OTOH Shigeru Faculty of Science, Toyama University, Associate Professor, 理学部, 助教授 (60194221)
KANAGAWA Kyuichi Faculty of Science, Chiba University, Associate Professor, 理学部, 助教授 (40185898)
NAKASHIMA Satoru Graduate School of Science, University of Hokkaido, Professor, 大学院・理学研究科, 教授 (80237255)
SHIMIZU Ichiko Graduate School of Science, University of Tokyo, Assistant, 大学院・理学系研究科, 助手 (40211966)
TORIUMI Mitsuhiro Graduate School of Science, University of Tokyo, Professor, 大学院・理学系研究科, 教授 (10013757)
Faults and intrafault processes are very significant, both academically and socially, in such problems as earthquake prediction, large-scale material circulations within the earth, and waste isolation. Yet they have not been studied comprehensively. The purpose of this project is to summarize major unsolved problems, to organize an interdisciplinary team for systematic fault studies, and to start investigation on the immediate tasks. The Geological Society of Japan has just started a research committee on "Geology and Earthquake" to elucidate the role of geology in future studies towards the earhquake prediction. The present project will be continued as one of the three tasks of this committee for the next three years. The major outcome from this two-year project are as follows.
(1) An ion polisher (GATAN691) was installed with the present grant-in-aid and this estabished a system for systematic observation of deformation microstructures under TEM.
(2) Great many descriptions of faults,
though mostly fragmentary, are scatterred over geological literature. The necessity of "Catalogs of faults and fault rocks of Japan" have been emphasized in this project, and catalogs of 4 faults (Tsurukawa fault, Akaishi fault, Median Tectonic Line, and Hidaka main thrust) have been made as a prototype.
(3) Complete transition from brittle, through intermediate, to fully plastic deformation under extreme shear has been studied for halite shear zones at temperatures increasing linearly with an increase in the normal stress to the fault (as in the case of geothermal gradient) using a high-temperature biaxial machine.These experiments have revealed for the first time the strength profile of lithosphere, conditions for mylonitic deformation, and the rheological meaning of the lower bound of the seismogenic zone. A new fault and plate-boundary model was proposed and experimental results also revealed that rheological properties of a fault is controlled by weaker constituent minerals even their content is as small as 5%, implying the significance of phylosilicates in the fault rheology.
(4) Two-phase instability model for the earthquake generation has been proposed based on the results of high-velocity frictional properties of faults, and the model may account for the seismic quiescence of the second kind. Studies of natural fault rocks have revealed evidence of high velocity fault motion. Fault constitutive properties at high velocities and under large displacements are an unexplored area that needs further studies both in laboratory experiments and in the analyzes of natural fault rocks. Less