- 1GFZ Helmholtz Centre for Geosciences, Potsdam, Germany (beatrice@gfz-potsdam.de)
- 2Institute of Applied Geosciences, Technical University Berlin, Berlin, Germany
- 3Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse (DiSTAR), University “Federico II” of Naples, Italy
- 4INGV Osservatorio Vesuviano: Naples, IT
- 5ITES (Institut Terre et Environnement de Strasbourg), Université de Strasbourg/CNRS, Strasbourg, France
- 6Landsvirkjun, National Energy Company, Iceland
Time-lapse absolute and relative gravity surveys, are directly sensitive to the mass redistribution in the subsurface. These well-established methods allow for the monitoring of geothermal fields and for assessing the sustainability of the anthropogenic activities (water injection and extraction).
We apply the hybrid gravimetry method, in order to characterize the fluid redistribution within the subsurface. The hybrid gravimetry method combines absolute and relative microgravity time-lapse measurements and continuously recorded gravity time series. At Theistareykir geothermal field (Northern Iceland), we collected yearly time-lapse data at 26 fixed locations, and we recorded continuous data with 2 superconducting gravimeters (SGs), deployed within the hydrothermal field. Data acquisition started just before the beginning of operation of the powerplant in 2017, allowing us to monitor the hydrothermal system behaviour before and during anthropogenic perturbation.
After 7 years of data collection, we present here the gravity datasets (discrete and continuous) from 2017 to 2024. In particular, we show the continuous SGs signals and we detail the modelled gravity contributions (e.g., local tidal model, atmospheric loading, instrumental drift, ground deformation contribution). These modelled contributions are subtracted from the raw signal, to obtain gravity residuals. These residuals are then compared to the results from the microgravity and absolute surveys. Our datasets evidence a gravity decrease towards the extraction area of the geothermal field, and gravity increase towards the injection area. Furthermore, maps of 2017-2024 microgravity residuals, namely after correction of vertical ground deformation, display localized areas of gravity decrease (-60 µGal), that can be associated to low permeability zones in the production area, as well as small gravity increase (about +15 µGal) towards north (around the centre of injection). The gravity increase trend appears to be controlled by a well-known fissure swarm that crosses the area of Theistareykir.
In order to identify and quantify the hydrothermal processes from the observed gravity variations, we develop numerical functionalities for multi-phase fluid flow models using CSMP++ (Weis et al., 2014) to predict the gravity responses of simplified hydrothermal systems.
References
Weis, P., Driesner, T., Coumou, D., Geiger, S. (2014): Hydrothermal, multiphase convection of H2O-NaCl fluids from ambient to magmatic temperatures: a new numerical scheme and benchmarks for code comparison. - Geofluids, 14, 3, 347-371.
https://doi.org/10.1111/gfl.12080
How to cite: Giuliante, B., Jousset, P., Riccardi, U., Pivetta, T., Hinderer, J., Weis, P., Krawczyk, C., and Mortensen, A.: Subsurface masses monitoring at Theistareykir geothermal field, Iceland, using hybrid gravimetry., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15606, https://doi.org/10.5194/egusphere-egu25-15606, 2025.
