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  The 2018 Geothermal Reservoir Stimulation in Espoo/Helsinki, Southern Finland: Seismic Network Anatomy and Data Features

Hillers, G., T. Vuorinen, T. A., Uski, M. R., Kortström, J. T., Mäntyniemi, P. B., Tiira, T., Malin, P. E., Saarno, T. (2020): The 2018 Geothermal Reservoir Stimulation in Espoo/Helsinki, Southern Finland: Seismic Network Anatomy and Data Features. - Seismological Research Letters, 91, 2A, 770-786.
https://doi.org/10.1785/0220190253

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Item Permalink: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5014936 Version Permalink: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5014936_2
Genre: Journal Article

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 Creators:
Hillers, Gregor1, 2, Author
T. Vuorinen, Tommi A.1, 2, Author
Uski, Marja R.1, 2, Author
Kortström, Jari T.1, 2, Author
Mäntyniemi, Päivi B.1, 2, Author
Tiira, Timo1, 2, Author
Malin, Peter E.1, 2, Author
Saarno, Tero1, 2, Author
Affiliations:
1External Organizations, ou_persistent22              
2Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum, Potsdam, ou_44021              

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 Abstract: A seismic network was installed in Helsinki, Finland to monitor the response to an ∼6‐kilometer‐deep geothermal stimulation experiment in 2018. We present initial results of multiple induced earthquake seismogram and ambient wavefield analyses. The used data are from parts of the borehole network deployed by the operating St1 Deep Heat Company, from surface broadband sensors and 100 geophones installed by the Institute of Seismology, University of Helsinki, and from Finnish National Seismic Network stations. Records collected in the urban environment contain many signals associated with anthropogenic activity. This results in time‐ and frequency‐dependent variations of the signal‐to‐noise ratio of earthquake records from a 260‐meter‐deep borehole sensor compared to the combined signals of 24 collocated surface array sensors. Manual relocations of ∼500 events indicate three distinct zones of induced earthquake activity that are consistent with the three clusters of seismicity identified by the company. The fault‐plane solutions of 14 selected ML 0.6–1.8 events indicate a dominant reverse‐faulting style, and the associated SH radiation patterns appear to control the first‐order features of the macroseismic report distribution. Beamforming of earthquake data from six arrays suggests heterogeneous medium properties, in particular between the injection site and two arrays to the west and southwest. Ambient‐noise cross‐correlation functions reconstruct regional surface‐wave propagation and path‐dependent body‐wave propagation. A 1D inversion of the weakly dispersive surface waves reveals average shear‐wave velocities around 3.3km/s below 20 m depth. Consistent features observed in relative velocity change time series and in temporal variations of a proxy for wavefield partitioning likely reflect the medium response to the stimulation. The resolution properties of the obtained data can inform future monitoring strategies and network designs around natural laboratories.

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Language(s): eng - English
 Dates: 2020-02-052020
 Publication Status: Finally published
 Pages: -
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 Rev. Type: -
 Identifiers: DOI: 10.1785/0220190253
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Title: Seismological Research Letters
Source Genre: Journal, SCI, Scopus
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Pages: - Volume / Issue: 91 (2A) Sequence Number: - Start / End Page: 770 - 786 Identifier: CoNE: https://gfzpublic.gfz-potsdam.de/cone/journals/resource/journals447