Regional-scale geophysical studies in Russia are used to be performed along separate profiles a few hundred to a few thousand kilometers long, verified by deep drilling.
Regional profile observations yield information on the deep structure of vast regions and allow solving some applied problems such as prognosis of oil and gas content in sedimentary basins, and delineating the zones perspective for solid mineral deposits. In active tectonic regions, data are obtained for studying the geodynamical conditions of the Earth's interior and forecasting the seismic activity.
Characteristic of regional studies is an integrated application of geophysical methods. This complex includes seismic, electromagnetic prospecting, gravity prospecting, magnetic prospecting and other methods including geochemical ones. The leading part in regional studies usually belongs to seismic: in most cases this method is capable of quite accurate location of geological boundaries. Other methods, first of all the electromagnetic prospecting, supplement these data with information about physical properties of rocks characterizing their lithology, fluid content, archeological conditions, etc.
Classification of the targets of regional deep geophysical studies:
- reference profiles (length more than 500 km, measurements duration 2-5 years). Customer: Ministry of Natural Resources of the Russian Federation
- regional profiles (length more than 100 km, measurements duration 1-2 years). Customer: Regional Subsoil Resources Management Agencies
Integrated geophysical studies:
- seismic prospecting
- electromagnetic prospecting
- gravity prospecting
- geochemical methods
- airborne magnetic prospecting
- other airborne techniques
Methods for electromagnetic studies along regional profiles:
MT: measurement sites spacing along the profile 3 km, f=0.0005÷200 Hz, record duration 12-16 hours, exploration depth 20-30 km
Long-period MT: measurement sites spacing along the profile 10-12 km, f=0.0001÷300 Hz, record duration 48 hours, exploration depth 40-60 km
AMT: measurement sites spacing along the profile 1 km, f=1÷100000 Hz (in case of MTU-5A), record duration 1 hour, exploration depth 0.5-1 km