Using array‐derived rotational motion to obtain local wave propagation properties from earthquakes induced by the 2018 geothermal stimulation in Finland

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http://hdl.handle.net/10138/329522

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Taylor , G , Hillers , G & Vuorinen , T 2021 , ' Using array‐derived rotational motion to obtain local wave propagation properties from earthquakes induced by the 2018 geothermal stimulation in Finland ' , Geophysical Research Letters , vol. 48 , no. 6 , ARTN e2020GL090403 . https://doi.org/10.1029/2020GL090403

Title: Using array‐derived rotational motion to obtain local wave propagation properties from earthquakes induced by the 2018 geothermal stimulation in Finland
Author: Taylor, George; Hillers, Gregor; Vuorinen, Tommi
Contributor: University of Helsinki, Institute of Seismology
University of Helsinki, Helsinki Institute of Urban and Regional Studies (Urbaria)
University of Helsinki, Institute of Seismology
Date: 2021-03-28
Language: eng
Number of pages: 11
Belongs to series: Geophysical Research Letters
ISSN: 0094-8276
URI: http://hdl.handle.net/10138/329522
Abstract: We estimate vertical rotation rates for 204 earthquakes that were induced by the 2018 stimulation of the Espoo/Helsinki geothermal reservoir from wavefield gradients across geophone arrays. The array-derived rotation rates from seismograms recorded at 6-9 km hypocentral distances vary between 10(-9) and 10(-7) rad s(-1), indicating a comparable sensitivity to portable rotational instruments. Using co-located observations of translational and rotational motion, we estimate the local propagation direction and the apparent phase speed of SH waves, and compare these estimates with those obtained by S wave beamforming. Propagation directions generally align with the earthquake back azimuths, but both techniques show deviations indicative of heterogeneous seismic structure. The rotational method facilitates a station-by-station approach that resolves site specific variations that are controlled by the local geology. We measure apparent S wave speeds larger than 5 km s(-1), consistent with steep incidence angles and high propagation velocities in the Fennoscandian Shield.
Subject: 1171 Geosciences
seismology
array analysis
induced seismicity
rotational motion
seismology
seismic arrays
seismic gradiometry
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