰夫, 佐藤 浩, 中埜 貴元, 岩橋 純子
    2013 年 122 巻 5 号 p. 854-874
    発行日: 2013/10/25
    公開日: 2013/10/31
    ジャーナル フリー
     SAR interferometry is widely used for dense measurements of surface displacements caused by earthquakes, but the method cannot be applied if displacements are too large. The near-epicentral area of the Iwate–Miyagi Nairiku Earthquake in 2008 is an inapplicable case. Therefore, we applied photogrammetry to measure surface displacement caused by the earthquake. The maximum horizontal and vertical displacements were found to be 5.3 m and 2.9 m, respectively.
     We recognized three lines where displacement changes abruptly. The displacement distribution is like that of a reverse fault along the first line (A–B), an east-rising fault along the second line (F–G–H; west of line A–B), and a left-lateral fault along the third line (B–C; between line A–B and line F–G–H).
     The earthquake source fault reaches or approaches the ground surface at line A–B, with slippage decreasing toward the ground surface. The fault-like large surface deformation found north of the Aratozawa Dam is on the first line. The fault-like deformation was caused by the motion of the earthquake source fault, and the relative displacement of the fault-like deformation was enlarged by local causes. A gravitational mass movement found north of the fault-like deformation is one cause.
     Because the width of the rising area is small, only 3.5 km, at the southwestern side of line B–C, the slip of the earthquake source fault is mainly distributed near the ground. Line F–G–H suggests the existence of a geological structure that causes the abrupt changes of vertical displacement without a horizontal displacement, for example a high-angle fault.
     We assumed: (1) the slip on the main fault is distributed only in a shallow area at the southern part of the main fault and only in a deep area at the northern part; and, (2) the difference of slip caused two lateral faults between southern and northern parts. The assumption qualitatively explains many observation results, such as why there is an abrupt change of horizontal displacement along line B–C and why line F–G–H has a convex part to the east.
     We found a correlation between the occurrence of large landslides and abrupt changes of displacement, in other words large surface strain. The following mechanisms are possible causes of the correlation: (1) stress from surface strain increased large landslides; (2) faults (not only the main fault) may exist under the focused areas, rupture of faults caused both large surface strain and large seismic motion, and seismic motion induced large land slides. We also found that landslides and slope failures occurred densely over the slipping area on the main fault, based on the assumptions in the previous paragraph.
     Because photogrammetric measurements need interactive observations, we could avoid observations on possible embanking areas. Because photogrammetry allows intensive measurements at interesting areas, we revealed a two flexure-like distribution of vertical displacement. Therefore, photogrammetry is an effective method for measuring surface displacement caused by an earthquake.
  • 長谷川 宏一, 尾身 洋, 比留間 祐太, 熊谷 聡, 山本 遼介, 泉 岳樹, 松山 洋
    2013 年 122 巻 5 号 p. 875-891
    発行日: 2013/10/25
    公開日: 2013/10/31
    ジャーナル フリー
     We estimated the leaf area index (LAI) of Cryptomeria japonica in Aso district, Kumamoto Prefecture using various methods. In advance, we selected seven sites, which had various values of the normalized difference vegetation index (NDVI), by analyzing satellite imagery (ALOS/AVNIR-2) of September 2006. Around the end of August 2007, we measured the diameters of breast height (DBH) and tree heights at these sites, which were substituted to the universal allometric equation to calculate the dry weight of leaves of Cryptomeria japonica, proposed by Hosoda and Iehara (2010). We then estimated LAI by assuming a typical histogram of green leaf diameters of Cryptomeria japonica. At the sites, we also measured LAI using LAI-2000 and took hemispheric photographs, from which we calculated LAI using LIA32. We also estimated LAI using NDVI calculated from ALOS/AVNIR-2 imagery. Theoretically, indirect estimations of LAI-2000 and hemispheric photographs must be smaller than the allometric LAI; however, at sites with a smaller DBH, indirect estimations were larger than direct ones. This implies the possibility that the allometric equation is not suitable for estimating LAI in densely planted forest stands with a smaller DBH. In addition, we demonstrated that we should measure DBH and tree height of broader trees more accurately to estimate LAI with the equation of Hosoda and Iehara (2010), based on a simple numerical simulation.
  • 増田 富士雄, 佐藤 智之, 伊藤 有加, 櫻井 皆生
    2013 年 122 巻 5 号 p. 892-904
    発行日: 2013/10/25
    公開日: 2013/10/31
    ジャーナル フリー
     We propose Shazam stratigraphy as a new analytical method based on facies analysis and sequence stratigraphy. This method is applied to a recently developed borehole database and subsurface geology in the Osaka Plain. Using the method, the shapes of lithofacies boundaries in subsurface sections are optimized for sedimentary faces and changes. The optimized boundary allows interpretation of seismic sections. The result is better recognition and reconstruction of depositional systems, geomorphological evolution, and tectonics. Irregular sequence boundaries, flat transgressive ravinement surfaces, and sawtooth downlap surfaces of the prograding depositional system are key boundaries for this method.
世界露頭百選(No.10)
  • デビッド M. ローア, ロバート B. ブロジェット
    2013 年 122 巻 5 号 p. 905-911
    発行日: 2013/10/25
    公開日: 2013/10/31
    ジャーナル フリー
     米国アラスカ州南部のグレイシャー・ベイ国立公園は,シルル紀の熱帯域の大陸棚から深い盆地にかけて堆積した厚い地層と,そのなかでの連続的な堆積相変化を観察する上で絶好の場所である。グレイシャー・ベイの氷河で削られた見事な露頭には非常に厚いシルル紀の地層が広大に露出している。それらは化石を多産する浅い陸棚相石灰岩から深い盆地の泥岩相へと側方に堆積相が連続的に変化する様子を明瞭に提示している。これらの地層から産する化石(二枚貝や巻貝など)は,北米(ローレンシア)大陸の内部に産する同地質時代の地層からの北米固有の群集とは大きく異なっている。このような特異な化石群集を含むアレクサンダー・テレーンは,もともと遠方より移動してきて,二次的に北米西岸へ衝突・合体した地塊と考えられている。
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