野島地震断層の性状  [in Japanese] Some Characteristics of Nojima Seismic Fault  [in Japanese]

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Abstract

兵庫県南部地震(M7.2)<1)>は、1995年1月17日午前5時46分に、淡路島北方の明石海峡の地下深部14.3km付近を震源<1)>として発生し、淡路島北部から対岸の神戸市〜西宮市にかけて大きな被害を与えた。その被害域は直線的に延びた帯状の範囲に集中し、直下型の活断層の影響を強く受け、淡路島北部では地震断層が出現した。この地震断層は、活断層とされている野島断層(水野他<2)>、活断層研究会<3)>)にほぼ一致して出現したもので、生々しい断層の実体像を我々の眼前に現してくれた(この地震断層を以後野島地震断層と呼ぶことにする)。地震断層を含む活断層は第四紀に入ってからの新しい断層運動によって生じ、その地質的な現象が地形に反映されることが多いことから、調査に当っては地質的・地形的な両面から断層を調べていくことが必要である。今回現れた地震断層は、地質・地形の両面で現れた断層であり、この断層から"自然の厳しさ"とともに活断層の実体像の多くを学びとる必要がある。ここでは、地震発生後に実施した地震断層の性状と被害に関する現地調査結果を報告する。今後の活断層調査の一助となれば幸いである。

Hyogo-ken Nanbu earthquake (magnitude 7.2) at Jan.17, 1995 was associated with ground surface fault displacement along the neotectonic Nojima fault on the Awajishima Island, Hyogo Prefecture, Japan.The characteristics of the Nojima seismic fault and the earthquake damage are follows.<BR>1) The seismic fault was formed just on the NE-SW trending Nojima active fault which was recognized on the boundary between the southeast mountainous part and the northeast hilly land.<BR>2) The on-land seismic fault trace in over 9 km long.The maximum right-lateral displacement and northwest side throw attains 1.7m and 1.3m respectively.<BR>3) The seismic repture which started at a point in the Akashi strait and propagated southwestward, stopped at the fault jog at Tomishima associated with some small scale fault branches.<BR>4) The seismic faulting was associated with various fault structures on the ground surface affected by the thickness of the surface soft sediments; right-lateral offset, fault scarplet, small scale landslide, undulation and distortion of ground surface, left-step echelon gash, pull-apart and push-up, and mole track.<BR>5) The fault striation at Nashimoto village, near the southern end of the Nojima seismic fault, is horizontal. In Hirabayashi village which is on the middle part of the fault trace, three striations with different orientations were observed;70°N at first, 20°N secondly and 30°S finally, suggesting the displacement splitting at the fault propagation.<BR>6) The earthquake damage, including the collapse of houses and irrigation ponds was concentrated not only in the narrow about 20 m in width on the both sides of the seismic fault but also in the areas on the soft ground.<BR>7) The shear zone of the Nojima fault has a zoned structure;granitic cataclasite, thin alternation of consolidated and very fine grained and consolidated gouge and pseudotachylyte-like rock, sheared Miocene sandstone and unconsolidated fault clay, representing rocks formed in the various depths.<BR>8) The after-slip attains 20 cm at the 55th after the main shock.

Journal

  • Journal of the Japan Society of Engineering Geology

    Journal of the Japan Society of Engineering Geology 36(2), 154-166, 1995-06-10

    Japan Society of Engineering Geology

References:  12

Cited by:  6

Codes

  • NII Article ID (NAID)
    110003334778
  • NII NACSIS-CAT ID (NCID)
    AN00026635
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    02867737
  • NDL Article ID
    3610036
  • NDL Source Classification
    ME15(地震)
  • NDL Source Classification
    ZM49(科学技術--地球科学--地質)
  • NDL Call No.
    Z15-263
  • Data Source
    CJP  CJPref  NDL  NII-ELS  J-STAGE 
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