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Sasao, Eiji; Yuguchi, Takashi*; Ito, Yasuto*; Inoue, Takashi*; Ishibashi, Masayuki
Proceedings of 10th Asian Regional Conference of International Association for Engineering Geology and the Environment (IAEG ARS 2015) (USB Flash Drive), 6 Pages, 2015/09
Understanding of the fracture network is important for disposal of high-level radioactive waste. We present our hypothesis on the formative mechanism of inhomogeneous distribution of fracture in the Toki Granite. In the Toki Granite, low- and high-angle fractures are abundant at the shallower part, while less at the deeper part where high-angle fracture is dominant. Distribution of the high-angle fracture is inhomogeneous. Thermochronological study revealed that the rapid cooling occurred at the early stage of granite formation. Paleomagnetic directions of the intact granite were dispersed. This suggests granite was plastically deformed during rapid cooling period. The rapid cooling might cause inhomogeneous distribution of cooling strain. When the granite reached to brittle deformation field, inhomogeneous fracture distribution was formed by the inhomogeneous strain. If so, recognition of the cooling history is essential to understand the distribution of the fracture network.
Takahashi, Yoshihiro*; Oki, Takahiro*; Nagasawa, Takaharu*; Nakajima, Yasuhito*; Kawanabe, Ryu*; Onishi, Kazunori*; Hirao, Toshio; Onoda, Shinobu; Mishima, Kenta; Kawano, Katsuyasu*; et al.
Nuclear Instruments and Methods in Physics Research B, 260(1), p.309 - 313, 2007/07
Times Cited Count：4 Percentile：35.71(Instruments & Instrumentation)no abstracts in English
Ito, Yasuto*; Amano, Kenji; Kumazaki, Naoki*
Island Arc, 15(1), p.165 - 177, 2006/03
Times Cited Count：3 Percentile：10.92(Geosciences, Multidisciplinary)Tectonic episodes in a sedimentary basin are described on the basis of an integrated study combining reflection seismic interpretation, drilling survey and paleomagnetism. A shallow inclined borehole penetrated a fault shown by reflection seismic and geological surveys in the Mizunami area, the eastern part of southwest Japan. Paleomagnetic measurements were executed on core samples successfully oriented using side-wall image logging of structural attitude. At six horizons, we confirmed stable characteristic remanent magnetization (ChRM) through thermal and alternating field demagnetization tests, which is carried by magnetite with minor amount of high coercivity minerals as revealed by experiment of stepwise acquisition of isothermal remanent magnetization. After correction of multi-phase deformation inferred from borehole structural analysis, ChRM directions are combined with previous data and confirm easterly deflection reflecting coherent clockwise rotation of the arc before the Middle Miocene. Compilation of reliable paleomagnetic data describes differential rotation of the eastern part of southwest Japan raised by collision of the Izu-Bonin arc since the Middle Miocene.
Ito, Yasuto*
JNC TJ7400 2002-012, 110 Pages, 2003/03
JNC-TJ7400-2002-012.pdf:3.66MB
It is of great importance to clarify deformation mode in an extensive tectonic event in order to evaluate stability of rock masses. Although such evaluation is based on structural geology in general, conventional methods are of little use for understanding of the temporal and spatial changes in deformation mode accompanying rotational motions, which are brought about by relatively large fault movements. Therefore, deformation mode of rock masses are quantitatively evaluated in this report on the basis of paleomagnetic data. Arrangements of geologic units in the central Japan form a large northward cusp around the Izu Peninsula, which is interpreted as a result of intense deformation of rock mass by repeated collisions of the Izu-Bonin Arc against the Honshu Arc since the Miocene Period. As the Izu Peninsula is considered to be actively transported northward with slips on the Kannawa Fault, understanding for development process of collisional deformation zone is quite important to evaluate geological stability of rock masses. This report presents the paleomagnetic data of Miocene rocks obtained from a borehole in the Mizunami underground Research Laboratory, in Mizunami City, Gifu Prefecture. Progressive demagnetization tests separated stable primary remanent magnetizations for the Toki Lignite-Bearing Formation and the Akeyo Formation in the early Miocene. Their declinations are characterized by a significant easterly deflection reflecting a tectonic event probably linked to the Japan Sea opening. Comparison of the contemporaneous paleo-magnetic data reported from the central Japan implies that a boundary of relative rotational motions under the influence of collision of the Izu-Bonin Arc exists between the Mizunami area and eastern areas, for example, Kakegawa area.
Ito, Yasuto*
JNC TJ7400 2005-055, 21 Pages, 2002/03
JNC-TJ7400-2005-055.PDF:1.12MB
no abstracts in English
