Next steps

The GeoLaB project is divided into several project phases: The exploration phase is currently underway, followed later by the planing and construction phase. Only then does the actual research begin.

Project phases| GeoLaB

Exploration phase

Seismic truck in operation on the Tromm. © GFZ

Drilling site with sound barrier on the Tromm. © KIT

In the exploration phase, scientists are conducting investigations in 2024 and 2025 in the areas of Wald-Michelbach, Grasellenbach and Rimbach. The goal is to answer the question: Is the area around the Tromm actually geologically suitable for the research laboratory?

Various investigations are planned, the approval of which will be applied for at the Hessian Mining Authority:

» Groundwater monitoring: Sampling and other measuring points relating to water for hydrogeological and hydrochemical data collection.

» Seismic monitoring: Passive monitoring of ground vibrations through seismometer measuring points.

» Seismics: Investigating the subsurface using sound waves generated by vibrations.

» Geophysical measurements: Additional surveys to determine, for example, the electrical and magnetic properties of the subsurface.

» Exploratory drilling: Drilling from the Tromm into greater depths to study the geological layers in more detail.

Seismics

In September 2025, our seismic team will conduct a second survey campaign on the Tromm. The measurements in the municipalities of Grasellenbach, Wald-Michelbach, and Rimbach will take about two weeks. The Helmholtz Centre Potsdam – GFZ German Research Centre for Geosciences is a GeoLaB project partner and has planned this campaign. Implementation will be carried out by DMT Group from Essen, which has many years of experience in this field.

Before measurements begin, the seismic team will again install geophones along the survey line in the ground. In addition, the team will place geophones in the borehole, creating an even more detailed image of the subsurface. After the measurements, all geophones will be removed.

Field work will take place Monday to Saturday between 7:00 and 20:00. Our seismic team will strive to keep noise and traffic disruption as low as possible.

Your on-site contact is again Tilo Hafner from IPS Informations & Planungsservice GmbH. He will answer your questions about the seismic campaign, record your concerns, and pass them on for clarification.
Tel.: +49 5141 9771470
Email: t.hafner@ips-celle.de

Here you can find all information on the 2025 seismic campaign in one place.
For the GeoLaB project, a seismic survey campaign was carried out on the Tromm in September 2024 in the municipalities of Grasellenbach, Wald-Michelbach, and Rimbach. The measurements lasted about two weeks. The survey was planned by GeoLaB project partner GFZ (Helmholtz Centre for Geosciences). The operational work was commissioned to DMT Group from Essen, a company with many years of experience in conducting seismic campaigns.

The method used was reflection seismics with vibration sources — a minimally invasive exploration technique for studying the upper Earth’s crust. Similar to medical ultrasound, waves are sent into the subsurface from the surface to image internal structures.

Information about the completed seismic survey campaign in September 2024 can also be found in the seismic survey flyer (german only).
Measurement Methods

Using sound waves generated by vibration, the subsurface geology is examined (seismic survey). Measuring devices (geophones) record the reflected waves.

MEASUREMENT METHODS
Reflection seismics is a geophysical method used to create an image of the upper Earth’s crust. The diagram illustrates how sound waves generated by a vibrator truck are sent into the ground. These waves travel through different geological layers and are reflected at their boundaries. At the surface, the reflected waves are recorded by geophones — instruments that detect weak ground vibrations. From the arrival time and properties of the returning echoes, a detailed image of the subsurface can be computed.

PROCESS
Before measurements begin, geophones are installed. For this, staff from DMT Group, supported by the GeoLaB team, place the devices into the ground along the survey line and remove them afterward. To generate the required sound waves, a so-called vibrator truck is used. This vehicle is equipped with vibrating plates that transmit sound waves into the ground.

Information about the completed seismic survey campaign in September 2024 can also be found in the seismic survey flyer (german only).

[Translate to Englisch:] Seismik Truck im Einsatz auf der Tromm. © GFZ

Geophysics

Research from the Air - for the energy of the future. At the end of May 2025, a helicopter will take off over the Tromm region with a clear mission: to survey the subsurface of the Odenwald from the air. Flying at low altitude and using cutting-edge magnetic technology, the Earth’s interior will be made visible.

What´s it about?

The GeoLaB research project explores the use of deep geothermal energy from crystalline rock. To make this possible, researchers need an accurate picture of the geological structure. One key puzzle piece comes from precise, airborne magnetic field measurements.

When & Where?

The survey flights are planned for May 23 and 24, 2025, with backup dates on May 26 and 27. Flights will take place between Rimbach, Weiher, and Münschbach in the west and Affolterbach, Aschbach, and Wahlen in the east — about 70 m above open terrain and slightly higher over settlements.

What does the helicopter measure?

It records natural variations in the Earth’s magnetic field — without any impact on the environment. The measurements are contactless, quiet, and completely safe for people, animals, buildings, and nature. No photos or video recordings are taken.

Important for residents:

Flights will take place only on weekdays and during daylight hours. The police have been informed, and the required permits from the German Federal Aviation Office (Luftfahrt-Bundesamt) are in place.

This is what research looks like from the air — with its distinctive nose-boom probe, the helicopter scans the Earth’s magnetic field for GeoLaB. © Neuwirth
As part of the first survey campaign, geophysics revealed geological features in some areas of the Tromm. With a second geophysical survey campaign, we want to investigate these features in more detail — for example, by studying a smaller area with a higher number of measurement points or by using longer geoelectric survey profiles.

Starting in summer 2025, specially trained experts will carry out measurements for the GeoLaB project. These are part of the geophysical investigations on the Tromm, which will extend over several months. Gravimetry, magnetics, and geoelectrics will be applied along survey profiles in different parts of the region.

Scientists from the Karlsruhe Institute of Technology (KIT), a GeoLaB project partner, have planned the campaign. It will be carried out by Geophysik GGD mbH and its partners — an experienced team with many years of practical expertise.

Permissions: To access and use paths, forest, and agricultural land, permission must be obtained from municipalities, HessenForst, other authorities, as well as private landowners and tenants. GeoLaB has commissioned IPS Informations & Planungsservice GmbH to obtain these permits.
From September to December 2024, various measurements were carried out on the Tromm for the GeoLaB project: gravimetry (gravity field measurements), magnetics, and geoelectrics were performed along six survey profiles. The campaign was planned by the GeoLaB project partner KIT (Karlsruhe Institute of Technology). The operational work was commissioned to Geophysik GGD mbH and its partners, who have many years of experience conducting such surveys.

The campaign has been completed. Detailed information about the completed survey can be found in this Geophysics Flyer (german only).
Measurement Methods

SURVEYING AND GRAVIMETRY
All measurement points are measured using a GPS (global positioning system) with high measurement accuracy. This enables precise determination of the positions and contributes to the improved interpretation of all other measurement data. Gravimetry measures changes in the Earth's gravitational field caused by density differences in the subsurface. A gravimeter is placed on the earth's surface and records minimal changes in gravity. By combining gravimetry and GPS, detailed maps of the density distribution underground can be created.

MAGNETICS
Magnetics is a geophysical method for measuring variations in the earth's magnetic field. These are caused by different magnetic properties of the ground and are measured with a magnetometer. The instrument is placed on the ground and measures for a few minutes to collect accurate data.

DC GEOELECTRICS
Geoelectrics is a method for investigating the electrical conductivity of the subsoil. An electric direct current (DC) is passed through the ground and the resulting voltage is measured. The electrical resistance of the subsoil is calculated from this. This method makes rocks and rock layers with different electrical properties visible. The illustration shows a typical geoelectric setup, where electrodes are connected to a measuring unit by a cable. Stainless steel spikes, serving as electrodes, are inserted by hand a few centimeters deep into the ground at regular intervals along the profile. The entire measuring process is controlled by software.

These methods, along with illustrations, are also presented in the Geophysics Flyer (german only) for the 2024 survey campaign.

Typical setup of a geoelectric survey with installed electrodes and connecting cables. © Terradat (UK) Limited

Site plan of the GeoLaB-1 exploratory borehole southwest of the Tromm natural playground. © KIT, aerial photo Tromm Google Maps, 2024

Construction site with drilling rig © KIT

First core from the GeoLaB-1 borehole on the Tromm © GeoLaB

Exploratory drilling

Drilling is being carried out on the Tromm to study the geological layers in more detail through exploratory drillings. The drilling site is located southwest of the nature playground on the Tromm. To significantly reduce noise emissions, the site has been enclosed with a 10-meter-high sound barrier.

The first borehole was drilled in February and March 2025 to a depth of about 500 meters. It was fully cored, meaning the extracted rock was preserved and recovered. These cores are now being thoroughly analyzed by GeoLaB researchers. For example, they are investigating the rock’s permeability (its ability to let fluids pass through) and its composition. After drilling, tests and measurements were carried out in April to further characterize the geological properties — in particular, to examine how fractured and water-permeable the subsurface is.

What did the first borehole reveal?

The findings are highly interesting for GeoLaB: over 500 meters of fractured granitoid rock were encountered. While data evaluation is still ongoing, researchers have already identified several fractured zones at various depths that indicate certain degrees of water permeability in the subsurface.

The second borehole

Because of the promising results of the first borehole, a second exploration borehole was drilled from the same site in June 2025. This second borehole was deviated — meaning it was drilled at an angle — reaching a depth of 585 meters and extending more than 350 meters horizontally. This allowed a broader section of the Tromm massif to be investigated.

Measurements from the borehole

The exploration boreholes not only provide direct insight into the Tromm’s rock and structure but can also be used for geophysical measurements. Sensors are installed directly in the borehole to collect valuable subsurface data.

Before these measurements can begin, the borehole must be prepared. During the week of August 4–8, the first borehole will be cleaned of cement residues. For this, the drilling rig will be set up again — but no new drilling will take place. The work serves solely to prepare the borehole technically for the upcoming measurements.

After the seconde borehole

Once the investigations around both boreholes are completed, the entire drilling site will be fully dismantled.

Between December 2024 and the end of January 2025, the drilling site was set up. Within the fenced area, machine platforms and storage zones were prepared, and containers for offices and staff facilities were installed. The site was enclosed by a 10-meter-high sound barrier, a requirement from the permitting authority to ensure optimal noise protection for residents and to support measures against African swine fever. Finally, the drilling rig was assembled. The borehole was drilled in February and March 2025 to a depth of about 500 meters with a diameter of 16 centimeters, operating around the clock (24/7).

To study the geological layers in detail, core samples with a diameter of about 10 cm were collected throughout the entire drilling process. After drilling, additional downhole measurements were carried out in April.

Who performed the drilling?

The Karlsruhe Institute of Technology (KIT) commissioned Daldrup & Söhne AG to carry out the drilling work.

What makes this borehole special?

It provides a direct, detailed look into the subsurface of the Tromm. The entire 500-meter core was recovered, examined, and is being further analyzed at KIT in Karlsruhe to better understand the geological composition.

What else was the borehole used for?

In addition to collecting rock cores, the borehole was used for further investigations and measurements over about two weeks to better characterize the subsurface.
The special feature of the second borehole: the engineers intentionally deviated it from the very beginning — about one degree every 15 meters. This way, after 730 meters of drilling, they reached a final depth of around 580 meters, more than 370 meters away from the drilling site. With this angled trajectory, researchers can examine a much larger volume of rock. This also increases the likelihood of encountering fractures in the rock — a key factor in assessing the Tromm’s geological suitability for geothermal research. Another important puzzle piece in the overall picture of the Tromm.

Planing and Construction Phase

If the investigations during the exploration phase show that the Tromm area is a useful research location, planning will continue. The construction phase starts in 2026 and extensive questions need to be answered:

» Where could the tunnel be built?

» How can the construction site and access be set up?

Of course, approvals from the Hessian Mining Authority as the responsible authority are also required. Finally, the tunnel for the GeoLaB research laboratory will be built into the mountain.

During the construction phase of the tunnel there may be disruptions for residents, for example due to noise or traffic. Ways are being sought to avoid traffic, for example by using the waste on site. As soon as it is clear when the construction site will be set up and what consequences this will have for local citizens, they will be informed directly.

The laboratory is set up in the tunnel. A visitor ramp and later an information pavilion are intended to make GeoLaB accessible to the population and visitors to the Tromm region and make the fascinating world beneath our feet visible. There will be regular events there by the GeoLaB team and the researchers involved.

Next steps

Project phases| GeoLaB

Exploration phase

Second Seismic Survey Campaign September 2025

Seismic Survey Campaign September 2024

Seismic Survey

GeoLaB takes off! Helicopter Survey Flights Over the Tromm

Geophysic Survey Campaigne 2025

Geophysic Survey Campaigne 2024

Geophysical Investigations

Exploratory drilling

Details on the First Exploration Borehole GLB-1 (Spring 2025)

Details on the Second Exploration Borehole GLB-2 (June 2025)

Planing and Construction Phase