5:15 PM - 7:15 PM
[MGI31-P06] 3D survey of structural geology using a high-resolution digital outcrop model -A case study of the Misaki Formation, Miura Group-
Keywords:SfM, Digital outcrop model, Structural Geology, Discontinuous structure
In recent years, the use of three-dimensional (3D) modeling using the Structure from Motion (SfM) approach has been applied in various fields, such as topographic and forest surveys. However, the application of 3D models to geological surveys remains underdeveloped. Geological surveys that utilize 3D information offer distinct advantages, including the ability to extract discontinuous structures, such as bedding planes and faults, through post-processing. This capability facilitates a more objective and quantitative investigation of geological structures, thereby reducing the limitations imposed by surveys in inaccessible areas. Therefore, the objective of this study is to investigate the applicability of a high-resolution 3D digital outcrop model generated using the SfM technique for geological structural surveys. The present investigation focused on rock outcrops of the Misaki Formation of the Miura Group, which are distributed along the Miura Peninsula in Kanagawa Prefecture.
The Misaki Formation in the study area consists mainly of alternating layers of black scoriaceous sandstone and gray-white siltstone–sandstone, and its stratigraphy and geological structure have been the focus of extensive research. The coastal region is characterized by the presence of outcrops that exhibit high-quality exposure, attributable to the constant action of waves washing the rocks. The wave-cut benches, featuring surfaces with distinctive washboard-like relief, result from the erosion resistance of the scoriaceous sandstone and siltstone–sandstone. These topographical features facilitate the identification of structures such as bedding planes, and the determination of the strike direction of the strata can be traced from the extent of the unevenness on the wave-cut platform. Given these characteristics, the Misaki Formation was deemed a suitable site for evaluating the applicability of 3D geological surveys.
In this study, a digital outcrop model was generated using Agisoft Metashape Professional from high-resolution digital images captured with a digital camera mounted on a monopod. To establish a connection between the coordinate system of the created model and a real-world coordinate system, ground control points were placed and a RTK-GNSS survey was conducted using a Trimble R10. Discontinuous structures were identified from the digital outcrop model using a density-based clustering algorithm (HDBSCAN), and discontinuous planes were automatically extracted using the RANSAC algorithm. A comparison of conventional compass-clinometer measurements and 3D model-based analysis revealed that the absolute errors of dip direction and dip were generally less than 10 degrees. This result suggests that this method is applicable to geological surveys using digital outcrop models. In the future, we endeavor to conduct detailed discontinuity extraction and consider methods to further improve the efficiency and accuracy of processing.
The Misaki Formation in the study area consists mainly of alternating layers of black scoriaceous sandstone and gray-white siltstone–sandstone, and its stratigraphy and geological structure have been the focus of extensive research. The coastal region is characterized by the presence of outcrops that exhibit high-quality exposure, attributable to the constant action of waves washing the rocks. The wave-cut benches, featuring surfaces with distinctive washboard-like relief, result from the erosion resistance of the scoriaceous sandstone and siltstone–sandstone. These topographical features facilitate the identification of structures such as bedding planes, and the determination of the strike direction of the strata can be traced from the extent of the unevenness on the wave-cut platform. Given these characteristics, the Misaki Formation was deemed a suitable site for evaluating the applicability of 3D geological surveys.
In this study, a digital outcrop model was generated using Agisoft Metashape Professional from high-resolution digital images captured with a digital camera mounted on a monopod. To establish a connection between the coordinate system of the created model and a real-world coordinate system, ground control points were placed and a RTK-GNSS survey was conducted using a Trimble R10. Discontinuous structures were identified from the digital outcrop model using a density-based clustering algorithm (HDBSCAN), and discontinuous planes were automatically extracted using the RANSAC algorithm. A comparison of conventional compass-clinometer measurements and 3D model-based analysis revealed that the absolute errors of dip direction and dip were generally less than 10 degrees. This result suggests that this method is applicable to geological surveys using digital outcrop models. In the future, we endeavor to conduct detailed discontinuity extraction and consider methods to further improve the efficiency and accuracy of processing.