Induced Earthquake Source Parameters, Attenuation, and Site Effects From Waveform Envelopes in the Fennoscandian Shield
Induced Earthquake Source Parameters, Attenuation, and Site Effects From Waveform Envelopes in the Fennoscandian Shield
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DOI：
10.1029/2022jb025162
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发表时间：
2022-07
期刊：
影响因子：
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通讯作者：
T. Eulenfeld;G. Hillers;T. Vuorinen;U. Wegler
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文献类型：
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作者：
T. Eulenfeld;G. Hillers;T. Vuorinen;U. Wegler
我们分析了芬兰赫尔辛基大都市区两次地热刺激引发的 233 次和 22 次 ML0.0 至 ML1.8 地震的包络线。我们分离源光谱和位点项，并使用基于辐射传输的合成包络确定 3–200 Hz 频率范围内剪切波的固有衰减和散射强度。位移谱产生的标度关系与自相似性存在普遍偏差，2020 年较弱的刺激产生了更强但更有争议的信号。与相同矩震级的 2018 年地震相比，2020 年地震的局部震级也往往较小。我们在流体对破裂速度或介质特性的影响的背景下讨论这些联系。站点项表明，相对于两个参考钻孔站点的光谱放大在其他传感器处不是中性的；在频率大于 30 Hz 的地面站观察到最大的变化。固有衰减非常低，20 Hz 时 Qi−1 ${Q}_{\mathrm{i}}^{-1}$ 值低至 2.4 × 10−5，这使得可以在 ∼50 km 深的莫霍面观察到漫反射。散射强度在全球观测到的数据范围内，Qsc−1 ${Q}_{\mathrm{s}\mathrm{c}}^{-1}$ 在 10−3 和 10−4 之间。将所采用的 Qopen 分析程序以回顾性监测模式应用于 2020 年数据，证明了其作为地震活动处理工具的多功能性。不同的结果对尺度关系、危险评估和地面运动建模，以及在结晶芬诺斯坎迪亚地盾环境中使用弹道和散射波场进行成像和监测都有影响。
We analyze envelopes of 233 and 22 ML0.0 to ML1.8 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 3–200 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 exceptionally low with Qi−1 ${Q}_{\mathrm{i}}^{-1}$ values down to 2.4 × 10−5 at 20 Hz, which allows the observation of a diffuse reflection at the ∼50 km deep Moho. Scattering strength is in the range of globally observed data with Qsc−1 ${Q}_{\mathrm{s}\mathrm{c}}^{-1}$ between 10−3 and 10−4. The application of the employed Qopen analysis program to the 2020 data in a retrospective monitoring mode demonstrates its versatility as a seismicity processing tool. The diverse results have implications for scaling relations, hazard assessment and ground motion modeling, and imaging and monitoring using ballistic and scattered wavefields in the crystalline Fennoscandian Shield environment.