Abstract
We propose a 3D-shape preferred orientation (SPO) measurement method of rigid grains using synchrotron micro-computational tomography (μ-CT). The method includes oriented sampling, 3D μ-CT imaging, image filtering, ellipsoid fitting, and SPO measurement. After CT imaging, all processes are computerized, and the directions of thousands of rigid grains in 3D-space can be automatically measured. This method is optimized for estimating the orientation of the silt-sized rigid grains in fault gouge, which indicates P-shear direction in a fault system. This allows us to successfully deduce fault motion sense and quantify fault movement. Because this method requires a small amount of sample, it can be applied as an alternative to study fault systems, where the shear sense indicators are not distinct in the outcrop and the fault gouge is poorly developed. We applied the newly developed 3D-SPO method for a fault system in the Yangsan fault, one of the major faults in the southeastern Korean Peninsula, and observed the P-shear direction successfully.
Highlights
The presence of fault planes under the ground can be used as the basis to study the stress field at the time of paleo-fault activation and is one of the biggest factors affecting the stability of the ground evaluated in civil engineering and geotechnical engineering [1]
shape preferred orientation (SPO) measurements conducted on 2D planes do not completely represent the direction of grains distributed in nature
Some previous studies attempted to apply 3D-SPO to fault systems to overcome the limitations of 2D-SPO and to investigate the spatial orientation
Summary
The presence of fault planes under the ground can be used as the basis to study the stress field at the time of paleo-fault activation and is one of the biggest factors affecting the stability of the ground evaluated in civil engineering and geotechnical engineering [1]. Recent studies that measured and analyzed AMS of a matrix composed of clay minerals included in the fault zone report that AMS is mostly affected by magnetic minerals such as hematite, but clay minerals are aligned to the fault slip plane [6] Their object minerals were mostly limited to clay minerals in matrix, and there are only a few results of the texture analysis of minerals for fault gouges that exist in the brittle deformation zone. SPO measurements conducted on 2D planes do not completely represent the direction of grains distributed in nature Regarding these problems, some previous studies attempted to apply 3D-SPO to fault systems to overcome the limitations of 2D-SPO and to investigate the spatial orientation. After the image filtering process, we attempted to automatize SPO measurement by coding the ellipsoid-fitting process of rigid grains and estimated the
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