Integrated Geophysical Studies in the East-Indian Geothermal Province |
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| Authors: | V C Baranwal S P Sharma |
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| Institution: | (1) Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, 721302, India |
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| Abstract: | Integrated geophysical surveys using vertical electrical sounding (VES), very low frequency (VLF) EM, radiation counting,
total magnetic field and self-potential (SP) measurements are carried out to characterize the geothermal area around a hot
spring in the Nayagarh district, Orissa, India that lies in the East Indian geothermal province. The study was performed to
delineate the fracture pattern, contaminated groundwater movement and possible heating source. VES interpretations suggest
a three- to four-layer structure in the area. Resistivity survey near the hot spring suggests that weathered and fractured
formations constitute the main aquifer system and extend to 60 m depth. Current flow measured at various electrode separations
normalized by the applied voltage suggests that fractures extend to a greater depth. Detailed VLF study shows that fractures
extend beyond 70 m depth. VLF anomaly has also very good correlation with the total magnetic field measured along the same
profiles. Study results suggest that a gridded pattern of VLF survey could map the underground conductive fracture zones that
can identify the movement of contaminated groundwater flow. Therefore, precautionary measures can be taken to check further
contamination by delineating subsurface conducting structures. Self potential (SP) measured over the hot spring does not show
a large anomaly in favor of the presence of a sulphide mineral body. A small positive (5–15mV) SP anomaly is measured which
may be streaming potential due to subsurface fluid flow. A high radiation is measured about four kilometers from the hot spring,
suggesting possible radiogenic heating. However, the exact nature of the heating source and its depth is not known in the
area. Deep resistivity followed by a magneto-telluric survey could reveal the deeper structures. |
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| Keywords: | Geoelectric VLF EM radioactivity magnetic geothermal East Indian province |
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