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

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http://hdl.handle.net/10138/326211

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Hillers , G , Vuorinen , T A T , Uski , M , Kortström , J , Mäntyniemi , P , 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 , vol. 91 , no. 2 , pp. 770-786 . https://doi.org/10.1785/0220190253

Titel: The 2018 Geothermal Reservoir Stimulation in Espoo/Helsinki, Southern Finland: Seismic Network Anatomy and Data Features
Författare: Hillers, Gregor; Vuorinen, Tommi A.T.; Uski, Marja; Kortström, Jari; Mäntyniemi, Päivi; Tiira, Timo; Malin, Peter E.; Saarno, Tero
Upphovmannens organisation: Department of Geosciences and Geography
Institute of Seismology
Datum: 2020-03
Språk: eng
Sidantal: 17
Tillhör serie: Seismological Research Letters
ISSN: 0895-0695
DOI: https://doi.org/10.1785/0220190253
Permanenta länken (URI): http://hdl.handle.net/10138/326211
Abstrakt: A seismic network was installed in Helsinki, Finland to monitor the response to an similar to 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 similar to 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 3.3 km/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.
Subject: 1171 Geosciences
FLUID-INJECTION
EARTHQUAKES
SENSITIVITY
SYSTEM
DEPTH
SCALE
ARRAY
SITE
Referentgranskad: Ja
Användningsbegränsning: openAccess
Parallelpublicerad version: acceptedVersion


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