If you have walked anywhere in Basel or the surrounding communities in the past couple of weeks, you have probably noticed little orange boxes that have suddenly appeared everywhere. These boxes, which are called geophones, are placed directly on the ground and tied to a pole or nearby structure with cable ties. Designed to sense the finest vibrations in the ground and record them, they are collecting information to create a map of what the soil looks like at a depth of several thousand meters.

Why are they doing this? The community of Riehen has used geothermal energy from a depth of 1.5 kilometers without incident for more than 27 years. In order to secure the future energy supply, they now need to build a second geothermal plant (called geo2riehen), which requires an in-depth exploration of the subsoil.

They are doing this with the use of a so-called vibro-truck, which is used to generate slight vibrations in the ground, and the little orange geophones, which measure the reflected waves from the subsoil. The vibro-truck, which weighs around 2 tons, drives around the region and goes into action every 20 meters. When it stops, a vibrating plate is lowered onto the road and the truck is jacked up. The plate vibrates the ground, simulating a mini-earthquake, while two men measure the amount of vibration that reaches the house facades. If a norm of 6mm per second is exceeded, the vibration is immediately stopped. These vibrations are also reflected by different layers of rock underground and that is where the 9,000 orange geophones that have distributed throughout the region come into play. They measure and record the vibrations that are created by the vibro-truck. Once they have done their work, they will be collected and the valuable data will be evaluated.

The geophones are also equipped with an inclination sensor that reports any movement of the device as well as a GPS so that they can be located at any time. The geophones are regularly checked to protect them against theft or vandalism. They are kindly asking the public not to disturb the geophones in their important work.

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