Characterization of Subsurface Cracks with Polarimetric Borehole Radar
Grant-in-Aid for Scientific Research (A)
|Allocation Type||Single-year Grants|
|Research Institution||TOHOKU UNIVERSITY|
NIITSUMA Hiroaki Tohoku University Faculty of Engineering, Professor, 工学部, 教授 (90108473)
ASANUMA Hiroshi Tohoku University Faculty of Engineering, Associate Professor, 工学部, 助教授 (50250717)
ABE Mamoru Tohoku University Faculty of Engineering, Associate Professor, 工学部, 助教授 (50005310)
MAKINO Kenichiro Geophysical Surveying and Consulting Cp., Ltd., 部長代理
IKEDA Ryuji National Reserach Institute for Earth Science and Disester Prevention, 防災科学技術研究所, 室長
SATO Motoyuki Tohoku University Faculty of Engineering, Associate Professor, 工学部, 助教授 (40178778)
池田 隆二 科学技術庁, 防災科学技術研究所, 室長
|Project Period (FY)
1995 – 1996
Completed(Fiscal Year 1996)
|Budget Amount *help
¥17,800,000 (Direct Cost : ¥17,800,000)
Fiscal Year 1996 : ¥4,800,000 (Direct Cost : ¥4,800,000)
Fiscal Year 1995 : ¥13,000,000 (Direct Cost : ¥13,000,000)
|Keywords||Radar Polarimetry / Polarimetric radar / Borehole Radar / Ground Penetrating Radar / Fault Survey / Nojima Fault / Subsurface Crack Measurement / レ-グポラリメトリ|
(Polarimetric Borehole Radar Sstem)
We developed borehole a radar system which is capable of radar polarimetric measurement in boreholes. The system uses the combination of dipole antennas and slot antennas to control the transmitter and the receiver polarimetry. The aim of the polarimetric radar measurement includes characterization of geological properties of anomalies such as the roughness of the subsurface cracks and geological boundaries.
Field experimental results in a borehole in Awaji Island, which was drilled to investigate the natural fault caused the Kobe earthquake in 1995 was discussed. In this measurement, co-polarization reflection and cross-polarization reflection were measured at the same depth with two different combinations of antennas. The material is granite and has frequent fractured zones. The Nojima fault, which caused the Kobe earth quake was observed below 1500m in this borehole. The polarimetric radar measurement was carried out in the section between 1000 and 1052m. The radar profile corresponds well to the other data such as electrical logging and BHTV (Ultra sonic imaging).
The difference of reflectivity depending on the polarization was also observed in this measurement was discussed. Reflected signal from single fractures is polarized in one direction, however, those from fractured zones are randomly polarized. Theses information could not be obtained with conventional radar measurement and will be a important tool for characterization of subsurface cracks.
Research Output (13results)