Ambient seismic noise monitoring and imaging at the Theistareykir geothermal field (Iceland)

Ambient seismic noise monitoring and imaging at the Theistareykir geothermal field (Iceland)

Toledo, Tania (German Research Centre for Geosciences; ETH Zürich; Technical University of Berlin)
Obermann, A. (ETH Zürich)
Verdel, A. (TNO)
Martins, Joana E. (TU Delft Mathematical Geodesy and Positioning; TNO)
Jousset, P. (German Research Centre for Geosciences)
Mortensen, A. K. (Landsvirkjun, National Power Company of Iceland)
Erbas, Kemal (German Research Centre for Geosciences)
Krawczyk, C. M. (German Research Centre for Geosciences; Technical University of Berlin)

2022

In autumn 2017 a network of 14 broadband seismic stations was deployed at the Theistareykir high temperature geothermal field (NE Iceland). This experiment was conducted as part of the current efforts to characterize the field's main structures, and possible short and long term stress variations due to the ongoing fluid injection and extraction operations which started in autumn 2017. In this work, we use two years of continuous seismic records (October 2017–October 2019) to compute a 3D shear wave velocity model of the geothermal field and to detect possible crustal stress changes related to the injection and production activities. From phase cross-correlations of the vertical component recordings, we measure the Rayleigh wave group velocity dispersion curves to obtain 2D group velocity maps between 1 and 5 s. Subsequently, we use a neighborhood algorithm to retrieve the 3D shear wave velocity model of Theistareykir. Mainly, two sets of elongated high and low velocity anomalies can be observed oriented in a NW/WNW direction, parallel to the lineaments of the active Tjörnes fracture zone. Velocity reductions west of Ketilfjall and at Baerjafjall could indicate the location of upflow zones of the magmatic reservoir or hydrothermal system. We analyzed the temporal evolution of phase and amplitude of phase auto-correlations using the stretching technique and discuss their behavior in relation to the geothermal field operations. We notice a slightly stronger long-term velocity decrease in the reservoir region compared to outer regions. This could be related to the mass depletion in that area (higher fluid extraction compared to the water reinjection). In summary, our findings show how a monitoring network can be set up to enable a detailed imaging and monitoring of reservoir behavior in general.

Ambient noise
Geothermal exploration
Seismic imaging
Seismic monitoring

http://resolver.tudelft.nl/uuid:2f116857-fe27-41fb-bf5e-b6d2f20a4219

https://doi.org/10.1016/j.jvolgeores.2022.107590

0377-0273

Journal of Volcanology and Geothermal Research, 429

Institutional Repository

journal article

© 2022 Tania Toledo, A. Obermann, A. Verdel, Joana E. Martins, P. Jousset, A. K. Mortensen, Kemal Erbas, C. M. Krawczyk