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Internal Structure and Permeability of the Yanagase Fault
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Keiji Sato* and Akito Tsutsumi*
Abstract : We investigated the internal structure and permeability of the Yanagase
Fault, an active fault in SW Japan, at two localities, Kamishimizu in Fukui Prefecture
and Nakakawachi in Shiga Prefecture, through field survey and laboratory measure-
ments. The Yanagase Fault of the studied area is developed in the Jurassic ac-
cretionary complex of the Mino-Tamba Belt. In both outcrops, the Yanagase Fault
consists of - zones : fault gouge zone, fault breccia zone and host rock. Permeability of
the core samples from the fault outcrops was measured with a gas-medium tri-axial
deformation apparatus using a pore-pressure oscillation method. Test results per-
formed at 3*MPa e#ective pressure indicate that the highest permeabilities are found
in the fault breccia zone and the lowest permeabilities in the host rock. In the
Kamishimizu outcrop, permeability is +*�+1-+*�+0m, for the fault breccia, +*�+3-+*�+1m,
for the fault gouge and +*�+3m, for the sandstone host rock. In the Nakakawachi
outcrops, permeability is +*�+2-+*�+1m, for the fault breccia and +*�+2m, for the fault
gouge. The permeable nature of the fault breccia zone of the Yanagase Fault is similar
to the previously reported permeability structure of the fault developed within a
granitic basement rock.
Key words : Yanagase Fault, permeability, fault rocks, active fault
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Smith, +321E' F�"�<� 34���-�GH9I*9JKL�+$M�6�NAOPQR����� ��ST���)���������)UV��6� �WXY)Z[�������ST�����\�$&�' ������� ��]^�$+,NC����<&�6��_?@��@ � F��� !"�"`N�1' ��ST������� �������_`Jab�%���M�2c$&�' de
���S������c1A� fghH�ij<�?@A1�DEvans et al., +331 ; Seront et al., +332 ;
Lockner et al., +333 ; �kl9� ,***E' N9N�<:� mn���ST������<I�W*�o$&p� ;@<�o��q�I�W*��rL��9�1*s ���t� l�uIvw��xy:@A1�1' ;NA� de���S����z{|�s}1C� 34�5�6�����v\��~���K<�?@A1�1�<��$&�' ��S������ ��ST�����r� ��S��� ������ �@�� -�������I��n��MJ��NAh�$&�' Wp�������z��s}1C34�5"�JKNA1HCb�� ��� mn���S�T���������J��N� ?:��F@:��<34�P����n��6������T���o��q�I�W*��rL��9J� ����T���W�A�:9�NA19��@ �:�1'�n� ��� �������2c$&�������c1A� ,� ����¡$T��J¢£�¤¥N� ¦§NC¨��c1A©ª«�¨� D�¬¨
*
,**,g 3 +*�®�' ,**-g - ,.�® '¯°±²±²³ ²ij´3µ!¶´²·¸Division of Earth and Planetary Sciences, Graduate
School of Science, Kyoto University, Kyoto 0*0�2/*,,
Japan
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�3¹� º .1»� .3�/0� ,**- DJapanese Journal of Structural Geology, No. .1, .3�/0, ,**-E
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Fig. + (a) The distribution of active faults around
the study area, SW Japan. (b) Localities of the
Kamishimizu and Nakakawachi outcrops (·) along the
northern part of the Yanagase Fault. Based on
Sugiyama et al., (+33.).
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Fig. , A photograph (a) and a sketch (b) of the Kamishimizu outcrop. Open circles represent the
sampling points for the permeability measurements.
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Fig. - A photograph (a) and a sketch (b) of the Nakakawachi outcrop. Open circles represent the
sampling points for the permeability measurements. The stereogram shows equal-area, lower hemisphere
projections of the fault plane (great-circles) and striations on the fault plane (arrows).
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e#ective pressure.
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Fig. 0 Variation of permeability at the Kamishimizu (a) and the Nakakawachi outcrops (b) across the Yanagase Fault.
Permeability of each sample at 3*MPa e#ective pressures are plotted against the distance of the sample point across the fault.
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N`KN��pqr�s ����Ktu +33- +33,v5^6�� _w�ex @¡d ¢£¤¥9IfG%x��>¦9I §/-¨� x��!" ++,
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