Induced earthquake source parameters, attenuation, and site effects from waveform envelopes in the Fennoscandian Shield ...

• Main Authors: Eulenfeld, Tom, Hillers, Gregor, Vuorinen, Tommi A. T., Wegler, Ulrich
• Format: Text
• Language: unknown
• Published: arXiv 2022
• Subjects: Geophysics physics.geo-ph; FOS Physical sciences; Fennoscandian
• Online Access: https://dx.doi.org/10.48550/arxiv.2207.05545; https://arxiv.org/abs/2207.05545

We analyze envelopes of 233 and 22 $M_{\text L}$0.0 to $M_{\text L}$1.8 earthquakes induced by two geothermal stimulations in the Helsinki, Finland, metropolitan area. We separate source spectra and site terms and determine intrinsic attenuation and the scattering strength of shear waves in the 3 Hz to 200 Hz frequency range using radiative transfer based synthetic envelopes. Displacement spectra yield scaling relations with a general deviation from self-similarity, with a stronger albeit more controversial signal from the weaker 2020 stimulation. The 2020 earthquakes also tend to have a smaller local magnitude compared to 2018 earthquakes with the same moment magnitude. We discuss these connections in the context of fluid effects on rupture speed or medium properties. Site terms demonstrate that the spectral amplification relative to two reference borehole sites is not neutral at the other sensors; largest variations are observed at surface stations at frequencies larger than 30 Hz. Intrinsic attenuation is ... : published in JGR: Solid Earth, v2: published version ...