Permeability and porosity are important hydraulic properties to understand fluid flow in underground. In this study, we focused on fluid flow in sediments and fault rocks, and measured gas permeability and porosity under isotropic high pressure. The samples were collected from the Quaternary deposits Uonuma Formation and Katakai fault zone in Ojiya city, Niigata. The Uonuma Formation in our study area consists of several different layers which are sand gravel, coarseto fine-sand and silt. The Katakai fault zone is composed of dark brownish gouge and deformed sand with many fractures.Gas permeability and porosity were measured using the constant pressure method and the gas expansion method, respectively. The measurements were conducted at confining pressures up to MPa. At low confining pressure, gas permeability of sand samples showed at MPa, sand samples were maximum .smaller than silt at MPa. The porosity of the fault gouge was sensitively affected by change of confining pressure and dramatically decreased with pressurization . at MPa .We also compared our data with reference data and the Kozeny-Carman equation to confirm the accuracy. As a result, porosity data approximately corresponded to reference data which were measured using drilling core from Niigata Basin. Permeability data did not conform to the value obtained from the Kozeny-Carman equation because of heterogeneity of grain size composed sample. Abstract
This study has revealed some characters of the Tottori-ken Seibu earthquake by observing outcrops and thin sections.The earthquake occurred in a place where no active fault was identified. After the earthquake happened, airphoto-interpretations were performed again. Consequently, some lineaments in the direction of northwest were newly recognized. Although the fault planes generally strike the west-northwest and the northeast, they disagree to the lineaments obtained from the airphoto-interpretations. The strike of fault plane allowed a distinction to be made between the exposed ones and the seismic ones on the aftershock area of the Tottori-ken Seibu earthquake as well. The fault planes which we observed at outcrops were formed before it. And most fault planes with west-northwest strike indicated left-lateral slip and most of those with northeast strike showed right-lateral slip.The foliated cataclasite and fault gouge were discovered in study area. The foliated cataclasites were exposed only on the aftershock area. The evidence proved that fault movement has repeatedly been occurring at least more than one time. The width in cataclasite ranged from mm to cm. The fault gouges were distributed in whole area, specifically around the Lake Ryokusui. The earthquake surface fault in this time also occurred there, and the displacement was about cm. The maximum fault density was more than per m at the outcrop of west of Lake Ryokusui and northeast part out of the aftershock area. The main thickness was to mm. The fault gouges showed various colors. A large percentage of color were white, pale yellow, pale red and black.Rhyolite, basalt-andesite and aplite dikes were formed in Miocene, which intruded the granite throughout study area. Their trend was similar to the fault planes. And the crush zones mainly formed around the granite/dikes boundary. AbstractCThe Geological Society of Japan 2005 737
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