Abstract
Intrafault materials derived from two localities within the Atotsugawa fault of Central Japan have been investigated to elucidate the characteristics of the fault. In each fractured zone within the fault, two different zones are clearly recognized; the one zone is composed mainly of very fine fragments and developing limitedly both side of the fractured zone in contact with parent rocks, and the other is composed mainly of coarse fragments and constituting the main part of fractured zone.
Textures of the intrafault materials are in random arrangement of fragments showing rounded-angular shape, or in complete arrangement of fragments showing lenticular-anastomising shape. The grain-size frequency curves indicate no peakes or the remarkable peak of d=10-3 μm. Quartz grains within the intrafault materials under the scanning electron microscope have smooth surfaces keeping breakage or fracture surface, or small undulated, a little corroded surface.
The mineralogy of 2μ<fractions from the intrafault materials is principally including illite, chlorite and montmorillonite, and occasionally with quartz and feldspar. Geochemically, within the zone composed mainly of very fine fragments, loss of SiO2, Na2O and K2O, addition of H2O+, H2O- and Total Fe, addition or loss of CaO have been relatively found, comparing with composition of parent rocks.
