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VLF-method of geophysical prospecting: a non-conventional system of processing and interpretation (implementation in the Caucasian ore deposits)
1 – Department of Earth Sciences, Faculty of Exact Sciences, Tel Aviv University Ramat Aviv 6997801, Tel Aviv, Israel
2 – Azerbaijan State Oil and Industry University 20 Azadlig Ave., Baku, AZ1010, Azerbaijan
Investigation of the electromagnetic (EM) fields from distant VLF (very low friquency) military transmitters is one of the fastest and low-expensive geophysical methods. At present, it finds frequent application in prospecting for various deposits, search of subsurface underground water, archaeogeophysical studies and various types of geological mapping. For geophysical investigation can be utilized a few dozens of the VLF transmitters disposed in various countries. The different frequencies and angles of registered EM radiation enable to obtain additional preferences by interpretation. A depth of investigation depends on the radiowave frequency and averaged resistivity of the host medium and usually ranges from several tens to several hundred meters (last values – under very favorable conditions). Both the electric and magnetic components of EM field are used in investigation by the VLF method. Generally only the magnetic field (H) is employed. A wide using of the VLF-technique was limited by absence of reliable methods for elimination of the EM field time variations, rugged relief influence and procedures for quantitative interpretation of the VLF-anomalies. These problems are successfully solved and the unified methodological system is developed. For elimination of the temporal variations a special procedure based on the direct continuous filtering is proposed. The correlation technique enables to significantly reduce the rugged relief influence. For quantitative interpretation is proved a possibility to use the modern interpreting methods elaborated in magnetic prospecting for complex geological-geophysical conditions. Finally, for revealing hidden objects against the high-intensive geological noise background, an application of non-conventional statistical, informational and wavelet algorithms is suggested. The main components of the developed system were successfully tested in the Caucasian polymetallic and copper deposits.
Keywords: VLF-transmitters, temporal variations, rugged relief influence, advanced quantitative analysis, ore deposits, geological-geophysical mapping, earthquake precursors
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