Multidimensional interpretation of radiomagnetotellurics and controlled‐source radiomagnetotellurics data: A validation study

Abstract

AbstractRadiomagnetotellurics (RMT) is an electromagnetic method that uses signals from radio transmitters broadcasting in the 10 kHz to 1 MHz frequency range. Due to its limited frequency range, RMT is commonly used as a shallow‐depth investigation tool. However, in remote areas, there is a lack of radio transmitters and only signals from very low frequency (VLF) antennas (10–30 kHz frequency range) can be measured. This can give rise to low signal‐to‐noise ratio. To overcome this disadvantage of RMT, a controlled‐source RMT (CSRMT) can be applied to measure signals of the low‐frequency (LF) and mid‐frequency ranges (30–1000 kHz). Moreover, the wider frequency range of the CSRMT method (down to 1 kHz) leads to a deeper sounding depth. We present the first RMT and CSRMT validation studies using two perpendicularly located horizontal electric dipoles to realize a 3D inversion of CSRMT data. The survey area in Alexandrova village in Kaluga region, Russia, a previously investigated area, was selected for a validation study. We acquired the data along 8 profiles with 175 stations. Transmitter lines for the CSRMT case were about 900 m long, and the minimum and maximum distances of the stations from transmitters were 450–1000 m, respectively. We applied 2D and 3D inversions over the far‐field data and compared with the previous results. The available geophysical information as well as the borehole data indicate a high agreement between the obtained models and the geological structure. We can confirm that the CSRMT method is a reliable approach for near‐surface explorations and that, the existing advanced and tested inversion tools for magnetotellurics, can be used to invert the RMT and far‐field zone CSRMT data leading to comparable results.