Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Poster

S (Solid Earth Sciences) » S-GL Geology

[S-GL30] Geochronology and Isotope Geology

Wed. May 23, 2018 10:45 AM - 12:15 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Takahiro Tagami(Graduate School of Science, Kyoto University), Yuji Sano(Division of Ocean and Earth Systems, Atmosphere and Ocean Research Institute, University of Tokyo)

[SGL30-P07] Geological and seismological conditions required for operating coseismic OSL zeroing of quartz gouge

*Minomo Yuki1, Akasegawa Koji2, Kiyokazu Oohashi3, Noriko Hasebe4, Kazumasa Miura5 (1.Yamaguchi University , 2.DAIWACONSUL CO. LTD, 3.Graduate school of Sciences and Technology for Innovation, Yamaguchi University, 4.Institute of Nature and Environmental Technology, Kanazawa University, 5.Kanazawa University)

Attempts to determine the age of faulting recorded on a rock have been made using methods such as the K-Ar dating, FT dating, and ESR dating(e.g.,Murakami & Tagami, 2004, GRL). Among the proposed methods, the luminescence dating method has an applicable time range of few decades to few hundred thousand years ago, and hence it is suitable for dating an active fault. Early trial demonstrated a successful determination of the latest earthquake event along the active fault in central Japan (Ganzawa et al., 2013, JGSJ). These methods are usually based on the idea that the age value will be reset due to heating event such as high-velocity fault slip or hydrothermal fluid flow. However, since a phenomenon in fault zone accompanied with seismic slip is quite complicated due to the combined frictional wear, fracturing, and thermally activated physic-chemical processes, the age resetting with seismic fault slip must be confirmed in a laboratory by conducting high-velocity friction experiment. Here we show the clear reduction (zeroing) of optically-stimulated luminescence (OSL) signal of quartz gouge after the laboratory experiments and estimate seismological and geological conditions required to occur age resetting in natural fault zones.
In the experiments, we used quartz powder with a particle size of <150 µm which is extracted from Tsushigawa granite, located in the northern part of Awaji island, Hyogo Prefecture. We irradiated 400 Gy of gamma-ray for the quartz powder before the experiments to simulate natural radiation damage. Friction experiments were conducted under the following conditions in darkroom environment using a rotary-shear, high-velocity friction apparatus in Yamaguchi University; slip rate of 200 µm ⁄ s to 1.3 m ⁄ s, normal stress of 1 to 5 MPa, and displacement of 2 to 10 m. To eliminate the effect of crushing on OSL signal, we measured coarse grains (75–150 µm) extracted from recovered sample. In the experiment conducted under normal stress of 1.0 MPa, OSL signal start to decrease from the slip rate of 0.25 m ⁄ s and becomes zero at slip rate ≧ 0.65 m ⁄ s. Signal zeroing was also observed from the experiments sheared at 1.3 m ⁄ s under water-added condition. At slip rates of 0.25 and 0.40 m ⁄ s, we found “partial resetting” which is characterized by coexistence of both particles with signal and without signal. OSL signal intensities (Lx ⁄ Tx) have a strong correlation between power density, τeV (DiToro et al., 2011, Nature) which is proposed as a parameter of heat generation during high-velocity friction, and measured ⁄ calculated temperature in the fault zone; that is, the measured ⁄ calculated temperature exponentially rises and Lx ⁄ Tx exponentially decreases with increasing the power density. The power densities required for the partial and complete resetting are 0.24 MW ⁄ m2 and 1.0 MW ⁄ m2, respectively. Assuming a coseismic fault slip rate of 0.65 m ⁄ s, depth conditions required for operating partial and complete resetting of OSL age are expected to be 35 and 141 m respectively.
[Acknowledgements] This work was supported by grants from the Nuclear Regulation Authority (FY 2015–2017). We thank Manami Kitamura (AIST) and Takehiro Hirose (JAMSTEC) for the temperature calculation using FEM software COMSOL.