The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 124, Issue 9
Displaying 1-9 of 9 articles from this issue
SPECIAL ISSUE Formation process of the Japanese Islands
Review
  • Jun-ichi Tazawa
    2018 Volume 124 Issue 9 Pages 655-673
    Published: September 15, 2018
    Released on J-STAGE: December 15, 2018
    JOURNAL FREE ACCESS

    We reviewed 124 studies (based mainly on brachiopods) of the Palaeozoic biogeography of Japan. The data indicate four tectonic events: 1) during the Silurian-Permian, Proto-Japan was located within the Central Asian Orogenic Belt, near North China; 2) after the late Permian, Proto-Japan was rearranged through large-scale, sinistral strike-slip faulting, probably during the Early Cretaceous to Palaeogene; 3) Akiyoshi-type limestone‒basalt blocks were derived from early Carboniferous to middle Permian reef-seamounts in the northern Panthalassa, near Proto-Japan; and 4) Mino-type limestone-basalt blocks were derived from late Carboniferous to late Permian reef-seamounts in the equatorial Panthalassa, near North America (Texas).

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  • Hiroyuki Hoshi
    2018 Volume 124 Issue 9 Pages 675-691
    Published: September 15, 2018
    Released on J-STAGE: December 15, 2018
    JOURNAL FREE ACCESS

    During the Miocene, Southwest and Northeast Japan rotated clockwise and counterclockwise, respectively, associated with opening of the back-arc basins of the Japan Sea. Kinematic models proposed in the mid-1980s suggest that the differential rotation of the two island arc slivers occurred simultaneously at ~15 Ma, over a period of ~1-2 Myr, and this view still has a strong influence on geotectonic studies of Japan. However, recent progress in biostratigraphic and radiometric dating has provided new data indicating that the clockwise rotation of Southwest Japan occurred a few millions of years earlier than was previously suggested. In addition, reinvestigation of middle Miocene (15-14 Ma) igneous rocks that have a northeast-directed remanent magnetization direction suggests that this direction represents a geologically instantaneous paleomagnetic record and should therefore not be used for tectonic analysis. Here we review paleomagnetic and geochronological data for Southwest Japan published during the last quarter century with the aim of revising the timing and amount of clockwise rotation. Results show that clockwise rotation occurred at 18-16 Ma. The maximum amount of rotation relative to the tectonically stable part of the Asian continent is estimated to be 41.7°±5.4°, based on the assumption that the main part of Southwest Japan rotated as a rigid block. The angular velocity of rotation was about ≥21°/Myr. These findings are incorporated into a model for the Japan Sea involving two stages of opening as follows: (1) during the earlier stage (Eocene-Oligocene), Southwest Japan was rifted from the eastern margin of the Asian continent with little or no rotation; and (2) during the later stage (Miocene, 18-16 Ma), Southwest Japan migrated to its present position via ~40° of clockwise rotation.

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  • Takeshi Nakajima
    2018 Volume 124 Issue 9 Pages 693-722
    Published: September 15, 2018
    Released on J-STAGE: December 15, 2018
    JOURNAL FREE ACCESS

    The opening of the Sea of Japan, associated with detachment of the Japan Arc from the Asian Continent, was the most significant Cenozoic event in Japan. Previous geophysical investigations in back-arc basins surrounding Japan have revealed that the Sea of Japan, the Shikoku Basin, and the Chishima Basin opened almost simultaneously from 24 to 15 Ma. However, the Sea of Japan’s opening mechanism and the paleoposition of the Shikoku Basin have been debated until now. Recently acquired high-resolution radiometric data have clarified that the Sea of Japan opened over multiple stages concurrent with repeated rifting events on land. Initial rifting occurred between 44 and 30 Ma, and its cessation is marked by an Oligocene unconformity (30-21 Ma). Rifting resumed at 21 Ma, increasing in intensity (18-15 Ma) before transitioning into a post-rift phase between 15 and 13.5 Ma.

    High-resolution age data have clarified the multi-stage, post-rift development of northeast and southwest Japan. Compressional tectonics, starting at ~12 Ma in NE Japan, caused uplift of the Ou Backbone Range and subsidence of the Onnagawa Basin. These events also had a marked effect on the paleoenvironment of the Sea of Japan, resulting in the deposition of hydrocarbon source rocks. This compression gradually intensified from 6.5 Ma, with an oscillating stress state indicated by stepwise post-Miocene basin inversion and fold growth along the coastline of the Sea of Japan. In contrast, uplift in SW Japan (at ~15 Ma) was associated with compressional deformation, and outer-arc and Setouchi volcanism. Following north-south compression in the late Miocene, the tectonic regime switched to compressional and transcurrent deformation at 6 Ma, probably due to the resumption of movement of the Philippine Sea Plate.

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Special Issue Structural geology: Progress in the past 25 years and prospectus for the future. Part 2
Review
  • Miki Takahashi, Takehiro Hirose, Yoshihisa Iio
    2018 Volume 124 Issue 9 Pages 725-739
    Published: September 15, 2018
    Released on J-STAGE: December 15, 2018
    JOURNAL FREE ACCESS

    Earthquakes occur when shear stress exceeds the static strength of a fault; thus, knowledge of fault strength is important. Various estimates of fault strength have been made over the last half century; however, there is still disagreement on whether faults are weak (~10 MPa), which would account for observed low stress drops and low heat flow anomalies, or strong (~100 MPa), as estimated from laboratory experiments using Byerlee’s law. We review methods to estimate fault strength and propose that a cause of the ongoing debate is the definition of strength used in different methods. High-speed friction experiments have played a significant role in resolving the debate. The experiments have shown that faults are only weak during an earthquake. Detailed seismic analysis, additionally, has revealed a heterogeneous distribution of fault strength. These findings require that fault models combine the deformation mechanisms of both strong and weak fault patches, which result in non-uniform strength and stress distributions. We propose that a multidisciplinary approach is required. Geological fieldwork should be used to test fault models that are developed based on seismology and rock mechanics.

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  • Hiroyuki Tsutsumi, Hisao Kondo, Tatsuya Ishiyama
    2018 Volume 124 Issue 9 Pages 741-757
    Published: September 15, 2018
    Released on J-STAGE: December 15, 2018
    JOURNAL FREE ACCESS

    We reviewed studies of active faults in Japan during the past 25 years, particularly since the 1995 Hyogo-ken Nanbu earthquake that drastically changed the system and budget for such studies. Active fault studies have been central to the national seismic hazard reduction program, led by the Headquarters for Earthquake Research Promotion (HERP). Many studies have examined ~100 major active fault zones, employing paleoseismic trenching and high-resolution shallow seismic reflection profiling. Several types of large-scale maps of active faults have been published, including digital maps with three-dimensional base maps. These data are fundamental to the long-term evaluation of earthquake occurrences on major active fault zones. New research techniques have been introduced to active fault studies, such as detailed digital elevation models (DEMs), light detection and ranging (LiDAR), photogrammetry using unmanned aerial vehicles (UAV), shallow subsurface geophysics, and OxCal age modelling of paleoseismic events. Since the 1995 earthquake, there have been several surface-rupturing inland earthquakes with highly variable earthquake magnitude and coseismic faulting behavior. These earthquakes illustrate the need for new criteria for long-term evaluation of seismic hazard, including the incorporation of non-characteristic earthquakes into seismic hazard models, rather than assuming only characteristic earthquakes for a given fault zone.

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  • Norio Shigematsu, Tomoyuki Ohtani, Kenta Kobayashi, Takamoto Okudaira, ...
    2018 Volume 124 Issue 9 Pages 759-775
    Published: September 15, 2018
    Released on J-STAGE: December 15, 2018
    JOURNAL FREE ACCESS

    We review research on the architecture of onshore fault zones. Drilling the Nojima Fault was a turning point in studies of shallow brittle faults, stimulating research on their hydrological and frictional properties. Investigations of the deep seismogenic zone of faults such as the Median Tectonic Line (MTL) have identified deformation mechanisms such as pressure solution, creep, and crystal plasticity of mica in foliated cataclasite. Cataclastic damage causes increased intracrystalline strain in surrounding rocks. Several studies of the Asuke shear zone and the MTL have estimated the stress and strain rate in the brittle–plastic transition zone. Some studies of the Hatagawa fault zone have revealed the processes involved in fracture nucleation and documented heterogeneous deformation on the scale of tens of kilometers. In the lower crust of the Hidaka metamorphic belt, evidence was found for plastic deformation of plagioclase and pyroxene by dislocation creep. It was also found that formation of fine-grained aggregates during deformation results in weakening by a change in deformation mechanism from dislocation creep to grain boundary sliding. Recently, evidence of fracturing has been found in deformed lower crustal rocks, possibly resulting from stress concentration at the down-dip termination of earthquake ruptures, although further studies are needed to confirm this inference.

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