Airborne Geophysics and Infrastructure Planning—A Case Study

Abstract

A helicopter geophysical survey of about [Formula: see text] was flown over an area of [Formula: see text] in southern Norway to aid in determining which route a proposed railroad should follow. Along any route chosen, extensive tunnelling would be necessary. The aerial geophysical survey aided geologists in mapping the area and provided information on the presence of geological structures, particularly faults and fractures, which could hinder tunnel construction if they are major water conduits. The helicopter survey collected magnetic, electromagnetic, radiometric, and very low frequency (VLF) electromagnetic data, and mapped a number of geophysical lineations and other structures. Most lineaments appear to be related to dikes, faults and fractures. Known major faults appear on all data sets, and minor faults appear on one or more of the individual data sets. Magnetic measurements proved to be the most useful geophysical tool for locating dikes in the area. Contacts between dikes and surrounding rock have been shown to be major water conduits, so the locations of dikes were as important as fault and fracture location. The combination of data sets proved valuable for corroborating the findings from any given data set. From the geophysical data, it appears that the western half of the survey area is more intensely fractured than the eastern half, although a few large lineations, presumably fractures of faults, appear in both areas. Ground follow up in selected areas confirmed the reliability of the airborne data.