Mapping of marine clay layers using airborne EM and ground geophysical methods at Byneset, Trondheim municipality

Abstract

Airborne and ground geophysical surveys were performed at Byneset, Trondheim in Autumn 2013. On 1st January, 2012 a landslide occurred in the centre of the area. Main aim for these surveys was to see usefulness of Frequency-domain Helicopter-borne ElectroMagnetic (FHEM) data in mapping of the clay ayers\/marine sediments and cross-check it with 2D resistivity and refraction seismic. The survey area was also visually inspected to detect exposed or very shallow bedrock. 2D resistivity and refraction seismic surveys were performed along parts of the FHEM lines. Two 1D codes from University of British Columbia (UBC) and Aarhus University are used to invert FHEM data. Aarhus software is found more appropriate and up-to-date to invert FHEM data with many additional features which UBC software does not offer e.g. laterally and specially constrained inversion, depth of investigation (doi) calculation etc. DOI calculated from Aarhus software suggests that only models down to approx. 40 to 150 m depth below the surface are reliable from FHEM data depending on the background resistivity in the area.