4:15 PM - 4:30 PM
[SGL38-10] ESR dating of the Itoigawa-Shizuoka Tectonic Line located at the northeast edge of Japan South Alps
Keywords:Japan South Alps, Itoigawa-Shizuoka Tectonic Line, ESR dating, Electron spin resonance, Fault rock, Smectite
Recent studies of fault rocks revealed that the Hoozan fault located at the southeastern extension of the Gofukuji fault may have moved during the Quaternary period (Fukuchi, 2015). As a result of the ESR dating of the Hoozan fault gouge collected from the Ishiutorogawa outcrop, the age (T) of the latest fault movement of the Hoozan fault is estimated as T<0.6 +or- 0.1 Ma, from the hyperfine structure of the Al center in quartz. This result suggests that the ISTL as a geological tectonic line located at the southward extension of the Hoozan fault may be still active during the Quaternary. Thus we carry out ESR dating of the ISTL distributed at the Dondoko-sawa outcrop, Nirasaki city, central Japan. The distribution maps of hypocenters indicate that the seismicity of micro-earthquakes is more active along the ISTL around the Dondoko-sawa outcrop. The X-ray diffraction analysis of fault gouge collected at the Dondoko-sawa outcrop indicates that the black fault gouge on the fault plane contains smectites, which can stably exist below about 110 degree C in natural environments (Yoshimura, 2001). We estimate the formation age of the smectites in the black gouge from the formation depth of smectites by assuming the average geothermal gradient of 3 degree C/100m and the average upheaval rate of 2-3mm/y. As a result, the ISTL around the Dondoko-sawa may have moved between about 1.7-2.5 Ma BP. The ESR dating of the black gouge shows that the age of the latest fault movement is estimated as T<0.55 +or- 0.12 Ma. We conclude that the ISTL around the Dondoko-sawa is still active during the Quaternary period.
T. Fukuchi, 2015, Assessment of fault activity by the ESR dating technique. Japan Geoscience Union Meeting 2015, SGL39-01.
T. Fukuchi, H. Inamura, D. Taguchi & T. Hirose, 2016, Distribution of active faults and change of seismic activity in and around Japan South Alps. Bulletin of the Faculty of Education & Human Sciences, Vol.17, p.219-226.
T. Yoshimura, 2001, Clay Minerals and Alteration. Chigaku-sosho 32, 293pp.