Vol.9 No.2 2016
Research paper : Three-dimensional urban geological map (T. NAKAZAWA et al.)−75−Synthesiology - English edition Vol.9 No.2 (2016) store data (although we greatly appreciate such information), and there is no case that shows geological interpretation such as subsurface geological structures in an easy to understand manner.The borehole data is a point data that merely shows one part of the strata that are distributed spatially. The geology of the urban areas can be understood only when many borehole data are used to show the spatial distribution of the strata. However, such geological interpretation can only be done by someone with advanced expert knowledge, and it is necessary to organize standard data with which the strata can be compared. While the 1:50,000 geological maps published by AIST show such distribution of strata and geological structures based on the survey and research by geologists, in the case of the geological maps of the urban plains, there is a limit to expressing the subsurface geoinformation planimetrically because the landform is flat. Therefore, we created and inserted many geological cross-section diagrams compared to the maps of mountainous and hill zones (Fig. 1),– but there were limits to such paper-based map publication. Also, the disclosure of fundamental borehole data was limited to the major ones due to the limitations of space or disclosure conditions, and they are not sufficient. It is necessary to display highly reliable interpretation of subsurface geological structures in an easy to understand manner, and to allow people to browse and use the borehole data that is the basis of such interpretation, in terms of reproducibility of the research and promotion of secondary data use.Recently, the computer processing technology has advanced, and delivery of various information over the Internet has become easy, and the Internet environment for the general public is widening. Assuming the delivery on the website, the degree of freedom of expression of the subsurface geological structure of urban plain areas will increase, and three-dimensional displays will be possible if necessary. It can be said that the organization of geoinformation that goes with the times is demanded.3 Scenario and elemental technologies for the 3D geological mapsConsidering the aforementioned awareness of the current situation, we started to study “3D geological maps” to be delivered on the web (Fig. 2) as urban geoinformation that is easy to understand, easy to use, and above all, highly reliable. Using as standard the data of drilling survey conducted originally by geologists, the borehole logs for public works disclosed by the local governments are correlated, and the 3D distribution of strata is analyzed by computer processing. A method is considered that allows a 3D geological model to be easily viewed on the web by anyone, and a system is constructed that allows browsing and use of the borehole data that is the original data used for 3D analysis. We thought this would enable the organization of geoinformation that is easy to understand, easy to use, and highly reliable. The scenario of the geoinformation for urban areas (Fig. 3) is composed mainly of six elemental technologies: use of the borehole data of public works of the local governments, basic drilling surveys, correlation of the strata, landform classification, 3D modeling technology, and data management and display technology. Our research group is working on the integration of these six elemental technologies taking into consideration the usability and reliability of geoinformation. Below is the explanation of the individual elemental technologies.3.1 Use of the borehole data of the public works possessed by the local governmentsThe local governments conduct geological surveys when engaging in public works such as civil engineering and construction projects in their administrative areas. The main method of their geological surveys is drilling. The conducted drilling surveys are normally the standard penetration tests defined by the common specifications for geological survey work by the local governments (Table 1), and the Fig. 1 Conventional style of geoinformation for urban areas“Noda” sheet of 1:50,000 geological maps. Since the urban area in a plain has flat landform, there is little geoinformation that can be presented on a sheet map. Although this geological map contains several geological cross-section diagrams, there is a limit to how much can be printed on paper.