Fault discontinuity of the western marginal fault zone of Fukushima basin around Iizaka Town in northeast Japan

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  • Mizumoto Tadaki
    Earthquake Research Center, Association for the Development of Earthquake Prediction
  • Tajikara Masayoshi
    Earthquake Research Center, Association for the Development of Earthquake Prediction
  • Matsuda Tokihiko
    Earthquake Research Center, Association for the Development of Earthquake Prediction
  • Matsu’ura Ritsuko S.
    Earthquake Research Center, Association for the Development of Earthquake Prediction

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Other Title
  • 福島盆地中部，飯坂付近における福島盆地西縁断層帯の不連続部について
  • フクシマ ボンチ チュウブ,イイザカ フキン ニ オケル フクシマ ボンチ セイエン ダンソウタイ ノ フレンゾクブ ニ ツイテ

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Abstract

The western margin of the Fukushima basin is bounded by active faults, that extend from north to south about 57 km in length. The Fukushima basin has been subdivided into northern and southern parts based on differences in morphology of tectonic landforms, horizontal geometry of the fault traces and subsurface fault structures in each part by previous studies. We focused on horizontal geometry of fault traces around Iizaka Town, which is located between the northern and southern parts of the basin, where fault traces seem bent. The northeast-trending Kori fault defines the western margin of the northern part of the basin. At the southern end of the Kori fault, fault traces were newly identified for 2 km long on the south in the basin area. Fault-related landforms were detected as fault scarps in Pleistocene to Holocene terrace surfaces. The Daiyama fault also extends from northeast to southwest in the western margin of the southern part of the basin. The northern end of the Daiyama fault is composed of several en-echelon faults. The Kori fault overlaps with the Daiyama fault for about 2 km long at Iizaka Town. An east-trending fault trace, Iizaka fault, was mapped by previous studies between the two faults. Numerous landslides are distributed in the mountains north of the Iizaka area, where we inferred existence of an old large-scale landslide. This landslide is eroded by small streams flowing to the south to form fluvial terraces, and is partly covered by recent landslide deposits. Scarps and tilting of fluvial terraces which were previously mapped as tectonic landforms in this area were probably formed due to gravitational movement of this old landslide deposit. No evidence for Holocene surface faulting can be found along the previously-reported Iizaka fault. Thus, the northern and southern parts of the western marginal fault zone of the Fukushima basin are probably not connected by the east-trending Iizaka fault, but separated by a 4 km wide stepover, in the central part of the basin.

Journal

  • Active Fault Research

    Active Fault Research 2013 (38), 29-40, 2013

    Japanese Society for Active Fault Studies

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