Using Geophysical Methods to Characterize a Fault Zone – A Case Study from the Møre-Trøndelag Fault Complex, Mid-Norway

The Møre-Trøndelag Fault Complex (MTFC) is one of the most prominent fault complexes in Scandinavia. Existing regional gravity and aeromagnetic data used to map the fault in large scale and delineate the main geophysical features related to MTFC. For studying the fault zone in more detail, we acquired multiple geophysical data sets across two segments of the MTFC. To detect the fault zones and their structural attributes, a series of magnetic, resistivity, shallow refraction and deep reflection seismics profiles were measured across these fault zones. Interpretation of the magnetic data shows the distinctive signature of near-vertical faults (~60°-65° towards the south), trending NNE–SSW. Quantitative interpretation of the data points to a width of 90 to 150 m for the Tjellefjorden Fault and 700 m for the Fannefjorden Fault. Inversion of 2D resistivity data reveals a three-layered subsurface until 130 m depth. The layers represent the thin low resistive topsoil underlain by weathered bedrock, and the resistive bedrock. Within the resistive bedrock distinct low resistivity zones can be observed, which can be associated with highly fractured bedrock. These low resistive zones correlate to low velocity zones in the shallow refraction profile.