From Monday 10 November and for the next two months, citizens between Randers and Hobro will be able to meet a four-wheel drive vehicle with a trailer that is fitted with a plumb bob, which is a kind of large hammer. The vehicle will drive around the 500 square kilometre area, stopping on the verge at carefully selected locations to take measurements. A cable about 100 metres long with geophones – small receiving units – is rolled out and the weight is released at three points along the line. The cable is then rolled back in and the driver and his partner drive to the next point to repeat the manoeuvre.
Dropping the plumb line to the ground causes slight vibrations that are picked up and recorded by the geophones. The recordings provide important information about the upper layers of the earth.
The activities take place at 500 points evenly distributed throughout the area and take approximately 20-30 minutes per point. All points are located along public and private roads, and permission has been obtained for each point in the three municipalities that the area affects: Randers, Viborg and Mariagerfjord. The Danish Energy Agency has issued the overall licence for the survey.
Why are we doing this?
The method is called refraction seismic or LVL – low velocity layer – and is used to collect data about the upper soil layers.
The refraction seismic data is combined with the results from the upcoming 3D seismic survey. Together, the two data sets will provide a complete picture of all the layers of the earth from the top few metres to approximately 3,000 metres depth.
The survey will start in Randers on 10 November and move northwards towards Hobro. A Ramboll representative will be present in the area throughout the process. The survey will last just over two months – with a break over Christmas – and will only take place during daytime hours from Monday to Saturday.
