250 geophones ‘listen’ for vibration noise
How much vibrational noise exists in the research and protection zone of the Einstein Telescope? And how does this noise penetrate deep underground? For example, near a motorway, in the agricultural countryside or not far from an airport or near a river. And how does that noise penetrate deeper soil layers?
To answer these questions, the Einstein Telescope EMR project office, in collaboration with the University of Liège (ULiège) and KNMI, will soon conduct a study in the German, Belgian, and Dutch border region. To this end, small seismometers, known as geophones, are being temporarily installed at about 250 different locations to measure ground vibrations that emit acoustic waves. Geologists refer to this as ‘passive seismicity’ or ‘noise measurements’.
10 x 10 centimeters
The study will last three to four weeks. The geophones are small, sealed boxes measuring 10 x 10 centimeters with a built-in vibration sensor. The device operates silently, emitting no signals. ‘We dig a small hole to place the geophones at a depth of around 15 centimeters. After three or four weeks, we retrieve them and close up the hole properly. You don’t notice much’, explains dr. Hadrien Michel, researcher at the University of Liège. After retrieval, the recorded data will be analyzed by seismologists collaborating with the Einstein Telescope project office. This will be the first of several campaigns, with subsequent installations planned for other locations.
Permission
Hadrien Michel has already obtained permission from many landowners in the region. ‘People are generally enthusiastic about the idea of taking part in research on the Einstein telescope. Of course, there are sometimes questions, but if we explain that it’s only for a few weeks and only requires a small 10-centimeter-by-10-centimeter area at a depth of 20 centimeters, without any further restrictions, most give their approval’, he notes.
In the coming weeks, Hadrien Michel and his colleagues will be travelling acrosse the border region of the three countries to secure permission for the remaining sites. ‘Basically, we go door to door, explaining who we are and what we’re doing. If no one is home, we leave a letter with our contact details. Though it’s time-consuming, this research is essential, and the Einstein Telescope is a project worth the effort.’