Reexamination of fault geomorphology and slip rates along the Chino fault in the middle Itoigawa-Shizuoka Tectonic Line Active Fault System, central Japan

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Other Title
  • 糸魚川−静岡構造線活断層系中部，茅野断層（茅野市坂室）の変動地形の再検討
  • 糸魚川-静岡構造線活断層系中部,茅野断層(茅野市坂室)の変動地形の再検討
  • イトイガワ-シズオカ コウゾウセンカツダンソウケイ チュウブ,チノ ダンソウ(チノシザカシツ)ノ ヘンドウ チケイ ノ サイケントウ

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Description

The Chino fault consists a section of the Middle Itoigawa-Shizuoka tectonic line active fault system (ISTL), central Japan. The Chino fault is characterized by a high average slip rate reaching 10 mm/yr., which is one of the highest slip rates reported from active faults onshore Japan. Along the linear fault trace, channels and terrace risers are systematically offset by left-lateral slip and fault scarps by vertical component is clear on Late Quaternary terrace surfaces. Intensive studies on fault topography were conducted at Sakamuro. We carried out 1) air-photo interpretation, 2) LiDAR DEM analyses, 3) geomorphic mapping of terraces and faults, 4) pit excavation for stratigraphy and chronology, 5) measurement of strike-slip and dip-slip offsets, and 6) estimation of recurrence intervals and slip-per-event. The fluvial terraces are classified into eight surfaces from H to L3 in descending order, based on terrace deposits, overlaying tephra layers and radiocarbon ages (H: older than 120 ka, M1: 100 ka, M2a: 60 ka, M2b: 40 ka, L1a: 30 ka, L1b: 10 ka, L2: 5 ka, L3: 1-2 ka). Through these analyses, an average left-lateral slip rate of the fault is estimated to be 8.5 to 14.8 mm/yr. The last faulting event is inferred to have occurred after 1,000-2,000 yr B.P. when the L3 surface was formed. In addition, the left-lateral and vertical slip amounts per event are estimate as at 4.5 to 5 m and 2 m, respectively. The average recurrence interval calculated from the slip rate and slip-per-event is about 1,700-5,000 years.

Journal

  • Active Fault Research

    Active Fault Research 2012 (37), 17-28, 2012

    Japanese Society for Active Fault Studies

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