Online ISSN: 1884-4111 Print ISSN: 0033-8303
Radioisotopes 70(3): 131-145 (2021)

特集Special Issues

ESR法による活断層の絶対年代測定と活動性評価糸魚川–静岡構造線活断層系を例としてAbsolute dating of active faults and the assessment of fault activity using ESR dating method: The case of the Itoigawa–Shizuoka Tectonic Line Active Fault System

山梨大学大学院総合研究部教育学域Faculty of Education, Graduate Faculty of Interdisciplinary Research, University of Yamanashi

発行日:2021年3月15日Published: March 15, 2021

南アルプス北東縁~東縁を通る糸魚川–静岡構造線活断層系に属する下円井断層及び鳳凰山断層の活動性評価をESR(電子スピン共鳴)法を用いて実施した。既に活断層に認定されている下円井断層の最新活動年代(Ta)は,Ta≤1.04±0.14 Maとなり,ESR法の原理が成立していることが確認された。一方,地形的な特徴から推定活断層と見なされている鳳凰山断層からは,Ta≤0.58±0.10 Maという結果が得られ,鳳凰山断層は中期更新世以降も活動した活断層である可能性が非常に高まった。

I carry out the assessment of fault activity of the Shimotsuburai and Hoozan faults belonging to the Itoigawa-Shizuoka Tectonic Line Active Fault System located at the northeast and east edges of the South Alps of Japan, using ESR (electron spin resonance) dating method. The age of the latest fault movement (Ta) of the Shimotsuburai fault, which is recognized as an active fault, is estimated as Ta≤1.04±0.14 Ma. This result means that the principle of ESR dating method of fault movement is sustained. On the other hand, the age of the latest fault movement of the Hoozan fault, which is regarded as an estimated active fault by a topographical feature, is estimated as Ta≤0.58±0.10 Ma. Therefore, I conclude that the Hoozan fault is probably an active fault having moved since the Middle Pleistocene.

Key words: electron spin resonance (ESR) dating; lattice defect center; active fault; Itoigawa-Shizuoka Tectonic Line

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