Improving the reliability of airborne and ground-based electromagnetic surveys by 3-D inversion (Its application to landslide investigations)

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15560702
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Earth system and resources enginnering
• Research Institution: KYUSHU UNIVERSITY
• Principal Investigator: SASAKI Yutaka Kyushu University, Graduate School of Earth Resources Engineering, Research Associate, 大学院・工学研究院, 助手 (10128027)
• Co-Investigator(Kenkyū-buntansha): NAKAZATO Hiroomi National Institute for Rural Engineering, Department of Geotechnical Engineering, Senior Researcher, 造構部, 主任研究官 (00373225)
• Project Period (FY): 2003 – 2004
• Keywords: airborne electromagnetic method / electromagnetic method / landslide / inversion / 逆解析

Research Abstract

In order to prevent natural disaster on slopes such as landslide, it is important to locate the area that can possibly cause damages by carrying out regional geological and geotechnical surveys. The electrical resistivity is a gephysical property that can be used to investigate geological conditions. The airborne electromagnetic method is the most suited for efficiently collecting the data associated with the electrical resistivity of the earth in a large area., but it has a problem that there is no practical interpretation method that can produce 2-D or 3-D images front the data. In this study, we developed a 3-D inversion method that can take into account topography checked the accuracy using synthetic data, and applied it to a real data set collected over a landslide area in Kouchi Prefecture. We confirmed that the results from inversion of airborne electromagnetic data are comparable to those from a ground-based electrical resistivity survey.
Ground-based electromagnetic methods with horizontal loops as the transmitter and receivers can be grouped into two types ; the first type uses a very small separation between the transmitter and receiver loops, say 1 m, and the second type uses much longer separation, say 50m or 100m. We compared the applicability of these two types to inversion. It is concluded for the first type that it is suitable for locating anomalies qualitatively, but cannot be used to image resistivity structures of the earth because the data, particularly in-phase data, are very susceptible to ambient noise. For the second type, we showed using synthetic and real data examples that the inversion can be successfully applied to the data to recover 2-D and 3-D resistivity structures.