Fault rocks in the aftershock area and the neighborhood of 2000 Tottori-ken Seibu earthquake

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  • Aizawa Yasutaka
    Department of Geology, Faculty of Science, Niigata University Present adress: Graduate School of Science, Kyoto University
  • Kobayashi Kenta
    Graduate School of Science and Technology, Niigata University
  • Umetsu Kengo
    Graduate School of Science and Technology, Niigata University Present adress: Mitsui Oil Exploration Co., Ltd.
  • Yamamoto Ryo
    Teikoku Oil Limited Company

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Other Title
  • 2000年鳥取県西部地震の余震域およびその周辺に分布する断層岩類
  • 2000ネン トットリケン セイブ ジシン ノ ヨシンイキ オヨビ ソノ シュウヘン ニ ブンプ スル ダンソウガンルイ

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This study has revealed some characters of the 2000 Tottori-ken Seibu earthquake by observing outcrops and thin sections.<br>The earthquake occurred in a place where no active fault was identified. After the earthquake happened, airphoto-interpretations were performed again. Consequently, some lineaments in the direction of northwest were newly recognized. Although the fault planes generally strike the west-northwest and the northeast, they disagree to the lineaments obtained from the airphoto-interpretations. The strike of fault plane allowed a distinction to be made between the exposed ones and the seismic ones on the aftershock area of the 2000 Tottori-ken Seibu earthquake as well. The fault planes which we observed at outcrops were formed before it. And most fault planes with west-northwest strike indicated left-lateral slip and most of those with northeast strike showed right-lateral slip.<br>The foliated cataclasite and fault gouge were discovered in study area. The foliated cataclasites were exposed only on the aftershock area. The evidence proved that fault movement has repeatedly been occurring at least more than one time. The width in cataclasite ranged from 1 mm to 15 cm.<br>The fault gouges were distributed in whole area, specifically around the Lake Ryokusui. The earthquake surface fault in this time also occurred there, and the displacement was about 2 cm. The maximum fault density was more than 11 per 5 m at the outcrop of west of Lake Ryokusui and northeast part out of the aftershock area. The main thickness was 1 to 3 mm. The fault gouges showed various colors. A large percentage of color were white, pale yellow, pale red and black.<br>Rhyolite, basalt-andesite and aplite dikes were formed in Miocene, which intruded the granite throughout study area. Their trend was similar to the fault planes. And the crush zones mainly formed around the granite/dikes boundary.<br>

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