Computer Modeling of Lateral Influence of the Ladoga Anomaly (Janisjarvy Fault Zone) on the AMT Sounding Results

Abstract

In the northern Ladoga Lake area in 2015 and 2017 the audio-magnetotelluric (AMT) soundings were performed. The main task of AMT was to study the deep structure of the high conductive anomalies discovered before by the di-rect current (DC) profiling. A special AMT experiment has been made over the Janisjarvi anomaly. This zone of anomalous conductivity is situated on the contact between the Proterozoic and the Archaean rocks. Several AMT sounding sites were situated symmetrically on the both sides of anomaly. Data processing al-lowed to make a conclusion about the quasi-two-dimensionality of the medium under investigation. The computer 2D modeling has been made with the use of grid method. Results of modeling showed that Janisjarvi conductive zone has sub vertical position. Its continuation to the depth is restricted in the range of 0.5 km. The influence of Janisjarvi conductive zone creates effects of fictitious conductive layers on results of AMT soundings. The depth of fictitious conductive layers increase from units to 10–20 km depending to increase of the distance between the center of the Janisjarvi conductive zone and AMT sounding sites. It means that all AMT soundings should be made with taking into account the influence from the steeply dipping uppermost conductive layers.