The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 112, Issue 3
Displaying 1-7 of 7 articles from this issue
Review
  • Tohru Ohta, Hiroyoshi Arai
    2006 Volume 112 Issue 3 Pages 173-187
    Published: 2006
    Released on J-STAGE: July 14, 2006
    JOURNAL FREE ACCESS
    Compositional data, represented as percent or parts per million, are subject to the constant-sum constraint that precludes compositional data from much of statistical analysis. Despite this constraint, a theory for statistically rigorous treatment of compositional data is currently under intense development. This paper reviews the utility of two main procedures for compositional data analysis, which will be termed "logratio analysis" and "simplicial analysis". Logratio analysis is a way to map compositional data from a simplex space to a Euclidean real space by transforming compositional data into logarithms of component ratios. This bijectional mapping allows the transformed data to be analyzed by many traditional statistical methods available in real space. On the other hand, simplicial analysis introduces proper classes of parametric distribution, translation operation, scalar multiplication operation, identity unit and metric function within the simplex space. These definitions permit the simplex space to be reviewed as a metric space and compositional data as an Abelian group. Moreover, simplicial analysis provides statistical methodologies for compositional data, which are analogous to those for data sets associated with real space. A brief overview of the constant-sum constraint is followed by mathematical descriptions of logratio and simplicial analyses. Practical analyses of real data sets based on logratio and simplicial analyses are provided to illustrate their potential and to encourage their use.
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Articles
  • Taku Komatsubara, Tsutomu Nakazawa, Yoshinori Miyachi, Rei Nakashima, ...
    2006 Volume 112 Issue 3 Pages 188-196
    Published: 2006
    Released on J-STAGE: July 14, 2006
    JOURNAL FREE ACCESS
    The Tamugiyama district in Kawaguchi Town, Niigata Prefecture is one of the most affected areas by the 2004 Mid-Niigata Prefecture earthquake. Though this district is located in a small (ca. 2 km2) basin, some colonies were damaged lightly and others severely. The worst-hit colony is located on the central part of the Tamugiyama fan underlain by thick (ca.20 m) muddy deposits with the N-values ranging from 5 to 20. On the other hand, lightly damaged colonies are located on the Tamugiyama-IV terrace underlain by gravel rich deposits with the N-values of over 50 and on the marginal area of the Tamugiyama fan. The Tamugiyama fan deposits were supplied from surrounding hill areas where weakly consolidated Pliocene to Lower Pleistocene sedimentary rocks occurred and a large number of landslides are recognized. The deposits filled a basin-like incised valley during the latest Pleistocene time. The close relationship between damages and thickness of the muddy fan deposits indicates that the fan deposits intensely amplified ground motions resulting in local severe damages. This fact is noteworthy for making seismic hazard maps.
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  • Naoto Ishida, Masafumi Murata
    2006 Volume 112 Issue 3 Pages 197-209
    Published: 2006
    Released on J-STAGE: July 14, 2006
    JOURNAL FREE ACCESS
    Mixed radiolarian assemblages, comprising fossils of different ages, were detected from the Unazawa Formation of the Southern Chichibu terrane, in the southeastern part of the Kanto Mountains. The Unazawa Formation composed of chert, siliceous mudstone and coarse clastic rocks in ascending order, represents a chert-clastic sequence. The mixed assemblages found in four samples from the Middle Jurassic (Aalenian to Bathonian) chert and siliceous mudstone, contain a few reworked radiolarians. The reworked components include six genera and twelve species, and their age assignments range from late Early Permian to Middle Triassic, but lack any Early Triassic representatives. Mode of occurrences of the reworked fossils and textural properties of their host sediments suggest that the reworked components redeposited individually from source sediments in pelagic and hemipelagic environments. Considering the reworking-features of pelagic sediments in the Central Pacific, it is suggested that plausible sources of the reworked radiolarians were the sediments on the flanks of submarine highs, like seamounts.
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  • Nobuhiro Kotake, Michiaki Fujioka, Akane Sato, Yasuhiro Ito
    2006 Volume 112 Issue 3 Pages 210-221
    Published: 2006
    Released on J-STAGE: July 14, 2006
    JOURNAL FREE ACCESS
    Stratigraphic position of the Kikai-Akahoya (K-Ah) tephra in the Holocene Numa Formation distributed in the southernmost part of the Boso Peninsula, Chiba, Japan was mainly examined from the viewpoint of bioturbation. The K-Ah tephra in muddy sediments of the Numa is not recognizable as a visible geologic record due to complete dispersion of volcanic glasses induced by the intense biogenic sediment mixing after the deposition. A muddy sediment interval, which is cropped out along the Tomoe-gawa River, Tateyama City was selected for this study.
    Petrographic and petrologic data on volcanic glasses in the muddy sediments show that the volcanic glasses of the K-Ah origin were found in mud interval above the Tsunami deposit T 3.1. Sedimentologic, paleontologic, and paleogeographic data indicate that biogenic sediment mixing process seems to represent the most important factor for controlling the diffusion mechanism and the final distribution pattern of volcanic glasses in the sediments. Stratigraphic distribution pattern of volcanic glasses of the K-Ah origin and mixing process strongly suggest that the initial stratigraphic position of the K-Ah in the Numa presents the restricted interval about 15 cm above the T 3.1 bed.
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  • Dohta Awaji, Daisuke Yamamoto, Hideo Takagi
    2006 Volume 112 Issue 3 Pages 222-240
    Published: 2006
    Released on J-STAGE: July 14, 2006
    JOURNAL FREE ACCESS
    The Tanakura Shear Zone is a NNW-SSE trending major fault which divides pre-Neogene basement rocks into NE and SW Japan. Within the study area, the fracture zone is 3 to 4 km in width, and consists of various kinds of fault rocks derived from the Jurassic accretionary complex of the Yamizo Belt, together with metamorphic and granitic rocks derived from the Abukuma Belt. Distribution patterns of brittle faults, fabric patterns and shear senses of fault gouge within the fault zone are described to interpret kinematics of the Tanakura Shear Zone during the Late Cenozoic. Based on paleo stress fields estimated from shear senses of fault gouge by multiple inverse methods (a technique to separate stresses based on heterogeneous fault-slip data), two brittle deformation stages (D1 and D2) are identified. During the Paleogene, a sinistral brittle fault set was originally generated. During exhumation of the shear zone, the fault kinematics inverted from a sinistral (D1 : 17 Ma) to a dextral movement (D2 : 15 Ma). Therefore, from Paleogene to the mid-Miocene, fault gouges within the Tanakura Shear Zone were reactivated under switched stress fields.
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