New sensor below Banholt measures seismic noise

Does the subsurface of the Euregio Meuse-Rhine dampen enough noise from human activity at the surface for the Einstein Telescope to measure gravity waves? A new sensor in the borehole near Banholt in the Netherlands is the first of a new network that should answer that question.

On Thursday 21 September, a seismic sensor went into the ground near the Dutch village of Banholt, which will record micro-movements of the soil at 200 metres below ground level. The borehole was already there; the sensor is new. A similar sensor had already been installed in a borehole near the Dutch village of Terziet. The Banholt sensor is the first of a new network of 10 that will go under the border area.

Attenuation

“The sensor at Banholt is at the same depth where the Einstein Telescope would be located,” explains geophysicist Wim Walk. As leader of the Subsoil Research Programme for the Einstein Telescope project in the Euregio Meuse-Rhine, he is looking for the best route for the Einstein Telescope’s underground chambers and tunnels.

Walk’s task is to find out where the solid layers of rock run to build the observatory into, but also where the least vibrations from human origin penetrate the earth’s surface. The soft top layer of soil in the area will dampen some of those vibrations, geologists know; the question is how much and whether that dampening is the same everywhere.

Network

Walk: “The sensor we installed today can measure vibrations that are far too weak for a human being to feel. With a network of these sensors, we will spend the next 18 months measuring how much noise from all the human activity on the Earth’s surface you still notice at the Einstein Telescope depth.

“Wind turbines, highways, a train track: they all cause vibrations that the Einstein Telescope might still feel. The measurement network we will build should show how much noise can actually be heard underground, and whether it is the same everywhere. We also want to know which sources we are hearing; by seeing if we hear extra noise when trains pass by or when there is a strong wind and the windmills are turning faster. That’s how we find the best spot for the Einstein Telescope.”