Depth to bedrock and bedrock morphology from gravity measurements at Melhus, Melhus Municipality, Sør-Trøndelag

Abstract

This report presents geophysical interpretation results of gravity data as part of a project entitled ORMEL. The main objective of the project is to discern the amount of groundwater, and hence energy, that can be withdrawn from the major sand and gravel sediments in Melhus. The object for this study was depth to bedrock and bedrock morphology. The gravity method is one of the best techniques when sediment thickness estimation is required due to its low cost compared to other methods and the fact that it can be easily implemented in urban areas. This is exactly the case with our study area which is surrounding Melhus city center along the river Gaula.The gravity survey contains 175 gravity stations with 133 of them positioned along 5 profiles with normally 100 m spacing between each station. The other 42 gravity stations are regional measurements mainly located on bedrock exposures found outside the sediment region. After the acquisition phase, the data has been transformed into Bouguer anomalies and the regional trend which is characterized by an increase in the field towards the southeast has been removed. The sediments in the valley are causing local anomaly lows along the measured profiles with a maximum of 8 mGal.