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Mapping of subsurface karst structure with gamma ray and electrical resistivity profiles : a case study from Pokhara valley, central Nepal
| Title: | Mapping of subsurface karst structure with gamma ray and electrical resistivity profiles : a case study from Pokhara valley, central Nepal |
| Authors: | Gautam, Pitambar Browse this author →KAKEN DB | | Pant, Surendra Raj Browse this author | | Ando, Hisao Browse this author |
| Keywords: | Nepal | | Pokhara valley | | karst | | electrical resistivity | | radioactivity methods | | Quaternary |
| Issue Date: | Sep-2000 |
| Publisher: | Elsevier |
| Journal Title: | Journal of Applied Geophysics |
| Volume: | 45 |
| Issue: | 2 |
| Start Page: | 97 |
| End Page: | 110 |
| Publisher DOI: | 10.1016/S0926-9851(00)00022-7 |
| Abstract: | Electrical resistivity (sounding with Schlumberger array and dipole-dipole imaging) and natural gamma ray intensity measurements were made over the karst features (subsurface flow-channels, solution cavities, sinkholes) in the Pokhara valley, central Nepal. In the Powerhouse area, the upper 60-80 m section of the basin-filling Quaternary sediments is represented by layered clastic sediments (gravel, silt, clay) that are represented by KQ-type (ρ1<ρ2>ρ3>ρ4) electrical sounding curves. The true electrical resistivity of the layers has a wide range of variation (a few hundreds to several tens of thousands of ohm.m) such that it is possible to determine both the vertical and lateral subsurface geological variations by integrating the electrical resistivity profiling and sounding techniques. Total gamma ray intensity profiles measured over various karstified locations reveal significant anomalies (up to 100 counts per second, cps) over the known or unknown subsurface openings. In the Powerhouse area, presence of a network of at least three linear NNE-SSW oriented subsurface channels, made by past and present underground flow-channels, is inferred. In interpreted electrical image profiles, contours of elevated resistivity reflect the cross-sectional geometry of cavities. The gamma-ray method is sensitive to near-surface cavities while the electrical image effectively locates the void spaces at intermediate (up to 5-20 m) depths. An exploration program involving rapid radiometric mapping followed by selective electrical imaging is recommended for future exploration of karst-prone areas in the valley. |
| Type: | article (author version) |
| URI: | http://hdl.handle.net/2115/42497 |
| Appears in Collections: | 創成研究機構 (Creative Research Institution) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)
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Submitter: Gautam Pitambar
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