Application or Radiomagnetotellurics on Geomorphological Studies

A radiomagnetotelluric (RMT) survey is carried out to solve geomorphological studies concerning the evolutionary history of the terraces of the river Rhine in the Lower Rhine Bay next to Cologne, Germany. Geomorphological studies concern e.g. the evolutionary history of the valleys and the classic geomorphologic approach is to take drilling samples to examine the spreading of the covering sediments. The geophysical task is to map continiously the two boundaries between tertiary sands, fuvial gravel and loess. The measurements were realized using the new tensor RMT-device developed recently. Horizontal components of the magnetic and electric fields were observed in the frequency range from 10 kHz to 1MHz. Military and civilian radiostations broadcasting in this frequency range were used as transmitters. Transfer functions (e.g. apparent resistivities and phases) are determined by spectral analysis using a newly developed processing software. The observed apparent resistivities and phases were reliable and they showed a smooth frequency dependence. The data was inverted for 2D conductivity models and compared with two-dimensional inversion results of DC measurements and with existing boreholes. The good comparability indicates that radiomagnetotellurics can be optimally applied to this kind of geomorphological questions.