This paper studied three-dimensional visualization for fault gouge (120×110×90 mm) by using a micro focus X-ray CT scanner which sampled from the outcrop of Shimogo fault in the central part of Yamaguchi prefecture. Composite planar fabrics, which characterized around fault, were observed like P foliation or R1 shears from CT images. In addition, many Rock fragments were observed around fault plane. Subsequently, rock fragments were extracted from CT images, and we evaluated its shape and orientation by approximating to ellipsoid. From fitting result, we conducted a statistical analysis of axial radius, aspect ratio, slenderness ratio, and flatness ratio. Additionally, we clarified the distribution of the ellipsoid volume and ellipsoid orientation with respect to the fault plane. These results indicated that the shape and orientation of rock fragments might be correlation with the fault behavior.

1. Introduction

The fault behavior is evaluated from structural analysis like fracture patterns around the fault. In general, the thin sections or the polished sections are made from block samples, which contain fault plane sampled from the outcrop or the boring survey. Subsequently, the sample is observed in detail by using imaging devices like microscope. In this method, the samples must be cut open and the observation surface must be exposed. In addition, this method is a two-dimensional evaluation method not a three-dimensional evaluation method. Therefore, the multiple observation surface is required to a three-dimensional evaluation. However, the multiple observation surface cannot expose if the size of the sample is too small or the sample is breakable.

Today, X-ray CT is utilized for evaluating the structure of fault gouge. X-ray CT non-destructively brings us the images of the internal structure of objects in three dimensions. The specific observation surface can be show in PC display using image analysis software. Additionally, high resolution images can be acquired by using micro focus X-ray CT scanner which size of the focal spot is of the micrometer orders. Therefore, the structural analysis done by using X-ray CT is expected to lead to increased efficiency for evaluating the geology.

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