Active seismic

As part of the Einstein Telescope feasibility study, the ‘active seismic’ research campaign will begin in January. In the Belgian and Dutch part of the search area, vibrations will then be sent into the soil for short periods. The reflections of these vibrations will provide information about the deeper soil layers. This information is linked to the results already collected from the drilling campaign carried out earlier. The active seismic campaign connects data between drilling locations, creating a comprehensive map of the soil. The survey is carried out in two ways.

Route survey

In the main part of the survey, a small, electrically powered vehicle (the Manitou) with seismic, electric measuring equipment (E-Vibe) drives along a route, sending vibrations into the soil, targeting the range of a low (Hertz) frequency.

The reflection of such a vibration is registered by geophones. These are sensors temporarily installed along the route and retrieved after the measurement. On some routes, a diesel-powered Manitou is used. Although it is noisier than the electric version, it remains much quieter than a typical truck.”

Vertical survey in vicinity of drilling sites (VSP)

The other part of the seismic survey takes place in the immediate vicinity of some locations where ground drilling has previously taken place. Here, so-called Vertical Seismic Profiling, abbreviated as VSPs, is carried out. The procedure is almost the same as for the Route survey. The difference: to get even more detailed information, the vibrations introduced into the ground are not only recorded by geophones. Fibre-optic cables installed in the boreholes to great depth also capture these vibrations. The information via both fibre-optic cable at great depth and geophones provides a more detailed picture of the soil around drilling sites.

When and where?

The campaign starts in the second half of January and is expected to last until the end of April. The vast majority will involve public roads. Agreements have been made with the municipalities and other bodies about this. In the VSP survey (see above), the soil is surveyed more intensively than elsewhere. Where the survey route crosses private land, agreements are or have been made with the owner. 

When and where: route surveys

For this purpose, geophones are installed manually during the day. The vehicle (Manitou) with equipment (E-Vibe) then carries out the measurements at night. In doing so, the vehicle makes short stops to direct the vibrations in the ground. Each stop, called a ‘sweep,’ lasts approximately one minute. Then the Manitou drives about 4 metres further for the next stop.

Each route, as part of the overall survey route, is several kilometres long on average, with a geophone recording the reflection of that vibration every 4 metres. These geophones are collected after each route, read out and then cleaned to be redeployed on the next route. In total, the campaign involves a route of nearly 100 kilometres.

This part of research will be carried out throughout the search area for the Einstein Telescope. That is, in parts of the municipalities of Voeren (Flanders), Plombières, Aubel, Welkenraedt, Thimister-Clermont, Herve and Dalhem (Wallonia), Lontzen, Kelmis (German-speaking Belgium) and on the Dutch side in Vaals and Gulpen-Wittem. This schedule may still change slightly.

When and where: Vertical examination

The VSPs concentrate in the immediate vicinity of previous drilling sites. These include in the planning the drilling locations in Obsinnich and Teuven (municipality of Voeren), Vijlen and Cottessen (municipality of Vaals), Henri-Chapelle (municipality of Welkenraedt) and Herbesthal (municipality of Lontzen). This part of the survey will be carried out during the day.

What will local residents notice?

The electric vehicle (Manitou) is virtually silent. The geophones do not produce any noise. The vibrations cannot be heard or felt from a distance. Only in the immediate vicinity of the vehicle with the equipment in operation can such vibrations on the ground be felt very briefly.

The diesel-powered Manitou makes more noise, but it is much less than that of an average truck.  Tests confirm that the noise level is well within permitted standards.

Traffic has little or no inconvenience from this seismic campaign. Where necessary, agreements have been made with municipalities on traffic measures. During the nighttime measurements, traffic is given extra warning by signalling and a flashing light carried on the Manitou or on the two accompanying cars.

Residents along the route will receive an information letter or flyer approximately ten days before the measurements.

Who is carrying out this work?

The client for this campaign is the Einstein Telescope EMR project office. Executor is the company Faraday Geophysics from Veldhoven (NL) in collaboration with TNO and Antea Group.

Why is this campaign needed?

This campaign provides geological information about the area between the locations where depth drilling was carried out recently and some years ago. With the information now collected through this active seismic and the results of the drilling, we will learn how the soil in the search area is constructed. This information is crucial for determining the precise locations of the Einstein Telescope’s vertices.